Mirror, firehose and cosmic-ray-driven instabilities in a high-β plasma

I consider low-frequency instabilities in a plasma with high-β plasma, with β the ratio of thermal and magnetic pressures. I derive the mirror and firehose instabilities, due to pressure anisotropy, for such a plasma. This derivation uncovers clear modifications with the more familiar, low-β case. I also consider the interplay between these instabilities and the current-driven instability (the Bel...