Electron Firehose instability and acceleration of electrons in solar flares

An electron distribution with a temperature anisotropy T-parallel to/T-perp endicular to > 1 can lead to the Electron Firehose instability (Here parall el to and perpendicular to denote directions relative to the background mag netic field B-0). Since possible particle acceleration mechanisms in solar hares exhibit a preference of energizing particles in parallel direction, s uch an anisotropy is expected during the impulsive phase of a flare. The pr operties of the excited waves and the thresholds for instability are invest igated by using linearized kinetic theory. These thresholds were connected to the pre-flare plasma parameters by assuming an acceleration model acting exclusively in parallel direction. For usually assumed pre-flare plasma co nditions the electrons become unstable during the acceleration process and lefthand circularly polarized waves with frequencies of about similar to ve rtical bar Omega(p)vertical bar are excited at parallel propagation. Indica tions have been found, that the largest growth rates occur at oblique propa gation and the according frequencies lie well above the proton gyrofrequenc y.