On the ionization and ohmic heating of a helium plasma

Abstract

A method which is used for the ionization and heating of helium plasmas in various stellarator models consists of inducing an approximately constant electric field along the main axial confining magnetic field. In this paper we present the details and results of various calculations pertaining to this method. The gas is assumed initially to be 10% ionized and at a temperature of a few electron volts. The major approximations on which the calculations are based are (1) Maxwellian velocity distributions for the particles and (2) negligible charged particle lose across the confining magnetic field. The equations for the power balance and number balance were integrated in time numerically for a variety of initial conditions. The results indicate that temperatures of a few hundred electron volts are attainable within milliseconds with an applied field of the order 0.1 volt per cm at densities of 3 × 1013 particles per cm3. It was found that the maximum temperature is limited by power loss in bremsstrahlung radiation.