High-frequency convective loss-cone instability in short mirror machines

The high-frequency convective loss-cone mode is found to be absolutely unstable, due to (exponentially small) reflection of waves at the mirror throats; the critical length for stability is only a few ion Larmor radii. For β>>m/sub e//m/sub i/, the following methods are shown not to substantially increase the critical length: (1) gradual tapering of the mirror throats (to reduce reflection); (2) partial filling of the loss cone with small amounts of warm plasma; (3) considering only low k/sub perpendicular/ modes (since high k/sub perpendicular/ modes may saturate at a low level). This result places serious limitations on the design of mirror fusion reactors