Current-driven modes in two-dimensional plasma configurations

Abstract

A search for current driven modes in two-dimensional (toroidal) plasma configurations is made for regimes where the effective collision frequency of trapped electrons is smaller than their average bounce frequency and the drift velocity of the circulating electron is smaller than the thermal velocity. If the current carrying part of the circulating electron distribution function is represented by a Spitzer-Härm type of model, no significant growth rates of possible current driven modes can be found whether their wavelengths along the magnetic field are long or short in comparison with the field connection length. One reason for this is that in a realistic toroidal configuration, there are very few electrons with longitudinal velocities much smaller than the electron thermal velocity, which are not trapped and carry current. The only significant current driven instability found depends on the assumption that collisions or, possibly, the effects of higher-frequency fluctuations, may induce a sufficiently finite longitudinal thermal conductivity of the circulating electrons.