Acceleration of plasma electrons

Abstract

The author studied plasma electron acceleration in toroidal devices where electron beam equilibrium on the annular orbit is secured by image currents appearing in a metallic housing that covers the vacuum chamber. The initial plasma was created in a toroidal magnetic field with the aid of electron injection along the lines of force of that field and neutral gas ionization in the chamber. The first series of experiments showed that the overwhelming majority of plasma electrons do not accelerate after the creation of an electric field up to 150 V/cm; at the same time powerful oscillations are excited in the plasma. These oscillations appear as a result of the effect on the plasma, of a non-uniform electric field. The results obtained in this series of experiments are analogous to those obtained on plasma betatrons.In the second series of experiments the accelerating electric field was created uniformly and simultaneously along the column of the preliminary plasma. Comparison of the plasma density obtained with the aid of a probe technique, and measurement of the currents that appeared in the plasma show that probably all plasma electrons are initially accelerated by the electric field. Subsequently, however, for reasons that are unclear so far, acceleration ceases and the plasma current becomes a purely ohmic current. Measurement of the x-ray energy that appeared in experiments with an accelerating field of 250 V/cm shows that the electron component of the plasma is, under these conditions, heated by a short electric field pulse (1.7 × 10−7 sec duration) to a temperature of 50 - 70 keV. It is assumed that these effects can be very significant for obtaining large accelerated currents in plasma betatrons. In a denser plasma, one does not succeed in accelerating the electrons to relativistic energies; however, the superposition of a strong electric field can be applied with success for heating the electron component of the plasma.