Stability of microwave-heated plasmas

Magnetically-confined plasmas, created and heated by electromagnetic fields near the electron gyrofrequency, can support several modes of instability driven by inherent temperature anisotropy or possible loss-cone effects. If T|| ≪ T⊥, both electrostatic and electromagnetic waves can grow in time; while if T||→T⊥, electrostatic waves at the hybrid frequency can be driven unstable by the loss-cone effect. Here the relevant known criteria are reviewed, and several new criteria to describe the stabilization of the temperature-anisotropy modes as T|| → T⊥, are developed. The results of a detailed analysis of the electrostatic loss-cone mode, for which temporal growth rates greater than anticipated electron bounce frequencies are obtained only for electron densities near microwave cut-off are also reported.