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Measurement of low frequency electric fields using electrodeless breakdown of gases Friedmann, Daniel E. 1983

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MEASUREMENT OF LOW FREQUENCY ELECTRIC FIELDS USING ELECTRODELESS BREAKDOWN OF GASES  by DANIEL E. FRIEDMANN B . A . S c , The U n i v e r s i t y o f B r i t i s h Columbia, 1979  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE  in THE FACULTY OF GRADUATE STUDIES (Engineering  Physics)  We a c c e p t t h i s T h e s i s as conforming to the r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA JANUARY 1983  ©  D a n i e l E . Friedmann, 1983  In p r e s e n t i n g  this thesis  r e q u i r e m e n t s f o r an of  British  it  freely available  agree t h a t  in partial  advanced degree a t  Columbia,  understood that for  Library  s h a l l make  for reference  and  study.  I  f o r extensive copying of  h i s or  be  her  g r a n t e d by  shall  not  the  be  of  further this  this  thesis  a l l o w e d w i t h o u t my  ir/U<s I AJ e. e R IAJ 6  of  :  The U n i v e r s i t y o f B r i t i s h 1956 Main Mall V a n c o u v e r , Canada V6T 1Y3 Date  DE-6  (3/81)  TA^  I  ft  (9  Columbia  83  my  It is  permission.  Department  thesis  head o f  representatives.  copying or p u b l i c a t i o n  f i n a n c i a l gain  University  the  f o r s c h o l a r l y p u r p o s e s may by  the  the  I agree that  permission  department or  f u l f i l m e n t of  p H V S (C S  written  ii  ABSTRACT There i s a need f o r an e l e c t r i c f i e l d meter to measure f i e l d s under h i g h v o l t a g e t r a n s m i s s i o n l i n e s and switchyards.  T h i s t h e s i s d e s c r i b e s a new  their associated  electric  f i e l d meter based on  e l e c t r o d e l e s s breakdown of gases i n i n s u l a t i n g v e s s e l s . f i l l e d w i t h a gas emits  field  The  r e s u l t i n g meter has  separated  An e l e c t r i c  the l i g h t from the gas  to an e l e c t r o n i c counter  field i t  number of p u l s e s per c y c l e of  i s p r o p o r t i o n a l to the f i e l d magnitude.  meter i s c o n s t r u c t e d by conveying (the sensor)  The  filled  a low weight, non m e t a l l i c sensor  the  field  glass bulb  (the d e t e c t o r ) w i t h an o p t i c a l t h a t can  from the d e t e c t o r e l e c t r o n i c s by any d e s i r e d d i s t a n c e .  shape d i c t a t e s i t s d i r e c t i o n a l s e n s i t i v i t y .  the  When a g l a s s bulb  (e.g. neon) i s p l a c e d i n an a l t e r n a t i n g e l e c t r i c  l i g h t i n the form of p u l s e s .  electric  environmental  be The  A s p h e r i c a l b u l b has  fiber.  sensor  an  i s o t r o p i c response to the f i e l d w h i l e a c y l i n d r i c a l bulb g i v e s a maximum response when i t s a x i s i s a l i g n e d w i t h  the f i e l d d i r e c t i o n .  The  s i z e of  b u l b i s i n v e r s e l y p r o p o r t i o n a l t o the t h r e s h o l d below which the f i e l d be measured.  A 25mm bulb has  l i g h t s i g n a l from the sensor The  a 10kv  threshold.  can  t r a n s m i s s i o n of  not the  noise.  because the f i e l d magnitude i n f o r m a t i o n i s  i n the number of p u l s e s not i n the magnitude of the p u l s e s .  This t h e s i s presents  the t h e o r e t i c a l , e x p e r i m e n t a l  which e x p l a i n the o p e r a t i o n of the meter and The  The  to the d e t e c t o r i s immune to e l e c t r i c a l  d e t e c t o r e l e c t r o n i c s i s simple  contained  m-1  the  b a s i c p h y s i c a l model f o r the sensor  r e l a t i o n between o p t i c a l p u l s e s and shape on t h i s r e l a t i o n ,  on the phenomena.  field  test  results  s u b s t a n t i a t e s i t s advantages.  i s e s t a b l i s h e d by d e s c r i b i n g the  f i e l d magnitude, the e f f e c t of  the o p e r a t i o n of the sensor  ( i n c l u d i n g harmonic) f i e l d s and  and  sensor  in e l l i p t i c a l l y polarized  the e f f e c t of bulb s i z e and  gas  composition  iii  The b a s i c p r a c t i c a l c o n s i d e r a t i o n s a r e i n v e s t i g a t e d b y s t u d y i n g environmental stability  of  effects  on t h e p e r f o r m a n c e  the meter,  the  effect  and the g e n e r a l e n g i n e e r i n g of This operation  of  understood.  the m e t e r ,  s e n s o r on t h e  the  lifetime  f i e l d being  and measured  meter.  work has r e s u l t e d i n a f u l l y is well  the  of  the  t e s t e d p r o t o t y p e m e t e r whose  basic  iv  Table  of Contents Page  1.0  Introduction  1  1.1  Environmental E l e c t r i c  Fields  1.2  P r i n c i p l e of Operation  of Existing Electric  1.3  Possibilities  2.0  E x i s t i n g Work R e l a t e d  3.0  P h y s i c a l Model  14  3.1  Introduction  14  3.2  The B r e a k d o w n M e c h a n i s m  15  3.3  Breakdown  20  3.3.1  Strong  3.3.2  Weak B r e a k d o w n  25  3.3.3  S t a r t up C o n d i t i o n s  25  3.3.4  The P e n n i n g  25  3.3.5  Finite  3.4  Breakdown G u i d e d  3.4.1  Introduction  29  3.4.2  Possible  29  3.4.2.1  Finite  3.4.2.2  Wall C o l l i s i o n  3.4.2.3  Extension  to Cylinders  3.5  Breakdown  i n Planar  3.5.1  Introduction  3.5.2  Breakdown i n C i r c u l a r l y  f o r a New  Electric  5  Field  to Electrodeless  Field  Meters  8  Meter  10  Breakdown  12  i n Insulating Vessels  22  Breakdown  Effect  Conductivity  27  Effects  by V e s s e l  29  Walls  Effects  Conductivity  31  Screening  32  Guidance of Finite  Rotating  width  Fields  33 34 34  Polarized Fields  34  V  Page 3.5.2.1  Cylindrical  Tubes  35  3.5.2.2  S p h e r i c a l Bulbs  3.5.3  Extension  3.6  Summary  4.0  Electric  4.1  Introduction  45  4.2  F u n c t i o n a l D e s c r i p t i o n o f GEM  46  4.2.1  The S e n s o r  46  4.2.1.1  The B u l b  48  4.2.1.1.1  Bulb  48  4.2.1.2  The H o l d e r  50  4.2.1.2.1  Holder  51  4.2.1 .3  Engineering  4.2.1.3.1  Humidity  52  4.2.1.3.2  Temperature  52  4.2.1.3.3  Harmonics  53  4.2.2  The F i b r e  54  4.2.3  The D e t e c t o r  56  4.2.3.1  Electrical  58  4.2.4  Overall Engineering  4.3  Summary  5.0  Experimental  5.1  Introduction  5.2  Experimental  36  to Elliptically  Polarized Fields  40 43  Field  Meter Design  Manufacture  Manufacture Considerations  Design considerations  45  52  56 62  Results  64 64  Apparatus  66  vi  Page  5.2.1  Introduction  5.2.2  Apparatus and  66  f o r Generating  Studying  Pulse  Uniform  Fields  i n a Fixed  Direction  Emission  f o r Generating  66  5.2.3  Apparatus  Planar  Rotating Field  69  5.3  Study  5.3.1  Standard  5.3.1.1  General  Pulse  Emission  5.3.1.2  Rate o f P u l s e Magnitude  Emission  5.3.1.3  Determination  of E  5.3.1.4  Pulse  5.3.2  P o s s i b l e Mechanisms  5.4  Sensor  5.4.1  S p h e r i c a l Bulbs  86  5.4.2  Cylindrical  87  5.5  Investigations of Planar  5.5.1  Cylindrical  5.5.2  S p h e r i c a l Bulbs  5.5.2.1  General  5.5.2.2  Rate of Pulse Emission  o f t h e B a s i c Phenomenon  73  Phenomena  73 as a F u n c t i o n  of Applied  Field 75  Emission:  Shape  73  78  D  Dependence  on A p p l i e d W a v e f o r m  t o Reduce  79  the Threshold  82  Investigations  86  Tubes Rotating Fields  94  Tubes  Pulse  94 94  Emission  in Circularly  Polarized  on a F u n c t i o n o f F i e l d  Shape  Fields  96  Magnitude and 96  5.5.2.3  Planar  Rotating Fields  and P e n n i n g  5.6  I n v e s t i g a t i o n s of E n g i n e e r i n g Problems  101  5.6.1  Field  101  5.6.2  Meter C a l i b r a t i o n  Perturbation Stability  Mixtures  100  103  vii  Page  5.6.3  Humidity E f f e c t s  103  5.6.4  Temperature  105  5.7  Field  5.8  Summary  6.0  Summary  7.0  References  115  Appendix  117  Effects  Tests  106  108  and  I  Appendix I I  Conclusion  109  122  viii  List  of Tables Page  Table  1  Breakdown P a r a m e t e r s  19  Table  2  GEM  63  Table  3  Meter  Preliminary Specifications C o n f i g u r a t i o n s and A p p l i c a t i o n s  114  ix  List  of Figures Page  Figure  1  Equipotentials  Figure  2  Field  Figure  3  Calibration  Figure  4  Optical  Figure  5  Geometry  Figure  6  Geometry o f R o t a t i n g  Figure  7  Photo of prototype  Figure  8  Photo o f t y p i c a l  Figure  9  Phasors  Figure  10  Block  Figure  1 1  Circuit  Figure  12  Experimental  Figure  1 3  Apparatus  Figure  14  Electric  Figure  15  Photo o f apparatus  Figure  16  Optical  Figure  17  Calibration  curves  for different  bulb  pressure  76  Figure  18  Calibration  curves  fordifferent  bulb  dimensions  80  Figure  19  Optical  pulses  f o r square  Figure  20  Optical  pulses  f o r Penning  Figure  21  Time  Figure  22  Calibration  Figure  23  Angular  Figure  24  Calibration  curve  f o r strong  Figure  25  Calibration  curve  i n circularly  around  strengths  (frequency  f o r weak  of f i e l d s  7  versus  21  field)  24  breakdown  26  for cylindrical applied  bulb  30  fields  37  meter  47  bulbs  f o r applied  diagram  body  a p p l i c a b l e t o the bulb  curve  pulses  a human  49  rotating  fields  with  harmonics  55  of detector  diagram  57  of detector  60  s e t up  67  f o r generating circuit  pulses  rotating  f o r generating  fields  rotating  f o r generating  f o r strong  response  fields  rotating  71  fields  72  breakdown  74  wave  83  bulb  84  i n t e g r a t e d photo o f discharge of c y l i n d r i c a l  70  i n a cylindrical  tube  of c y l i n d r i c a l  tube  89 91  tube  93  breakdown polarized  95 field  97  Page Figure  26  C a l i b r a t i o n curves  in elliptically  Figure  27  Field  by  Figure  28  Bulb  Figure  29  Electric  Figure  I  Geometry of c o n d u c t i n g  Figure  II  Theoretical calibration fields  perturbation measurement field  polarized  fields  bulb  stability  99 102  graph  u n d e r a 500kV  shell  104  line  i n the a p p l i e d  curves  107  field  in elliptically  118  polarized 1 26  xi  ACKNOWLEDGEMENT The  i n i t i a l stimulus  interested intitial author is  i n developing  which  resulted t o R.R.  encouragement  they  Science  B.C.  Science  also  encouraged  the  Silva, The  the  support  was  G. D.  of  continuous  Heering  while  f o r the  of a  F.  the  models with  R.  Gayton and thankfull  during  and  F.L.  P.  A.  by  of  Cheuck,  in  the the  the  device.  execution  facilities,  have  field  tests.  also  Most n o t a b l y  E. W i l l i a m s , L.  Heminsley  for  of  the  Wong. F.  but  NSERC.  Many o t h e r s  meter.  the  author  f o r the p r o j e c t  p l a n n i n g and  the  The  MASc p r o g r a m  provided  Curzon.  and  the  exploitation  the  t o J . Rothe and  help with  the  experimental  Allan,  (US). for  The  Young  developed  support  also  c o n s t r u c t i o n of  Easton,  being  commercial  development of  e n c o u r a g e m e n t and  was  Nodwell  was  fields.  of J e f f  06/142,815  financial  e q u i p m e n t was  effort  effort  R.A.  project  t o the  joint  and  and  H e m i n s l e y who  environmental  No.  Subsequently  physical  D.  i s very  the  the  Auchinleck,  author  R.R.  only provided  experiments  Parfeniuk,  application  development  F.  a collaborative  Laboratory.  c o n t r i b u t e d t o the  execution Feeley,  provided  development  experiments  greatly  Parsons,  459  for monitoring  from  i n patent  C o u n c i l not  Some f i n a n c i a l The  a meter  invention resulted  indebted  Applied  f o r t h i s w o r k came f r o m  their  De  M.  1  1.0  INTRODUCTION  Electric developed  power i s c e n t r a l  countries.  intensiveness substantial To  had  the  utilities  at voltages  length  voltage  of transmission of the l i n e s  1000 k V .  above  evergrowing electric  of this number  fields  substations.  operating  generated  exposure  Accompanying growing  regulatory  concern bodies  lines  and h i g h e r  i s expected  a t 500 k V .  lines  of higher  and t h e i r  (especially  which  States  alone  then  the  Furthermore operating at at  i s an  associated  t o the l a r g e r  However o t h e r s or substations  living  also  fields)  and/or  receive  fields. of the e l e c t r i c  power  the p o s s i b l e h e a l t h e f f e c t s  voltage  lines  operated  there  long  to increasingly larger  among t h e p u b l i c , t h e E l e c t r i c a l about  over  Since  Lines  are being  and v o l t a g e )  powerlines  near powerlines  i s e x e m p l i f i e d b y a number  construction  and r e l i a b l y  continuously.  exposed  exposed  expansion  continue.  i n t h e U.S. h a s d o u b l e d .  power i n d u s t r y .  this  operating  ( i n mileage  to electric  to  prices,  I n 1977 t h e U n i t e d  experimental  being  the energy  o v e r h e a d A.C. t r a n s m i s s i o n  lines  by t h e s e  Most o f those  equipment  substantial  growth  of people  i n the e l e c t r i c  concern  sector  o f C a n a d a and t h e  to reduce  conservation  has i n c r e a s e d  voltages  Because  need  of transmission  1  common, w h i l e  a  efforts  o f 500 k V a n d a b o v e .  765 k V a r e now  work  through  i n the e l e c t r i c  electric  20,000 km  total  present  systems  move l a r g e amounts o f power e c o n o m i c a l l y  distances, operate  Even w i t h  o f t h e economy  growth  t o the energy  of hearings  lines  i n the  i n d u s t r y there i s  Utilities  and t h e  of these  fields.  on t h e p r o p o s e d  U.S.2  The  2  There  are  60Hz) e l e c t r i c 1.  t h e o r e t i c a l reasons fields  can  cause  biological  or  other  e f f e c t s can  neurological currents is  induced  partially  being  the  lighting  for  transmission  incandescent show t h a t  external  fields  could  cell  involve  such  as  or  arc  potential  which  touches  object  unwanted  signals  makers, h e a r i n g  Studies  Soviet  and  Union  adverse  health  other  impotency  groups  i n Sweden and  electric support  the  among 500  observed  fields  studies  e f f e c t s s u c h as  sexual  difference  published  and  findings  the  kv  those in  at  minimal  the  be  headaches,  no  not.  U.S.A. and  60Hz;  Sweden.  of  on  etc.; at  one  in  also  lead  teeth,  and  claim  by  a  in  the  number  of  and  studies  by  significant  been exposed studies  pace-  dangerous.  irritability However,  In  electric  processes  supported  statistically  Recently  pro-  and  countries  had  of i t  nerve,  r e s u l t s obtained  workers.  60Hz  frequency.  near  (fillings  fatigue,  body  continuous  of  uncomfortable  of  4  from Eastern  had  of  p o t e n t i a l may  devices  Presman  switchyard  60Hz  presence  effects  t h o s e w o r k e r s who  who  the  are  another  can  to  Although  stimulation  have been p a r t i a l l y by  -  power b e c a u s e  r e s u l t when a p e r s o n  U.S.A. r e p o r t e d  between  AC  enzyme r e c o g n i t i o n  etc.)  (50  interfere in biological  is prosthetic  t h e o r e t i c a l concerns  experiment.  for  psychological  aids,  50  field.  bone g r o w t h p r o c e s s e s ,  discharges an  by  illusion  a f f e c t e d by  hormone and  t o p h y s i o l o g i c a l and  These  are  frequency  i t i s a hazardous  muscle  directly  membrane s u r f a c e s ,  small  4.  threshold  of  the  lamps,  cardiac  caused  electric  frequency g i v i n g  and  fields,  3.  chosen  muscle  that  be  external  with  low  effects:  the  skeletal  cesses  that  by  lowest  Experiments^  2.  to b e l i e v e  in  a l l these  to  strong  Canada^ studies,  the  3  number o f p e o p l e be  inferred  occurrence periods the  investigated  would not  of  known, s i n c e t h e r e h a s  could  the not  continuous  devices shows  devices  have d i r e c t i o n a l  by  harmonic  and  thus  that  electric  For  this  are  based  of  dependent  the  create a hazard  field  field  induced  dormant  Finally,  fields  i s not  makes desired  exposures.  A  Firstly,  and  are  Secondly,  them b e c a u s e  two  of  of  metal  most  adversely  they  which  survey  c u r r e n t between 6  using  far.  a d e v i c e was  can  of  long  detector that  of disadvantages .  field.  to workers  with  to e l e c t r i c  sensitivities  applied  frequency  effects  reason,  on  low  information  s t u d i e s done s o  m o n i t o r i n g of e l e c t r i c  t h e y h a v e a number  content  the  reliable  have a  investigated,  b e e n an  ( a l l of which  plates)  no  A l s o , adverse  people  monitoring possible.  provide  existing  rates).  that  which  h a v e b e e n d e t e c t e d by  exposure,  continuous  s m a l l so  concerning health effects (e.g. m o r t a l i t y  actual  was  influenced  are  made o f  the  risk  metal  of  flashover. The  initial  m o t i v a t i o n f o r t h e work d e s c r i b e d i n t h i s  develop  a m o n i t o r i n g d e v i c e which would  above.  I t would  correlation effects. example, crane  by  However s u c h many c r a n e  done  meter  a d e v i c e would  i s based  new  electric  is totally on  out  the  better  fields,  and  have o t h e r  Existing  from  possible  i n B.C.  field  to  effects  s t u d i e s on  promising  (2  electric  the  was  cited  the  adverse  health  applications. last  y e a r ) when  d e t e c t o r s do  c o n s t r u c t i o n equipment of  For the  not  the dangers  posed  lines^.  T h e s i s d e s c r i b e s the  which  suffer  o p e r a t o r s have been k i l l e d  transmission  a  to carry  to e l e c t r i c  the p o w e r l i n e .  to develop  principle  possible  warn o p e r a t o r s o f heavy  overhead This  be  between exposure  touches  reliably  then  not  thesis  theoretical, field  different  electrical  experimental  meter. from  The  that  breakdown o f a  meter  and  i s based  of e x i s t i n g low  e n g i n e e r i n g work on  meters.  p r e s s u r e gas  in  a The an  new  4  insulating during  envelope.  the course  were o b t a i n e d  This  phenomenon  of developing  concerning  i s known  the e l e c t r i c  a s e l e c t r o d e l e s s b r e a k d o w n and  field  the p h y s i c a l processes  m e t e r , many new  occurring  results  i n electrodeless  breakdown. The  remainder  measured, the  new  the e x i s t i n g e l e c t r i c  electric  Section w h i c h GEM Model  Section obtained  field  2 presents  i s based.  f o r GEM,  contains  of the i n t r o d u c t i o n describes field  m e t e r GEM  meters  (Gaseous  and i n t r o d u c e s  Ellectric  a review o f the l i t e r a t u r e  Section  i t contains  3 i s devoted  a l l the b a s i c  Section  theory.  5 i s a d e t a i l e d account  i n the l a b o r a t o r y  experimental conclusions  basis  and e x p e c t e d  future  3 and 4 .  t o be  the concept of  Meter).  r e l a t e d t o the e f f e c t  The d e s i g n  considerations,  o f GEM,  on  field  Finally,  developments.  t e s t s which  Section  which  i s given i n  o f the major e x p e r i m e n t a l  and i n p r e l i m i n a r y  of Sections  Field  fields  t o a d e s c r i p t i o n o f the P h y s i c a l  t h e a c t u a l p h y s i c a l and e n g i n e e r i n g 4.  the t y p i c a l  results  form the  6 contains  the  .1  Environmental E l e c t r i c  Fields  Environmental e l e c t r i c  f i e l d s are due t o the p o t e n t i a l  between e n e r g i z e d conductors the ground  (powerlines) ( t y p i c a l l y  and v o l t a g e o f the c o n d u c t o r s , the ground  e n v i r o n m e n t a l c o n d i t i o n s and any o b j e c t s p r e s e n t  e l l i p t i c a l l y polarized i n a v e r t i c a l plane.  cover, the  nearby.  T y p i c a l f i e l d s under 3 phase t r a n s m i s s i o n l i n e s  are a p p r o x i m a t e l y  The major a x i s o f the  i s n e a r l y v e r t i c a l due t o the presence o f the h o r i z o n t a l  plane ( e l e c t r i c conductors). phase.  100V t o 1000kV) and  ( O v ) . The f i e l d ' s magnitude and d i r e c t i o n depends on the  number, d i s t r i b u t i o n  ellipse  difference  ground  f i e l d s a r e p e r p e n d i c u l a r t o the s u r f a c e o f good  The e l l i p s e  i s a result  o f adding the f i e l d s from  A t an e q u a l d i s t a n c e from each w i r e the a c t u a l f i e l d s  each  cancel out  to zero (a major p r o p e r t y of three phase t r a n s m i s s i o n ) . However, when the d i s t a n c e s t o each wire are not i d e n t i c a l vanish.  Thus the magnitude o f the e l e c t r i c  the r e s u l t a n t f i e l d  does not  f i e l d under a t r a n s m i s s i o n  l i n e e x h i b i t s a two hump camel shape having a minimum near the c e n t e r conductor  (approximate  conductor  (least  c a n c e l l a t i o n ) and a maximum near each outer  cancellation).  A typical  field  CONDUCTORS  o  o  o  i s sketched below.  ~\$~ rrrs HUxU '•v-/_~n APPART  6  The of  powerlines  the  field The  objects. For than due  the  i n a s w i t c h y a r d i s much more c o m p l e x due of d i f f e r e n t  a t any  so  f a r has  These o b j e c t s can the  ambient  v o l t a g e s , h e i g h t s and  given position  description  example  field field  near  electric  must o p e r a t e  relative  field  the head  i n the  and  elliptically  distort  the  of a person  absence lines  m e t e r must n o t  of  of  can  the head  be  10  conducting  field  lines  times  larger^  .  T h i s enhancement i s (see F i g u r e 1 ) .  these  complex  c o n d i t i o n s (±40°C, 0 noise  number  However,  large  electric  o n l y measure  extreme e l e c t r i c a l  large  polarized.  the p e r s o n .  near  to a  directions.  i g n o r e d the p r e s e n c e  i n extremes of weather  humidity)  harmonics).  is still  severely  to a c o n c e n t r a t i o n of f i e l d An  but  field  ( a t 60  Hz  -  fields  100%  and i t s  7  8  1.2  P r i n c i p l e of Operation  Invariably separated induces to  present  of Existing Electric  electric  b y an i n s u l a t o r .  When  an a l t e r n a t i n g c h a r g e  meters  immersed  (metal  halves)  between value  proportional  (or current)  t o the charges  of the r e c t i f i e d  (assuming The sensing  i n both  which  signal,  a uniform  sinusoidal  calibration  constant  electrodes  electronics  as w e l l  required  the meters  geometry.  the s i g n a l from  electrodes.  favourable  they  c a n be m i n i a t u r i z e d  The 1.  i f a readout  (or  an o p t i c a l  to  the readout  meters have they of  i n rms  of the  T y p i c a l l y the  yield  a  i s housed maximum  a n d a minimum  (close  reading  fiber  attributes:  have  t o the s i z e  i s required  been d e v e l o p e d  f o r them;  o f a c i g a r e t t e box.  (rather  at definite  l i n k ) m u s t be u s e d  than  time  just  storage  of  i n t e r v a l s ) wires  to connect  the d e v i c e  meter.  the f o l l o w i n g  disadvantages:  a r e m e t a l l i c and t h e r e f o r e  flash-over  t o the average  t o the f i e l d .  2.  field  electrodes  the electrode  The m e t e r s  many o f t h e m e a s u r e m e n t s t a n d a r d s  electric  respond  depends on t h e shape and s i z e  the f o l l o w i n g  the  from  a  field).  1.  However,  the f i e l d  proportional  on t h e s e n s i n g  the d i r e c t i o n o f the f i e l d  z e r o ) when p e r p e n d i c u l a r These meters have  i s directly  b u t are c a l i b r a t e d t o read  to detect  when a l i g n e d w i t h  field  halves  proportional t o the current  a s on t h e f i e l d  between o r i n s i d e t h e m e t a l reading  induced  cases  c o n s i s t o f two m e t a l  T h e m e t e r s work b y m e a s u r i n g  o r by m e a s u r i n g a q u a n t i t y  the electrodes.  Meters  i n an e l e c t r i c  the magnitude o f the s i n u s o i d a l f i e l d .  quantity  to  field  Field  the high  dangerous  voltage  because  equipment  o f the r i s k  to the  sensor;  9  2.  they  are d i r e c t i o n a l l y  depends  on  the  sensitive  orientation  of  ( i e . the  the d e v i c e  sensitivity i n the  electric  field); 3.  because  the  rectified field of  output  signal  i s proportional  the presence  i n t r o d u c e s an  the harmonic  error  average  of harmonics  which  components.  the phase d i f f e r e n c e  t o the  d e p e n d s on  The  between  i n the  error  the  also  the harmonics  electric  amplitude  varies and  with  the  fundamental; 4.  they and  a r e made o f m e t a l thus  a meter  accurate 5.  a  self  and  which  calibrated  i n a non-uniform  c o n t a i n e d meter  display  are  greatly  p e r t u r b s the  i n a unform  field  may  field not  be  field;  ( i e . one  together with  i n which  the  the  electronics  sensing electrodes) i s  heavy; 6.  a meter  i n which  electrodes is  an  electrodes battery  electronics  and  the  sensing  ( f o r example meters  for  cranes)  to e l e c t r i c a l  metallic  optical  display  separated  susceptible  connecting by  are  the  wires.  fiber^  the  n o i s e because I f the  two  electronics  becomes more c o m p l i c a t e d  o r power s o u r c e  ( t o modulate  of  the  p a r t s are  with and  the  sensing  requires  the  light  separated  its  own  emitting  diode). Environmental are  not w e l l  adverse given  effects  documented.  effects  of  temperature  However one  f o r temperatures  f o r temperatures  from  below z e r o ) .  4 0 ° C v a r y i n g h u m i d i t y was  also  found  and  study 0° Over  1 6  humidity  shows t h a t  t o 40°C the  on  meters  there are  no  ( i n f o r m a t i o n i s not  temperature  t o h a v e no  these  adverse  range effect.  of 0  to  10  1.3  Possibilities  An  electric 1.  f o r a New  field  the sensor the  2.  detector  into  devices)  separate  A  the sensor  Three  they  3 sensor  dimensions.  reducing  becomes  reduces  A sensor  from  detector  noise  However the f i e l d  f o r use as  Typically  sensitivity,  warning  ( w i t h one  sensors  these  flashover risk  components  they  shaped  n o i s e from  dictates  another each  be o v e r c o m e by  The non m e t a l l i c  the sensor metal  to electrical  t o the  parts therefore  t o measure  objective.  other  by 2 o r  the prospect o f g r e a t l y  shape w i t h o u t The n e e d  other  are separated  can a l s o  sensor.  and a f f o r d s  each  a d e t e c t o r which n e c e s s a r i l y  must be s e p a r a t e d f r o m i s immune  unless  be  i n three  influence  independence  isotropically  of symmetrical  c a n be p l a c e d  sensor,  One o f t h e  can t h e o r e t i c a l l y  sensors  lines)  (metallic  etc.)i s desired.  sensitivity,  Directional  the sensor with  which  t h e s e n s o r and  t h e main d i s a d v a n t a g e s  t h e main d e s i g n o b j e c t i v e .  electrical  system  overcomes  the coupling of e l e c t r i c a l  detector.  signal  distort  a non m e t a l l i c also  and d i s p l a y s ( o r  combine  (mostly  and d e t e c t o r .  of the a v a i l a b l e  (because  proportional to  and  However o t h e r s  directional  orthogonal directions.  sensor  a signal  i s a wire.  sensitivity,  main d i s a d v a n t a g e s ,  using  field  with  the s i g n a l .  one p a c k a g e .  new m e t e r w h i c h  overcome.  responds  parts:  some o f t h e p r e s e n t m e t e r s  the link  directional  Meter  the d e t e c t o r which d e t e c t s , a m p l i f i e s  c a n be s e e n  exception^)  Field  i s made o f two  which  electric  stores) As  meter  Electric  and q u a n t i f y the employs  The s e n s o r a n d  by a s i g n a l t r a n s m i s s i o n  n o i s e , and which  does n o t a d v e r s e l y  11  affect  the  practice along axis  sensor's  a  sensor  the  research ideal  sensor  nonisotropic Of the A  the  shape  of  based  light on  (spherical  insulating Initial  bulbs  filled  bulbs  emit  optical  with  to  advantage  of  to  insulating  electric  In  field  when t h e p r e f e r r e d  electrical  spatially  fields  for  equipment.  isotropic  Thus  or  carried  of  out  light.  strength of  a digital  and  noise  maximum a c c u r a c y  work on  and  metallic  of gases  presence  and  be  and  gases metal,  emits  electric  i s most can  be  fields,  promising. made o f  any  signal  transmported  by  exposing  to  the  detector  by  electric The  the  electrodeless glass  fields  number  applied field The  while  the  the  meter as  a whole the  was  pulse  information i s  t h e r e f o r e making  the  second  t h a t the  the  design  of  the  immune. the  complex  minimum d a n g e r sensor  environmental  ( t o the  i s required.  person  The  meter  in electrodeless glass vessels.  the  per  that  fact  gives  system,  revealed  of pulses  e l e c t r o d e l e s s breakdown o f gases  the development of  a  of  link.  c o n c l u s i o n , t o measure  breakdown  solids  can  number o f p u l s e s  a non  i n the  response)  seem i m p o r t a n t .  being  simple  discusses  of  with  neon t o a l t e r n a t i n g  the  i n the  meter with  the  field).  i s h i g h l y d e s i r a b l e f o r many  phenomenon i n v o l v e s no  experiments  contained  the  available  r a d i a t i o n ) which  d i d not  with  manufacture  for isotropic  amplitude  In  this  by  intense pulses  proportional  detector  be  field  the  mapping o f e l e c t r i c  many phenomena t h a t o c c u r  (electromagnetic an  the  accurate  f o r the  should  component o f  g i v e s a maximum r e s p o n s e  example or  distort  sensitivity.  emission  sensor  the  i s aligned with  For  purposes  ( i e . does not  measures  a x i s and  sensor  applications.  the  which  a specified of  performance  GEM.  electric using can The  done by  fields  it) a be  based  new on  next  section  others  prior  12  2.0  Existing  The and  Work R e l a t e d  t o E l e c t r o d e l e s s Breakdown  breakdown o f gases  neon  signs  electrodes  by e l e c t r i c  i s a familiar  sight.  are i n contact with  case) a r e separated  physics the  of t h i s  type  play  a major  role.  electrodeless (less  than  processes the in  breakdown  takes  occurs  The d i s c h a r g e  one h a l f  As t h e f r e q u e n c y  c y c l e remain  i n threshold f i e l d  breakdown) r e s u l t s .  becomes  less  dominant threshold stop  than  role,  The  the d i s c h a r g e  decreases.  colliding  increases  the length  with  forms  1 0  .  i s governed  their  of the v e s s e l ,  almost  t h e gas m o l e c u l e s  high  independently  and  secondary  p l a y a dominant  role i n  o f the discharge and a  t h e e l e c t r o n s a r e swept a oscillation  the w a l l s  becomes c o n t i n u o u s  Eventually a t very  field  t h e gas w i l l n o t  frequencies when  after  A t low f r e q u e n c i e s  the subsequent d i s c h a r g e s ,  cycle:  because  the v e s s e l walls  by p r i m a r y  below which  The  mostly  of the a p p l i e d  as c u r r e n t p u l s e s  A t even h i g h e r  d i s t a n c e i n each h a l f  Instead  occurs  lines i n  plasma  i s increased, products  (field  shorter  circuit.  The v e s s e l w a l l s  to assist  metal  vessel.  becomes a c o n d u c t i n g  different  lighting  cases  voltage  different,  on t h e f r e q u e n c y  a s i n D.C. b r e a k d o w n .  discharge.  decrease  Depending  cycle.  (the high  t h e g a s by a n i n s u l a t i n g  an e l e c t r i c a l  100Hz) d i s c h a r g e  each h a l f  i n a l l these  o f breakdown i s t o t a l l y  form  i n fluorescent  E l e c t r o d e l e s s breakdown  the f i e l d  e l e c t r o d e s and the gas (which  breakdown) c a n n o t  in  from  However  the gas.  when t h e e l e c t r o d e s t h a t g e n e r a t e this  fields  amplitude  no l o n g e r  play a  and t h e breakdown  frequencies  and t h e d i s c h a r g e  the e l e c t r o n s  threshold  rapidly. high  application  frequency  regime has been  t o plasma d i s p l a y p a n e l s .  s t u d i e d because However,  of i t s  t h e low f r e q u e n c y  regime  13  received  attention  for a brief  disappeared  even from  preliminary  work on GEM  period during  many w e l l known t e x t was  done w i t h o u t  the  1 9 5 0 ' s and  books.  In  knowledge o f  then  fact the  quickly  the published  results. Harries  and  electrodeless understand  occurs  and  develops  the  also  they  field  section  '  1  d i d most o f  3  One  the  observing lead  theory  concern  the  the  study  i n terms  has  i t s starting  von  Engels'  single itself  the  work.  on  in electrical  i n which  the  light light the  They  pulses  field.  studied  to  with  v e s s e l s of  different  t h e work on  D.C.  current  pulses  breakdown,  T h e i r work was  fields  also  i n the l a b o r a t o r y . shapes nor  with  vessel walls.  i s d e s c r i b e d i n the  f o r the  each  the a p p l i e d  sinusoidal  model  the  with  during  phase  o p e r a t i o n o f GEM  to  equipment  produced  emission  the  was  e l e c t r o d e l e s s breakdown  current pulses  discharges with  of a p h y s i c a l p o i n t on  used  work  main m o t i v a t i o n s  insulation).  c u r r e n t or  of on-going behind  their  the  t o t h e b a s i c e x p l a n a t i o n o f why  d i d not  uniform  d i d not  of  insulation  t o d e r i v e a measure o f  interaction The  by  correlate  done o n l y w i t h It  1 2  small a i r pockets  T h i s work  However  d i d they  electric  >  eventually destroys  discharge.  nor  1 1  breakdown o f  breakdown mechanism  occur.  Engel  b r e a k d o w n a t 50Hz.  the  (insulation  von  sensor.  breakdown  The and  next  physical on  model  Harries'  and  14  0  Physical  1  Model  Introduction  The sensor based  physical  used on  carried  to explain  the out  There  m o d e l f o r GEM and  literature during  is a  theoretical  understand  how  ( s e e S e c t i o n 2)  the development  a r e many p r a c t i c a l  the  and  o f GEM  approximation  sensor works.  n u m e r o u s new  to  The  the model i s  experiments  (see S e c t i o n 5 ) .  (engineering) reasons  to develop  a  physical  model: 1.  i t a l l o w s a deeper therefore  the  understanding  theoretical  of  the  advantages  basic  and  phenomena  limitations  of  and the  device; 2.  3.  i t sheds  light  ( s u c h as  threshold  methods o f c o n t r o l l i n g and  i t allows prediction experimentally  This  on  section  will  response  of r e s u l t s  ( s u c h as  the  homogeneous  linear  fields  or  fields  ( i e . more t y p i c a l  rotating  considerations are  such  as  first.  d e f e r r e d t o S e c t i o n 4.  which are hard of  parameters  effects)  and  to obtain  harmonics).  b r e a k d o w n phenomena f o r  Results w i l l  environmental  meter  to environmental  influence  d e s c r i b e the b a s i c  major  then  environmental effects,  be  extended  fields).  harmonics  and  to  plane  Practical meter  design  15  3.2  The  As the  Breakdown Mechanism  stated previously  same as D.C.  3.3.  i n the  fields  i s governed by  the T o w n s e n d  14  is  Subsection mechanism  been i n t e n s i v e l y s t u d i e d because of the important r o l e i t p l a y s  formation  following  of sparks between metal e l e c t r o d e s .  an e l e c t r i c  field.  The  atoms by c o l l i s i o n s . distance  __. dx  e l e c t r o n s are a c c e l e r a t e d by  The  number of new  dN  , the  coefficient.  formulated  constant  which i s exposed the  field  e l e c t r o n s produced per  i s p r o p o r t i o n a l t o the number of  and  to  ionize  unit  electrons.  c< N  3x Where  Townsend  theory.  C o n s i d e r N e l e c t r o n s p r o p a g a t i n g through a gas  i s given  frequencies  reason f o r t h i s w i l l become apparent i n  Breakdown i n D.C.  which has  the  The  the breakdown mechanism a t low  of p r o p o r t i o n a l i t y , i s the  Thus the number of new  electrons  (DN)  f i r s t Townsend  a f t e r a d i s t ance  d  by  DN  Where No  No  (e ot d  i s the i n i t i a l number of  Photons e m i t t e d containing  =  v e s s e l and  by  -  1)  electrons.  the e x c i t e d atoms bombard the i n t e r i o r  of  the  produce more e l e c t r o n s which can a l s o c o n t r i b u t e  the growth of i o n i z a t i o n w i t h i n  the gas.  secondary e m i s s i o n from the w a l l s be  %  L e t the p r o b a b i l i t y of (per e l e c t r o n from the  primary  to  avalanche) avalanche after  where  &  starts  the f i r s t  i s known a s t h e s e c o n d  with  one e l e c t r o n  avalance  will  t h e number  the p r o c e s s  avalances  1  will  +  i s continuous  t h e number  of e l e c t r o n s a f t e r  tf(e<*  d  - 1)  +  - 1)2  tf (e* 2  d  1  X(e^  -  a  important  mean f r e e  path.  to  a n atom,  ionize  +  . . . .  ionized ie.  i f the  i f  breakdown  criterion.  The  o b s e r v a t i o n s c a n be made:  d e p e n d s on t h e e n e r g y  a c q u i r e d by t h e e l e c t r o n  The e l e c t r o n  not  increase.  and  t h e Townsend  is  be  o f the above e x p r e s s i o n v a n i s h e s ,  1.  many  1)  e x p r e s s i o n i s known a s t h e Townsend  following  electrons  1)  _  a l l the gas i n the c o n t a i n e r w i l l  denominator  This  of secondary  I f an  be  ~ Clearly  coefficient.  be  tf(e*d  If  Townsend  otherwise  must  t h e number  Thus below a c e r t a i n criteria  the t h r e s h o l d f i e l d  E  D  a c q u i r e enough  cannot  energy  of electrons w i l l  field  o( t e n d s  be s a t i s f i e d .  f o r avalanche  per  growth;  to 0  This  field  17  2.  the dependence therefore material  3.  Y i s governed  weak.  ( i e . the v e s s e l w a l l s  X  Since given  i n this  material  emitter  and geometry.  of the energy gained  Thus  p e r mean  <X  =  and oi i s  control.  surface  i t i s constant f o r  oid i s constant,  free  f (E  case)  path  and  emission  o n ot i s l i n e a r ,  f o r threshold  i s s e t by t h e s e c o n d a r y  sensor  function  most i m p o r t a n t  i s logarithmic  by t h e s e c o n d a r y  the dependance o f the c r i t e r i o n therefore  a  on V  of the c r i t e r i o n  c* i s a  (EQA )  A)  n  A A  where  follows  i s t h e mean  free path  and  f  the a r b i t r a r y function.  Ii  that  f  ( E X)  d  0  =  constant  A or  since  V  0  A  =  Where 0 i s a n o t h e r  = constant/  E d  function,  and  V  the  P a s c h e n S c a l i n g Law.  Q  i s the threshold  constant (E two  Q  i n v e r s e l y with  important  (gas p r e s s u r e )  0 (pd)  (1)  (related to A  p i s the gas p r e s s u r e  voltage.  and d i s v a r i e d  varies most  =  Q  p  This  remarkable  What e q u a t i o n the threshold  (1) says field  d f o r constant  E  pd).  r e s u l t s i n the c o n s t r u c t i o n  Q  result  i s known as  i s i fp d i s held c a n be c o n t r o l l e d  This  i s one o f t h e  o f low  )  threshold  18  sensors.  The o t h e r  be  deduced  from  no  molecules  breakdown. very  high  voltage  a broad Table  different  used  because  not  substantially  Q  versus  are  typical  a r e s o many c o l l i s i o n s  pd resembles  that a  D  decomposition). Pyrex  than  i s the best  f o r other  these  parabola.  Typically  0  mm.  o f the parameters  of i t sa v a i l a b i l i t y , worse  an a s y m m e t r i c  discussed for  are h i g h l y d e s i r a b l e because  no c h e m i c a l low V .  between  must be o p e r a t e d .  10 t o 60 T o r r values  almost  i s required to start  a minimum  pd t h a t t h e s e n s o r  near pd  of t h e i r  because  of V  I n e r t gases  (very stable,  there  somewhere  minimum  gases.  there  low p r e s s u r e  T h u s (? m u s t h a v e  minimum  1 shows  pressures  .The s h a p e o f 0 c a n  f o r the e l e c t r o n s t o g a i n  A graph  life  material  high  of pd.  i s required i n order  energy.  i s at this  has  At very  and t h e r e f o r e a l a r g e v o l t a g e  two e x t r e m e s . It  the b a s i c p h y s i c s .  At very  sufficient  c o n s i d e r a t i o n i s the value  of their  Neon a n d A r g o n choice  c a n be  f o r sensor  ease o f use, toughness glasses.  long  and v a l u e  of  ^  19  gas  V  0  (v)  pd  minimum  neon  230  4  argon  220  1 .5  air  350  6.0  Table  1  a)  Breakdown p a r a m e t e r s  for different  (Torr  gases  material  pyrex metal  very electrode  1  b)  1  10  0.3  Breakdown p a r a m e t e r  Table  than  0.01  photomultiplier coating  Table  low ( l e s s  for different  Breakdown  Parameters  materials  - 3  )  mm)  20  3.3  Breakdown  In a previous gas  in Insulating Vessels  normal  spark  subsection  and  (plasma) forming  insulating in  a D.C.  al  field  which  linear  continues the  as  orientation matter.  breakdown o c c u r s ,  there  the  and of  spherical  the  small pulse  Suppose and  respect  that a spatially  v a r i e s i n time  quency.  In what f o l l o w s  breakdown w i l l accordance  the  with  the  by  the with  E . A  counteracts effects  of  discharge  circuit.  of the  field,  magnitude the  at high  no  enough  field  gas  of  time  electric  of  intern-  a contin-  alternating Clearly  of  the  applied field,  Figure  ionized  1 4  i n which  effect  Eg  does  fixed  the not  direction  W  and  fields  s t r e n g t h s , and  the  partially  Instead  an  Thus  is  t  s e p a r a t i o n produces  the  an  expression  charge  (see  in  and  ions  a space  than  will  and  evolve  breakdown  by  in the  electrons  charge  Since or  fre-  Electrical  After  2b).  i s less gas  .  the  i s denoted  subscript omitted.  field  ionized  separate  E^,  c o n v e n t i o n a l Townsend T h e o r y partially  ionized  vessel walls.  applied field  t i s the of  vector  the  the  the  However  conductivity.  the  sin W  the  with  m o d e l f o r an  t o the  to  in  discharge.  The  c o n d u c t i v i t y of  described  i s s e t up.  uniform  according  symbol w i t h occur  is filled  separated  by  amplitude  appropriate  as  charges  the  vessels with  v e s s e l with  i s the  which  the  applied field  i s one  where E^  bulb  steady  electrical  =  the  a  f o l l o w i n g d i s c u s s i o n develops  field  applied  breakdown s t a r t s  b r e a k d o w n i s i n t e r r u p t e d by  cancels  uous d i s c h a r g e The  one  the  p a r t of  v e s s e l the field  gap  Eg  equal  i s l a r g e enough  field,  are Eg  i s produced t o Ej^. the  If  21  •  Figure  2  (a)  Field  Strengths Applicable  a)  Field  E -  sinusoidal  A  strengths versus  (vertical  applied lines  Ej-  sawtooth  Eg-  stepwave space  "E Q  b)  breakdown  time.  field  are superposed  internal  field  t o the Bulb  field.  charge  field.  strength.  G e o m e t r y o f E , _Eg a n d E j A  optical  pulses)  22  internal  field,  Ej  i s r a p i d l y brought  -  If,  however,  total Eg,  the  degree of  separation  which  remain  of  ions  i s weaker  i n the  +  and  and  Hence a  will  be  t o d i s t i n g u i s h between  breakdown'  (_Ej- =  than to  0 after  occur  0 just  after  breakdown).  in strong  One  weak b r e a k d o w n .  The  separated  inner  the  glass  surface  polarization be the  of  forces.  changed by glass  increase  3.3.1  on  la.  charges  cases  are  by  space  as  Ej  E^.  the  amplitude  r e s i d e , between are  held  'strong (Ej  greater  optical  pulses from  breakdowns, i n place  immobile,  The  charges  extra  field,  will  to a r i s e  therefore  and  on  the  by Eg  can  transported  already  the  It is  terms  pulses  low,  charge  field  large amplitude  e i t h e r n e u t r a l i z e those 1 1 - 1  i s too  'weak b r e a k d o w n '  where t h e y  charges  concentration  there,  only to  or  ^.  Breakdown  e v o l u t i o n of  The  applied  lines  signify  space  charge  assumed  lower  shell,  such occasions  The  axis.  expect  subsequent breakdowns.  their  Strong  The  two  b r e a k d o w n ) and  and  a  same d i r e c t i o n  these  would  breakdown,  produce  residual internal  i n the  convenient  that  f o l l o w i n g breakdown  electrons w i l l  A  so  1 1  Eg  ionization  than E .  bulb,  to z e r o  the  field  the field  has  occurrence i n the  I t i s constant immobility  fields  of  a of  bulb  for strong  s i n u s o i d a l waveform,  and  optical  which  i s the  between o p t i c a l charges  b r e a k d o w n i s shown i n  adhering  pulses.  Eg,  the  to  the  vertical  represents  stepped waveform below pulses  the  i n accordance with glass.  Figure  E j , which  time the is  the  the  23  sum of E^ and Eg i s the saw-tooth wave form. the breakdown f i e l d  ( E ) o f the gas i n the b u l b , a breakdown o c c u r s , Q  accompanied by a f l a s h of l i g h t , r e c u r s when E-j- a g a i n reaches breakdown correspond  and E-j- i s r e s e t t o z e r o .  a value of E .  t o changes i n E .  Therefore  A  the change i n E  A  F i g u r e 2 ) . Thus f o r s t r o n g  0  breakdown the average number o f p u l s e s  The process  Changes i n E-j- between  Q  between o p t i c a l p u l s e s i s simply E ( s e e  is  Each time t h a t E-j- reaches  (n) p e r c y c l e o f the a p p l i e d f i e l d  g i v e n by the e x p r e s s i o n ^ 1  n = 2[2E /E ] A  Q  where the square  b r a c k e t s denote the i n t e g e r p a r t o f the r a t i o  2E /E .  If  o f the a p p l i e d f i e l d  (fg) of  the frequency  is f  A  then the frequency  A  0  the o p t i c a l p u l s e s i s g i v e n by the e x p r e s s i o n  f  B  Thus f g depends i n a stepwise A s t e p o c c u r s each time average breakdown f i e l d a s i z e of 2 f inside  A  = 2[2'E /E Jf A  0  f a s h i o n on E tha E  A  o f the gas.  (2)  A  A  (solid  l i n e i n F i g u r e 3)  i n c r e a s e s by E^/2, where E ^ i s the The s t e p i n the p u l s e frequency has  (see F i g u r e 3 ) . S i n c e , i n s t r o n g breakdown the c o n d i t i o n s  the b u l b a r e i d e n t i c a l f o r the p r o d u c t i o n of each s u c c e s s i v e  p u l s e , one would a l s o expect much l e s s v a r i a t i o n i n p u l s e amplitude f o r s t r o n g breakdown than f o r weak breakdown.  — H  Figure  3  4 5  KV/m  Frequency  ( f g ) o f the o p t i c a l  amplitude  ( E ) f o r 25mm d i a m e t e r  a)  High  b)  Low  pulses  A  pressure pressure  neon neon  (10 (1  '  K -  Torr)  Torr)  versus  bulb.  applied  field  25  3.3.2  Weak  In the  Breakdown  weak b r e a k d o w n s ,  change  equal  i n the applied  that  line  effect  t o a good  3.3.3  operation  of the bulb  long  particularly  In  will  t o make  the i n t e r n a l  than  E .  will  B  pulse  i n Figure  be s m a l l e r ,  depend  4 which  (E-j-)  i t is  be s m o o t h e d o u t ,  linearly  f o r weak  field  o f the  on E ^  (dotted  the change  in E  the p u l s e s .  shows t h e o p t i c a l  field-waveform  Hence  t o the next,  3 will  the weaker  strength  i s E^ = E /2 Q  A  This  pulses  breakdown.  value  t o maintain  (equation  Q  2).  steady  I t would  to intiate  this  t h e gas has a breakdown f i e l d  the s t a t i s t i c a l  breakdown o c c u r s  true  required  E^ = E /2 i s too small  enough  The P e n n i n g  the case  f  Because  Q  t o be a n t i c i p a t e d t h a t  i n Figure  minimum f i e l d  the f i r s t  The  by a breakdown.  Conditions  of strength  waits  that  3.3.4  pulses  h a s been assumed t h a t  one  exhibited  I t i s also  on t h e a p p l i e d  Start-up  field  the step  i s illustrated  The  i s smaller  approximation  3).  optical  superposed  it  that  i n Figure  between  required  t o zero  f l u c t u a t i o n s i n E-j- f r o m one o p t i c a l  be e x p e c t e d  and  field  t o t h e breakdown f i e l d  statistical to  E-j- i s n o t r e s e t  properties  appear  regime  of E . Q  that  a  because However i f  o f t h e phenomenon e n s u r e  e v e n when E ^ i s l e s s  i n t h e weak b r e a k d o w n  state  than  E . Q  This i s  regime.  Effect  o f t h e breakdown f i e l d  of simple  inert  gases  E  0  i s governed  by t h e P a s c h e n law.  s u c h a s A r a n d Ne t h e t h r e s h o l d  is  set  Optical  p u l s e s superposed  25mm d i a m e t e r Ei  = field  neon-filled  amplitude.  on a p p l i e d  field  bulb a t 1 Torr  wave f o r m  (weak  (E ) for A  breakdown  case).  27  by V / d .  One  Q  only  be  Thus  Penning  effect  (say  and  Ar then  because of  by  Ne)  and  level  of  mixture.  inert  gas  electrons  The  Eip.  produce  Appendix  i s exposed I*). At  low  sensors  the  c a n be  ionization  net e f f e c t  (which  has  metastable  into  energy  i s that  This  The  i s used  states  (99%  happens  them and energy  of  i s not  of gases  lowered.  put  can  l o w e r i n g Vo.  When a m i x t u r e  ionize  of  the  the m i n o r i t y  more e l e c t r o n s  are  more  gas component used  for  raised).  f o r l o w e r i n g the  with  avalanches  the  can  to a f i e l d  E , T  pulses.  I was  developed  gas  doping  the  (say t r i t i u m ) .  p r o v i d e more  The  "seed"  grow.  on  I f the which  the  assumption  conductivity  is different  the model remains  frequencies severe  optical  atoms and  include  Effects  conductivity.  However,  threshold  of r a d i o a c t i v e  models p r e s e n t e d above depend  gas  by  is  Conductivity  the  Appendix  The  which  zero e l e c t r i c a l  larger  the energy  small percentage  has  f o r a g i v e n gas,  Q  atoms p r o v i d e d t h e e x c i t a t i o n  emissions c o l l i d e  from  Finite  retain  E ,  t o c o n s i d e r ways o f  f o r breakdown  possibilities with a  and  majority constituent  exceeds  ( i e . c><  radioactive  3.3.5  the  gas  metastable  Other  larger  i s that  a possibility.  the metastables  gas  o f GEM  i t i s important  i s such  the m i n o r i t y  the  making  the t h r e s h o l d  ionization  *  the drawbacks  decreased  desirable)  Ne)  of  valid  F.L.  bulb  is finite,  then  from E  s c r e e n i n g o c c u r s and  Curzon.  the  provided E  A t h i g h e r f r e q u e n c i e s the  by  that  (see  A  is  A  replaced  the bulb ceases  field  (E ) T  which  to  penetrates This E  T  means t h a t  versus  increases high  the  time  g l a s s i s phase s h i f t e d graphs by  operate.  slightly  in electrical  temperature.  of E  A  versus  time  displacing  conductivity  Therefore  but  i n these  the can  not can  attenuated be  curves be  significantly.  converted t o the  produced  c o n d i t i o n s the  by  into  left. high  bulb  may  plots  of  Drastic humidity cease  to  o:  29  3.4  Breakdown  3.4.1  Introduction  So  with  electrons, accurate  stop  the discharge  as l o n g  direction.  ( f o r those  which  the discharge  ie. directional  1 6  must a l s o o c c u r  require  This  do n o t  provide This  to build  photo-  picture i s and a l i g n e d a  cylindrical  t h e measurement o f one must  the c o n t a i n e r  end o f t h e v e s s e l t o the o t h e r .  interaction  treat  walls  interaction  t o the e l e c t r i c  electric  the case i n  as i t t r a v e l s from must o c c u r  field.  A  when t h e  similar  i n a l l v e s s e l s when c o m p l e x r o t a t i n g  fields  present. In  the following subsections  depicted  applied  i n Figure  field.  discharge  First  5.  the p h y s i c a l model i s e v o l v e d  A cylindrical  v e s s e l a t an a n g l e  two p o s s i b l e p h y s i c a l e f f e c t s  are introduced.  Then each  effect  t h a t may  i s discussed  f o r the  9 with  the  govern the  independently.  Possible Effects  Free lines. and  the charges.  sensitivity)  i n t e r a c t s with  v e s s e l i s a t an a n g l e  3.4.2  only  However i n a t t e m p t i n g  cylindrical  case  fields)  v e s s e l s whose w a l l s  The w a l l s  and t r a p  a p p l i c a t i o n s which  components  are  (linear  as t h e v e s s e l i s s p h e r i c a l o r c y l i n d r i c a l  field  one  Walls  the evolving discharge.  the f i e l d  sensor  by t h e V e s s e l  f a r t h e d i s c u s s i o n has d e a l t w i t h  interact  with  guided  thus  e l e c t r o n s which  As s e e n  i n Figure  one w o u l d e x p e c t  intiate  discharges  5 these  lines  the e l e c t r o n s  move a l o n g  are v e r t i c a l t o move  electric  (direction  in a vertical  field of E ) ft  direction  30  Figure  5  Geometry of a p p l i e d  field  E  A  = applied  E  E  N  = field  field;  p  and b r e a k d o w n  = field  normal t o tube-axis;  along  discharge.  tube-axis;  9 = angle  between  tube  axis  and  vertical (z). Shaded  region  - breakdown d i s c h a r g e  with  internal  field  along  z.  31  until soon of  they h i t the as  they  very  h i t i t then  narrow  tubes.  many c o l l i s i o n s mechanism the  tube  internal applied tube  may  Ep,  the  to  from  the  one  other  end  or  the  tube w a l l s  to  the  i s not, if a  e i t h e r the guide  the  on  the  (see  h i s work, b e l i e v e s  that  the  Thus from  one  one  other  E ,  that  E^  will  proceed  the  the  next  The  N  from  applied two  along  one  the The  normal  i s screened  of  the  is i f  5):  possible  end  i n which  Figure  proceed  as case  stick.  in  tube a x i s .  normal component o f discharge.  wall  the  discharge i s to  least  discharge  to  the  to  Suppose  discharge  at  A n o t h e r way  tube  to  the  will  is parallel  tube.  then  based  the  stick  breakdown,  (A).  of  components  has  conclusion,  no  "guide"  two  other  to by  the some  Ep.  end  of  the  field  is  screened  subsections  tube  describe  models.  Finite  The  vessel  Conductivity  screening  inversely  dimension. Thus  while  is  Ep If  axial  due  proportional  vessel.  an  5)  to  E ,  p  electrons  electrons  vessel)  the  3.4.2.1  before  the  to  these  be  (inside  A  E  the  will  tube w a l l s  parallel  mechanism but In  required  travel  field,  there  If  However, H a r r i e s ,  in Figure  field  and  are  is for (C  electrons  vessel walls.  this  A  i t may  Screening  to  the  finite  (for a given  small be  conductivity glass  vessel will  possible  surface  screen  i n a narrow  the tube  of  the  glass  varies  condition)  with  field  than a  for  more to  be  the large  screened  not. i s the  field  of  case  then  the  gas  will  strength  Ep  = E  A  cos  9  b e h a v e as  i f i t were  immersed  in  32  and  will  yield  2 with  3.4.2.2  replaced  Wall  by E ) .  Collision  Now  assume  effect. vessel  a corresponding  frequency  C l e a r l y when 9 i s 9 0 ° t h e r e  p  a r e no  finite  conductivity i s not responsible  Furthermore  assume  that electrons  bounce o f f and a r e a g a i n  a l m o s t no e n e r g y  the  end o f the tube.  other  i s lost  where L i s t h e l e n g t h  ends o f an i n c l i n e d with  o f the tube  expression  equation  pulses.  will  energy gained  (assuming  L  towards the  I f during  the e l e c t r o n s  the w a l l  be g u i d e d t o  by t h e n w i l l  be  the width d i r e c t i o n i s very  t h e p o t e n t i a l d i f f e r e n c e between t h e  Thus an i n c l i n e d  of length  f o r the  cos 9  i s simply  tube.  the f i e l d  then  L  A  are accelerated  accelerated.  The e f f e c t i v e  E  This  (ie.  Guidance  collision  aligned  o f breakdown  that  walls  small).  value  e  tube  (assuming  i s equivalent  the tube  to a  tube  is infinitely  thin)  L  e  = L cos 9  Experimental correct.  Thus  (3)  r e s u l t s presented  the frequency  i n Section  o f breakdown  i n electrodeless  governed  by t h e p o t e n t i a l d i f f e r e n c e between  provided  the discharge  tube  therefore  axis  (ie.  measures  produces  i s guided  reading  this  model i s  tubes i s  t h e ends o f t h e t u b e ,  by t h e tube w a l l s .  t h e component  a maximum  5 show t h a t  A thin  o f the e l e c t r i c when a l i g n e d  field  with  cylindrical along i t s  the f i e l d ) .  33  3.4.2.3  Extension to Cylinders  If its is  the  cylindrical  l e n g t h , then no  tube  of F i n i t e  has  a  term  ( i e . along  not  treated  application.  the  cos  proportional  maximum r e a d i n g i s m o s t  are  which  is a  significant  Basically,  the  fraction  effective  of  length  longer  includes  field  a width  the model i s c o m p l i c a t e d .  L  but  Width  likely  largest  i n any  6  t o the w i d t h  of  at a small angle  path  more d e t a i l  or d i a g o n a l of because  the from the  t h e y do  tube.  Furthermore  alignment tube).  not have  with  "Fat" any  the tubes  obvious  the  34  3.5  Breakdown  In Planar  3.5.1  Introduction  Rotating  The p h y s i c a l model d e v e l o p e d uniform  electric  however,  fields  of f i x e d  Fields ^ 1  so f a r has c o n s i d e r e d direction  i s a p p l i c a b l e t o non u n i f o r m  dimensions  are smaller  is  the case.  usually  than  ( i n an e l l i p t i c a l  physical  m o d e l must  the length  envelope,  be e x t e n d e d .  conducting  crane,  ( i e . person,  the f i e l d  the  objects  surface)  the  objects  radius  The  3.5.2  then  vessels  i n plane  be e x t e n d e d  Breakdown  rate  of  i s the f a m i l i a r  field  direction.  will  i t should  direction  and  thus  This  planar  the  be m e n t i o n e d  that i n  near a  '  large  t o a good ( i e . perpendicular  a s c a l e a few t i m e s  (60 Hz)  discuss  Polarized  the model  smaller  to  than  polarized  spatially  The  results  fields.  Fields  has a c o n s t a n t  i n the plane  f o r s p h e r i c a l and  polarized fields.  elliptically  polarized field  at a constant this  are t y p i c a l l y  1.1)  e t c . ) where  circularly  to plane  in Circularly  A circularly  over  sensor  curvature.  following subsections  cylindrical will  of  fields  meter i s p l a c e d  i s i n a fixed  and u n i f o r m  the  The m o d e l ,  s c a l e o f t h e non u n i f o r m i t y .  However,  field  spatially  fields).  provided  see S e c t i o n  many a p p l i c a t i o n s t h e e l e c t r i c  approximation,  fields  Environmental e l e c t r i c  rotating  object  (linear  only  magnitude E  of p o l a r i z a t i o n . uniform  field  in a  A  but  rotates  Any p r o j e c t i o n fixed  35  3.5.2.1  Cylindrical  The  extension  rotating  fields  component  o f the p h y s i c a l model  i s simple.  of the e l e c t r i c  irrespective Due  Tubes  measured  component  (length,  5 5 mm,  component  Cylindrical field  along  of whether the f i e l d  to the f i n i t e  for cylindrical  aspect  tubes  the tube  i s planar  ratio  o f the f i e l d  4 mm).  along  axis  rotating  o f the c y l i n d e r ,  i s i n e r r o r by r o u g h l y  diameter  measure  The  +  mainly  to planar  the  (see S e c t i o n  2.4.2.2)  or not. the d i r e c t i o n  2° f o r a typical  cylinder  the t u b e ) ,  tubes  responds  only  o f the  tube to E  (the  i f the f o l l o w i n g c o n d i t i o n i s  satisfied  E  where  i s the f i e l d  length is  cylinder axial E  N  the  component  of the c y l i n d e r  not strong  enough  ( L = 5 0 mm,  breakdown  exceeds  0  (L/D)E  Q  perpendicular  and D i t s d i a m e t e r .  t o the c y l i n d e r  This across  the tube.  D = 4 mm),  twelve  times  then  before  E ^ c a n be  i t i n f l u e n c e s the response  i t i s convenient  to define  axis,  c o n d i t i o n means  t o cause a breakdown  field  LE /D,  <  N  t h a t EJQ  For a  typical  as l a r g e as the of the b u l b .  a rejection  ratio  and p e r p e n d i c u l a r  field  expression  r  where  E  p  and E  components  N  = 1 -  E  p / E N  are the r e s p e c t i v e p a r a l l e l  required  t o produce  a given  f  B  .  L is  i t i s readily  shown  that  If r , by  36  r  =  1 -  Thus  (D/L),  in a circularly  cylindrical the  which  full  tube  length  irrespective  3.5.2.2  of  for a  typical  polarized  measures (L) o f  E  the  o f magnitude  i n equation  cylinder.  The  2,  has  the  (E <  L/D  A  where  E  measurement  value, E ) Q  the  i s governed  Q  i s the  0.9.  by  same  S p h e r i c a l Bulbs  spherical  complex.  Assuming  that  the  uniform still  internal (this  occurs  addition  of  bulbs the  the  field  E  assumption every  the  time  fields  where  the  sum.  In  uniform E  A  straight the  extension  b a s i c phenomena i n the  B  will the  be  where  i t is easily  seen  from  Q  an  caused  charge  by  the  later), changes For  E  then by  E  A  F i g u r e 6 t h a t f o r the  [(1  - cos  9)  by  + sin  2  or cos  9  =  1  -  JL 2  2 E  o 2 E  A  the  same  and  separation i s  new  breakdown  however  the  one  must  of  the  vectorial  polarized  2  =  Q  a  i s more  have  0  the magnitude  9 given  E ,  breakdown  is circularly  angle  model  remains  I =  indiciates  case  E  _B  physical  ( S e c t i o n 2.3)  discussed  +  special  2  the  vectorial.  -A  brackets  must r o t a t e t h r o u g h  bulb  of  applied field  i s now  I  Q  bulb,  orientation.  For  E ,  field  as  A  cylindrical  9 ] 2  field  and  E_g i s  t o change  by  37  Figure  6  Geometry  of Rotating  E (1)  - applied  E (1)  - "wall  E (2)  - applied  A  R  a  E  n  = breakdown  field  charge" field field  Applied  Field.  a t 1 s t breakdown. field,  1 s t breakdown.  a t 2nd  breakdown.  38  2 which  Thus e q u a t i o n f  B  f  =  expressed  2JT  A  =  the f  (f  important  I  B  versus 1 .  be  -  1 Eo^  Y"  2  )  EA2  made c o n c e r n i n g  the  calibration  curve  E ): A  the  steps  This  changes Steps by  associated with  effect  previous  2.  can  becomes (4)  cos-1/1  observations  o f breakdown  TT  2  A  9  Two  frequency  can  case  be  occur  understood  were due  i n sign.  will  any not  the  s i n e wave).  due  to r o t a t i o n  are  no  The  number o f p u l s e s  E  A  are  This  i s apparent  fact  change  cycle  E^  of  E  rotating  less  brackets) f  B  4.  and and  At  decreases. E  the  Q  followed  peaks  changes  4  field  of  in  therefore  i n equation  except  the  in  than  f o r a given  field  in  then  ( i e . near  same s i g n  the  Eo  of  the  equation  =  A  i s constant  second  steps  i n c r e a s e s and  A  (integer  per  A  t h a t the  to a pulse  case  always  from  E  the  lead  discontinuities  i s i n c r e a s e d by  The  increase i n E  In t h i s  disappeared.  intuitively.  to  I n one  because  a decrease  s t r o n g breakdown have  E^  there .  amplitude  at threshold.  threshold,  ,  2  the  number  2.  However,  gives-a (well  for E  bigger  above  becomes  of pulses  A  is  f  larger  value.  For  A  as than  i s also  obtained  with  threshold equation  example  threshold) 9 approaches  for E  A  much  E /E  A  and  Q  4  equation always  larger  than  equation  4  E  Q  39  f  Thus  ( n e g l e c t i n g the "TT/2  e n c h a n c e d by enhancement Now in  real  bulb. of non  factor  consider life  Eg  the  have  where  the  vector  sum  further 1.  of  angular  not  over  the  where on  the  here.  5 i s very  Qualitively  two  This  of  Eg  i s because  can  circle).  TT/2  Eg  as  E  Clearly charges  are  A  to  this  pulses The  at  actual  i s the  the  a l i g n e d the  ends non  This  section.  is  i s increased.  this  p h y s i c a l model.  some f o r m  bulb. the  The field  A  of  case  of  i s why is  for E  A  near  geometry  can  and be  much g r e a t e r  ( s i n c e Eg  will  not  of  be  than  E ^ the  previous  regime E  and  Eg  significant equation  4.  role  and  non  are  u n i f o r m i t y of  must c h a n g e  the  the  because is  not  treated  made  and  A  average  i s required  neglected  t h r e s h o l d the  the not  non  results  apply.  approximately  aligned; 2.  the  uniformity  When E g  spatial  average  to solve  observations  in this  the  number o f  becomes  complex  be  the  uniform.  up  f o r l a r g e a p p l i e d f i e l d ^E uniformity  of  1 to  the  c o n d i t i o n d e p e n d s on  Equation  steps)  and  indicate  volume o f  Q  localized  neglected  brackets  E  from  Eg  effect  was  2__A  2  circumference  i s f o r m e d by case  7L  of  c o n d i t i o n f o r breakdown  breakdown  uniform).  the  little  u n i f o r m i t y o f Eg the  presence  case  s i n c e Eg  should  1  =  varies slowly  However i n t h e  uniform  the  (1/4  A  count  Eg  can  play  rate given  by  a  40  3.5.3  Extension to E l l i p t i c a l l y  Elliptically except E ) ft  that  these  extreme  as  polarized  E^ r o t a t e s  fields  reduce  Polarized  fields  circularly  (very narrow e l l i p s e ) direction.  fields  l i e somewhere i n b e t w e e n .  axis the  this  section  of  the e l l i p s e .  equations  the  they  single  In  the  circularly  symbol E  linear  be  fields  extreme  (constant  one  fields,  case  and  t o denote  of E  carry  the  fields  for e l l i p t i c a l l y  used  s t a n d a r d use  fields  polarized  t o the u n i f o r m  expected  will  A  At  polarized  reduce  effects  T h i s non  f o r the  like  i t changes magnitude.  t o the  Thus  are  Fields  the  in a  polarized  semimajor  i s desirable  A  over  to this  other  because  elliptical  case. In  the  case  measure m a i n l y reading In changes second effects the  of c y l i n d r i c a l  the component o f  when a l i g n e d the  case  of  also  manner a s  and  i s treated  two  effects  1.  an  the  semi  Q  magnitude  and  developed  axis  by  of  II*.  By  give a  The  steps.  proceeds E  the  B  is  These  Appendix  **  The enhancement i s d e f i n e d as the r a t i o o f f i n an f i e l d of semimajor a x i s E to f i n a linear field,  in a  yields  1 at  Curzon B  B  elliptical E A  of  uniform)  result  r a n g i n g from  two  per  derivation  *  ft  cause  of pulses  the  (assuming  frequency  maximum  fields  fields  analogy  tubes  ellipse.  out of  polarized  The  number  fields.  of equation 4  F.L.  the  i n the  polarized  thus  polarized  smoothing  pulse  change.  will  circularly  i n Appendix  enhancement** i n the  I I was  major  in elliptically  the d e r i v a t i o n  in detail  and  enchancement  in elliptically f  t h e r e i s no  field  bulbs  model:  given f i e l d occur  the  spherical  pulse frequency  similar  with  to the p h y s i c a l for a  tubes  41  threshold  t o 1/4 t h e c i r c u m f e r e n c e  at  high  fields  above  o f the e l l i p s e  divided  by E  A  thresholdi e .  e =  E /E G  A  and fg  f&  =  circumference  e 2.  A disappearance threshold. disappear This  o f the steps  In the c i r c u l a r l y because  is still  the change  the case  semiminor a x i s f i e l d field.  Thus v e r y E  Q  i s larger  field  (except  ellipse  Otherwise  by E  A  the bulb  behaves  at fields  fields  o f t h e same  polarized  i s larger be  fields  than  TT/2)  i s g r e a t e r than  E .  Non u n i f o r m  count  rate f o r fields  near  threshold.  sign. i f the  breakdown  as i n a u n i f o r m  when  effects  above  visible.  i s 1/4 t h e c i r c u m f e r e n c e  than  high  the steps  a x i s and as i n a c i r c u l a r l y  field  In  A  i n E^ i s always  still  i e . less  Q  polarized  of the e l l i p s e  t h e semi minor  vs E  B  in elliptically  t h a t t h e enhancement  divided  f  steps w i l l  qualitatively  than  of  field  polarized o f the  t h e semi minor  o f Eg a l s o  when  axis  change the  conclusion: 1.  Cylindrical  bulbs  rotating  fields  be  fully  used,  provided maps  the  measure  along  the c y l i n d e r  of a planar  axis.  As s u c h  t o c h a r a c t e r i z e the f i e l d  i n space  one o r i e n t s field.  t h e component  the bulb  in different  they can and  time  d i r e c t i o n s and  42  Spherical rotating field  bulbs field.  geometry  spatially  non  calibrated  an  "average"  and  magnitude.  uniform  field  a r e t o be made  meters).  On  field.  Because  Eg e f f e c t s  the other  dependent  of this  the b u l b  geometry  (this  independent o f the o r i e n t a t i o n the  o f the p l a n a r  This average i s h e a v i l y  f o r any g i v e n  measurements existing  measure  the  and be  i f accurate  i s also  hand  must  on  the case  with  the measurement i s  of the bulb with  respect to  43  3.6  Summary  When a n e l e c t r o d e l e s s g a s f i l l e d uniform  field  emmited  with  f  where field  a  A  2[2 E / E ] A  and m a g n i t u d e  in a  (E ) light  spatially  pulses are  A  f  E  Q  (2)  A  o f the a p p l i e d f i e l d  i s given  by t h e P a s c h e n  and E  i s the breakdown  Q  Law  0 (pd)  =  Q  Q  i s the frequency  of the gas.  E  direction  i s immersed  frequency  =  B  f  of fixed  bulb  (1 )  d  where the a  i s a function with  dimension  E  c a n be c o n t r o l l e d  0  p i s t h e gas p r e s s u r e f o r a sphere  by t h e gas t y p e  and d  and t h e l e n g t h f o r  and t h e d i m e n s i o n  of  vessel. A cylindrical  (2)  however In  the  tube equal  fields Also  rotating  tubes  axis. to  brackets  i m m e r s e d a t an a n g l e  E  A  field  fields  must  f  B  is E  A  bulbs  i n equation  4)  fields  disappear.  obeys  A  2  must  the count 2 .  be m o d i f i e d .  r a t e i s always  larger  a t very  of the e l l i p s e  for f a tellipses)  For  o f the f i e l d  The enhancement  t o 1/4 o f t h e c i r c u m f e r e n c e ( o r lower  still  cos 9 n o t E .  equation  g i v e n by e q u a t i o n  fields  9 t o the f i e l d  be r e p l a c e d by t h e c o m p o n e n t  For spherical  i s equal  a t high  tube  the e f f e c t i v e  planar  cylindrical  or  minimum,  of the v e s s e l (the diameter  cylinder).  the  a broad  than  large  divided  the steps  along  by E . A  (integer  44  The physics  p h y s i c a l model p r e s e n t e d of  the  sensor  so f a r  in a controlled  has d e a l t w i t h  laboratory  s e c t i o n d e s c r i b e s the  f u l l meter  environmental  e s p e c i a l l y on t h e s e n s o r .  effects  the p r e d i c t i o n s Section  5.  in this  (sensor  s e c t i o n and t h e  environment.  and d e t e c t o r )  following  the  basic The  ideal next  and d i s c u s s e s  Experiments  confirming  are d i s c u s s e d i n  45  4.0  Electric  4.1  Introduction  This electric voltage  Field  fields,  of  bulb  with  filled electric  gas,  a  specifically  transmission  electric  Design  section describes  application  the  Meter  the  lines  typical  and  field.  (the  The  Since  i t i s r e f e r r e d to  gases  f o r measuring  fields  encountered  pulses  device  b e l o w by  pulses per  d e p e n d s on  the  The  frequency high  i s based  envelopes.  of  light  second  A  on  when e x p o s e d  breakdown o f  (gaseous  the  glass  i s a measure of  electrical  a c r o n y m GEM  low  under  meter  in dielectric  sensor) emits  number o f  the  meter  in substations.  breakdown o f  a gas  field.  complete  electric  to  the a  field  meter). The  sensor  metal parts  and  sensitivity. emitting of  the  can  be  which  Since  rather  digital  processing.  readily  on  made t o h a v e  than  the  field  portable.  for  periods  of  the  sensor,  the  well  i n noisy  good  time  in their  height  the  s e v e r a l months.  to a  output  to  the  sensor)  environments. sec).  The  or  I t contains  strength  detector  i n the  by  without  number  of  the  suited  confer  following  output  i s small, and of  is easily  It is also  the  to  rugged  and  remains c a l i b r a t e d  light  pulses  s h i e l d e d and safe  use  pulses  is ideally  meter  no  directional  field  ( b e t t e r t h a n 5%)  Due  (detector +  r e s o l u t i o n (~1  the  above c h a r a c t e r i s t i c s  measuring meter.  electrical  about  i s contained  I t i s accurate  meter  properties.  isotropic  transported  information  The  an  information  is easily  the  emitted  benefits  f o l l o w i n g important  I t provides  light  metal.  has  t o use  and  from operates has  46  I n what description meter  4.2  covers  operation  design  aspects  i n environmental  left of  i n Figure  light  optical light  whose f r e q u e n c y fibre  electric  the e l e c t r i c  The fields the  with  t o the users use of a long  fibre,  considerations f o r  1 9  parts  (see Figure  the e l e c t r i c  field  7 ) : the sensor and g e n e r a t e s  i s p r o p o r t i o n a l t o the f i e l d ' s i n Figure  the detector  7 ) , which (lower  and g e n e r a t e s  magnitude. or stored optical  transmits  right  f o r later  pulses  the pulses of 7 ) , which  reading  reading  proportional  c a n be  easily  retrieval.  (at least  2 m^)  permits  electrical  o f the person  making  A c o m p a c t v e r s i o n o f t h e GEM c a n be made b y u s i n g  o r by mounting  such a system  the f i e l d  the bulb  directly  on t h e d e t e c t o r .  i s d i s t u r b e d by t h e u s e r  The f o l l o w i n g s u b s e c t i o n s  describe  and by t h e p r e s e n c e each  of the three  The S e n s o r  sensor  dielectric  case.  i s a gas f i l l e d  glass bulb  enclosed  a  However  i n detail.  The  (lower  magnitude; the  i n Figure  a digital  The o u t p u t  fibre  The  fields.  t o be m e a s u r e d u n d i s t o r t e d by t h e p r e s e n c e  the detector.  parts  senses  of l i g h t  field  observation.  short  of three  (upper p a r t  the pulses  displayed  of  7 ) , which  t o the detector,  counts to  GEM i s c o m p o s e d  are described.  as w e l l as p r a c t i c a l  F u n c t i o n a l D e s c r i p t i o n o f the G E M  The  4.2.1  f o l l o w s , t h e GEM a n d i t s p a r t s  i n a protective  Figure  7  Photo showing prototype (66% o f r e a l s i z e ) .  of  instantaneous  display  unit  48  4.2.1.1  The  Bulb  The  bulb  i s most e a s i l y  with  neon  to a  (ie.  P a s c h e n minimum  directional i.e.,  electric scale  field  cylindrical product  bulb,  on  However,  4.2.2.1.1  and  To system  broad  has 5%  started,  than  the  (10  at  15  a slight  is  isotropic  direction.  the  kV/m  and  diameter cylinder  Paschen For  while  The  the  while axis.  minimum  mm  when bulb's  for  a  For  a  a  25  bulb  f o r low  mm  ( s e e S e c t i o n 3.3)) r e a d i n g can  be  A  field  obtained  to  the  field  (  1  greater  i s r e q u i r e d to  bulb  filled  electric  pressures  fixed  threshold  I n t h e weak b r e a k d o w n r e g i m e  kV/m)  A  length  the  example,  a 38  startup hysterisis.  a reliable  diameter  cylinder.  p r o p o r t i o n a l t o the  t o 60  mm  filled  dictates i t s  field  pressure  the the  the  p r o p o r t i o n a l t o L.  is directly  more  of  the  l e n g t h of  10 kV/m.  bulb  25  ( s e e F i g u r e 8)  axis of  f u n c t i o n of  t h r e s h o l d of  ranges  the  of  and  h a n d , g i v e s a maximum r e a d i n g  the  length scale  threshold of  sensor  than  start i t .  in fields  equal  threshold.  Manufacture  fill by  a  frequency  once  Bulb  other  the  (typically  higher  the  L becomes  a  of  bulb  bulb,  over  threshold  spherical  b u l b L becomes  pulse  The  shape  spherical  T o r r has  Torr).  The  S e c t i o n 3.2)  f o r a bulb  a  of p r e s s u r e  magnitude  1 torr  i s aligned with  t o 1 T o r r has  output  or  A  strength i s inversely  filled 0.66  f o r neon).  threshold i s a  For  of  (see  same r e a d i n g i r r e s p e c t i v e  direction  (L).  field  the  cylindrical  field  pressure  sensitivity.  i t gives  narrow the  typical  made o f p y r e x  a  the 100  bulbs mm  with  aperture  gas  they  diffusion  are  pumped down on  pump e q u i p p e d  with  a copper a  liquid  vacuum  Figure 8  Photo showing  typical  bulbs.  50  nitrogen  trap  diffusion Duoseal base and  1402, p u m p i n g  with  than  reagent  5 x 10~  grade  4 hours.  gases,  The s e c o n d  Torr.  o i l pump  The c o m p l e t e  After  the bulbs  pumping  are f i l l e d  s e a l e d , and then  baking  o b t a i n e d from  improves  are helium  impurities  are present a t the l e v e l  filled  with  (  of  the d e s i r e d  diameter,  at  t h e Paschen  minimum  d, a r e f i l l e d  system  has a  f o r 24 h o u r s ,  to a  baked  suitable a g a i n a t 280°C o f the  occurs.  (99.999% pure)  2ppm).  o f 0.1 ppm.  available  (Model  I n t h e neon,  8ppm) a n d n i t r o g e n (  commercially  The  the performance  the Matheson Co.  impurities  and a r g o n  the chief  I n argon  Some b u l b s h a v e  dry a i r or nitrogen. t o a p r e s s u r e , p, such  some also  The b u l b s that  pd i s  (determined e x p e r i m e n t a l l y ) .  The H o l d e r  The holder  bulb  serves  i s placed i n a protective three  to protect  2.  to hold  3. The  dielectric  the bulb  the o p t i c a l  from fiber  environmental close  two c r i t e r i a  criterion  the holder.  The  c o n d i t i o n s and h a n d l i n g ;  t o t h e b u l b and a l l o w t h e  o f l i g h t p u l s e s t o t h e f i b e r and  t o p r e v e n t most o f t h e ambient last  case,  functions:  1.  coupling  first  rotary  o f t h e b u l b s h a v e b e e n made u s i n g n e o n  (99.9995% p u r e )  4.2.1.2  6  170 l i t r e s / s e c ) .  b u t i t i s n o t y e t known why t h e i m p r o v e m e n t  Most  been  speed  160 l i t r e s / m i n ) .  a t 280°C f o r 4 h o u r s ,  another  bulbs,  170, p u m p i n g  by a S e r g e n t Welch  speed  pressure of less  pressure  Diff  pump i s b a c k e d  baking  for  (Balzer's  light  from  entering  c a n be met b y m o s t p l a s t i c s .  i s more s t r i n g e n t .  Glass  the f i b e r .  However t h e  i n c r e a s e s i t s c o n d u c t i v i t y by  51  orders  of  because  m a g n i t u d e when h a n d l e d  mobile  reliable  alkali  operation  conductivity  ions  the  i s not  can  bulb  worked w e l l  m u s t be  i n f l u e n c e d by  (humidity these  i n very  u n d e r 70%)  holders  bulbs  exposed  humid  to  large relative  d i s s o l v e i n adsorbed  ( p o l y t e t r a f l u o r e t h y l e n e ) which has  or  enclosed  these  i s hydrophobic  be  dropped  from  i s the For  2 m  2 0  for  whose  Teflon ideal  material  more t y p i c a l  plexiglass (polymethylacrylate) can  Thus  i n a container  effects.  environments.  water.  humidity  onto  conditions  i s adequate.  concrete  and  floors  With with  no  damage.  4.2.1.2.1  Holder  For  research  cylindrical one  stock  c l o s e d end  fiber  is fitted  replace  the  of  test the  purposes  i s capped with to  the  black  light  cap.  teflon).  a screw-on In  i s reduced  ( i n s i d e ) or  In p r o d u c t i o n (with  holders  desired material.  electronics is sensitive  holder  bulb  and  this  cap  manner  are  made by  The  resulting  of the  the  drilling  out  c y l i n d e r with  same m a t e r i a l .  holder  can  be  The  opened  to  bulb.  Ambient the  Manufacture  the  the  fiber  by  not  need  t o be  to pulses  not  D.C.  s i g n a l s ) by  putting black  holder  glued  ( i t does  to  will  most  i t ) into  eliminated  electricians  likely  be  tape  made by  molten holder  because  painting outside.  dipping  material  (say  the  the  52  4.2.1.3  Engineering  There sensor  a r e two t y p e s  when o p e r a t i n g  (temperature  4.2.1.3.1  glass  and under  fields:  that  apply  environmental  and t h e e f f e c t s o f f i e l d  4.2.1.3.2  earlier  extreme  humidity  conditions  increases  t o the  effects  harmonics.  the c o n d u c t i v i t y  can c o m p l e t e l y  T h e e f f e c t c a n be e l i m i n a t e d  suitable  o f the  s h i e l d the gas from the  by p r o t e c t i n g  the bulb with  a  holder.  Temperature  Temperature performance  parameter  i s increased  changes w i t h  between -40°C caused  and 40°C  because  adhering  c a n have b o t h  of the s e n s o r .  the g l a s s  t o the bulbs  temperature  Direct with  the t y p i c a l  interior  i t can i n f l u e n c e  e f f e c t s are minimal  range.  surface.  combined.  I n d i r e c t e f f e c t s are  surface  properties  coefficient  X  such and  of  materials  The m a t e r i a l s  On v a r y i n g  i s r e v e r s i b l e whereas  on t h e b u l b  the c o n d u c t i v i t y  the gas breakdown  the concentration  and e x t e r i o r  glass  emission  and b e c a u s e  operation  or chemically  e f f e c t s on t h e  because  Both o f these  influences  of material  secondary  e f f e c t s occur  temperature  physical absorption  Absorption 1.  d i r e c t and i n d i r e c t  temperature.  temperature  p h y s i c a l l y absorbed  not.  considerations  i n environmental  and h u m i d i t y )  mentioned  field.  be  of p r a c t i c a l  Humidity  As  of  Considerations  may  the  "chemisorption"  is  h a s two e f f e c t s : as c o n d u c t i v i t y  or the  53  2.  i t can  change  the  gas  composition  and  t h e r e f o r e i t s breakdown  properties. To  minimize  protected  (by  bulb.  This  bulbs  during  of  4.2.1.3.3  i s the  the  the  effects  effect  one  holder)  as  w e l l as  must be  must k e e p  the  bulb  minimize  the  impurities inside  and  main m o t i v a t i o n  in Section  f o r properly baking  and  for using  gases.  very  pure  evaluated  experimentally.  on  operation  clean  the  pumping  the  The  Results  and  extent are  5.  1 8  harmonics have  Cylindrical Since  field  sensor  d e p e n d s on  the  shape  Tubes  a cylindrical  along  linearly  i t s axis, polarized  major harmonic  tube  i t i s only field.  The  components:  If Ejj/E ^1/9  the  per  the  E . H  largest content.  The  A  value  A  c y c l e of  number of  of  the  harmonic  field  will  then  component  consider  normally  the  the  i s not  3f , A  number  of  of  two  f , A  of  EJJ) .  extrema by  determined  strength, irrespective  the  effect  amplitude  affected  i s therefore s t i l l  of  contain  (frequency,  (frequency  fundamental  counts  t o the to  fundamental  E /E <0.1.  field  third  field  Typically  H  the  the  only  necessary  E ) A  and  responds  amplitude  of  exterior  sensor.  a)  a  effects  production  Harmonics  The of  using  temperature  presented  these  the  the by  in  value the  harmonic  54  b)  S p h e r i c a l Bulbs The  given  analysis  above.  fundamental  component  of  the  typical  counts  caused  by  the  rotating  circumference  of  the  phasor,  to  largest  field  the  The  optical  Welch-Allyn.  and  sensor  light  The  the  assuming  order no  in E /E H  harmonic  A  the is  equal  distortion bulb  only  component o f  the  applied field.  The  can  occur This  error  of  uses a  Shorter  needed  enhancement i n  spherical  or  i s strong, a  most i m p o r t a n t  m u s t be  60  frequency).  sensor  are  polarized  p r o p o r t i o n a l to  to f i r s t  the  during  field  the  oscillation  period  i s t h e r e f o r e measured  E /E . H  A  vinyl  clad  longer narrow  t o enhance  purchased  glass fibre  fibres fibre  the  from  can  can  be  collection  be  used.  used of  bundle  and  light  2mm  Since no at  the  fibre.  which Hz  long.  output  reflectors  be  The  the by  elliptically  that  the  H  GEM  of  to  approximation  + E .  A  will  cycle  i s determined  For  i s a commercial product  prototype  2 m  field which,  s t r e n g t h which is E  cycle.  phasor  fundamental  fibre  The  diameter  to  the  a maximum f r a c t i o n a l  Fiber  input  the  of  is identical  breakdowns p e r  i s shown i n F i g u r e 9.  a first  fundamental  The  special  phasor  Thus as  responds  with  s t r e n g t h i n the  circumference  =0).  H  of  fields  applied field  a  the  polarized  number  fields  of  the  the  field  (E  in  Hence  greatest  to  4.2.2  for linearly  very  i s exposed  low  property of (<  10  - 1 2  This property i s not  changed  mho  the m~  1  ensures  fibre  cable  i s i t s conductivity  for typical t h a t the  significantly  by  fibres  field the  in fields  to which  fibre.  Low  the  of  55  Figure  9  Phasors dotted solid  for Applied Field, curve  curve  distorition,  - elliptical - elliptical E . H  E  A  polarization polarization  - no with  harmonic 3rd  distortion,  harmonic  56  conductivity to  the  with the  a l s o reduces  detector  a metal fibres  sets  of  with  months h a d  meets  near  an  bundles shrink  are  tubing.  The  detector an  has  photodetector and  standard  a  of  for  the  fibre  i n the  field  the  To  overcome  the  the  same e f f e c t  electrical  appliances.  i s a small  plastic  the  block  metal  certain  the  During  of  box  sheet  frequency  diagram  detects  shaped.  pulses  this  of  the the  this  the  only)  as  springs  detector  near  the  The of  a l l pulses  (same a m p l i t u d e  and  the  fibre  graded the  a  bundle fibre  heat  junctions  e l e c t r o n i c s which  light  the  pulses  since  i s shown i n F i g u r e  this  ( s e t above  i s only  lead  field.  pulses  threshold  was  f u n c t i o n of  weak o p t i c a l process  two  four  commercial  with  containing  occurence  This  the  caps  electric  of  eventually  flexible  problem  liner.  fact  application is  can  bundle.  b u n d l e where  set  of  high conductivity.  bundle  of  fibre  protected  In  a period  earlier  fibre  i n the  are  resin.  over  The  the  However, many  conductive  unacceptably  a l l fibres  internal  a  from  bundles  of  i s p r o p o r t i o n a l to  simplified  than  s e t had  noise  unsuitable.  conductivities.  r e - i n f o r c e d (near  i s t o measure  frequency  higher to  and  Detector  amplified  cap.  This  The  A  caps  with  fibre  same m a n u f a c t u r e r  property  some o r  electrical  obviously  coated  the  second  end  have been  detector  The  of  inflexible  s h i e l d e d by  this  the  the  between w i r e s  4.2.3  are  different  of  Many c o m m e r c i a l are  C o n t i n u o u s use  breaking  problem  metal  important  robustness. the  These  s u p p l i e d by  but  Another  to  no  widely  satisfactory  coupling  electronics.  shield.  fibres  the  which  noise  duration).  are  10.  then  whose a m p l i t u d e level)  are  These p u l s e s  is  converted are  then  LIGHT  PHOTO DETECTOR  PULSE AMPLIFIER AND SHAPER  DIGITAL COUNTER  DIGITAL DISPLAY DIGITAL STORAGE  Figure  10  Block  Diagram  of Detector  and D i s p l a y  System.  58  counted  over  a s h o r t time  the  counter  the  more a c c u r a t e  change  i s reset to zero  during  resolution  time  fields  be  counts  either  which  d i s p l a y e d t o the user  prototype  employs  battery.  The d e t e c t o r measures  for  at least  10 h o u r s  microprocessor slightly average eight  larger.  In t h i s  electric  hour  field  period.  reading  for typical  tends  At threshold  time  fluctuation  constant,  the e r r o r i s t y p i c a l l y  fields.  110 x 60 x 30 mm Another  f o r example, every  The e l e c t r o n i c s  five  can  One l a b  rechargeable  and t h e b a t t e r i e s  l a b prototype  last  contains  a  This prototype i s  t h e minimum, maximum a n d  minutes  o f both  field  retrieval.  d i s p l a y and has a  7).  does n o t  alternating The  t o be  i n s t e a d o f the d i s p l a y .  case,  the f i e l d  the b e t t e r the  or stored f o r later  (see Figure  The l o n g e r A t ,  p r o p o r t i o n a l t o the e l e c t r i c  crystal  a n d some memory  that  o f one s e c o n d .  f o r stronger  are d i r e c t l y  p e r i o d o f l e n g t h A.t  again.  o f course  i n t e r v a l At  strength.  a liquid  t o count  compromise  interval  i n each  lower  every  The s h o r t e r At,  A good  of the f i e l d  5% a n d c o r r e s p o n d i n g l y The  provided  i s a time  t h e number o f c o u n t s  After  and a l l o w e d  span.  of the meter.  irrespective  (At).  the reading,  this  environmental in  span  c a n be s t o r e d o v e r  detectors  an  a r e amenable t o  further minaturization.  4.2.3.1  Electrical  The (and  detector electronics  boards).  shapes  Design  The f i r s t  the pulses  consists component  p a r t which  i s specific  of a d i g i t a l o  counter  o f most d i g i t a l  c a n be s e p a r a t e d basically  to this  into  application.  and w i l l  parts  d e t e c t s , a m p l i f i e s and  and d i s p l a y system  devices  two d i s t i n c t  The s e c o n d  i s a very  n o t be d e s c r i b e d  part  standard further.  which  59  The shaper shelf  circuit  components  noise  is  by  FET  only  to a  at  the  only  electric supply  from  can  those  above  a 9v  certain  be  packaged  gain  next  each  design  the  the  combined  into x  50  one mm  Overall Engineering  Most of  the  been d i s c u s s e d  are  30,000.  Each  the  pulse  chip.  board  height  pulse.  above  the  60  the Hz  lower and  noise  noise  right  The  the  of  the  shaper  uses  If desired  (at a setup  circuit about  the  cost  stage  through  threshold so  as  for  to  ( i e . when  the  power  11. operate  hours.  detector  present  chip)  reduce  d i s p l a y e l e c t r o n i c s can  continuous  size  to  (R21)  Figure  low  by  f u r t h e r the  of  a  i s put  level  the  through a  amplifier  pulse  a variable resistor  f o r 10  example  a m p l i f i e r and  i n a 50  with  counter  battery  For  off  Light is  ( i e . capacitor followed  standard  reduce  i s p o s s i b l e to reduce applications.  40°C) .  i s fed  amplified voltage  shown i n t h e and  signal  standard  o p e r a t i o n a l a m p l i f i e r ) i n order  s i g n a l s which  as  The  i s about  stage  to a  To  i s made w i t h  pulse  operational amplifiers ( a l l within  adjusted  is of).  a m p l i f i e r and  b e t w e e n - 3 0 ° C and  (FPT100).  Finally  rechargeable  photodetector, be  the  of  circuit  operate  total  to  photodetector,  The  four  converted  i s decoupled  It  could  The  input  and  field  The  can  of  noise.  comparator  detect  4.2.4  series  coupled  frequency  comparator  the  11.  a phototransistor  A.C.  resistor  a  (which  amplification.  low  f o r the  i s shown i n F i g u r e  detected  for  diagram  i f required for  four  the ICs.  whole d e t e c t o r of  less  for  than  These could  be  $50,000).  Considerations  engineering  considerations apply  i n S e c t i o n 4.2.1.3.  Electrical  to  noise  the  sensor  affects  the  and  have  detector  -TEST Ftoi K/T 4  ojrfKT  To D/CrrAL •r  =r c/i Rio  loo  Figure  11  Circuit  Diagram  for Photodetector  Amplifier  and  Pulse  Shaper.  o  61  but  c a n be v i r t u a l l y  low  pass In  considering of nearby  between  the sensor  when a p e r s o n distances  other  enters  conducting  very  from  objects  an e l e c t r i c  (or people)  field  care  Thus  should  enhancing  i n using  large  This  field  that  discharge  produces  In  a l l measurements  distance  i s derived  metallic  parts  is has  required  and i n v a l i d a t e s t h e t r u e  the detector  should  experimentally)  from  be m a i n t a i n e d  do n o t i n f l u e n c e t h e r e a d i n g .  i n which  the sensor  and d e t e c t o r  t o be c a l i b r a t e d a s one u n i t a n d c a n o n l y  fields.  The  reading  the sensor  about  corona  o f the meter.  i n order  0.5m  (this  that i t s  I f a compact d e s i g n  be u s e d  mm  to corona  at least  a r e one u n i t ,  10  pointed  can lead  i n t h e a i r and i n t h e gas i n s i d e the s e n s o r . light  c a n be  because  discharge  On  near a  be m a i n t a i n e d  they  a  objects.  the sensor  i s required  effect  t h e meter f o r  conducting  then  should  that  i n maintaining  the enhanced  the sensor  revealed  i s distorted at  be t a k e n  of a person)  are the  and t h e s e p a r a t i o n  the f i e l d  t o measure  metallic objects.  considerations  Experiments^ have  o f meters) from  However,  such a l a r g e  the major  the person.  ( s a y the head  close.  pointed  have  (order  i f one w i s h e s  object  objects  measurements  distance hand  as a whole  and t h e d e t e c t o r .  u p t o 2 m away f r o m  reasonable  away  the meter  conducting  making u n d i s t u r b e d  brought  b y s h i e l d i n g t h e e l e c t r o n i c s and b y u s i n g a  filter.  effects  the  eliminated  then  reliably  o f GEM  the meter i n uniform  62  4.3  Summary  An  electric  insulating and  the  field  vessel  i s constructed  detector.  The  proportional  to  the  where  detector The  entry  the  sensor  electric  of  on  the  field.  are  counted  specifications  for  the  i s derived  breakdown o f  three  produces  they  f o r temperature  Section  meter based  light  The and  meter  parts:  the  pulses  fibre  gas  in  an  sensor,  the  whose number  conveys  these  fiber is  pulses  to  displayed.  are  summarized  experimentally  and  i n Table  2.  The  further discussed  in  5.  The  last  sensor  and  series  of  physical  two  the  s e c t i o n s have p r e s e n t e d  design  experiments model.  of  the  meter.  performed  These  during  These experiments  are  the  p h y s i c a l model  sections  are  the  development  the  subject  of  for  partly of  GEM  Section  the  based and 5.  its  on  a  63  Table 2  GEM  Preliminary  Specifications  Accuracy  better  t h a n 5%  Calibration  seldom  required  ( e v e r y few m o n t h s )  Size Sensor  (including spherical  holder,  45mm d i a m e t e r  x 55mm  length  bulb)  Fibre  2mm d i a m e t e r  Detector  110 x 60 x 30mm  x 2m*  length  Power  9v r e c h a r g e a b l e b a t t e r y (10 h o u r s o p e r a t i o n )  Threshold  14 kV/m ( c a n be r e d u c e d b y i n c r e a s i n g sensor dimensions)  Environmental  effects  Humidity  *  no  effect effect  Above  room  temperature  no  Below  room  temperature  unknown  variable  64  5.0  Experimental  5.1  Introduction  The  purpose  performed  generated just  are  outside  the  detector  with  s i g n a l can  sensor  (often without fibre  Four its  This  with  s e r i e s of  the  pulse  experiments  sensor the  3.2  and  shape.  physical  vessel walls.  The  where e l e c t r i c  study  be  viewed  are  fields are  transmission  performed  Thus  since  lines  and  with  a  full  the  the  and  The  oscilloscope  therefore  i n the  is  (ie.  distorted)  laboratory  environment  to  only  the  controlled)  used. c a r r i e d out  described.  emission  The set  model t o operation  The  first  i n uniform  e s t a b l i s h e d , the  This  on  amplified  counter.  3.3).  are  performed  i t i s more d e s i r a b l e  directly  t o be  are  Most  environmental e f f e c t s .  typical  tests  experiments  are  i t s p h y s i c a l model.  laboratory  holder,  meter  vicinity  (Sections  extending the  of  the  experiments  more s e n s i t i v e p h o t o m u l t i p l i e r .  a digital  the  phenomena o f set  model  of  major  immediate  basic  with  the  out.  the  s i g n a l would have  counted  the  a  to  in detail  Some e x p e r i m e n t s  under  field  in  and  plates.  i n order  and  However,  GEM  laboratory  carried  outside  and/or  and  i n the  t e s t s both  have been  detector  of  parallel  some f i e l d  photomultiplier the  large  meter.  i s to describe  development  laboratory  Experiments  replace  section  performed  the  substations  prototype  this  the  between  Furthermore, in  of  during  experiments  Results  of the of  fields of  s e r i e s of  experiments  the  laboratory  series deals  validity  second  in  of the  basic  physical  experiments the  breakdown  a directionally  the  fixed direciton.  provided  c a s e when t h e  with  and  deals  backing i s guided  s e n s i t i v e sensor  for by is  65  based  on t h e s e  experiments in  planar  deals with rotating  understanding fields and  which  4.2).  be  Finally,  given  such  effects  the l a s t  similar  and f i e l d  In detail.  of the e x p e r i m e n t a l sensor  presented.  the procedure  Finally,  results  (see S e c t i o n  deal with  3.5  engineering  accuracy,  results  with  temperature I t should  presented  in a  many d i f f e r e n t  bulbs  obtained.  what f o l l o w s t h e l a b o r a t o r y e x p e r i m e n t a l Then  environmental  d e s c r i b e d i n the s e c t i o n .  have been performed  have been  to  p e r t u r b a t i o n (by the s e n s o r ) .  a r e f o r the s p e c i f i c  results  object  of calibration,  sensors  p r o v i d e s an  m e a s u r e s when e x p o s e d  s e t of experiments  s e tof  and c y l i n d r i c a l  s e t o f experiments  by a c o n d u c t i n g  as s t a b i l i t y  However, most e x p e r i m e n t s and  This  the sensor  that the d e t a i l s  section  The t h i r d  the o p e r a t i o n o f s p h e r i c a l  are not perturbed  humidity noted  (see S e c t i o n 3.4).  fields.  o f what  considerations and  experiments  and r e s u l t s from  field  f o r each tests  s e t up i s d e s c r i b e d i n s e t o f experiments  are given.  are  66  5.2  Experimental  5.2.1  Introduction  The  experimental  generating light  generates  and  electric  pulses.  field  of variable  description  plate  field  ellipticity.  electric  rounded field  The d e v i c e  field  square  corners  i s generated  sheets  purposes.  The upper p l a t e  rods  plate  plates  which  normally  rotating  One  rotating  uniform  fields  f o l l o w e d by a  fields.  i n a F i x e d D i r e c t i o n and  between 12.  the p l a t e s o f a  The p l a t e s c o n s i s t  o f p o l i s h e d aluminum w i t h  are quipped  serve  with  i s supported  c a n be s c r e w e d  into  t o be a l i g n e d c o r r e c t l y  are parallel  fields.  be d e s c r i b e d f i r s t ,  t o each other  hinged  with  doors  for safety  25mm  diameter  lucite  sheet  and t h e v a r i a b l e  The s e n s o r  a t high  sheets  r e s p e c t t o the lower  (+ 1mm)  s e t a t a d i s t a n c e o f 150mm.  lucite  the upper  o f 600mm x  corona  on l u c i t e  by t h r e e  parallel  b e v e l l e d edges and  t o reduce  They a r e mounted h o r i z o n t a l l y  10mm) w h i c h  lucite  electric  that generates  Fields  ( r a d i u s f \ f 150mm) w h i c h  strengths.  and s t u d y i n g t h e  the other a planar  for generating planar  Uniform  a device f o r  Emission.  (thickness  this  direction  c a p a c i t o r , a s shown i n F i g u r e  600mm x 3mm  for monitoring  for producing  equipment w i l l  f o r Generating Pulse  o f two m a i n p a r t s :  and equipment  i n a fixed  of the device  Studying  consists  a r e two d e v i c e s  monitoring  Apparatus  The  apparatus  fields  There  uniform  the pulse  5.2.2  Apparatus  i s mounted  threaded  and p e r m i t o n e . The  spacing i s on a  lucite  67  50:1  o  TRANSFORMER  BULB  OPTICAL FIBRE  Figure 1 2  'A  PHOTO MULTIPLIER  ~~T"  LUCITE  ^  ALUMINUM  E x p e r i m e n t a l S e t Up  AUTO TRANSFORMER  68  bracket does  a t the center of the f i e l d  not influence  location  the charge  of the sensor  also  generated  distribution  ensures  that  by t h e p l a t e s ,  on t h e p l a t e s  the a p p l i e d  2 1  so that i t  .  This  field  i s spatially  uniform. The  capacitor  autotransformer 6kV  o f 40kV m  programmable 1000,  power  maximum  frequency range  931A long,  2mm  are  instead  o f 60Hz. (Kepco,  facilitates  directly  difference of  to a  the o s c i l l o s c o p e )  field  M o d e l OPS  5000,  response.  The  clad  The v o l t a g e  a r e conveyed  glass  a t -1kV w i t h  a M o d e l CA p l u g - i n  fibre  applied  bundle  The  contains a replica  i s f e d t o the counter  The c o u n t i n g i n t e r v a l  divider.  t o an RCA (1.5m  photomultiplier  r e s p e c t t o ground.  amplifier).  The  signals  (Tektronix  The o u t p u t  of the s i g n a l  from the displayed  (Advance I n s t r u m e n t s ,  i s usually  gain  frequency  with a high voltage p o t e n t i a l  the v i n y l  i n the range  Model  o f one t o  seconds. All  experiments  environmental relative  (except f o r those  effects) humidity.  are carried  involving  a  o f the e f f e c t of  o b t a i n e d from W e l c h - A l l y n Co.  (which  f e d b y an  I n some e x p e r i m e n t s  studies  e m i t t e d by the b u l b s  through  amplifier  TC9A, 32 m H z ) .  70%  This corresponds  a few Hz u p t o 600 H z .  i t s cathode  M o d e l 549 w i t h  oscilloscope  ten  of light  potential  recorded photographically using a storage oscilloscope  Inc.,  on  This  from  i n diameter)  operated with  a maximum  s h a p e on t h e s e n s o r  i s measured  photomultiplier  i s used  5kV).  extends  flashes  that  the p l a t e s .  supply  a n d wave f o r m  the p l a t e s  such  (rms) a t a f r e q u e n c y  -1  output  employed  The  is  ('Variac')  (rms) o c c u r s between  strength  to  i s n o r m a l l y p o w e r e d b y a 50:1 t r a n s f o r m e r  the study o f  o u t a t 293 + 4 K e l v i n  and l e s s  than  69  5.2.3  Apparatus  The  60 Hz p l a n a r  plates.  vertically  on  sheets  13).  hollow  lucite  four  from  Rotating  fields  and form  x 760mm  network which  phase w i t h  voltages  (V-j ,  elliptically field  each  generates  other  network  (see R21» Figure  by  changing V .  30  kV/m.  0  The  The a p p a r a t u s  flashes of light  previously.  14).  Figure  transformers  consists of a out  each o f these  p l a t e s o f t h e c a p a c i t o r an  The magnitude  a r e conveyed  each  a n d V-j, V 4 ) 9 0 °  The e l l i p t i c i t y  the r e s i s t a n c e values  i s capable  circuits  By c o n n e c t i n g  c a n be g e n e r a t e d .  c a n be v a r i e d by c h a n g i n g  2  i n s i d e the  (see Figure 13).  T h e two  (V-j , V  from the  o f the device  i s mounted  Each c i r c u i t  14).  V 3 and V 4 ) t o a d j a c e n t polarized field  fibre  b y two p a r a l l e l  two v o l t a g e s  (see Figure  of polished  i n the center  f e d by a " V a r i a c " .  metal  They a r e mounted  a t the bottom  d r i v e n by s i g n a l s 180° o u t o f phase.  bridge  sheets  vertical  a r r a y when v i e w e d  The o p t i c a l  the apparatus  b y a 50:1 t r a n s f o r m e r  x 3mm  a square  p l a t e c a p a c i t o r i s powered  by f o u r  corners.  i s mounted  rod.  Fields'^  are produced  and rounded  The s e n s o r  r o d and emerges  powered  of  on l u c i t e  a vertical  The  are  rotating  b e v e l l e d edges  (see F i g u r e  lucite  Planar  T h e p l a t e s c o n s i s t o f 260mm  aluminum w i t h  top  f o r Generating  ofthe  i n the bridge  of the f i e l d  of generating  c a n be v a r i e d  fields  t o t h e same a p p a r a t u s  15 shows a p i c t u r e o f t h e a p p a r a t u s .  o f up t o  described  70  71  Figure  14  Electric  Circuit  f o r Generating  Rotating  Fields  Figure  15  Photo fields the  showing  plates  (right),  transformers  f o r production  5 channel (left),  o f 60Hz r o t a t i n g  photomultiplier^variacs and  electronics  (bottom)  electric  for driving  73  5.3  Study  The  experiments  described of  of the Basic  by u s i n g  Standard  5.3.1.1  General Pulse  filled  to investigate  different  gas  the b a s i c  deals  deals  with  with  phenomena a r e  a l l major  attempts  features  t o reduce the  compositions.  Phenomena  Emission  experiment  with  The f i r s t  phenomena, t h e s e c o n d  5.3.1  This  performed  i n two s u b s e c t i o n s .  the standard  threshold  Phenomenom  neon  i s performed  to a pressure  with  a pyrex bulb  o f 10 T o r r .  o f 25mm  The a p p l i e d  diameter  field  i s a 60Hz  w a v e f o r m whose m a g n i t u d e i s v a r i e d . The field the  relation  i s observed  by a d d i n g  photo-multiplier  shows t h e l i g h t oscilloscope Figure of  between p u l s e  16.  the sine  trace  and t h e phase o f t h e a p p l i e d voltage  across  the p l a t e s  The o s c i l l o s c o p e d i s p l a y o f t h i s  superposed  triggered  The p u l s e s wave.  t h e measured  output.  pulses  emission  on t h e a p p l i e d  on t h e a p p l i e d  of l i g h t  appear  field  field.  has been  on t h e r i s i n g  From many s u c h p i c t u r e s  A  typical traced i n  that  pulses  on a g i v e n  slope  o f the a p p l i e d  field  are spaced  change  i n the magnitude  of the a p p l i e d  field  i s approximately,  This  change  E  approximately in  field  pulse  D  i n the a p p l i e d  field  t h e same on r i s i n g  between  required  and f a l l i n g  t o produce slopes.  slopes  the  light  so that the constant.  a new p u l s e i s  However t h e c h a n g e  the l a s t  pulse  in a rising/falling  slope  of a f a l l i n g / r i s i n g  slope  i s usually  less  slightly  signal  and f a l l i n g  i t i s observed  and  and t h e than  E . 0  first This  74  Figure  16  O p t i c a l pulses 25mm d i a m e t e r  superposed  A  = field  applied  n e o n - f i l l e d bulb  case). E  on  amplitude.  at  10  field Torr  wave f o r m (strong  (E ) A  for  breakdown  75  difference causes the  i s consistant with  the f i e l d  applied field  versus  time  pulses  a and c  threshold  the bulb  very  long  than  E  decreased a start  breakdown  5.3.1.2  one  This  experiment  but the bulb fields  into  measuring  and  For E  A  i s less  results  than the above  i t can take  0  For a f i e l d ,  E ,  a  higher  A  As the a p p l i e d f i e l d i s  decreases  A  A  time)  i s increased  A  of E  strength.  close to E /2  immediately. E  versus  T  field  As E  to appear.  until  These  Emission  below E / 2 .  Thus  Q  are consistent with  pressure above  A  f  E . A  of size  B  i s also  , t h e number  there  the s t r o n g  120 Hz i n f a plot.  pressures,  except  B  higher  plot  The number  of this  per second  of steps  ( i e . twice  The same e f f e c t that the steps  as the p r e v i o u s  than  f  A  effect  E /2 D  , the frequency  i s observed  become  sharper.  emitted per  o f times  i s obtained  (averaged  of size  10 T o r r t h e  of pulses  d e p e n d s on t h e i n t e g e r number  consists  Magnitude  varied.  of pulses  a plot  shows s u c h  t h e same e q u i p m e n t  i n F i g u r e 16.  An i l l u s t r a t i v e  Such  with  of Applied Field  t h r e s h o l d and p r e s s u r e s  i s as d e p i c t e d  2E .  as a F u n c t i o n  i s performed  o f the a p p l i e d f i e l d  versus  at idential  respect to  model.  situation  fits  are observed  of Pulse  cycle  pulse  up" a l m o s t  up h y s t e r e s i s .  (becoming E  are seen.  pulses.  f o r the f i r s t  Rate  For  t o emit  pulses  with  i f the graph  A  D  "starts  shifted  In f a c t ,  t o the l e f t occur  c o n d u c t i v i t y which  2 E , o f the a p p l i e d f i e l d  E , no l i g h t  pulses  t o be p h a s e  A  starts  time  T  of f i n i t e  ( E ) (see S e c t i o n 3.3.5).  t o peak v a l u e ,  the bulb  Q  (E  ( i n F i g u r e 16) w i l l  field,  E /2 Q  the bulb  i s displaced slightly  When t h e p e a k  is  inside  the e f f e c t  over  i n applied  f o r higher  A  E  by  one  of E ) .  that  second) field  Figure  17  bulb  However f o r t h e  lower  Q  76  500  400  300  200  100  10  20  30  E  Figure  17  Pulse emission frequency (EA)  for  different  B u l b d i a m e t e r was  (fB)  40  A* ( kv  1  Rns )  as a f u n c t i o n o f  bulb pressures. 25mm.  m" ,  50  applied  field  77  pressures  the steps  a r e g r a d u a l l y smeared o u t u n t i l  relationship  between  pulse  Figure  Another  effect  18).  sharply  d e f i n e d a t E /2  results  are not r e l i a b l e  applied  bulbs field  pressures  filled  fluctuates  t h a t 10 T o r r  by a f a c t o r  amplitude  waveform  for a  shown i n F i g u r e  smear __E  A  by  the p u l s e  The p u l s e  height  bulbs.  Pulse  pressures  the v a r i a t i o n  Figure  4.  These pressures. It  avalanche.  At high  increases with  results  i s i n this  regime  between E f i e l d  pressures,  from  typical  10 T o r r  E  in AE  that  Figure  4  a  A  that  i s much l e s s increment  of the f i r s t  pulse  t h a t one rate  i t i s harder  on t h e than  a t low  between  successive  a s c a n be  occurs  GEM  or the  different  a t the  seen i n  lower  to reset Ej completely  needs t o o p e r a t e i s desired.  emitted  varies at a l l  depends  t h a t weak b r e a k d o w n  pressures  and c o u n t  for a  a s t h e one  exceeding  height  pressure  the f i e l d  the h e i g h t  indicate  A t these  i n t h e same way  o f t h e amount o f l i g h t  at a given  pulses  1 Torr  height.  variation  A t lower  at  I t commonly  i t i s the v a r i a t i o n s  The  pressures.  However  F i g u r e 4 shows a  I t i s also clear  i s a measure  o f the breakdown  pressures.  17.  than  at pressures  Clearly,  i n Figure  d e p e n d on  strength  less  the change i n  constant.  to fluctuate.  obtained  In comparison,  out the steps  However  Q  or greater,  in effectively  begins  A  bulb,  15%.  (see  the t h r e s h o l d i s not  A  A  than  i s linear  for E <E /2.  ( E ) o f the a p p l i e d f i e l d .  16.  less  o f 10 T o r r  o f two a t p r e s s u r e s  low p r e s s u r e  the  regime.  pulses _ E  i s that  are emitted  to pressures  A  constant  fluctuates  i n this  (_\E ) b e t w e e n  less  and a p p l i e d f i e l d  o f low p r e s s u r e s  and p u l s e s  Q  For  frequency  at 1 Torr  i f a linear  t o 0.  relation  78  Finally, (for  i t m u s t be o b s e r v e d  an example  to  30 T o r r .  of  i t s height.  emitted)  see i n s e r t  Furthermore  that pulse  i n Figure  the t o t a l  The a r e a  under  shape  i s remarkably  16) f o r t h e p r e s s u r e s  duration  the pulse  o f the pulse  profile  constant  t e s t e d from 1  i s independant  ( i e . t h e amount o f l i g h t  i s therefore proportional to i t s height  as has been  assumed  above.  5.3.1.3  Determination  This ranges 30  of E  experiment  from  Torr.  Q  i s performed  with  a series  o f bulbs  12.5mm t o 38.1mm a n d whose p r e s s u r e  The a p p l i e d v o l t a g e  ranges  whose  diameter  f r o m 0.66 T o r r t o  i s a 60Hz w a v e f o r m whose m a g n i t u d e i s  varied. We h a v e It  i s t h e change  (averaged in  seen  over  applied  that E  f a l l i n g and r i s i n g  field  pulse  pressure  required  results.  b y 240Hz  are observed).  The series  results pulse  A  comparison  pressures  a r e observed  obtained  bulbs  field  filled  widely.  required  o f low p r e s s u r e  this  i s a true  E <E /2. A  rates  Q  t o change and h i g h  for  lowered  bulb  u n t i l 120  threshold,  However,  greater  the applied f i e l d  with  t h e change  as the t h r e s h o l d  with  f o r count  r a t e was p l o t t e d a g a i n s t  o f 25mm d i a m e t e r  fluctuates  i s s t a r t e d and t h e v o l t a g e  At high  pressures.  t o o b t a i n a new p u l s e  i n the applied  allows  for high  A t low p r e s s u r e s  Q  pulses  are only  slopes).  = E /2 i s defined  the bulb  a t low p r e s s u r e s ,  reliable  E  necessary  t o o b t a i n a new p u l s e  as t h e change  Also  (assuming  pulses/sec but  Q  frequency  operation  defined quantity  i n the a p p l i e d f i e l d  However d e f i n i n g E the  i s a well  Q  than  120Hz.  magnitude  neon a t p r e s s u r e s  for a  o f 30, 10, 5  79  and  1 Torr pressure.  had  an E  bulb  o f around  Q  result  independent  Equation having  pd.  Paschen  bulbs  The  not  interact  with  fields  checked  f o r three  with  bulb  (see  diameter  Figure  18).  for By reduced  Q  Q  = 1000/d.  Fortunately the  t o encompass a p r e s s u r e  that pulse  bulbs  The r e s u l t s  t h e t h r e s h o l d , E / 2 , c a n be  broad  frequency  described so far establish  of fixed  the discharge.  to further  of  1 Torr  i s proportional  direction However,  and frequency  check  the basic  and f o r b u l b s another  whose w a l l s do  set o f experiments i n  of the applied f i e l d  the b a s i c assumption  physical  i s v a r i e d was  of constant  E  Q  and t h e  of finite conductivity.  Pulse  This filled  i n , 0, ( s e e  minimum  1000 v o l t s  since E  such  The r e s u l t s a r e  field.  t h e wave p r o f i l e  effect  a broad  inversely  minimum,  size,  s e t o f experiments  performed  5.3.1.4  of convenient  o f 59kV/m.  12.5mm, 25mm a n d 38mm).  t o be a b o u t  diameter  Q  o f the  threshold i s relatively  l a w was a l s o  varies  i ssufficiently  for uniform  which  of this  had an E  b e l o w 10 T o r r .  law w i t h  (diameters  the Paschen  the bulb  the applied  model  The v a l i d i t y  Q  minimum  t h e 30 T o r r b u l b  the Paschen's  bulbs  i s within the r e p r o d u c i b i l i t y  for pressures  E d was f o u n d  pd near  This  t h a t t h e 10, 5 a n d 1 T o r r  that the optimal  the threshold f i e l d  increasing  with  indicated  a p d o f 25mm T o r r  setting  to  with 1 ).  indicated fixed  However  of pressure  consistent  indicated  42+3 kV/m.  characteristics. This  by  Results  Emission:  Dependence  investigation  with  programmable  on t h e A p p l i e d  i s performed  with  n e o n t o a p r e s s u r e , o f 10 T o r r . w a v e f o r m whose f r e q u e n c y  Waveform  a pyrex  bulb  o f 25mm  The a p p l i e d f i e l d  c a n be v a r i e d  from  1 Hz  diameter i sa t o 600Hz.  Figure  18  P u l s e e m i s s i o n frequency as a f u n c t i o n of different  bulb  diameters.  B u l b p d was 25mm T o r r  applied f i e l d  for  81  Different  Frequencies  V a r y i n g the frequency phenomenon. field  of the a p p l i e d f i e l d  The number o f p u l s e s e m i t t e d  magnitude  does not change the  per c y c l e depends only on the  (1Hz t o 600Hz) not on the r a t e o f change o f the f i e l d .  P i c t u r e s o f the p u l s e s superposed on the a p p l i e d f i e l d and 600Hz f r e q u e n c i e s are very s i m i l a r p r o v i d e d scales  (50 ms/d, 5ms/d,0.5ms/d)  a r e chosen.  common t o see r e l i a b l e o p e r a t i o n s  for 2E  the a p p r o p r i a t e  time  However a t 600Hz i t i s  = E  A  f o r 6Hz, 60Hz  Q  with one p u l s e on the  maximum and one on the minimum o f the s i n e wave.  A t t h i s frequency the  s c r e e n i n g e f f e c t s due t o the b u l b c o n d u c t i v i t y a r e n e g l i g i b l e . Operation  above 600Hz has not been i n v e s t i g a t e d due t o the l a c k o f  equipment f o r g e n e r a t i n g  the f i e l d s .  e f f e c t w i l l be s i m i l a r u n t i l p u l s e width  (kHz r e g i o n ) .  is unreliable: threshold.  However, i t i s c l e a r t h a t the  the frequency  approaches the i n v e r s e o f the  For f r e q u e n c i e s below 1 Hz the bulb  pulse emission  i s s p o r a d i c even f o r f i e l d s h i g h above  F o r time independent f i e l d s ,  p u l s e s are observed  field  i s turned o f f or on.  times  ( e s p e c i a l l y f o r bulbs a t low p r e s s u r e ) , cause p u l s e s  • separated gas  by a few seconds.  pressures  operation  M a i n t a i n i n g a very h i g h s t a t i c  However t h i s  i s only observed  when the  field  w i l l , at  t o be e m i t t e d f o r very low  (0.65 T o r r ) .  D i f f e r e n t Waveforms  The Of  above experiments can be repeated  with v a r i o u s waveform shapes.  s p e c i a l i n t e r e s t i s a square wave s i n c e i t c o n t a i n s  l a r g e time  82  intervals  of  constant  shows s u c h a wave,  field,  pulses  Triangular  waves f o r w h i c h  confirming  the  constant  time  These range  of  experiments  shape  magnitude  a Penning  A Figure  mixture  of  the  field  Figure  19  changes.  useful in  checking  for emission  slope  equation they  phenomena, o n l y  of  the  at  field.  2 for a  broad  confirm  that  peak  t o peak  field  o f Ne  height  non  Penning  of  first  be  and  pulses  seen  0.3%  Ar  the  threshold  small pulses pulse  the  i s very  mixtures.  frequency  i n Figure  for this  effect  of  close  (fg) of  18.  Penning bulb  i s one  has  (ie. within can  be  i s much l o w e r optical a much  pulses  with  The  i s shown  Instead  The  the  from F i g u r e  (2 t o versus  larger slope  of  large pulse  1kV/m) t o  deduced  filled  Torr.  getting progressively closer.  However a s  but  18  Penning  is varied.  is different. there  i s the  a 25mm p y r e x b u l b  to a pressure  e q u a l l y spaced,  to normal bulbs line  reduce  i s performed with  f o r subsequent pulses the  to  Threshold  i s a 60Hz wave f o r m whose a m p l i t u d e  As  the  dotted  by  Q  Furthermore,  to Reduce  can  of  E  validity  the  appear.  are  rising/falling  to  20.  threshold  i s constant  600Hz).  oscilloscope trace  for  similar  the  typical  a series  graph  <  each  not  o n l y when t h e  constant  mechanism  experiment  field  uniform by  at  should  matters.  This  applied  A  slope  important  most p r o m i s i n g  effect.  each  confirm  (1 *C f  i s not  observed  during  P o s s i b l e Mechanisms  The  are  emission  intervals  frequency  waveform  5.3.2  pulse  where p u l s e s  10  in the  followed threshold  threshold 21  times).  the Thus  applied field as  shown by  for  the  is  a  Figure  19  Optical pulse  superposed  on a p p l i e d w a v e f o r m  (E ) A  CO  -  pulses  occur  o n l y where  E  A  varies i n  time.  84  Figure  20  Optical  pulses superposed  Penning  mixture  bulb  on  10  ms/div  5  ms/div  2  ms/div  the a p p l i e d  (time runs  left)  wave f o r m E  A  for a  85  the  Similar  results  are  expected  Penning  mechanism works  first  one  and  obtained  i s t h e r e f o r e not  with  other  only  Penning  f o r the  mixtures.  pulses  useful i n reducing  the  Clearly  following  the  t h r e s h o l d of  the  sensor. Another tritium  to a  Since  2  would It  with for  was  the  threshold  i s the  a d d i t i o n of  gas.  or  have  clearly bulb  to reduce  impurities affect  radioactive H  alternative  not on  breakdown  t h a t even  defined steps  design  irrespective  e x p e r i m e n t s were c a r r i e d  the  found  breakdown  are  the  they  t o d e t e r m i n e what  are  effects  characteristics.  very which  inert  out  of whether  small percentages  of  are  Thus  gases  undesirable. (Ne  and  Ar).  H  2  produced the  best  bulb gases  86  5.4  Sensor  The of  a  field  main  of  0.66 is  is  bulb  to  an  to  the that  deviates  from  pointing  observed  for  real  simple  to a  the  operation  uniform  experiment  i s described  with  a  applied  placed  with  equipotential  to  a  The  typical  field  to  electric show  the  first.  s p h e r i c a l bulb  (38mm  60Hz w a v e f o r m  whose  is a  this  the  the  bulb  of  the  1%.  the  Thus  line  The  and  bulb  the  threshold  the  about  The  response with  (see  by  19%.  the  This  how  8)  threshold  field  a vertical  diameter  line  Next  through as  is  threshold  is isotropic.  increases  horizontal  the  the  the  bulb  nipple  nipple  vertically.  The  change  r e s u l t i s not  i n c o n s i s t a n t with  is isotropic,  however  the  nipple.  s p h e r i c a l bulb  d e p e n d s on  Figure  variation in  h o r i z o n t a l l y to p o i n t i n g  b u l b was  ideal  surface)  plates).  line.  provided  i t s nipple  capacitor  about a h o r i z o n t a l  Clearly  very  spherical bulb  neon).  is first  i s less  length  a r b i t r a r y angle  However, a  i s performed  perpendicular  of  an  for different rotations  rotated  extra  at  i s to understand  varied.  (perpendicular observed  a  experiments  Bulb  Torr  parallel  measured  of  experiment  magnitude  (ie.  these  tube p l a c e d  response  This  The  of  fixed direction.  Spherical  diameter  Investigations  thrust  cylindrical  isotropic  5.4.1  Shape  well  i t i s sealed  off after  the  isotropy  filling.  87  5.4.2  Cylindrical  This  Tubes  experiment  i s performed  The  f a t tube  i s 12.5mm  to,  0.5 T o r r A r ( t h i s  The  thin  tube  i s 6mm  The  tube  under  (diameter,  with  two c y l i n d r i c a l  D) b y 55mm  i sw i t h i n the Paschen (D) b y 55mm  gas f i l l e d  tubes.  ( l e n g t h , L) and i s f i l l e d minimum  (L) and i s a l s o  f o r both  filled  dimensions).  t o 0.5 T o r r o f  Ar.  horizontal the  lower  The  angle,  investigation  insulating plate  r o d made o f l u c i t e .  (see Figure  0, b e t w e e n  t h e tube  to  the r o d .  A  f  B  , light  ( F i g u r e 5 AD a n d B C ) . tube  observed  by s e t t i n g  BC,  the fibre-axis  with  light  emission  various plane  points along  o f F i g u r e 5.  directed  away f r o m  Time-integrated the  form  goes  from  portion  i na vertical  from  The l i g h t  These  s e t along the  was a l s o  o f F i g u r e 5.  The  perpendicular t o the  from  which  field  the l i g h t  (E-j-) i s  i s emitted.  show t h a t t h e b r e a k d o w n d i s c h a r g e  the -z d i r e c t i o n  C t o D t o A and i s t h i c k e s t  of the discharge  s i d e s o f t h e tube  that the i n t e r n a l  r e g i o n i n F i g u r e 5 when  When E j i s a l o n g  i s omitted  a t A.  from  fitted  the end o f t h e f i b r e a t  the f i b r e - a x i s  t h e s i d e o f t h e tube also  plane.  a t v a r i o u s p o i n t s a l o n g AD o r  by s e t t i n g  s t u d i e s showed  photographs  both  emission  perpendicular t o the plane observed  above  ( i e . the d i r e c t i o n  therefore i s normally  o f F i g u r e 5.  AD o r BC, w i t h  o f t h e shaded  direction.  axis  the end o f t h e f i b r e  was a l s o  i s 75mm  o f ± 1 ° b y means o f t h e p r o t r a c t o r  h a s t o be c o l l e c t e d  The f i b r e  radius i n the plane  The r o d , which  a x i s and t h e v e r t i c a l  E ) c a n be s e t t o a n a c c u r a c y  measure  a t i t s mid p o i n t t o a  1 2 ) , r o t a t e s t h e tube  of  To  i s attached  E j i s along t h e breakdown  takes  t h e +z_ discharge  F o r t h e sake o f c l a r i t y  F i g u r e 5 b u t c a n be s e e n  this  i n the  88  photograph that the  21).  t h e breakdown internal The  breakdown  axis  along  t o be t h o s e  the applied  E  where E p and E Q  parallel above  reliably  was m e a s u r e d  Q  o  /E  i f f >120Hz.  a t which  f  B  = 12.4kVm- /50kVm-  N  t o the a p p l i e d  1  -  by  conditions are  The t h r e s h o l d  to i t .  I t was  field  the tube found  that  D/L  threshold  field.  accelerated  (D = 12.5mm) w i t h  or perpendicular  the idea  walls.  = 120Hz.  tube  1  O  with  Threshold  B  f o r the wide  field,  by e l e c t r o n s  by the tube  are the r e s p e c t i v e  N  or normal  equation  p  are consistent  i s maintained  E j and i s g u i d e d  operate  defined  The o b s e r v a t i o n s  discharge  field  tubes  therefore for  (Figure  fields  I t therefore  f o r the tube follows  axis  from the  that  V(0) = V(90)  where V ( 0 ) = E  0 p  L  i s the p o t e n t i a l d i f f e r e n c e  t u b e ends w i t h 9 = 0 ° , threshold consistent Paschen also  across with  rule  conduction outside  the v e r t i c a l the notion  (Equation  show t h a t  and V ( 9 0 ) = E  the f i e l d s  currents  and i n s i d e  0 near  tube).  This  conditions  i t s broad  are not s i g n i f i c a n t l y (ie.  between t h e  i s the p o t e n t i a l d i f f e r e n c e a t  t h e breakdown  i n the glass the  D  diameter with 9 = 90°.  that  1) with  Q N  a t threshold  minimum. attenuated  equation  satisfy The  is  the  results  by t h e f l o w o f  h a s t h e same s t r e n g t h  both  Figure  21  Time  i n t e g r a t e d photographs  cylindrical  tubes.  showing  The e l e c t r i c  the breakdown  field  discharge i n  is vertical.  90  To (AB  minimize  and  CD  the  i n F i g u r e 5)  (D = 6mm,  L =  breakdown  ( f g ) was  V  A  =  E  A  L  Figure  a  55mm).  l° g  the  n  22,  f (9),  E  Am ^  in  =  of  3 k V m  1  frequency between To produces mounted  f  was  a function  of  the  the d i s c h a r g e ,  the  (9 = 0 ) , t h e  of  narrow  calibration  tube  frequency  the p o t e n t i a l  for V  this  To  a t an  maximize  angle,  i n the gap  was  measured  I f the  the  of  difference  equation  provided that  A  (see  0.85kV  <  the  t o the  maintained  0.85kV  frequency applied  o n l y on  define E  the  A  as  This curve  with  of the  the  not  difference  value  field  i s shown  lose then  A  = E  A m  of E / E A  L  A m  cos  amplitude f , with  which the  B  a g a i n s t cos9  remains  (6)  s h o u l d be  a straight  tube  therefore occur  a c r o s s t h e tube  9'  the  9.  i e . that  E L  of  difference  angle  breakdown f r e q u e n c y ,  potential  the  the w a l l ,  same b r e a k d o w n f r e q u e n c y w i l l the  breakdown  field,  the p o t e n t i a l  irrespective  of  at i t s largest  9-? 7 5 ° .  in i t s interaction  h y p o t h e s i s we  The  ^  ft  breakdown d i s c h a r g e does  tube,  value of  9,  for 0 <  s h o u l d depend  ends o f  vertically.  a plot  vertical  satisfies  B  part  w e r e done w i t h  0.54)  then  a particular  unchanged,  as  amounts o f e n e r g y  two  tube  i n Hz.  B  (curve b ) .  check  when 9 = 6 '  Thus  and  o f breakdown  the  studies  travel"  V  field  « f B^®^  significant  -  A  inclined  the  F i g u r e 22  the  "free  0  i s i n kV  amplitude  f  380(V  i n a tube  B  With  measured  =  A  the  a)  =  B  of  further  tube.  curve  f  where V  effect  line  of  unit  91  0  cosG  0.1  0.3  0.5  VA  Figure  22  Frequency  o f breakdown  along  the tube  angle  ( c o s 9) f o r f i x e d E  6mm  and  filled  (V )  as a f u n c t i o n  A  (curve  w i t h 0.5  A  (kv, Rms)  of p o t e n t i a l  a) a n d as a f u n c t i o n = 53kVm~'(curve  Torr  Ar.  1.0  OS  b).  difference  of o r i e n t a t i o n Bulb  i s 55mm  x  92  slope, the  passing  through  potential difference  (0.85kV i n our  form  It  should  of  the  The Figure from  case), be  function  p l o t of  22  as  curve  obtained  23  potential  difference  is  by  the  wall-discharge  above.  Finally  gas-filled, frequency  E L  cos  count  2.92kV E /E A  in the  than  can  (say  from  curve  that  f  the  B  0.29. specific  is  a  graphically  400), a  cos9.  The  Equation  low  frequency  fields,  not  value  be  show t h a t  used  tube-axis.  predicted that  a  e  obtained A / A I T I •*E  S  that  in  i s governed  provided energy  the  losses  If  t h e y were,  by  the  narrow,  t o measure  the  i t is  valid.  breakdown  tube,  significant.  fact  6 is  of  the  is  from  0.055m).  frequency  ends of  cos9'  (1.59kV).  the  r e s u l t s demonstrate  the  value  cosQ  of  that  obtained  rate  versus  A m  They a l s o  the  be  ( i e . 53kV/m x  indicates  between  along  provided  can  by  i n s u l a t i n g tube  field  9'  i s obtained  tube w a l l s .  the  21)  A  immersed  larger  provided  that  A  i n t e r a c t i o n are  t o be  threshold  6 i s independent  (Figure  r e s u l t s show t h a t tubes,  6 applies  the  requires  V .  straight line  electrodeless  have  Equation  shows a p l o t o f  above  above d i s c u s s i o n  tube exceeds  Equation  s e l e c t any  A  The  the  Ej^/E^ against  ( 0 . 5 8 ) and  excellent  would  that  dividing E L  Figure  guided  that  of  follows:  b  by  The  across  so  noted  origin.  c a l i b r a t i o n curve  single-valued  an  the  model  by  the  discharge in then  the V(9)  presented  cylindrical, component o f  a  low  93  0.1  0.2  0.3  0.4  0J5  0.6  0.7  0.8  0.9  1.0  cos 6  Figure  23  Normalized response of  cylindrical  tube as a f u n c t i o n of  a n g l e between the tube a x i s and the f i e l d  direction.  the  94  5.5  of  I n v e s t i g a t i o n s of Planar  Rotating  The m a i n  experiements  spherical  experiment the  thrust bulbs  of these  i n planar  rotating  i s described f i r s t  component  of the e l e c t r i c  Fields  i s to understand  fields.  However,  t o show t h a t a c y l i n d r i c a l field  along  the bulb  axis  the o p e r a t i o n  a very bulb  simple responds  to  (see S e c t i o n  3.5.2.1). These Section  5.5.1  experiments  are performed  with  the apparatus  described i n  5.3.2.  Cylindrical  This  Tube  experiment  i s performed  with  the t h i n  cylindrical  tube  (Section  5.4.2). A circularly is  generated  cylindrical field.  field  rotating  i n a horizontal  b y t h e e q u i p m e n t d e s c r i b e d i n S e c t i o n 5.2.3. tube  i s placed i n various directions  The m e a s u r e m e n t  orientation is  polarized  (fg) remains  constant  aligned with  a uniform  field  i n a fixed  obtained  direction  a t 60Hz  The  i n the plane  irrespective  and i s e q u i v a l e n t t o t h e measurement  plane  of  of the tube  when t h e  tube  o f t h e same  magni t u d e .  5.5.2  S p h e r i c a l Bulbs  This  experiment  i s performed  b u l b whose c a l i b r a t i o n of  fixed  direction  curve  with  has v e r y  (see F i g u r e  24)  a 38mm, 1.3 distinct  T o r r Ar lead  steps  glass  i n a uniform  field  95  f (Hz) B  500  +  400  +  300  +  200  +  100  -+  10  F i g u r e 24  20  Pulse emission frequency 38mm,  1.5 TorrAr,  30  as a f u n c t i o n  lead glass  50  40  spherical  of  applied  bulb.  field,  96  5.5.2.1  General Pulse  Emission  in Circularly  The p u l s e e m i s s i o n o b s e r v e d fixed  direction,  spaced  i n time  field. every  5.5.2.2  except  E  A  rotates  Figure circularly generated  Emission  polarized  by g r o u n d i n g  disappear.  1.67.  from  itself. the  that  As e x p e c t e d ,  polarized  F o r the l i n e a r l y  field  the  t o the t h e o r e t i c a l  enhancement  Furthermore, polarized lower high  fields  i s observed  the threshold  field.  fields  factor  field  9 i s s m a l l and  Shape  field  for a  (which i s connected  i n the  to  ,  linear  field  i t i s the l i n e The  lower  in a  experiment  t o the assumption  that  A  E  enhancement  0  above  and Eg a r e a p p r o x i m a t e l y  However  threshold.  circularly  and  g  field.  through  for E /E ^2. A  to  curve  drawn  observed  f o r a l lvalues of E  field  polarized  i s the c a l i b r a t i o n  curve.  between  line  polarized  for a linearly  is slightly  This descrepancy  i s p r o b a b l y due  for circularly  (TT/2) e x p e c t e d  value  field  of the slope o f a  the l i n e  polarized  occurs  a s d e f i n e d i n S e c t i o n 3.5.2.2 i s  curve  t o p o f t h e s t e p on t h e c a l i b r a t i o n close  polarized  the steps observed  curve  a pulse  electric  w o u l d n o r m a l l y be  factor  the c a l i b r a t i o n  that  equally  applied  M a g n i t u d e and  the a p p l i e d  the r a t i o  the c a l i b r a t i o n  the c i r c u l a r l y  the model  of  angle.  and a l i n e a r l y  the p l a t e s  in fields  t o the phase of the  with  versus  B  The e n h a n c e m e n t  one c o n s t r u c e d f r o m For  of f  I t i s o b t a i n e d by t a k i n g  constructed  is  field  a fixed  observed  The p u l s e s a r e  as a F u n c t i o n o f F i e l d  25 shows a p l o t  V j i n Figure 14).  field  f o r one m a j o r d i f f e r e n c e .  through  Fields  to that  a n d do n o t h a v e a n y r e l a t i o n  Rate of Pulse  and  i s similar  This observation i s consistant time  Polarized  theory a t the  i s uniform. antiparallel  At  10  20  30  40  50 EA'  Figure  25  Pulse  emission  linear lead  field  glass  frequency  (b) bulb.  as  circularly  a  function  polarized  of  applied  field.  < k v  nf ,  field  38mm, 1 .5  1  Rms)  (a) Torr  Ar^  98  (± a  few  have  degrees).  little  For  effect.  this  situation  However  i n Eg  and  w h i c h may  more f a v o u r a b l e  are  180  the  above  explanation.  The  same e x p e r i m e n t  pulses/sec at  different axis in  aspect  field.  the  These  electric  results. rounded theory  earlier  semimajor  threshold  the  at  also  to the  These bulb  i n planar  that  for fields  observation uniform  field.  the  high  14kVm  - 1  near  which  with  planar  by  from  a theory  ellipse  of 2),  24kVm ) but - 1  This e f f e c t circularly  the  fields  of  uniform  E  E *).  aspect  polarized near  B  of  i s consistent with  of  E  should  ( i e . of disappear  almost  represents  the  and  is  probably  threshold. operation of a  i s not  as  spherical  They a l s o  accurate,  possible effects  semimajor  at  enhancement  indicate  an  due  to a  spatially  the  elliptical  B  A  steps  (see  B  E .  that E  the  the  the  1:1/2  t o the  to  f o r more  disappear  w e l l above t h r e s h o l d . theory  2  close to  ratio  field  of  of R i  i s a plot  steps  is similar  basic theory  t h r e s h o l d the  ratio  uniform  they  there  semiminor  However,  A  the  to  earlier  with  straight  fields  field  F i g u r e 26  4  not  i s consistent with  v a r y i n g the  by  120°)  Since  rotating  axis  should  B  (say  180°.  enhancement i s v e r y  axis ratio  o f non  =  which  semimajor  divided  f o r an  ).  confirm  rotating  at 9  120  90°  which are  (progressively  field  expected  t h r e s h o l d i n the  results  of  disappear  example,  effect  a path  generated  t h r e s h o l d (around  ( i e . at  observed  recall  are  a x i s to semiminor  twice  due  ratio  circumference  than  For  than  shown i n F i g u r e 14.  steps  and  (the e l l i p s e  Appendix I I ) .  non  the  ellipses)  disappear  near  fields  than  t o breakdown paths  i s repeated or  circuit  Again  lead  u n i f o r m i t y of E  larger  t h r e s h o l d 9 m u s t be  ratios  non  9 becomes  non-uniformities be  can  as  the  axis f i e l d  of  R  2  99  ellipse slope aspect experiment/ ratios theory  f (Hl) R  O  O  | 1.62/1.57  400 + 1-5/1.32  300  200  100 +  E ' semi major axis (kv m ) _1  A  F i g u r e 26  P u l s e e m i s s i o n frequency as a f u n c t i o n o f a p p l i e d magnitude f o r d i f f e r e n t for  elliptically  polarized  field  fields.  Slopes  l i n e s a r e n o r m a l i z e d t o the s l o p e o f the l i n e through the  top o f the s t e p s o f the c a l i b r a t i o n 38mm, 1.5 T o r r Ar l e a d g l a s s b u l b .  curve f o r the l i n e a r  field.  100  5.5.2.3  Planar Rotating Fields  This (Section  experiment  a  field  exhibits  closer  experiments  a very  large  continuously increasing polarized  and  at a fixed  occurs  pulses).  the Penning  just  5.3.2) r e v e a l e d t h a t  p u l s e f o l l o w e d by p r o g r e s s i v e l y s l o p e o f the f i e l d .  field  field  ( i e . a ramp) w h i c h  ( i e . the change  r a t e ) one e x p e c t s  The c o n t i n u o u s  the metastable  pulses  t o the p r e v i o u s except  (Section  t o g e t h e r p u l s e s i n each  circularly  of  i s identical  Mixtures  bulb  5.3.2) i s u s e d .  Linear bulb  and P e n n i n g  state.  a weak D.C.  light  signal.  f t  s m a l l e r and  basically  always  what  this  glow  to  represents a  h a s t h e same  sign  ( i e . no  by a c o n t i n u o u s  i s exactly  Penning  Extrapolating  a continuous  glow i s m a i n t a i n e d This result  in E  a  replenishment  i s observed;  no  101  5.6  Investigations  Four  basic  perturbation effects  5.6.1  The  a  the  experiments sensor,  bulb  of  this  can  be  experiment  Torr  of  Problems  have been  meter  c a r r i e d out:  field  calibration stability,  humidity  Perturbation  purpose  conductor  0.66  to  Engineering  temperature e f f e c t s * .  Field  The  types  due  and  of  Ne.  The  experiment  i s to  brought before  i s performed applied  field  the  find  out  field  with  the  is a  60Hz s i n e  how  is  close  to  a  disturbed.  38mm d i a m e t e r  bulb  wave o f  filled  to  variable  strength. Calibration distance, that  as  L,  the  increases count  to  one  bulb  for a  rate  curves  as  a  the  author  did  is a  than  sensor  20%  are  A  used to  the  from  radius the  away f r o m  participate in  plate  the  the  these  function  Figure The  count  i s no  measurement o f  a planar  a  count  plate.  i n the  there  as  capacitor.  magnitude.  enhancement  bulb  obtained  i n the  field  distance  influences  radius  not  one  E )  closer  of  plate)  one  plates  function  greater  of  versus  applied  distances  distance  B  constant  the  the  the  i s brought  (touching  Thus  of  (f  It is rate 27  (fg)  shows  the  maximum e f f e c t  rate.  At  effect. the  the  found  field  up  conductor.  temperature  of  experiments.  to  a  102  Figure  27  Response D  o f Bulb Near  = bulb diameter;  C  Q  one P l a t e = counts  of a  Capacitor.  at large distance  from  plate.  103  5.6.2  Meter  A and  s e t of  placed  count  A  small plates i d e n t i c a l  outside  typical  result  Experiments and  l a b o r a t o r y and  This .5  Torr  as  of  can  neon.  be  The  varied.  relative  h u m i d i t i e s can  directing  o p e r a t i o n of  penetrate  the  conductivity effect  breathing  bulb  field  the  direct  rain.  was  monitored  over  The  variation  i s less  can on  The  the  the  i n the  be  be  produce  a 25mm d i a m e t e r  the  As  soon  pulse  as  the  humidity  by  reliable  the  be  to water  reached:  applied  i s screened  slowly at f i r s t  and  Higher  glass  from  the  emission  gas.  while with  the  the  water  C o n t r o l l e d experiments  As  the  then  be  field  a l t o g e t h e r ; as  condensation  (1)  can  bulb.  g l a s s s u r f a c e i s fogged stops  filled  o f 95%  the b u l b .  the  pulse  bulb whose  i n c r e a s e s the  monitoring  returns to normal.  c o n c l u s i o n can  to  r e q u i r e s t h a t the  emission  l a b o r a t o r y due  to values  b r e a t h i n g on  applied field  observed A  by  pyrex  i s a 60Hz w a v e f o r m  a h u m i d i f i e r on  obtained sensor  emission  rate decreases  with  a i r from  the  vapour,  hard  pulse  the  bulb.  pulse  two  that bulbs  than  f o r months.  applied field  material.  easily  evaporates t o do  demonstrate  R e l a t i v e h u m i d i t i e s up  i n c r e a s e s and  condensed water  the  at fixed  i s performed  by  However  s h i e l d e d from  constructed  Effects  obtained  The  these  calibrated  experiment  amplitude  The  bulbs  l a r g e o n e s was  i s shown i n F i g u r e 28.  such  remain  Humidity  with  the  t o the  months.  results  5.6.3  Stability  rate for different  summer  3%.  Calibration  on  the  humidity  rapidly  for  are  plates. increases relative  105  humidities bulb  a b o v e 95%;  i s .  teflon  (2)  Encasement of  provides for reliable  95%  B r e a t h i n g on  rain  were a l s o  5.6.4  plexiglass  temperatures.  for  0°  Effects  inconclusive  h o l d e r has  i s performed  no  effect.  by  around  flowing  material  humidities Field  From 0°C  bulbs. and  t o 40°C are seen.  Results  further  no  effect  The  such  of at  trials  in  the as least light  i s observed.  range  required.  varying  b u l b i s mounted  occurring  Furthermore  i n this  work i s  dry a i r of  the b u l b .  to p r e v e n t c o n d e n s a t i o n from  d r a m a t i c changes  different  at relative  clean  (Preliminary Results)  (-40°C t o 4 0 ° C ) box  d e p e n d e n t - on how  the b u l b i n a h y d r o p h o b i c operation  the t e f l o n  experiment  temperature  i s strongly  satisfactory.  Temperature  This  to  the e f f e c t  at  low However f r o m  t h e s e changes  are  in a  therefore  are  still  -40°  different very  106  5.7  Field  The lines  Tests  meter has been  (265kV t o 765kV),  The  purpose  the  detector)  of these  Although shielding has  i n noisy initial  worked v e r y  tested at various  i n substations  tests  and o p t i c a l  Because it  field  has been  electrical prototypes fibre  times  and i n h i g h  to confirm  under  voltage laboratories.  meter o p e r a t i o n  shirt  revealed  problems with  c o n d u c t i v i t y - the prototype  detector described  The enhancement  field  p e r t u r b a t i o n and s i z e  i s about  and t h e p e r s o n  the  head  and  the exact  o f t h e GEM  stands  position.  These  transmission  lines.  u n d e r a 500kV t r a n s m i s s i o n cylindrical Actual  the sensor  erect.  field  results  t h e human  i s placed  When t h e s e n s o r  are consistant with  sensor  i n the  i s placed  on  on t h e p e r s o n Deno's  8  calculations.  O t h e r measurements have under  two when  t h e e n h a n c e m e n t r a n g e s b e t w e e n 6 a n d 10 d e p e n d i n g  theoretical  here  well.  of the small  pocket  (mainly  environments.  has been p o s s i b l e t o measure enhancement f a c t o r s a r o u n d  body.  transmission  sensor.  the conductors  is  enhanced  Figure line  The g e n e r a l  magnitudes  of  i n c l u d e d t h e mapping o f t h e e l e c t r i c  are hard  29 shows a p l o t  with  a GEM  with  shape o f the curve t o compare  v a r i e s g r e a t l y from p l a c e  by t h e o b s e r v e r .  fitted  obtained  to place  a 100mm  i s as  to theory  by  field  walking long  expected.  because  the height  and t h e b u l b  reading  107  10  20  30  40  distance (m)  Figure  29  Electric  Field  Under  Long C y l i n d r i c a l  a Typical  Sensor About  500kV L i n e 2m A b o v e  the  Obtained With Ground.  a 100mm  108  5.8  Summary  This the  section  physical  has  summarized  model f o r i t s s e n s o r .  makes p r e d i c t i o n s  which  are  However, some d i s c r e p a n c i e s threshold. assumption reliably effects  experiments  These  in typical observed  i n good are  discrepanceis  of a uniform Eg.  are  Results  freezing  i n planar  l i k e l y due also  electric  are  show t h a t  t o d e v e l o p GEM the p h y s i c a l  and  model  agreement w i t h e x p e r i m e n t a l r e s u l t s .  observed  environmental  below  Results  performed  not  rotating  t o the  erroneous  shows t h e GEM fields.  understood.  fields  meter  However  near  basic  operates  temperature  109  6.0  Summary and  Adverse fields now  health  i n the  a matter  accidents with  and  on  electric  the  concern.  meters  electric  are  lines  In  and  electric  switchyards  addition  ( i e . cranes)  the  coming  into  contact  ideal The  electrodes.  for  meters  As  such  i n most c a s e s  electrodes)  studying  large  measure the  the  induced  sensors  (where  and  and  are  the  heavy.  field  meter  e l e c t r o d e l e s s breakdown of  gases  in insulating vessels.  allows  separated filled  by  with  are  direct  electric  principle  an  not  fields.  s e n s i t i v e and  i s housed with  to high  increase.  field  thesis describes  shell  transmission  public  between m e t a l  directionally  detector  glass  are  current  principle: This  overhead  heavy equipment  environmental  electronics This  of  considerable  lines  monitoring  metallic,  vicinity of  Existing  or  e f f e c t s r e s u l t i n g from exposure  r e s u l t i n g from  power  charge  Conclusions  the an  construction  optical  gas.  As  of  fibre.  such  the  based  on  a meter w i t h  The  sensor  m e t e r has  a  different  the  sensor  consists  the  of  a  following  advantages: 1.  i t i s very  light  2.  i t is spatially  and  small;  isotropic  or  directionally  sensitive  (as  desired); 3.  i t has  no  distance fibre 4.  metal or from  length  i t remains because by  the  conducting sensor.  within  distance  an a r b i t r a r y  i s s e t by  the  optical  and  calibrated for  i t uses a  electrical  The  parts  digital  noise.  long  periods  signal)  and  of  time  i s not  (essentially  adversely  affected  110  Two t y p e s and  of sensors  a cylindrical  tube.  have been  The s p h e r i c a l  sensitivity  t o the e l e c t r i c  distortion,  i t responds  the  field.  applied  field. field  along  greatest  i t s axis  field  threshold  accurately  careful  irrespective  with  measuring  hand,  i s best  by t h e s p h e r i c a l  geometry  of the f i e l d .  electric gas  field  cannot  threshold.  control,  polarization,  fitted  Thus  accurate  i s dependent  larger  lines  sensor  millimeters) they  field  both  fully  bulb,  on t h e  i n which  The measurement  on t h e m a g n i t u d e  and t h e  the f i e l d .  The t h r e s h o l d depends on t h e t y p e o f  unperturbed  and s w i t c h y a r d s .  i n unique  a spherical  type  o f gas a l a r g e r  very  on t h e m e t e r .  Thus  though  situations  bulb  has a  advantageous  f o rthreshold  A reasonable  size  10kV/m.  fields  found  t o measure  On t h e o t h e r h a n d  c a n be made a n d e v e n  c a n be u s e d  against  i s a t h r e s h o l d below which the  For a given  limitation  i s required.  s e l e c t i n g the  and thus  applications  typical  power  and measures the  not uniquely characterize  there  be d e t e c t e d .  field  i s not possible.  i t does  of sensor  with  slightly near  of the  i s most s u i t a b l e f o r  has a t h r e s h o l d o f about  than  component o f  By s u i t a b l y  of the e l e c t r i c  f o r less  bulb  tube  (40mm b u l b d i a m e t e r ) higher  harmonic  on t h e p o l a r i z a t i o n  direction.  This property, although  i s t h e main  isotropic  t o the tube-axis.  and t h e b u l b d i m e n s i o n .  lower  frequency  one c a n d i s c r i m i n a t e e n t i r e l y  o f the sensor  type  of f i e l d  A meter  suited  small  bulb  t o t h e component o f t h e e l e c t r i c  that  components  provided  either  depends  a cylindrical  the f i e l d .  orientation  For  responds  a r e normal  fitted  characterizing other  bulb  For s u f f i c i e n t l y  also  a spherical  b u l b has a s p a t i a l l y  t o the fundamental  o f the tube,  which  A meter  only  strength along  field  components  fields.  The r e s p o n s e  A cylindrical  studied i n detail:  very  This  field i s  a t ground  these  level  low f i e l d s  small bulbs  they have a v e r y  sensor  a  (a few  large threshold  as d i s c u s s e d l a t e r on.  111  Although by  the  H a r r i e s and  their  von  work b o t h The  study  explanation electric  basic  field.  based  on  more b a s i c  T o w n s e n d ' s work  p h y s i c s and  thesis  been  o c c u r when t h e  extends  the  this  developed  thesis  extends  engineering aspects.  breakdown had  current pulses  This  b r e a k d o w n was  basic  c o n f i n e d t o the  gas  i s exposed  physics to a  basic  to  an  theoretical  of:  1.  the  relation  and  the  2.  the  effect  3.  the  dependence  fields 4.  This  of e l e c t r o d e l e s s  electrodeless  o f why  explanation  Engel  into of  theory  between  applied  field  o f gas of  ranging  in elliptically  E  the  geometry  5.  the  effects  6.  the  breakdown e f f e c t  f  on  B  many new  (fg)  f  to c i r c u l a r and  E ; A  polarized  polarization;  orientation  of bulbs  on  A  on  f  versus  B  i n Penning  on  the  E  and  A  mixtures.  engineering  effects  versus  B  E ;  of harmonics  environmental  A  linear  dependence  1.  on  B  pulses  A  f  the  presents  light  (E );  from  of  of  on  effects  also  frequency  pressure  the  thesis  of  the  results:  performance  of  the  sensor  and  meter; 2.  lifetime  and  stability  of  3.  meter d e s i g n  to reduce  electrical  sensor 4.  the  Even w i t h the  study There  further  of  are  study:  against environmental  influence  a l l these  the  of  at least  the  sensor  meter; n o i s e and  effects on  the  and  field  e x t e n s i o n s much work r e m a i n s  phenomena and  bulb  the  on  meter  three areas  of  p r o t e c t the  handling being  t o be  and  measured.  done b o t h  on  design. the  basic  c o n s t r u c t i o n , temperature  phenomena  effects  and  that  require  operation i n  112  planar by  rotating  fields.  The  f a r t h e most i m p o r t a n t  similar bulbs  bulbs  are  curves.  each  presently  that  uniform have clear  are  and  bulbs  field  practical spherical  a  case  here  will  related  of about  of  by  for different  the  rotating  this  the  bulbs). It is  of  impurities  model f o r  fields  could  the  at  no  form  the  be  of  the  non  more r i g o r o u s m o d e l  may  With present understanding t o be  meter,  adsorption of impurities  control  two  calibration  yet understood.  proper  However,  no  detector adjusted to  i s understanding  need  70%  t h r e s h o l d s and  not  and  Although  reproducible bulbs with  i n plannar  Eg.  rate  rigorous quantitative  application. bulbs  also  view.  exploitation  each  t o the  produced  Finally,  bulb  due  i s the  main problem  internal  that  they  c o u l d be  spherical The  little  a yield  commercial  are  most l i k e l y  p o i n t of  different  calibrated  If this  manufacture.  developed.  i n the  below f r e e z i n g  effects  of  with  are  mean p u l s e h e i g h t i s d i f f e r e n t  believed  operation  areas  a practical  made r o u t i n e l y  b u l b m u s t be  temperatures.  during  two  They have s l i g h t l y  effects  temperature  from  i s a problem  ( i e . the  Temperature  low  be  alike. This  because bulb  can  first  calibrated  i t is  f o r each  field  geometry. Future The  work on  p r e s e n t p r o t o t y p e which  separated  by  an  demonstrations specific sensor the  optical and  field  applications.  dimensions  fibre  size be  meter d e s i g n w i l l  length  harder  than  fibre  The  guided  of a  the  typical  the  main p a r a m e t e r s  zero  the  that on  l e n g t h o r no  example  market size  can  sensor  (40mm)  suited  be  changed  and  Making  are:  the  geometry,  the d e t e c t o r  these  small sensor  for  modified for  t h r e s h o l d ) and  fibre)  type.  a very  developments.  d e s i g n must be  effect  i s d e s i r e d ) and For  by  detector i s well  However,  i n mind  (including  apparent.  from  tests.  (keeping  ( i f miniaturization  consists  be  or  changes a  long  may fibre  113  may  required  applications different major  one  warning  of  or  presence totally  done  at  the  encompass  metal  i s dangerous  in  fields  predicting  assembly.  fields  the  need  inside Another  therefore  of  non  electric  metallic be  used).  beehives  (the  more p r o m i s i n g  future  have  field  These sensor One first  transformer  in  mentioned most  i s enhanced  greatly  appeared.  applications ( i e . i n other  example device  These  require  is  was  the  for  a  very  of  this  measurementof  T h e s e m e a s u r e m e n t s may malfunctions  cannot  applications  i s measurement sold  by  detectable.  measurement which  application  transformers.  As  The  (ie. personal  usually  recently field  information).  However  measured  possible  (ie.  devices.  threshold. be  types  field  warning  objects  (in o i l ) large possible  electric  to  and  3 summarizes  detector  (low)  areas  can  and  unperturbed  existing devices.  but  Table  and  limitations is  low  millimeters)  inside  the  different applications  (few  fields  lengths  for monitoring  major  a l l with  application).  detector.  conveying  conducting  small  electric  for  are  i n which  of  i n the  different fibre  monitoring)  applications be  gain  electronics  applications  Other  for  applications  before  the  larger  during  assist  transformer  114  Table  Meter  3  C o n f i g u r a t i o n s and A p p l i c a t i o n s  ^ v ^ f ibre ^\length detector^"^  no fibre (one p a c k a g e )  short  fibre  (< 2  meters)  warning device  Personal warning device (workmen)  Testing v i c i n i t y of live high tension line (crane operators, hydro r e p a i r men, e t c . )  direct read out  Hand h e l d (workmen,  microprocessor  Unsupervised field monitorying (operators,  f i e l d measurement d e v i c e researchers, evaluators)  Personal exposure meter (workmen)  researchers) Personal exposure me t e r (workmen)  histogram device  same a s m i c r o p r o c e s s o r h i s t o g r a m ( i e . no time  long  fibre  (>  meters)  2  Unperturbed accurate field measurement Line testing (workmen, r e s e a r c h e r s )  Unperturbed field meeasurements over long periods of time (researchers, evaluators)  b u t o n l y comp> i l e s resolution)  a  115  7.0  References  1.  Kronberg  H.A.,  2.  New  S t a t e P u b l i c S e r v i c e C o m m i s s i o n C a s e s 26529 a n d 26559 c o n d u c t e d o v e r t h e p e r i o d 1975 t o 1978, New Y o r k S t a t e P u b l i c S e r v i c e C o m m i s s i o n ( A l b a n y , N.Y.)  3.  Banks,  York  R.S.,  Concern Overhead, J u n e / J u l y , 1977  Kanniainen, Safety Lines: Board,  CM.,  5.  Janischewskyj,  6. K o t l e r ,  7.  R.F.,  a n d C l a r k , R.D.,  Fields  Plenum P r e s s ,  Life  New  H e a l t h and  (translated  from  Russian)  York  W. a n d S t o p p s , J . G . , "An E p i d e m i o l o g i c a l S t u d y o f P e r s o n n e l W o r k i n g on a c T r a n s m i s s i o n L i n e s " , C o n f e r e n c e t h e CEA, V a n c o u v e r , B.C., M a r c h , 1979  of  M i s o k i a n , M., AC T r a n s m i s s i o n L i n e s F i e l d M e a s u r e m e n t s , I n s t i t u t e f o r B a s i c S t a n d a r d s , NBS, W a s h i n g t o n , D . C , November, 1977  " E v a l u a t i o n of P r o x i m i t y Warning D e v i c e s , F e b r u a r y 22, 1980  8. Deno, W.D.,  Public  E f f e c t s o f High-Voltage Overhead T r a n s m i s s i o n An A n a l y s i s f o r t h e M i n e s o t a E n v i r o n m e n t a l Q u a l i t y M i n e s o t a D e p a r t m e n t o f H e a l t h , O c t o b e r 1977  4. P r e s m a n , A . S . , E l e c t r o m a g n e t i c 1970,  EPRI j . , V o l . 5, No. 7, pp 7 - 13,  South-West Research  Institute,  C u r r e n t s I n d u c e d i n t h e Human Body b y H i g h V o l t a g e T r a n s m i s s i o n L i n e s E l e c t r i c F i e l d - Measurement and C a l c u l a t i o n o f D i s t r i b u t i o n a n d D o s e , I E E E T r a n s a c t i o n s on Power A p p a r a t u s a n d S y s t e m s , V o l . PAS-96, N . J . S e p t e m b e r / O c t o b e r , 1977  9. S p e i g e l , R . J . , K e r n s , D.R., C o o p e r , E.H. a n d B r o n a u g h , E . L . , "A S m a l l , A c c u r a t e , O p t i c a l l y I s o l a t e d E l e c t r i c F i e l d Probe", IEEE PES Summer m e e t i n g , V a n c o u v e r , B.C., J u l y 15-20, 1979 10.  Francis,  G.,  "Ionization  Phenomena  i n Gas", B u t t e r w o r t h P u b l i c a t i o n s  ( L o n d o n ) 1960, p p . 137-172 11.  H a r r i e s , W.L.  12.  H a r r i e s , W.L.,  13.  H a r r i e s , W.L.  14.  Dutton,  J.,  and von E n g e l , Proc.  I.E.E.E.  and von E n g e l , (1954)  A., P r o c .  P h y s . S o c . B64, 915  I I A , 100, 132 - 7 A., P r o c .  (1951)  (1953)  R o y . S o c . ( L o n d o n ) A - 2 2 2 , 490  i n E l e c t r i c a l B r e a k d o w n i n G a s e s , e d i t e d b y J.M. Meek a n d J.D. C r a g g s ( W i l e y , New Y o r k , 1 9 7 8 ) , p p . 209-318  116  15.  Friedmann,  16.  Curzon,  17.  D.,  C u r z o n , F . L . and Y o u n g , J . F . ^ A New E l e c t r i c a l B r e a k d o w n Phenomenon! i n g a s - f i l l e d I n s u l a t i n g B u l b s , A p p l . P h y s . L e t t 3 8 ( 6 ) , 15 M a r c h 1981. ( E r r a t u m App. P h y s . L e t t . 3 9 ( 8 ) , 15 O c t o b e r 1981)  F.L.,  Friedmann,  F r i e d m a n n , D.E., F e e l e y , M. O r i e n t a t i o n - Dependent E l e c t r o d e l e s s B r e a k d o w n o f Gas i n G l a s s T u b e s , J o u r n a l A p p l i e d P h y s i c s (In PressDecember 1982)  D.E.,  Curzon, G.,  An  Gases, 18.  Friedmann,  D.E.,  19.  Young, J . and  20.  H o l l o w a y , D.G.,  F.L.,  Electric Rev.  Curzon,  F.L.,  in Rotating  for  submission  F r i e d m a n n , D.E., A p p l i c a t i o n No.  Lorrain,  22.  Da  23.  Jackson,  Silva,  P.,  and  the  Young, J . F . ,  and  Based  Breakdown  53_, 1273  Feeley,  Electric to  M.,  Meter  M.  on -  the  1277,  Auchinleck, of  1982  E l e c t r o d e l e s s Breadown  Fields  a t 60Hz,  Canadian Journal of  of  in preparation Physics  E l e c t r i c F i e l d D e t e c t o r , U.S. Patent 0 6 / 1 4 2 , 815, f i l e d 22 A p r i l 1980  P h y s i c a l P r o p e r t i e s of Glass",  (London) L t d . , 21.  Field  Sci. Instr.  Gas  "The  Feeley,  of  1973,  Chapter  Wykeham P u b l i c a t i o n s  3.  and C o r s o n , P., " E l e c t r o m a g n e t i c F i e l d s and Waves", San F r a n c i s c o , W.H. F r e e m a n and Co., C h a p t e r 4, F i g u r e 4.22, p g . 169, 1970  L.,  J.D.,  "A R o t a t i n g E l e c t r i c F i e l d D e v i c e " , 4 t h p h y s i c s p r o j e c t , UBC, J a n u a r y 4, 1982 " C l a s s i c a l E l e c t r o d y n a m i c s " , New Y o r k , S o n s , 1975, C h a p t e r 2, p p . 60 - 62  year  engineering  John W i l e y  and  117  APPENDIX  Effects  For  the  consists water  purposes  of  glass  i s the  move as  i s the on  the  spherical field,  therefore  =  _n  the so  electric that  i s the  along  frequency,  given  by  the  that V  the  satisfies  leached  mechanism .  This  2 0  (E )  g  the  9 and the  t the  A  z-axis  are  occurs  ions  t i m e and  the j  2  =  that  as  The  the  there by  P,  and  £  0  i s the  the  net  hand  oscillating  shown i n  Figure  poloidal field  (1/a)( i v / d 9 )  shell. the  element of  of  i s no  right  EQ  (Figure I These  (1-1)  ) r e s u l t s from motion of  c h a r g e s have a d e n s i t y  of S  charges  coulombs  equation,  (I-2)  Q  i s an  ions  v = jj Eg,  er d £ / 4 T T £ R  where d £  shell  absorbed  surface  (ie.  uniform  shell, -1.  in  the  described  spatially of  spherical  means t h a t  m o b i l i t y ) , and  sphere  <j>.  the  t a n g e n t i a l to  Q  , the  that  expression.  sin 9 -  of  of  ohmic c o n d u c t i o n  potential V at point P surface  conduction  P o s i t i o n s on a,  Conductivity  i t i s assumed  field  v e l o c i t y , and,  -E^eJ^t  where t h e  m  surface  transport  applied  s  Finite  Appendix  co-ordinates ^  A  is  over  the  sphere.  E eJ ^ t  where ^  e  of  ion  polar  1^  E  i n which  I t i s a l s o assumed  where v charge  this  main c h a r g e  a result  sphere.  of  of  I  area  at Q  p e r m i t t i v i t y of  (Figure  free  space.  I ^ R The  i s the  distance  domain o f  from Q  to  integration is  118  Figure  I  Geometry  of  the  conducting  shell  i n the  applied  field  (E ). A  119  surface  of the s h e l l .  following  Change c o n s e r v a t i o n r e q u i r e s  +  o (E sin Q  w h e r e -TL. i s t h e r e s i s t a n c e  as  to eliminate 6  9)/^9= 0  of the s h e l l  from  (1-3)  i n ohms p e r s q u a r e .  Using  ( 1 - 2 ) e n a b l e s V t o be e x p r e s s e d  this  i n terms  o f Eg  follows:  "cW/^t = -  By  s a t i s f y the  equation:  a - T L s i n 9(2<s/£t)  equation  that  ^ ( 4 T T 6 a R JL 0  differentiating  (1-1)  (1-1 ) w i t h  and (1-4) t o y i e l d  ^E /3t = - j W E e J e  sin 9 )  w t  A  _  $ E s i n 9/<j9)d£  1  r e s p e c t t o t i m e ^ V / ^ t c a n be e l i m i n a t e d  an i n t e g r a l  sin9 +  (1-4)  e  (a/^Q)  from  e q u a t i o n f o r Eg, namely;  ( K d £  (1-5)  where  K = (4TTa £ 2  To  solve  E  9  =  where ^ equation  sin  0  Rjlsin9)  _ 1  (oE  sin9/^9)  e  (1-6)  t h e e q u a t i o n we w r i t e  ^.E (sin A  9)e3^t  (  i s a c o n s t a n t which  i s t o be d e t e r m i n e d .  With  this  I  _  7  )  assumption  ( 1 - 5 ) becomes  9 = - sin9  + ^ 9  \  (2TJjwa c" 2  0  RJU  - 1  cV(cos 9 ) d £  (1-8)  120  The  integral  field  can  EQ produced  From J a c k s o n ' s field  E  be  e v a l u a t e d by  by  a s u r f a c e charge  solution  a p p l i e d to a  Comparing  the  (1-8)  be  can  o t s i n 9=  2 3  to  the  conducting  = -(^/<J9) j c ( c o s  Q  noting that i t i s related  9)  integrands written  problem  sphere,  d£/4TT£  in  d e n s i t y fi' o f  0  (1-8)  aR  and  the  r e g a r d i n g the  i t is readily  =  t o the  forms' effect  shown  poloidal  = c cos  of a  constant  that  (c sin9/3£. )  (1-9)  9.  (1-9)  Q  i t i s apparent  that  equation  as  - s i n e -2<*. s i n 9 / 3 j a f JL  (1-10)  Q  Hence  o( =  -1 [1 - j ( w ' / V ) ] -  (1-11 )  1  where  v/v' = 2 / ( 3 a f A )  (1-12)  0  Using  (1-17),  given  by  €  =  the  2E (cos  Again charge  A  having  ( 1 - 1 1 ) and  (1-3)  shows t h a t t h e  s u r f a c e charge  d e n s i t y £> i s  equation,  9)  eJwt/laSL  recourse  produces  (jv^ + vV ) ]  to Jackson's  a uniform  field  (1-13)  book i t i s r e a d i l y  EQ i n i t s i n t e r i o r  shown t h a t t h i s  g i v e n by  the  surface  equations:  121  Ej, = -w E ke> /(Jw+w') ,  (1-14)  t  A  where k i s a u n i t Hence  E  For  the t o t a l  T  applied field  = Ec + E ^ = j v j E e D  of strength E , switched A  the s h e l l  (E ) T  is  (1-15)  on a t time  t = 0 i ti s readily  = E e~ 't  shown  (1-16)  w  T  A  Equation  ( 1 - 1 5 ) shows  (E  [1  tan  inside  (Figure 1-1).  fort > 0  E  T  the z-axis  + jw)  w t  A  a field  that  vector along  = E  A  + (W'/w) ]  <)>= (VJ'/W).  significant.  that 2  - 1  /  2  i s attenuated ) and i s a l s o  F o r the case  of interest  by t h e c o n d u c t i n g  phase  shifted  (w'«w),  only  shell  by an a n g l e t h e phase  <J> w h e r e  shift i s  122  APPENDIX  Rate  In  a  linearly  eccentricity) polarized the  field  polarized bulb  caused  occurs the  fields  \EA  by  every  +  proceed  elliptical  E  and  A  time  =  E  the  field  i n Planar Rotating  (an  elliptical  relation  (2).  the  to extend  same and  applied field For  field  Fields  with  In e l l i p t i c a l  t h a t the  separation i s uniform,  vectorial.  changes  breakdown  then by one  E , Q  the  or  new  field  the  addition  A  With  to  i t i s assumed  major  t h a t the  phasors  for E  A  (and  Eg)  are  axis  (II-3)  axis,  (n-4)  0  is a  factor  which determines  the  the  breakdown  voltage of  the  gas.  these  variables  the  can  be  angles,  A  of  (II-2)  E  E ,  the  have  0  e A=eYE  where Y  in  still  = YE ,  minor  Assuming  (Eg)  breakdown  however  must  circularly  basic theory.  internal a  unit  0  further with  Emission  i t i s necessary  remains  charge  i s now  Egl  obeys  however  b a s i c phenomena  bulb  To  the  of Pulse  II  and  B and  the  fields  equations  ratio  of  ForVO,  the  applied field  breakdown does  d e s c r i b e d p a r a m e t r i c a l l y by  amplitude  not the  occur.  123  E  ft. = ^ E ( ( & s i n  A)  D  i _+  (cos A ) _ )  —  (II-5)  E__= - r E ( ( f s i n B)_i + (cos B)j_ Q  where  i i s a unit  vector (II  along  -5)  the  that  |E^ +  the  breakdown,  E_| B  along  the  corresponding  |EA + E  Since  vector  R  =  minor  major  magnitude  of  |  (£ (sin  E  =  2  y E 2  2  E  A  2  a t breakdown  Q  satisfies  the  +  (linearly  1=V(cos B -  Since axis p, =1  E of  cos  A  the  B  and  A-B.  E  A  cos  through  A  E (cos A  A  are  equation  or,  sin B )  by  +  2  from  the  j is a  which  E  A  unit  equations  expression  (cos  the  and  A - cos  above  B) ) 2  result  ((A+B)  the  B -  the  (II-7)  /2 ) + £ ] / 2  1  that,  at  (II-6)  2  above e q u a t i o n  cos  A)  = E  components  to  of  the  form  (II-7)  Q  the  fields  i s consistent with (II-6)  reduces  a l s o has  the  along  equation simple  the  major  (II-1).  For  solution  ((A-B)/2)  I t therefore follows  2TTf /(A-B)  phasor  I t follows  i s given  A -  fields)  p o l a r i z a t i o n ) equation  (1/2V) = s i n  angle  A ) , or  ellipse,  (circular  The  polarized  cos  Eg  the  equation  2  B =0  axis.  of  i t f o l l o w s from  (1/2r) = s i n ( ( A - B ) / 2 ) [ ( 1 - £ ) s i n  For  axis  (II-8)  r o t a t e s between that  the  s u c c e s s i v e breakdowns  number o f  breakdowns per  i s however,  cycle,  fg, is  124  f  B  =TTf /sin  Comparing the  (1/2Y)  1  A  this  result  with  breakdowns p e r c y c l e  polarization  "  for fields  e q u a t i o n (Il-I) shows  that, f o r strong  i s increased i n going of constant  from  amplitude.  linear  In f a c t ,  to  where  and f  c  circularly  as  Y a o  (11-10)  a n d t h e r e s p e c t i v e number  L  and  linearly  more g e n e r a l c a s e s to  a quartic  successive the of  f  E  / f  the  a t t h e same f i e l d  polarization,  f o r B, a n d h a s e i t h e r  case  of very  Hence  strong fields  the enhancement  E  becomes  Q  ratio  ( I I - 6 ) c a n be  2 or 4 real  solution  reduced  solutions.  For  w h i c h e x c e e d s A.  an e l e m e n t  resulting  For  from  In  of arc length  the  elliptical  (II-11 )  i s the frequency  E  E(m ) 1  i s an e l l i p t i c  i s analogous  ellipse  E(m )  circular  insight  1  o f breakdown integral  i n the e l l i p t i c a l l y  o f the second  to that obtained  i s the length of a quadrant  polarization  concerning  m  1  =  the e f f e c t s  b e g u n by s e l e c t i n g £ , Y a n d  kind, with  for a circularly  of changing  an i n i t i a l  polarized m^  = 1-£  polarized  o f the e l l i p t i c a l  1 a n d E ( 1 ) =T/2  e q u a t i o n (lI-6) has been s o l v e d i t e r a t i v e l y is  0,  equation  in  strengths.  = E(m., )  L  f  result an  fields  per second  becomes  where and  of e l l i p t i c a l  equation  the phasor.  field  polarized  o f breakdowns  breakdowns B i s the s m a l l e s t r e a l  limiting  1)  circular  L  f  (Y>^>  fields  f /f -+TT/2 c  (II-9)  as expected.  the p o l a r i z a t i o n with  value  a computer. of B (B  1  field  2 #  field.  For  phasor.  For  To g a i n o f the The  say).  This  more  field  calculation A solution i s  125  obtained  for A  repeated  f o r twenty  field  (E )  using  the  and  B  average  $  and  =  and  B i s then  reset  t o the  s u c c e s s i v e breakdowns.  the _ - a x i s  (Figure  6)  i s then  v a l u e A-| .  The  angle  .The  process  (j>(n) b e t w e e n  e v a l u a t e d on  the n t h  tan  (p t a n B )  bulb  iteration  angle  <}> t h r o u g h  (11-12)  n  which  Ej^ r o t a t e s  f o r breakdown i s then  (<}>(20)-A )/20  given  by  (11-13)  1  the  the  is  result  <)>(n) = a r c  The  (A-|),  s t a n d a r d d e v i a t i o n , 6 , by  the e x p r e s s i o n  20 g- 2  =  ^  (<|)(n)-$) /20.  (11-14)  2  j=1  (The  standard deviation  interval  f  B  Figure The 1.  2.  asp  =  g i v e s i n f o r m a t i o n on  between breakdowns).  The  the  variability  number o f b r e a k d o w n s p e r  i n the second  2Trf /<f  I I shows g r a p h s  of f  B  for0 =  f e a t u r e s of  i n c r e a s e s from  0  the  (linear  1,  .66,  response  .5,  graphs  become p r o g r e s s i v e l y  the  graphs  become s m o o t h e r  less  0.33  curves  polarization)  the  decreased;  is  thus  (11-15)  A  significant  time  are  to 1  "stepped"  at successively  and  in  larger  0. as  follows:  (circular  polarization)  form; values of  as p  is  126  400  300 I  200  100 1  Figure  II  Pulse  Emission  Magnitude  \-  1  2  as  a  Function  of  Normalized Applied  for Different Elliptically  Theoretical 26.  H  Result  Assuming Eg  Polarized  i s uniform.  Field  Fields.  Compare w i t h  Figure  127  3.  the curves a l l s t a r t a t  the  same p o i n t  (ie.  the  threshold f i e l d  and breakdown f r e q u e n c y a t t h r e s h o l d are independent of 4.  strength,  polarization);  at high f i e l d strengths,  the  response curves are asymptotic  to  lines  the  origins.  that  which pass through  breakdown  frequency  at  The m o d e l a l s o shows  l a r g e f i e l d s i s e n h a n c e d by a f a c t o r  comparison t o the v a l u e of  fg observed with  The  TJ/2  l a r g e s t enhancement  polarization.  is  the  fE/fL,  linearly polarized  and o c c u r s i n the c a s e o f  straight  in  fields.  circular  

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