Heterodyne detection of CO2 laser radiation scattered from a plasma arc jet

Masters, D. L.; Rye, Barry J.

doi:10.1016/0375-9601(76)90512-0

Cited by 16 publications

(3 citation statements)

References 14 publications

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“…For large k, ion thermal conduction will dominate damping because the temperature gradient is proportional to k. When k approaches zero, the width of the entropy peak will reach a constant which is determined by the energy transfer between ions and electrons. Under the conditions (p l ) 2 <&(kC s ) 2 and A<^\/kC s , the ion acoustic peaks assume Lorentzian forms,…”

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confidence: 99%

Density fluctuation spectra of a collision-dominated plasma measured by light scattering

1989

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The low-frequency electron density spectral function Sik.co),having an ion acoustic peak (at co -kCs) and an entropy peak (o>=0), has been measured by light scattering in a thermal collisional argon arc plasma. The entropy peak is observed in a plasma for the first time. A prediction of the spectrum derived from Braginskii's equation is adopted to estimate the transport coefficients. The ion viscosity, ion thermal conductivity, and electron-ion energy-transfer frequency determined from fitting to the data differ from predictions by -39%, 4-16%, and -22%, respectively.PACS numbers: 52.25.Fi, 52.25.Gj, 52.25.Rv The electron density fluctuation spectrum S(k,co) of a collisional plasma is a fundamental quantity closely related to transport properties. Previous measurements of S (k,co) in collisional-dominated plasmas failed to resolve structure near zero frequency, 1 " 5 and theories of this regime are not in agreement. 6 " 10 We report here observation of S(k,co) in the low-frequency region for a collisional plasma in near equilibrium by means of CO2 laser light scattering. The observed spectrum consists of three peaks, two representing ion acoustic waves propagating in the opposite directions, and the third a nonpropagating peak centered at zero frequency and attributed to entropy fluctuations. The ion acoustic fluctuations have been previously observed, 1 " 5 but the observation of the entropy fluctuations in a plasma has not heretofore been reported, although such fluctuations are well known in ordinary fluids. 11 Most theories of the electron density fluctuation spectrum of a collisional plasma 6 " 8 predict collisional narrowing of the ion acoustic peaks, which are heavily Landau damped in a collisionless plasma, and the appearance of the zero-frequency peak. Two theories 910 suggest that collisions cause the ion acoustic peaks to broaden further and merge into a single featureless peak.In Ref. 1, in which only the ion acoustic peaks were observed, it was concluded that the Bhatnagar-GrossKrook kinetic theory, 7 modified for adiabatic rather than S(k,ca) -2n e A+Bpi/Dico)isothermal density fluctuations, gave the best fit to experiment. However, this theory fails to account for electron-ion collisions. A one-fluid theory of Mountain 12 also gave a moderately good fit to experiment. This theory relates the shapes of the scattering features to transport coefficients, but is clearly of limited use when applied to a plasma, where transport effects of electrons and ions are quite different. In the present experimental work the frequency of the slowest collisional process (ion-ion) exceeds even the highest fluctuation frequencies in the ion acoustic features, so it appears that a fluid theory would be applicable. We have accordingly calculated the fluctuation spectrum from the two-fluid theory of Braginskii 13 and have compared several transport coefficients from this theory to the experimental data. For a highly collisional plasma, the equations of Braginskii may be applied to calculate an ac electrical conduc...

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confidence: 99%

Density fluctuation spectra of a collision-dominated plasma measured by light scattering

1989

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“…Thomson scattering quickly became a standard diagnostic on magnetic confinement devices and much of the development in the following years was stimulated by the magnetic fusion energy community. This continued theoretical development included the addition of magnetic fields [28], collisional effects [29], relativistic effects [30], nonthermal plasmas [31], as well as plasma impurities [32], which were confirmed experimentally.…”

Section: History Of Thomson Scatteringmentioning

confidence: 85%

Measurements of Relativistic Effects in Collective Thomson Scattering at Electron Temperatures less than 1 keV

Ross

2010

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“…Several authors [50]- [58] considered the effect of e-i, e-e and e-neutral collisions on the line shapes from thermal equilibrium plasma scattering. Predictions that the ion feature would suffer reduced damping due to i-i collisions was first confirmed by Masters and Rye [59], and then shown in better detail by Holzhauer [60]. It was shown by Zhang and DeSilva [61] that in the case of a highly collisional plasma, not only did the ion acoustic peaks become sharper due to reduced Landau damping, but that a zero-frequency feature, called an entropy fluctuation, appeared in the scattered light spectrum.…”

Section: Collisional Plasmasmentioning

confidence: 94%

The Evolution of Light Scattering as a Plasma Diagnostic

DeSilva

2000

Contrib. Plasma Phys.

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Heterodyne detection of CO2 laser radiation scattered from a plasma arc jet

Cited by 16 publications

References 14 publications

Density fluctuation spectra of a collision-dominated plasma measured by light scattering

Density fluctuation spectra of a collision-dominated plasma measured by light scattering

Measurements of Relativistic Effects in Collective Thomson Scattering at Electron Temperatures less than 1 keV

The Evolution of Light Scattering as a Plasma Diagnostic

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