NOTES ON NUMBER DENSITY FLUCTUATIONS AND THE SCATTERING CROSS SECTION FOR ELECTROMAGNETIC WAVES SCATTERED FROM A THERMAL NONEQUILIBRIUM PLASMA
The scattering cross section and the Doppler spectrum for electromagnetic waves scattered by the electron density fluctuations of a plasma, where the mean kinetic temperature of the electrons T/sub c/ may differ from that of the ions T/sub 1/, was obtained among others, by Fejer, Buneman, Renau, Camnitz, Flood, and Salpeter. Different methods of approach were used to calculate the autocovariance of the electron number-density fluctuations (from the mean) and then obtain the scattering cross section. Because of the differing results, the methods, concepts, and derivations of the scattering cross section were carefully examined. It is shown that the short-time dynamical considerations incorporated in the formulation of the statistical theory of the electron number-density fluctuations of plasma as used by several authors leads to results of limited validity. In addition, a fundamental error in calculating the electron density fluctuations leads to an incorrect scattering cross section. The theory of scattering of electromagnetic waves from a plasma, where the electrons are not in thermal equilibrium with the ions but statistical equilibrium exists, was developed in a general way. The covariance of the number- density fluctuations from the mean of the charged species of the plasma and the scattering cross section sigma /(q) were obtained. It is shown that for a wavelength lambda much greater than the effective Debye length d, the backscattering cross section increases and approaches complete incoherent scattering as T/sub e//T/sub i/. increases. This result is explained by noting that in the case of thermal equilibrium, the predicted value of the backscattering cross section is smaller than that of the backscattering cross section from completely uncorrelated electron density fluctuations because the electrostatic interaction between the charged particles of the plasma, which is a function of T/sub e/ and T/sub i/, introduces a certain amount of organization in otherwise completely uncorrelated electron density fluctuations. The spectrum function of incoherent scattering of electromagnetic waves from a nonequilibrium plasma was obtained and some cases were plotted. (auth)
- Research Organization:
- Cornell Aeronautical Lab., Inc., Ithica, N.Y.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-18-021420
- OSTI ID:
- 4004520
- Journal Information:
- Z. Physik, Vol. Vol: 177; Other Information: Orig. Receipt Date: 31-DEC-64
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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