COLLISIONLESS BALLOONING MODES IN A TOROIDAL 2-ION-COMPONENT PLASMA

A toroidal two-fluid model allowing for arbitrary magnetic field curva ture is used to describe a contaminated plasma consisting of two ion s pecies. A higher-order ballooning mode is identified in the high- and low-alpha regimes, and coexists with the ordinary ballooning mode in t he medium-alpha regime (alpha=ballooning parameter). In the low-alpha regime the temperature-gradient-driven eta(i) mode is present. The imp urities are, in general, found to be stabilizing-lowering the growth r ate and narrowing the instability regime. Comparisons are made with id eal magnetohydrodynamics (MHD) and with a semilocal approximation of t he eigenfunction, which are found to give a higher growth rate. (C) 19 95 American Institute of Physics.