Collisionless nonideal ballooning modes

The nonzero inertia of the electron is shown to destabilize pressure-driven ballooning modes in collisionless tokamak plasmas that are stable in the ideal magnetohydrodynamic (MHD) approximation. The effect of the electron mass is characterized by the collisionless electron skin depth d e =c/ω pe , where ω pe = 4πne 2 /m e is the electron plasma frequency. The growth rate of electron inertia ballooning modes increases with the magnitude of d e , and also with the magnitude of the ratio β of the plasma thermal pressure to the pressure in the confining magnetic field.