Forces on Charged Particles of a Plasma in a Cavity Resonator

Abstract

FOLLOWING the methods adopted by Boot et al. ¹, we have recently undertaken an analysis of the conditions required for the containment of an ionized plasma by electromagnetic waves at high frequency, taking collisions and space-charge forces in the plasma into account. During this work, now being prepared for publication, one of us (H. G.) directed attention to the fact that two types of confining force are present when the plasma interacts with the wave in the presence of large field gradients. One is due to the electric, or induced electric, field acting directly on the electrons, as analysed by Boot et al. For this force to be unidirectional, certain relations between amplitude, gradient and frequency of the electric field and electron density must be fulfilled. We call this the Mathieu force, since these relations may be obtained by examining the differential equation which is of the Mathieu type². The other unidirectional force we call the electromagnetic force. This force results from the interaction of the electron current set up by the electron moving in the electric field with the magnetic field component of the electromagnetic wave. This is the force considered by Volkov³.