Propagation of microwaves through a magneto-plasma, and a possible method for determining the electron velocity distributions

Abstract

Sagdeyev and Shafranov have shown that the absorption of microwaves in a hot plasma in a steady magnetic field can be calculated in simple closed form with the help of theBoltzmann equation, provided that the effect of collision can be ignored. The special case of propagation of circularly polarized waves parallel to the magnetic field, and the extraordinary ray, in magneto-ionic terminology, were studied. It is shown that the formula given by Sagdeyev and Shafranov for this case can be deduced by considering the motions of individual electrons by elementary dynamical methods, using the concepts of Doppler shift and velocity distribution functions to obtain a macroscopic conductivity formula for a high-temperature plasma. From this, the absorption is calculated. It is emphasized that the calculation in no way depends upon the assumption of a Maxwellian velocity distribution function. The absorption can in fact be obtained in closed form for any arbitrary velocity distribution function. This suggests that a diagnostic technique for the determination of velocity distribution could be based on measurements of absorption of the extraordinary ray, and the potentialities and limitations of this proposal are briefly discussed. (auth)