Limit currents in a plasma betatron

Abstract

The radial motion of a plasma column is considered for electron acceleration in a plasma betatron. The limit value of the relativistic currents which can be obtained in devices of this type is computed.

G. I. Budker [1] proposed using the runaway effect in a plasma with a strong electric field for converting a cold ring plasma into an intense compensated beam of relativistic electrons. To confine such a beam within an annular vacuum chamber one can use either a betatron-type magnetic field or the field of the image currents produced in the metal shell enclosing the vacuum chamber with the electron beam. In the latter case, as estimates show, the number of accelerated electrons must already be considerable; this leads to an increase in the difficulties which impede the successful acceleration of all plasma electrons.

Accordingly, most of the experiments on accelerating plasma electrons have employed betatron fields in devices called plasma betatrons [2–4], A feature of these accelerators is total compensation of the space charge of the accelerated electrons and hence an increased possibility of obtaining high accelerated currents. In this article, we compute the magnitude of the limit currents which may be obtained in a plasma betatron as a function of its parameters and operating conditions.

The first results in this direction, published in 1949 [5], were rough estimates. Subsequently, other more accurate calculations were published [6], but these, in our opinion, did not give sufficient information on the characteristic quantities.