Scattering of Electromagnetic Waves by a Plasma Cylinder

Abstract

The scattering of an electromagnetic wave by a plasma cylinder is investigated. The problem of the homogeneous cylinder is solved analytically. Numerical solutions are obtained for two selected examples in which the plasma is cylindrically symmetrical but inhomogeneous. In the calculations, the thermal motion of the electrons is taken into account approximately by a scalar pressure term. The results of the calculations show that resonant scattering takes place at several frequencies. At the lowest resonant frequency the thermal motion of the electrons plays little part, and the plasma behaves essentially as a dielectric. Thermal motion plays a prominent part in the resonances which occur at the higher frequencies and which are caused by standing ``plasma waves'' (electron acoustic waves). These higher resonant frequencies are rather closely spaced (starting from just above the plasma frequency), if the plasma cylinder is homogeneous and its diameter is much greater than the Debye length. The separations between the resonant frequencies increase, however, if the electron density is taken to be substantially greater on the axis of the cylinder than at the boundary. The results of the present computations for such an inhomogeneous cylinder appear to be in qualitative agreement with data obtained from experiments on the resonant scattering of microwaves by a gas discharge column.