Effect of parametric instabilities on entrainment currents: II. Toroidal plasma systems

The production of entrainment currents due to the action on a plasma of variable electric fields with frequency on the order of the electron plasma frequency is considered. Experiments have been performed in a small stellarator in which a nonisothermal plasma with an electron temperature substantially greater than that of the ions is confined. It is shown that the unequal damping rates of waves propagating in opposite directions in a plasma with a anisotropic particle velocity distribution can be utilized to form an hf wave spectrum which is asymmetric in the longitudinal wave number. It is shown that the parametric instabilities that occur in the plasma when the level of input hf power is sufficiently high cause a current to appear and accelerate electrons. 8 refs., 5 figs.