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Study of half harmonic plasma waves in CO laser-plasma interactions Zhu, Yueqiang
Abstract
Half harmonic plasma waves, which can be generated by the two plasmon decay (TPD) and stimulated Raman scattering (SRS) instabilities in the regions with plasma density near nc/4, are studied experimentally in the interactions of an intense (I l≤10¹⁴W/cm²) CO₂ laser beam with an underdense plasma. The plasma is produced by focusing the CO₂ laser pulse (2 ns FWHM) onto a stabilized laminar nitrogen gas jet flowing from a Laval nozzle into low pressure helium. The plasma waves were investigated with ruby laser Thomson scattering. The absolute TPD and SRS instabilities were observed at pump intensities greater than 1.3 x 10¹³ W/cm² for a plasma with a density scale length of 2400 µm and an electron temperature of 300 eV. The difference predicted by the theory between plasma waves generated by the two plasma decay instability and those due to the stimulated Raman scattering deduced from theory are experimentally confirmed. Two plasmon decay is found to dominate the generation of half harmonic plasma waves. The TPD plasma waves appear in series of up to 8 bursts. The intensity distribution of the unsaturated TPD plasma waves is determined to be well described by linear theory. The intensity distribution of the saturated TPD plasma waves is shown to be governed by the saturation and quenching mechanisms. The angular distribution of ( 3/2)ω₀ emission deduced from the intensity distribution of the saturated TPD plasmons agrees well with the experimental results. The experimental evidence shows that the coupling of plasma waves to ion acoustic waves and the steepening of the density profile are the dominant saturation and quenching mechanism for the TPD instability.
Item Metadata
Title |
Study of half harmonic plasma waves in CO laser-plasma interactions
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1994
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Description |
Half harmonic plasma waves, which can be generated by the two plasmon decay (TPD)
and stimulated Raman scattering (SRS) instabilities in the regions with plasma density
near nc/4, are studied experimentally in the interactions of an intense (I l≤10¹⁴W/cm²)
CO₂ laser beam with an underdense plasma. The plasma is produced by focusing the
CO₂ laser pulse (2 ns FWHM) onto a stabilized laminar nitrogen gas jet flowing from a
Laval nozzle into low pressure helium. The plasma waves were investigated with ruby
laser Thomson scattering. The absolute TPD and SRS instabilities were observed at
pump intensities greater than 1.3 x 10¹³ W/cm² for a plasma with a density scale length
of 2400 µm and an electron temperature of 300 eV. The difference predicted by the theory
between plasma waves generated by the two plasma decay instability and those due to the
stimulated Raman scattering deduced from theory are experimentally confirmed. Two
plasmon decay is found to dominate the generation of half harmonic plasma waves. The
TPD plasma waves appear in series of up to 8 bursts. The intensity distribution of the
unsaturated TPD plasma waves is determined to be well described by linear theory. The
intensity distribution of the saturated TPD plasma waves is shown to be governed by
the saturation and quenching mechanisms. The angular distribution of (
3/2)ω₀ emission
deduced from the intensity distribution of the saturated TPD plasmons agrees well with
the experimental results. The experimental evidence shows that the coupling of plasma
waves to ion acoustic waves and the steepening of the density profile are the dominant
saturation and quenching mechanism for the TPD instability.
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Extent |
4095496 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-04-16
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0085649
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1994-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.