TOROIDAL-ETA-I MODE-STABILITY IN A MULTISPECIES PLASMA

The effect of an impurity ion species on the stability of the toroidal ?i mode is investigated using the kinetic ion response. Impurities have a stabilizing effect on this mode in the flat density limit because of increased dilution. However, for moderately peaked density profiles, the ?i mode can be destabilized because of resonance with the magnetic drift frequency of impurities.