Measurements of the Charged Particles of an Equilibrium Turbulent Plasma

Guthart, H.

doi:10.1063/1.1761931

Cited by 14 publications

(5 citation statements)

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“…To determine these quantities for the turbulent plasma of this experiment, a comprehensive program of diagnostic measurements was undertaken which has been described in great detail elsewhere [Guthart, Weissman, and Morita, 1966]. In this paper, we shall present the results of this diagnostic program as they pertain to the electromagnetic scattering experiment.…”

Section: Diagnostic Measurements Of the Turbulent Plasma Volumementioning

confidence: 99%

“…It is seen from (1) that the rms electron density as well as the power-spectral-density function (or correlation coefficient) of the electrons must be known to predict the radar cross section of an underdense 'turbulent plasma. To determine these quantities for the turbulent plasma of this experiment, a comprehensive program of diagnostic measurements was undertaken which has been described in great detail elsewhere [Guthart, Weissman, and Morita, 1966]. In this paper, we shall present the results of this diagnostic program as they pertain to the electromagnetic scattering experiment.…”

Section: Diagnostic Measurements Of the Turbulent Plasma Volumementioning

confidence: 99%

“…To investigate the electromagnetic scattering properties of a turbulent plasma [and examine the validity of (1)] in a controlled laboratory environment, an extended turbulent plasma was formed by seeding (with potassium chloride) a premixed ethylene-oxygen flame in a combustion chamber and then exhausting it through an expansion nozzle into a low-pressure vessel with dimensions of 1.2 X 1.2 X 2.4 m. The facility has been previously described [Rothman, Guthart, and Morita, 1963;Guthart, Weissman, and Morita, 1966]. The measurements to be reported were made at an ambient pressure of 16 mm Hg, a combustion chamber pressure of 32 mm Hg, and a mass flow of 1 g/s.…”

Section: Introductionmentioning

confidence: 99%

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Microwave Scattering From an Underdense Turbulent Plasma

1966

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The bistatic radar cross section of an underdense, inhomogeneous turbulent plasma was measured at X-band and the results were compared with a theoretical model. The turbulent plasma was formed by seeding a premixed ethylene-oxygen flame in a combustion chamber and exhausting it through an expansion nozzle into a low-pressure vessel. Electrostatic probes, biased for ion collection, were used to map the variation of the mean and rms electron density throughout the turbulent regions and to measure the·correlation coefficient of the plasma fluctuations. A theoretical scattering model was constructed using the Born approximation and the results of the diagnostic measurement program. Good agreement between theory and experiment has been obtained for the dependence of cross section on bistatic angle and for the spectrum of fluctuations of the scattered microwave signal. The predicted cross section underestimates the measured cross section by 6 to 11 dB when the measured cross sec· tions are in the range from 10-s to 10-• m2• The measured cross section was observed to have a square-law dependence on electron density in agreement with the Born model for densities up to one percent of the critical electron density. For densities beyond this, the Born approximation breaks down and the cross-section dependence becomes linear.

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Section: Diagnostic Measurements Of the Turbulent Plasma Volumementioning

confidence: 99%

Section: Diagnostic Measurements Of the Turbulent Plasma Volumementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microwave Scattering From an Underdense Turbulent Plasma

1966

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“…terferometer[Weissman et al, 1968a]. The linear dependence of probe-current fluctuation on electrondensity fluctuations was demonstrated by calibrating it against a microwave impedance probe having equally high spatial resolution[Guthart et al, 1966b]. The mean and fluctuating response of these probes is consistent with modern probe theory[Zakharova et al, 1960;Su and Kiel, 1966].…”

mentioning

confidence: 99%

“…To a reasonable approximation, the mean velocity is given by the slope of the line of a •/r diagram, where r is the time delay for maximum correlation at the separation 8. Velocity measurements made in this way have been calibrated against Pitot-tube measurements with very good agreement[Guthart et al, 1966b]. The axial distribution of velocity can be represented as follows' the height above the nozzle.…”

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confidence: 99%

Scattering From a Turbulent Plasma

Guthart¹,

Graf²

1970

Radio Science

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The scattering of electromagnetic waves from a dense turbulent plasma has been examined experimentally. The experiments include measurements of bistatic radar cross section, Doppler frequency, backscattered cross-polarized signals, and distribution of scattered power by a radar interferometer. Comprehensive diagnostic measurements were made on the plasma so that the radar measurements could be compared to a proposed scattering model. Using the model, the radar cross section of the inhomogeneous plasma can be calculated for peak electron densities well beyond critical. The agreement between calculations and experiments is excellent. INTRODUCTIONThe interaction of microwave energy with turbulent media has been a subject of interest for several years, especially in the prediction of radar cross sections for atmospheric inhomogeneities, reentry wakes, and rocket exhausts. The rigorous calculation of scattering from turbulent plasmas is formidable and has only been successfully accomplished, using first-order Born theory, when the electron density in the plasma is low. Several strong-scattering theories have been proposed [Watson, 1969; Feinstein and Granatstein, 1969; Ru•ne and DeWot/, 1965; DeWot/, 1967; Bassanita et at., 1967; Frisch, 1968]. For the most part, these theories are not of a form that can be easily applied by the experimental physicist. Guthart et at. [1966a] and Granatstein and Buch•baurn [1967 and 1968] have examined, in the laboratory, some of the aspects of scattering. The present experiments were designed to investigate more fully the important parameters affecting the scattering, so that a scattering model could be proposed that would be useful for a wide range of plasmaparameters. The proposed model will be shown to accurately account for the measured cross sections when the peak electron density in the plasma is varied over a range from well below to several times the critical electron density.In section 2, the bistatic scattering model is briefly described. This model incorporates several fea-Copyright ¸ 1970 by the American Geophysical Union. tures that have been previously proposed, such as the diffraction effects of the finite scattering volume, the effect of the mean plasma properties, and the attenuation of the waves traversing the medium. A new way of handling multiple small-angle scatter is proposed. According to the method, effects of multiple small-angle scatter can be accounted for, in part, by 'adjusting' the attenuation coefficient due to scatter. This technique may appear ad hoe, but it has much merit, owing to its simplicity. The improvement in the agreement between calculated and measured cross sections that results when this feature is added to the model is very encouraging. It is hoped that further experiments and theoretical calculations will specify how multiple scatter and the attenuation coefficient can be related, and how the coefficient can be defined more rigorously in terms of the plasma parameters.Measurements were made on a plasma flame with cylindrical symmetry. The...

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Radar Interferometry Measurements of a Turbulent Plasma

1968

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A laboratory experiment has been conducted that demonstrates the applicability of radar inter· · ferometry to the measurement of the width of a turbulent plasma column. This is done by inferring the spatial distribution of the incoherent electromagnetic power backscattered from the column. The measurements of the spatial correlation of the backscattered electromagnetic fields are in good agree· ment with a function derived theoretically by using extensive diagnostic data.

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Measurements of the Charged Particles of an Equilibrium Turbulent Plasma

Cited by 14 publications

References 10 publications

Microwave Scattering From an Underdense Turbulent Plasma

Microwave Scattering From an Underdense Turbulent Plasma

Scattering From a Turbulent Plasma

Radar Interferometry Measurements of a Turbulent Plasma

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