UBC Theses and Dissertations

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UBC Theses and Dissertations

Ion source development Kinnear, James Kerr 1949

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ION SOURCE DEVELOPMENT by JAMES KERR KINNEAR  A thesis  submitted i n p a r t i a l f u l f i l m e n t o f  the requirements  f o r the degree o f  MASTER OP ARTS in  t h e Department of PHYSICS  THE UNIVERSITY OP B R I T I S H COLUMBIA August,  1949  I ABSTRACT A radio frequency excited p o s i t i v e i o n source has been designed and c o n s t r u c t e d . is  excited i n a discharge  oscillator The of  hydrogen i s d i s a s s o c i a t e d and i o n i z e d . the order  tube.  of 2 kV i s used to accelerate canal  A  voltage  the p o s i t i v e  I n t h e end o f t h e  disoharge  The p o s i t i v e i o n s a r e t h e n a c c e l e r a t e d a n d f o c u s -  i n t o a beam b y two c y l i n d r i c a l e l e c t r o s t a t i c  U3lng v o l t a g e s  of the order  purposes o f a n a l y s i n g celerating  focussing  o f 10 k V a n d 50 kV.  a one l e n s  r e s o l v e s up t o mass t h r e e  them i n t o a F a r a d a y c u p .  a beam c o n t a i n i n g  45$ p r o t o n s .  lenses For  system i s used, a c -  t h e beam t o a n e n e r g y o f t h e o r d e r  A magnetic analyser  800  frequenoy  a t a f r e q u e n c y o f 210 m c . / s e c .  operating  ions through the e x i t  sed  tube b y a r a d i o  Hydrogen gas  o f 15 kV. ions,  The s o u r c e d e l i v e r s  A total  current of  microamperes o f p o s i t i v e i o n s has been measured.  II ACKNOWLEDGEMENTS  Th©  a u t h o r wiahea t o express h i s thanks f o r  the a s s i s t a n c e and guidance vised  this  o f D r . K.H. More, who  project. He w o u l d f u r t h e r  to  super-  the N a t i o n a l Research  like  to express  appreciation  C o u n c i l f o r awards a n d g r a n t s  w h i c h were made I n c o n n e c t i o n w i t h t h i s r e s e a r c h . The  author a l s o would l i k e  t o acknowledge  t h e a s s i s t a n c e o f Mr. S.B. Woods who s p e n t much t i m e o n this project  and s p e c i a l l y  did  blowing.  i n glass  Finally,  t o t h a n k h i m f o r t h e work h e  the author wishes  to mention h i a  a p p r e c i a t i o n t o h i s c o l l e a g u e on t h i s p r o j e c t ,  Mr. R.H. Chow,  f o r h i s c o o p e r a t i o n and e a r n e s t endeavour throughout the work.  a l l of  ION SOURCE DEVELOPMENT Table of Contents Page Introduction  1  Design and Construction The Discharge Tube  3  The Lens Assembly  4  The Vacuum System  5  The Hydrogen Supply  6  The Radio Frequency O s c i l l a t o r  7  The Magnetic C o l l s  9  The Magnetic Analyser  11  The Power Supplies  13  Operation and Experimental Results  18  D i s c u s s i o n of R e s u l t s  25  Conclusion and Recommendations  26  PLATES AND  ILLUSTRATIONS  Plat©  I  Plat©  II  Plat©  III  n  5  Plat©  IV  tt  6  Plate  V  Plate  VI  Plat©  VII  Plate  VIII  Diagram o f the Ion Source  p P h o t o g r a p h o f t h e Ap/aratus  f a c i n g page  n  3  II  4  Diagram o f the Magnetic A n a l y s e r  13  Circuit  14  o f th© 50 k V S u p p l y  B l o c k W i r i n g Diagram o f the Power S u p p l i e s  n  16  G r a p h o f th© A n a l y s e d Beam  u  22  1.  ION  SPURGE DEVELOPMENT  INTRODUCTION P r o t o n s and energies  other  are used f o r nuclear  research.  e q u i p m e n t i s d e p e n d e n t u p o n the of  i o n beam i t oan  t h e r e f o r e be  able  positive  The  i o n source  f i n a l l y produce. to supply  An  the  source  duced per ions in  gas  c a n be  d e f i n e d as  ( s a y p r o t o n s ) compared w i t h  the output  beam.  In these  have h i g h e f f i c i e n c y . a high  The  c u r r e n t d e n s i t y and  d e s i r a b l e a l s o t h a t the and  cluding  Rutherglen an  oscillator  Cole  2  hydrogen d i s c h a r g e .  respects  be  the  ions  spread.  of rugged  It la  construction  life.  i n 1947  The  pro-  with  types  i n the  sources.  operating  ions  beam must be w e l l f o c u s s e d  type which i s b e i n g and  efficiency  t h e number o f o t h e r  of p o s i t i v e  literature.  Other types  c a p i l l a r y a r c , magnetic f i e l d  last  current  must  e l e c t r o d e l e s s or r a d i o frequency this  must  The  small angular  have b e e n d e s c r i b e d  types^were c a n a l r a y  i o n source  source  Several different sources  kind  t h e number o f d e s i r a b l e  two  source  have a l o n g o p e r a t i n g  f o r the  t h e number o f  m o l e c u l e u s e d o r as  various  accelerating  a l a r g e enough i o n  w h i c h i s as m o n o - e n e r g e t i c a s p o s s i b l e . of  ions of  output  first  followed i n -  reflection  described here.  a t 180  The  and  excited sources.  describes  ion  It is  A paper  auch a source  mo./sec. t o e x c i t e a was  400  microamperes  by  using  2. w i t h 60% p r o t o n s . oscillator protons  and deuterium  ions.  oscillator this  to get deuterons.  They r e p o r t a  Hall  4  d e s c r i b e s In a paper  o p e r a t i n g a t 450 m c . / s e c .  h i s source  Thonemann  5  ions.  et a l . t e l l  of their  source  a f o c u s a e d beam o f 500 jua w i t h 90% a t o m i c  for  i s used  that  hydrogen.  t h e u s e o f an e x t r a c t i n g  i s due t o t h e f a c t  percentage catalyst  magnetic  spread.  by  of Hall  4  voltage gives the f i n a l This opinion i s not held spreads.  This  that the e x t r a c t i o n voltage i s a c t u a l l y  a c r o s s a v e r y s m a l l space  the d i s o h a r g e  A  It i s felt  o t h e r w r i t e r s who r e p o r t s m a l l e n e r g y  developed  that the  the l a t e r a l motion  i n the discharge tube.  beam a s e r i o u s e n e r g y by  indicated  i n the d i s c h a r g e tube as i t c o n c e n t r a t e s  the d i s c h a r g e by r e s t r i c t i n g eleotrons  delivering  e m i t t e d s i n c e m e t a l a c t s as a  the recombination o f atomic  field  publi-  ions.  e x p o s e d t o t h e d i s c h a r g e th© h i g h e r  protons f i n a l l y  400  In a reoent  Previous l i t e r a t u r e  with  voltage  The s o u r c e d e l i v e r e d  m i c r o a m p e r e s w i t h 60% a t o m i c  l e s s metal  60%  A new f e a t u r e o f  s o u r c e was t h e e l i m i n a t i o n o f a n e x t r a c t i o n  cation,  an  i o n c u r r e n t o f 500 m i c r o a m p e r e s w i t h  across the discharge tube.  of  used  3  f r e q u e n c y o f 15 m c . / s e c . u s i n g h y d r o g e n t o g e t  useful positive atomic  Th© s o u r c e o f B a y l y a n d W a r d  near  the e x i t  canal of  t u b e where i o n f o r m a t i o n d o e s n o t t a k e p l a c e . Th©  d e s i r a b l e f e a t u r e s o f the Radio  PLATE I  3. Frequency positive  Ion source are the combination of i o n c u r r e n t w i t h s m a l l energy  centage Atomic a l s o has life,  i o n s and  the advantage  hence s a v i n g  low  s p r e a d , good p e r -  consumption  that  sufficient  of hydrogen.  t h e d i s c h a r g e t u b e has  It  long  i n t e r r u p t i o n o f o p e r a t i o n t o renew  cathodes e t c .  DESIGN AND  CONSTRUCTION Plate  I i s a drawing of the i o n source  has b e e n c o n s t r u c t e d d u r i n g Plates and  I I , I I I , and  the a u x i l i a r y  when t h e f i r s t The  the course o f t h i s  IV are photographs  equipment,  showing  which  research.  of the i o n source  i t as  I t appeared  s a t i s f a c t o r y beam c u r r e n t s were o b t a i n e d .  D i s c h a r g e Tube The  d i s c h a r g e t u b e i s made o f p y r e x  t u b i n g 1-|- i n c h e s i n d i a m e t e r a n d long.  A glass  cone  is ring has  in  i s the e x i t  i t s apex.  from  This  The  constriction  b u l b w i t h a tungsten probe the c o n s t r i c t i o n  i n t o one  an opening about  the d i s c h a r g e tube.  t u b e has a s h o r t  approximately 8 inches  sealed  d i s c h a r g e t u b e and  end  3/16"  of the  i n diameter  opening f o r p o s i t i v e  to which  i s sealed a The  the metal probe  the r e c o m b i n a t i o n o f p r o t o n s and  e l e c t r o n s upon the  inlet  tube f o r hydrogen  of  a s much a s  thu3  An  glass  purpose  p o s s i b l e f r o m the main d i s o h a r g e  surface.  ions  o t h e r end o f t h e d i s o h a r g e  anode i n i t .  i s to i s o l a t e  glass  d e c r e a s i n g somewhat  e n t e r s the s i d e  metal of  PLATE I I View of Apparartus showing dischsrge tube at l e f t w i t h magnetic c o i l mounted around i t , the o s c i l l a t o r a t r i g h t of discharge tube, power supplies below and i s o l a t i n g transformer i n bottom l e f t hand corner.  4.  th©  discharge  tube near the bulb  structure f i t s with  snugly  vinyl-seal  end.  over a s t e e l  The w h o l e  glass  cone a n d I s f a s t e n e d  a n d made vacuum t i g h t w i t h b l a c k wax. The  m e t a l cone a c t a a s t h e c a t h o d e f o r t h e e x t r a c t i n g v o l t a g e . Through the c e n t r e drilled, canal  into which i a f i t t e d  i s made i n t h e i n s e r t .  different The  o f t h e cone a l o n g  exit  the magnetic f i e l d through the e x i t steel  i s 3/4 I n .  The g l a s s  the e l e c t r i c f i e l d  through the e x i t  electrodes.  with  air  blast  The  Lena  bolted to two  upon i t d u r i n g  and a s s i s t i n g  shapes ions  most o f t h e operation,  i n fooussing  ions  around  tube t o a c t aa t h e r a d i o i s mounted  t u b e a t t h e cone e n d .  i s needed t o c o o l t h e d i s c h a r g e  conAn  tube.  Assembly m e t a l cone i n t u r n i s mounted t o a  s t e e l f l a n g e by a clamping r i n g . to a ateel  "T" aection.  t h e vacuum pumps. other  cone  i n fooussing  covering  A magnetic c o l l  the discharge  The large  The s t e e l  copper r i n g s a r e f a s t e n e d  the middle o f the d i s c h a r g e  centric  with  canal.  Two f l a t  frequency  inserts  1 / 1 6 " , 3/32 i n . , 1/8 i n .  which then a s s i s t s  canal.  The e x i t  There a r e three  cone h a s a c h a r g e b u i l t  forming  a dural insert.  canal diameters,  length o f the i n s e r t  i t s axis a hole i s  This flange i a  The s t e m o f t h e "T" l e a d s  At the other  s i d e o f t h e "T" s e c t i o n  l a r g e s t e e l f l a n g e s a r e mounted, s e p a r a t e d  by  PLATE I I I  View of the apparatus showing the e x i t f l a n g e and the Faraday cup assembly.  5. porcelain  c y l i n d e r s and b o l t e d t o g e t h e r  These l a s t  two f l a n g e s  electrodes. while  The f i r s t  together  system.  with  last  T h e s e two  steel  discharge  which  I n i t , comprise the e l e c t r o s t a t i c gap i s & i n c h l o n g w h i l e t h e  diameter  cylinders a r e co-planer.  f l a n g e has a & i n c h d i a m e t e r e x i t h o l e  Rubber g a s k e t s and  cylindrical  t h e b a s e o f t h e m e t a l cone,  The f i r s t  ends o f t h e d i f f e r e n t  rods.  c y l i n d e r h a s a d i a m e t e r o f 1 1/8 i n .  a & inch diameter hole  focus3ing  The  t h e two b r a s s  textolite  t h e s e c o n d h a s a d i a m e t e r o f 2jj|- i n c h e s .  cylinders has  support  with  a r e u s e d between a l l these  to p o r c e l a i n j o i n t s .  In i t .  steel to s t e e l  The common a x i s o f t h e  tube and l e n s assembly l i e s h o r i z o n t a l l y . A F a r a d a y c u p was c o n s t r u c t e d b y m o u n t i n g  a glass  c y l i n d e r b e t w e e n two b r a s s  f l a n g e has a hole through a hole  flanges.  o f 3/8 i n c h d i a m e t e r  i n the centre  The f i r s t  in i t .  Sealed  o f t h e second f l a n g e  isa  K o v a r s e a l u p o n w h i o h i s mounted a d u r a l c u p o f % i n c h diameter. the  The F a r a d a y c u p a s s e m b l y  e x i t hole  positive  i n the l a s t  i o ncurrent.  i s mounted  f l a n g e f o r measuring  The m a g n e t i c a n a l y s e r  against total  c a n be p l a c e d  b e t w e e n t h e l a s t f l a n g e a n d t h e F a r a d a y cup when d e s i r e d .  The  Vacuum S y s t e m The  with  the exception  used t o i s o l a t e  w h o l e vacuum s y s t e m i s made o f m e t a l o f a 10 i n c h s e c t i o n o f g l a s s c y l i n d e r  t h e "T" w h i c h may b e a t 50 k V a b o v e  ground.  Plate  IV  To f a c e  page  6.  View o f a p p a r a t u s s h o w i n g o s c i l l a t o r a n d f l a n g e s a t l e f t , P i r a n i a n d I o n i z a t i o n gauge c i r c u i t s a n d 50 k V c o n t r o l p a n e l a t c e n t r e , h y d r o g e n t a n k a t r e a r a n d 50 k V u n i t a t r e a r r i g h t hand bottom c o r n e r .  6 An  o i l d i f f u s i o n pump b a c k e d b y two W e l c h m e c h a n i c a l pumps  I s u s e d f o r pumping down t h e vacuum s y s t e m . baffle  from entering  t h e m a i n vacuum.  brass p i p i n g of i f inch diameter.  A l l pump l i n e s a r e  Sylphon bellows a r e  t o damp t h e t r a n s m i s s i o n o f m e c h a n i c a l  along  cooled  i s mounted a b o v e t h e d i f f u s i o n pump t o p r e v e n t o i l  vapours  used  A water  t h e pumping l i n e s .  vibrations  Two vacuum Gauges a r e u s e d — a  P i r a n i o n t h e f o r e pump a n d a n I o n i z a t i o n gauge o n t h e m a i n vacuum s y s t e m . sired  The  Hydrogen  hydrogen  Supply  tank.  glass bottle.  hydrogen  controls  A glass  the rate  A needle valve  o f f l o w o f hydrogen  glass  A glass  "T  o f pump o i l .  to the discharge The  i n the feed  line  just  To t h e s t e m o f t h e "T" a l o n g v e r t i c a l l y down i n t o a  The s u r f a c e o f t h e o i l i s o p e n t o The r i s e  of o i l into  i s directly proportional to  flowing  line  i s measured b y a type o f  r o d i s j o i n e d whioh runs  atmospheric p r e s s u r e . tube  used  i s inserted  n  the needle valve.  bottle  i n this  the d i s c h a r g e tube p r e s s u r e .  o f f l o w o f hydrogen  before  commercial  tube l e a d s f r o m t h e s t o r a g e b o t t l e  tube and hence c o n t r o l s  manometer.  i s supplied from a  I t i s stored a t atmospheric pressure i n a  the discharge tube.  rate  i s a l s o u s e d when i t i s d e -  t o measure t h e p r e s s u r e i n t h e d i s c h a r g e t u b e .  The  to  A Pirani  a t atmospheric p r e s s u r e .  the v e r t i c a l  t h e volume o f h y d r o g e n  7. The  Radio Frequency The  4-65 A. tetrode.  tube used  f o r the o s c i l l a t o r  This i s a small radiation-cooled  i s an Eimac  transmitting  T h i s tube has been chosen because o f i t s low  interelectrode important  Oscillator  c a p a c i t i e s and s h o r t heavy l e a d s which a r e  factors  f o r s t a b l e and e f f i c i e n t  high frequencies.  I t a l s o has rugged  shape o f t h e g l a s s e n v e l o p e  operation at  c o n s t r u c t i o n and the  i s s u i t a b l e f o r strength, per-  haps t o w i t h s t a n d h i g h enough p r e s s u r e t o b e u s e d Van de G r a a f f T a n k .  I t c a n be o p e r a t e d w i t h  ina  plate  v o l t a g e s up t o 3000 V w i t h p l a t e d i s s i p a t i o n o f 65 w a t t s . The  oscillator  circuit  and  heater l i n e s .  i s p u s h - p u l l w i t h tuned p l a t e ,  The p l a t e a n d g r i d  shorting bars while the heater l i n e s variable  condensor.  the h e a t e r l i n e . O.D. c o p p e r put  with  a r e tuned w i t h a i s run inside  A l l o f t h e l i n e s a r e made o f 3/16 i n c h  r o d orjbubing.  through a matching tube.  a r e tuned  The h e a t e r r e t u r n w i r e  l i n e s mounted n e a r  charge  lines  grid  The o u t p u t  the plate  I I section  i s taken from  lines.  out-  I t i s then f e d  to the rings  on the d i s -  The impedances o f t h e I I s e c t i o n a r e made  o f 3 l i n e s w h i c h have s h o r t i n g b a r s o n them i n p a i r s . The  lines  a r e J- wave l e n g t h l o n g s o t h a t a n y d e s i r e d  Impedance may b e o b t a i n e d w i t h a n y p a i r . however, have t h e i r  shorting bars  Two o f t h e p a i r s ,  c o u p l e d so t h a t  a l w a y s p r e s e n t t h e same impedance as e a c h o t h e r .  they To s e e  8. how t h i s f u n c t i o n s , c o n s i d e r a f o u r t e r m i n a l n e t w o r k sisting  of three reactances  When a n impedance o f Z  a  u R  as s h o w n —  Q  4 jX@ i s c o n n e c t e d  one p a i r o f t e r m i n a l s , t h e Impedance pair  i s given by the f o l l o w i n g  i/ (x,+x )z l  ^ 0 =  Ro  -t-j  X  0  =  2  Z  E  between  between t h e o t h e r  relation—  e  X . * « ) j X,  -  j ( zX, + x ) z - x,x - X, e  2  This equation  con-  2  2  shows t h a t y o u c a n t r a n s f o r m a n y impedance  i n t o a n y d e s i r e d impedance Z Q b y s u i t a b l e c h o i c e o f  X i and X £ . Philips  A r e p o r t on t h i s matching u n i t  Research R e p o r t s  Adjustable  6  where  i s published i n  i ti s called  T r a n s f o r m e r f o r U.H.P."  "A U n i v e r s a l  A matching device can  be c o n s t r u c t e d , w o r k i n g o n t h i s p r i n c i p l e f o r u s e w i t h wave g u i d e s ,  c o a x i a l cable o r open l i n e On a t e s t  1500 load.  systems.  operation o f the o s c i l l a t o r a t  V o l t s , 120 w a t t s o f power was d e l i v e r e d t o a dummy I t i s n o t known what power  delivers  to the discharge  tube.  the o s c i l l a t o r  actually  9.  The  Magnetic  Coils A p a i r of Helmholtz c o i l s  the  magnetic f i e l d  i n the d i s c h a r g e tube.  c h o s e n w h i c h w o u l d be discharge tube.  T h e s e were; c r o s s  —  2.46  cms.  U s i n g No. i n s u l a t i o n we 544.  The  find  total  i n series  magnetic f i e l d ^  cms.;  the — distance  faces.  copper w i r e w i t h enamel  ohms.  colls  Assuming  t h e n draw 8.8  p o n d i n g t o a c u r r e n t d e n s i t y o f 750  t h e n be H « 0.9  7.54  were  f r o m t h e w i r e t a b l e s number o f turn3 a r e  f e e t w i t h a r e s i s t a n c e o f 2.72  The  —  l e n g t h o f w i r e o n t h e two  s u p p l y the c o i l s  around  s e c t i o n of c o l l  between near  12 B&S  designed f o r  Dimensions  s u i t a b l e f o r mounting  a 2 i n c h s q u a r e ; mean r a d i u s o f c o i l between c o i l s  was  a 24  amps,  circular  is  168Q volts  corres-  mils/amp.  o n t h e a x i s midway b e t w e e n c o i l s  will  gauss  is  =  570  gauss.  This f i e l d  10.  e x p e c t e d t o be a u f f i c l e n t . colls  i s 274 i n .  watts. coils  This  Now  the surface area of the  Power d i s s i p a t e d a t 8.8 amps  2  i s less  t h a n one w a t t p e r s q u a r e  should not overheat with t h i s  The f i e l d  H  a t 300°P f o r  takes Into account the  dimensions o f the c o i l . i . e . —  =  P  impregnated  i s c a l c u l a t e d f o r a c u r r e n t o f 5 amps,  u s i n g the f o l l o w i n g formulae which finite  This design  T h e y were  w i t h G9555 g l y p t a l b a k i n g v a r n i s h a n d b a k e d two h o u r s .  Inch so t h e  current.  was t h e n a d o p t e d a n d t h e c o i l s made.  i s 212  2irrT*(Cx-Hb)  I  I  p  n  -  ^  c - d  t  ^  i  t ^ x  +  i  ^  b )  S  2 +  ^  ^  ^  ( a - d )  2  _ *y W) L a + d + :j_fe^blL±J£L±d2l (pc  o)  In  n  c  _  Where Hp i s t h e f i e l d a t p o i n t the  coil  section.  d  ^ ^  +  "p", *$ u  n  2  )  +  (  c  The r e s u l t s  x(cms)-  o f the c a l c u l a t i o n s  215  188  121  78  0  2.54  5.08  7.62  We p o i n t o f one c o i l  see the f i e l d  field  gauss f o r t h i s  _  d  )  8  cross  a r e h e r e shown;  51  32  10.16  12.70  on the a x i s a t the mid-  i s t h e 215 g a u s s .  The c o l l  end o f t h e d i s c h a r g e t u b e has t h e s t e e l The m a g n e t i c  L  i s the current i n  a n d "n" i s t h e number o f t u r n s p e r u n i t  H (gauss)-  215  b  cone  a t the e x i t at i t s centre.  then near the s t e e l  cone w i l l be a r o u n d  current.  only this  Actually,  one  coil  11.  has b e e n u s e d using  s i n c e no a d v a n t a g e  the Helmholtz c o i l  has been e x p e r i e n c e d i n  arrangement.  mains a r e u s e d t o s u p p l y t h e r e q u i r e d coil.  The r e q u i r e d r e s i s t o r s  The 110 v o l t  D.C.  current f o r this  are i n series  w i t h a n am-  meter and t h e c o i l .  The  Magnetic A n a l y s e r The  w i t h the purpose  magnetic  a n a l y s e r has been designed  i n mind t h a t  and 4 i o n s o f 50 k V e n e r g y .  Using the formula;  s  Hev e  (where H i s t h e m a g n e t i c  i t c o u l d r e s o l v e mass 3  field  my2 r  i n gauss,  on t h e i o n i n e.s.u., v i s the v e l o c i t y m i s  e i s the charge of the i o n In  c m . / s e c , / i t s mass i n grams, c i s t h e v e l o c i t y  of l i g h t In  cm./sec., a n d r i s t h e r a d i u s o f a r c i n cm.) t o g e t h e r w i t h the  other  relation; eV 300  (where h e r e the  magnetic  $  s  mv2  V i s t h e e n e r g y o f t h e i o n i n v o l t s ) we field  required  t o b e n d t h e i o n o f known  energy through an a r c o f g i v e n r a d i u s .  H  =  find  c r  /~my  y 150e  The r e l a t i o n i s  12.  Assuming the 10^  g a u s s i n a i r we  o f 50 k V  e n e r g y w i l l be  i n c h e s , mass 3, inches,  1.79  this w i l l  2 and  inches,  a pole piece  at  find  by  t h i s formula  bent  1 ions and  1.26  of 2 square  t h a t mass 4  in a circle  inches  cross  3 inches  f r o m t h e magnet.  With these designed  using  l a y e r o f 3/16  No.  18  The  of r a d i i  2.23  respectively. s e c t i o n , as  Ions w i l l  1  cm.  have b e e n  c a l c u l a t i o n s i n mind the Formel wire  i n c h c o p p e r t u b i n g was  runs of  shown,  45°.  T h e r m o - c o u p l e s were a l s o I n s e r t e d Test  With  4 ions by  f o r the  i n t o the  temperature r i s e  magnet  2 coils.  wound i n e a c h  These tubes are used f o r water c o o l i n g o f the  winding*  ions 2.53  into circles inches  of  of radius  mean a s e p a r a t i o n o f mass 3 and  bent through approximately  was  magnet w i l l p r o d u c e a f i e l d  A  coil.  coils.  coils  while  at various  currents  Plat© V  To f a c © page 13  13. were made a n d t h e w a t e r c o o l i n g s y s t e m was satisfactory  service. The  pole pieces  o f t h e magnets were made  f r o m 2 i n c h diameter i r o n and shaped w i t h such that  the I n c i d e n t  netic field enters  m e t e r wave g u i d e ,  enter  leave  Sections  together  sides  t h e mag-  the Faraday cup.  The magnet  the  wave g u i d e f i t s  the  pole  The  Power  field  of rectangular  centi-  to ^  inch  making a bend o f 4 5 ° .  on each end f o r f a s t e n i n g t o t h e  of the electrode  piece.  the magnetic  w h i c h h a s one d i m e n s i o n e q u a l  F l a n g e s were f i t t e d  system and f o r f a s t e n i n g t o i s mounted a t t h e b e n d a n d  e x a c t l y i n t o t h e £ i n c h gap b e t w e e n  Plate  V shows a d i a g r a m o f t h e  analyser  Supplies The  standard  side.  soldered  exit flange  two f l a t  n o r m a l t o one s i d e a n d t h e e x i t beam w h i c h  normal t o the other  It  beam o f i o n s w i l l  t h e F a r a d a y cup w i l l  were s i l v e r  found to give  full  power s u p p l y  wave c i r c u i t  with  f o r the o s c i l l a t o r choke c o n d e n s o r  is a  filtering.  i s c a p a b l e o f d e l i v e r i n g up t o 2000 v o l t s a t 400  milliamperes.  In the h i g h  load relay c o i l input  switch.  This  lead an over-  i s c o n n e c t e d w h i c h s w i t c h e s o f f t h e A.C.  t o t h e power s u p p l y  milliamperes.  volt%ge negative  when t h e c u r r e n t  An A.C. o p e r a t e d relay protects  coil  400  resets the r e l a y  the o s c i l l a t o r  damage due t o s u d d e n e x c e s s i v e  reaches  currents.  tubes  against  Plate  VT  To f a c e page 14  14.  A f u r t h e r power s u p p l y waa supply  18 kV.  tripler one  I t u s e s 8013  circuit.  The  2 watt r e s i s t o r s ,  c o n d e n s o r p l a t e s and  to  the  c o r r e c t p o s i t i o n s on  is  Inserted i n series with  bleeder  c u r r e n t and  supply.  The  t h e D.C.  output.  first  the  across  are a l l tapped A 6 ma. m e t e r  the b l e e d e r f o r measuring s u p p l i e d by  m e a s u r e d and  found  lens voltage.  this  t o be  power  O.Q%  intended  to  However a  lens voltage.  A 20 ma.  of supply  second  been used to supply probe voltage  endent o f the f i r s t series with  cases  T h i s power s u p p l y was  and  power s u p p l y has  voltage  i s connected  this bleeder.  hence v o l t a g e  r i p p l e was  probe v o l t a g e  in a  to  A bleeder resistance, consisting of  h u n d r e d 4 7 K ohm,  the o u t p u t .  rectifiers  constructed  Indep-  meter Is i n  l e a d to the probe f o r measuring probe  cur-  rents. A 50 is  k V power s u p p l y ,  shown i n P l a t e VI, has  f o r m e r and oil.  two  rectifier  or negative  tubes are  v o l t a g e as  the h i g h v o l t a g e output  cable.  is  output  connected across  farads. reading  in a  case  so  that  voltage  supplied.  of  The  which trans-  immersed  in  either  d e s i r e d i s d e l i v e r e d to A bleeder  o f 60 megohms  i n p a r a l l e l with  A c u r r e n t meter i s i n s e r i e s w i t h  w i t h a choke and is  the  circuit  a l s o been designed.  A s w i t c h i n g arrangement Is used  positive  the  The  shown f r o m w h i c h t h e f u n c t i o n o f t h e  micro-  the b l e e d e r  A p r o t e c t i v e spark  neon tube a r e u s e d .  0.5  gap  circuit  switching  for  together diagram arrange-  15 ment a n d p r o t e c t i v e is  Intended  quired  f o r the f i n a l  that the p o s i t i v e In  and  secondary  other. case is  circuits  c a n be seen.  T h i s power  a c c e l e r a t i n g gap when i t i s r e i o n s h a v e 50 k V o f  energy.  a l l o f t h e s e power s u p p l i e s t h e p r i m a r y  of a l l transformers are i n s u l a t e d from  One s i d e o f t h e D.C. o u t p u t  Is connected  t o t h e c h a s s i s o f i t s own power s u p p l y .  connected  i n each  A common  O n l y one e a r t h c o n n e c t i o n  This  e a r t h p o i n t i s a l w a y s made a t t h e o u t p u t  lens  system i n u s e so t h a t t h e output  will  be a t e a r t h p o t e n t i a l .  former. in  Also  from  the Input  The i n p u t s u p p l y  supply.  end o f t h e  measuring  equipment  i n a l l power s u p p l i e s  supply f o r the r e c t i f i e r  each case  line  i s made t o t h e  water mains and t o t h e e a r t h s i d e o f t h e A.C. mains  independently  each  b e t w e e n a l l p o i n t s w h i c h a r e t o be h e l d a t t h e  same v o l t a g e .  the h e a t e r  supply-  tubes  i s controlled  t o the high voltage t r a n s -  to the high voltage  i s c o n t r o l l e d by a v a r l a c .  transformer  A l l control  knobs,  w h i c h must be u s e d when t h e h i g h v o l t a g e i s o n , a r e mounted o n l o n g i n s u l a t i n g r o d s .  A l l circuits  are pro-  tected with fuses. Since the output always maintained and  end o f t h e l e n s s y s t e m i s  a t ground p o t e n t i a l ,  t h e d i s c h a r g e tube  core and probe w i l l  p o t e n t i a l s u p t o 50 k V a b o v e g r o u n d . oscillator  the other  power s u p p l y ,  electrodes  be a t h i g h  Consequently the  the probe voltage supply and the  18 k V s u p p l y must be i n s u l a t e d f r o m  earth.  T h i s was done  t o r.f. e l e c t r o d e s  t o probe  t o cone  t o f i r s t electrode  Isolating Transformer  fo  mains  Plate VII.  Block  Wiring  D i a g r a m o f t h e Power  Supplies.  r - t o second electrode  16  by  c o n s t r u c t i n g a one  a t i o n from A.C.  t r a n s f o r m e r , w i t h 50 k V  to secondary,  110  second volt  The  were t a k e n f r o m a p o l e t r a n s f o r m e r v o l t windings.  winding  input.  was  The  winding  varnished with g l y p t a l .  found  high  voltage only  then  volts with  wrapped w i t h empire  The  whole was  During  to give s u f f i c i e n t  volts  leaving  was  oil.  insul-  Then u s i n g Formel w i r e  wound t o d e l i v e r 110  drum o f t r a n s f o r m e r  110  I n s u l a t i n g m a t e r i a l was  mounted a r o u n d t h e s e w i n d i n g s .  was  to s u p p l y the  t o t h e power s u p p l i e s i n q u e s t i o n .  windings the  primary  t o one  then  a  110  cloth  and  Immersed i n a  o p e r a t i o n the  current without  transformer  breakdown o r  overheating. All  power s u p p l i e s f e d b y  t r a n s f o r m e r a r e mounted on a n  Isolation  i n s u l a t e d deck.  d i a g r a m o f t h e s e power s u p p l y c o n n e c t i o n s Plate  the  A  block  i s shown i n  VII. In measuring the p o s i t i v e  ion current with  a microammeter, u s i n g t h e F a r a d a y  cup,  that the  to p o s i t i v e  secondary  ardment o f t h e  cup  e l e c t r o n s , due and  the  i t is essential i o n bomb-  cup m o u n t i n g f l a n g e , a r e  measured.  T h i s Is a s s u r e d by p u t t i n g s m a l l  potentials  i n s u c h a d i r e c t i o n as  retarding  to f o r c e the  secondary  electrons  to r e t u r n to the s u r f a c e from which they  emitted.  Dry  potentials.  cell batteries See  are used  d i a g r a m on next  to supply  page.  not  are  these  17. P" 7  V  /  /  V  cup •  f l Cinge  -flange  Z. 2  7  0  1.  V  + 1 llllllllll^  135  V  WI$h t h e a r r a n g e m e n t shown i n t h e d i a g r a m we s e e t h a t t h e cup  i s 135V p o s i t i v e t o entrance  135  v o l t s p o s i t i v e to the cup.  f r o m t h e cup and f l a n g e which they  are emitted  microammeter.  give f u l l  exception  emitted from  a n d w i l l n o t be m e a s u r e d i n t h e fitted  the currents  A g a l v a n o m e t e r was u s e d w i t h  tube a n d c i r c u i t ,  gauge t u b e a n d t h e 50kV s u p p l y  shunts  with the  the i o n i z a t i o n  has been designed  t r u c t e d by the author and c o l l e a g u e .  t o be  5p.a, a n d 5 0 u a .  o f t h e equipment d e s c r i b e d ,  o f the P i r a n i  2 is  r e t u r n t o the s u r f a c e  scale deflections of ljia, All  1 and f l a n g e  Secondary e l e c t r o n s  With the analyser  measured a r e s m a l l e r . to  2 will  flange  and cons-  18.  OPERATION AND EXPERIMENTAL RESULTS On f i r s t b l u i s h white. Balmer l i n e s  c a n be seen through  the pressure  high pressures the  electrodes.  a spectroscope.  throughout  t h e whole t u b e .  fills  As t h e p r e s s u r e  A t about.  tube t h e d i s c h a r g e i s  increases the redness  the discharge  appears  i t turns r e d and t h e  i n the discharge  r e d and spreads  creasing  the d i s c h a r g e  A f t e r a few minutes  30 m i c r o n s p r e s s u r e bright  striking,  In-  b u t a t very-  o n l y t h e space between  decreases  b e l o w 30 m i c r o n s  t h e d i s c h a r g e becomes p a l e r a n d a p p e a r s t o g e t t h i n n e r l o o k i n g u n t i l a t v e r y low p r e s s u r e at can  l a s t goes o u t .  i t becomes b l u e r a n d  When t h e d i s c h a r g e h a s gone o u t y o u  s e e t h e g l a s s i n t h e tube f l o u r e s c e .  voltage  i s increased the discharge  l e a v i n g a s m a l l dark space. plasma surrounding positive across  ions.  this  this  As the probe  recedes  f r o m t h e cone  The s u r f a c e o f t h e d i s c h a r g e  dark space r e p r e s e n t s a source o f  Most o f t h e e x t r a c t i o n v o l t a g e  space.  When t h e m a g n e t i c f i e l d  the d i s c h a r g e plasma shapes a t h i r d o f t h e tube w i t h  itself  Is developed  i s turned on  I n t o a l o n g cone  i t s apex a t t h e e x i t  along  canal.  When t h e v o l t a g e was t u r n e d h i g h o n t h e l e n s e l e c t r o d e s , s e r i o u s a r c - o v e r was e x p e r i e n c e d , was  due t o t h e p r e s s u r e  being  r u n s were made t o d e t e r m i n e d i f f u s i o n pump f o r l o w e s t determining  this  too high.  which  Because o f t h i s  the best heater  current ofthe  pressure p o s s i b l e .  After  c o n d i t i o n t h e h i g h vacuum p r e s s u r e was  19. of t h e order pressure  o f IO"* mm.  was o f t h e o r d e r Further  hydrogen a t d i f f e r e n t ferent the  exit  exit  mercury while  5  canals.  canal  o f 20 m i c r o n s .  r u n s were made o f r a t e s discharge  of flow of  tube p r e s s u r e s  with  Note t h a t t h e r a t e o f f l o w  i s independent o f the pressure  s y s t e m b u t depends o n l y o n t h e e x i t the p r e s s u r e  t h e forepump  i n the discharge  tube.  dif-  through  i n the main  c a n a l dimensions and The r e s u l t s  a r e here  tabulated.  E x i t Canal Diameter l/8  Pressure Discharge  inch  in tube  Rate o f H>> f l o w  25 m i c r o n s 15 10  8.8 c c . / h r . 5.3 3.5  3/32  inch  50 m i c r o n s 25 15  9.6 c c . / h r . 4.4 2.6  1/16  inch  50 m i c r o n s 25 15  3.7 c c . / h r 2.3 1.4  Runs were made o f t h e p o s i t i v e with  probe voltage  ting positive  value  o n l y and v a r y i n g magnetic f i e l d .  i o n current a g a i n s t probe voltage  peak o f c u r r e n t . the  i o n current  Increasing  o f the current  the magnetic f i e l d  Plot-  shows a inoreases  a t t h e p e a k a n d moves t h e p e a k t o  higher  probe v o l t a g e s .  This  seems t o i n d i c a t e a f o c u s s i n g  effect  i n the discharge  t u b e b u t t h e a c t u a l mechanism i s  20 not  clear.  The g r a p h shows t h r e e  magnetic f i e l d  o f 0,  currents  curves f o r  1 a n d 2 amps.  peak t h e c u r r e n t a p p e a r s t o r i s e secondaries  typical  again  A f t e r the  hut this  i s due t o  which had n o t been suppressed d u r i n g  these  readings.  1  1  -n  1  \  i-  C •>  -L  -  _  V.  =2 /  n *i  HV  ...  /  / /  |  jy  /  Q~  y  i r  /  1  V /  IV  i  1  1 .1  itf I> Ii ^\ tI 1  •  V  i j  1 i  1  i I. i i i  o r  I2  i  i  i  I  ii  VO  When a r e t a r d i n g v o l t a g e secondaries  j i , i  -  dotted  -  1 1  i  1  c  a  1  J La T  ren  1 i 1  t>  i  a  I  1  ~"  -  '  -  i  i i  and t h e p o s i t i v e i o n  probe voltage  (indicated  lines).  probe v o l t a g e  i n the f i r s t  from s t r i k i n g  i s p u t on t h e f i r s t  the p o s i t i v e i o n current  t h a t measured w i t h  the f i r s t  1 1  t h e peaks a r e a i m i l i a r  i s found that  the f i e l d  1  Tl  a r->i t  i s put on t o suppress the  When t h e v o l t a g e it  i  iC  TS 1I  current drops t o zero f o r higher by  1  1  T 3 0 0 0  non  1 | i  i >1  i  i  _-_  i l - a —z.  l£  SfSr  -ir  i _  o  -  n  \  the w a l l s  above.  increases This  l e n s gap p r e v e n t i n g of the e x i t  canal.  l e n s was v a r i e d a n d t h e v o l t a g e  lens over  i s due t o  so many i o n s The gap i n ratio  between  21. the probe v o l t a g e and t h e f i r s t  lens voltage  ( V i a n d V&)  was m e a s u r e d f o r e a c h c a s e when t h e l e n s f o c u s s e d a p a r a l l e l beam.  An a p e r t u r e  to aperture  constructed with aperture diameters s p a c i n g between a p e r t u r e s compared w i t h o t h e r The  cylinder  The  of  gap (inches)  to aperture  aperture  to aperture  to cylinder  1/8  9.5  1/2  7.5  1 3/8  7.5  1 1/8  5  l e n s was much s t r o n g e r  stopped  positive  w i t h the probe and f i r s t  The p o s i t i v e  lens voltage on.  i n the discharge  until a field  magnetic f i e l d  d i d not increase the p o s i t i v e  increased  o f a r o u n d 250 g a u s s .  i n the discharge  Higher  i o n current.  tube  i o n c u r r e n t f o r a range o f pressures  m i c r o n s t o a b o u t 80 m i c r o n s  aperture.  The m a g n e t i c  magnetic f i e l d  maximum  some  i o n c u r r e n t was m e a s u r e d  i o n current increased with  V a r i a t i o n o f the pressure  than t h e  that  by the f i r s t  was v a r i e d a n d a l s o t h e p r e s s u r e  tube.  Vg Vj~  t y p e s b u t i t was t h o u g h t  t h e i o n beam was b e i n g  field  ratio  here:  to oylinder  The  3/8 i n c h a n d  1 l / 8 inch and the voltage  type  aperture  cylinder  both  lens.  results are tabulated Lens  l e n s was a l s o  showed  f r o m 30  indicated by the P i r a n i  gauge.  Plat©  VIII  To f a c e page  g  2  P l o t o f a n a l y s e d beam s h o w i n g mass 1, mass 2 a n d mass-3 p e a k s l e f t t o r i g h t .  22.  A p o s i t i v e i o n c u r r e n t o f 800 voltage, voltage  2000 V.;  p r o b e c u r r e n t 7.6  12.35kV; d i s c h a r g e  magnetic f i e l d ,  240 The  i n c r e a s i n g R.F. R.F.  had  an  other  effect  on  The  higher  p o s i t i v e Ion  this  38  lens  microns  increased  seemed t o be  1/8  conditions.  and  a  with  particular  current.  size  a large canal  The  the  The fluxmeter.  The  f o u n d t o be  current  the magnet was  v e r y n a r r o w so o n l y  Plate  used  However b e f o r e  beam.  is a  since  t o pump t h e  high  collisions  (See  the  c a l i b r a t e d with The  hysteresis  field  every  from  analysis  g r a p h on n e x t  V I I I i s a g r a p h showing the  a t y p i c a l analysed  canal  molecules.  i s shown b e l o w .  demagnetized.  be  to a v o i d  a n a l y s e r magnet was  is plotted.  exit  However t h e r e  enough p r e s s u r e  curve  first  r u n s were made  l a r g e r the  e x i t w h i c h may  p o s i t i v e i o n s w i t h gas  tube.  c a n a l was  analyser  i t i s more d i f f i c u l t  vacuum s i d e t o a low of the  of  i f the  c a n a l however g a v e a much  I t seems t h a t  to the  This  i n the d i s c h a r g e  inoh diameter e x i t  inch diameter  canal.  I t a p p e a r e d as  l a r g e r the p o s i t i v e i o n c u r r e n t .  limitation  for  there  current  the f o c u s s i n g  1/16  used.  was  first  tube p r e s s u r e ,  p o s i t i v e Ion  The  with  ma.;  probe  power w h i c h g a v e t h e p e a k p o s i t i v e i o n c u r r e n t .  R.F.  the  measured w i t h  gauss.  power b u t  power v a r i e d w i t h  with  ua was  The  mass 1 and  a loop  zero run  page.) results  mass 2 p e a k s  23.  were f o u n d but of  t o be f a i r l y n a r r o w a n d s l i g h t l y  t h e mass 3 p e a k was b r o a d e r .  flat  topped  The i n s t r u m e n t a l  t h e a n a l y s e r i s n o t known so t h e p e r o e n t  spread  protons i s  estimated by comparison o f the h e i g h t s o f the peaks. a n a l y s e s was made w i t h f e r e n t magnetic  ions o f energy  o f 14kV w i t h  fields.  C a l i b r a t i o n of Analyser  1 1  I  iQ  ft \J  i  ' K  1  /  s  . 1  i  /  ?  u. V. q n  •/  /  /  / /  /  t  /  /  <i  f  /  1  /  cii  /  1  i  <  •  d~\ ir r •if  •  i  fe »  •  rr  i  1  n  fTF  i  i  "1 j  R  An  dif-  24. A n a l y s e s o f Beam Magnetic F i e l d Current  21 % 25 38 46 46.5 28.5  9 amps 7.8 6.9 6.08 5.58 4.6 From t h e s e r e s u l t s is  not effected  Mass 2  Mass 1  i t appears  Mass 3  38$ 46 42 39 40 33 that  41$ 24 20 15 13 38  t h e mass 2 p e r c e n t a g e  a s much b y t h e change o f m a g n e t i c  as t h a t o f the o t h e r i o n s .  There  seems t o be a n  field inter-  change o f mass 1 a n d mass 3 i o n s w i t h v a r i a t i o n i n magnetic of  field.  This  i s thought  mass 3 Ions i n t h e e x i t  canal which  some e x t e n t b y b e t t e r f o c u s s i n g w i t h change o f m a g n e t i c  t o be c a u s e d b y f o r m a t i o n  field.  i s prevented to  through the e x i t  canal  25.  DISCUSSION OF RESULTS This of p o s i t i v e deliver  i o n s o u r c e c a n d e l i v e r 800 m i c r o a m p e r e s  i o n s 45$ o f w h i c h a r e p r o t o n s .  360 ^ua o f p r o t o n s .  installed energy.  With  That  i s i t can  t h e power s u p p l i e s a l r e a d y -  t h e s e p r o t o n s c a n be a c c e l e r a t e d  t o 50 k V o f  T h i s s o u r c e o f p r o t o n s t h e n c a n be u s e d f o r some  nuclear experiments. hydrogen  I f deuterium  i t i s expected that  i a used  instead of  the source w i l l  then supply  d e u t e r o n s w i t h a p p r o x i m a t e l y t h e same p e r f o r m a n c e . these deuterons  o o u l d be used  in a  Again  deuteron-deuteron  r e a c t i o n c o n v e r t i n g the source t o a n e u t r o n s o u r c e . The  source can supply s u f f i c i e n t  i o n s a n d c a n be m o d i f i e d f o r I n s t a l l a t i o n generator.  A straight  and magnetic  fields) It  aource  i n a Van de G r a a f f  through a n a l y s e r (crossed  c o u l d be i n c o r p o r a t e d  is felt  that  c a n a t i l l be improved  adjusting  atomic  t h e many p a r a m e t e r a  electric  i f desired.  the performance  o f the  w i t h more t i m e t o a p e n d involved.  26.  CONCLUSION AND  RECOMMENDATIONS It  centage o f atomic the  ia felt ions  that there  i n the discharge  c o l o r o f the discharge,  analyser.  I s a much h i g h e r  tube, judging by  than i s b e i n g measured i n t h e  T h i s may b e due t o f o r m a t i o n  in  the e x i t  canal.  be  made much s h o r t e r .  of triatomic  I t i s recommended t h a t t h e e x i t T h i s may n e c e s s i t a t e a n e x i t  o f l e s s d i a m e t e r due t o pumping p r o b l e m s . t h e m e t a l cone t h e n s h o u l d the l a r g e s t p o s s i b l e h o l e the  exit  canal  as  o f the f i r s t  close to the e x i t  very  Therefore  short.  core.  F o r these  the cone.  give least  of the f o c u s s i n g .  I s we  wish  effective prevents  the inside walls of  two r e a s o n s t h e n ,  loss of ions  c y l i n d r i c a l electrode  That  c a n a l as p o s s i b l e as t h i s  The v o l t a g e  there  s i n c e we  a c c e l e r a t i n g g a p t o be  to use a short c y l i n d r i c a l side  lens  i t is difficult  o n l y one l e n s  l o s s o f ions by c o l l i s i o n against the  The d e s i g n o f  an e l e c t r o s t a t i c  a p a r a l l e l beam w i t h  the f i e l d  canal  3hort.  i n t h e cone be v e r y  want t h e o b j e c t d i s t a n c e  canal  i n i t a t t h e base end and t h a t  a minimum o b j e c t d i s t a n c e .  to focus  ions  be a l t e r e d s o t h a t t h e r e i s  In designing is  per-  i t i s suggested  electrode which reaches i n o n i t c a n be a d j u s t e d t o  i n the e x i t  canal.  Then a n o t h e r  c a n b e mounted w h i c h w i l l  do most  I n t h i s way i t i s b e l i e v e d t h a t a  beam o f s m a l l d i a m e t e r may be p r o d u c e d .  A retarding  27.  l e n s may be u a e d i f a s t r a i g h t corporated.  A final  through analyser  a c c e l e r a t i n g e l e c t r o d e may t h e n be  used o f l a r g e r diameter than  the o t h e r s  a c c e l e r a t i o n t o 50 k V w i t h o u t  i n order  hole  i n t h e pumping s i n c e t h e r e  i n the cone.  path f o r the ions may p r e v e n t  This w i l l  lengthen  i n s i d e the e x i t s  of undesirable  also  i s a l a r g e r diameter t h e mean f r e e  c a n a l a n d cone a n d so  some c o l l i s i o n / w h i c h a r e c a u s i n g  ions or formation  to give  overfocussIng.  T h i s a d j u s t m e n t t o t h e cone w i l l assist  is in-  loss of  ions.  I t may b e w o r t h y o f c o n s i d e r a t i o n t o b u i l d an o s o i l l a t o r say  operating  a t a much l o w e r  5 o r 6 mc./sec. s i n c e a t t h i s f r e q u e n c y  power w o u l d be d e l i v e r e d b y t h e same t u b e s . this  frequency  little  less  t h e beam.  much more Also a t  matching and s h i e l d i n g problems a r e a  difficult. Since  enclosed  frequency,  t h e whole e l e c t r o d e assembly i s  i n porcelain or steel  i t i s impossible  I t w o u l d be a n a d v a n t a g e  t o see  i f i t c a n be a r -  r a n g e d t o s e e t h e beam a t a s many p o i n t s  i n the lens  a s s e m b l y a s p o s s i b l e , e s p e c i a l l y where i t i s j u s t emerging from the cone. With these felt  m o d i f i c a t i o n s suggested  t h a t f u r t h e r improvement  realized.  i n performance w i l l  i t is be  REFERENCES 1.  C r a g g a , J.D. P r o c . P h y s . Soo. L o n d o n 54:439.  1942.  Lamar, E . S . B u e c h n e r , W.W., & Van de G r a a f f , R . J . J . A p p l i e d P h y s . 12:132. 1941. Zinn, W.H. P h y s , R e v . 52:655. 1937. F i n k e l s t e i n , A.T. Rev. S c i . I n s t r u m e n t s 2. 3.  4.  11:94. 1940.  J.G. R u t h e r g l e n & J . F . T . C o l e N a t u r e , V o l . 1, #4068, O c t 18, A . J . B a y l e y & A . 3 . Ward, Canadian J o u r n a l o f Research,  1947. A,26:69-78  R.N. H a l l Review o f S c i e n t i f i c I n s t r u m e n t s ,  19:905;  March/48.  1948.  5.  P.C. Thonemann, J . M o f f a t t , D. R o a f , J . H . S a n d e r s ; P r o c e e d i n g s P h y s i c a l S o c i e t y , V o l . L X I , P483, 1948,  6.  J . H . v a n Hofweegen & K.S. K n o l P h i l i p s R e s e a r c h R e p o r t s , V o l . 3, No. 2, A p r . 1948,  

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