Heavy ion acceleration in impulsive solar flares

The abundance enhancements of heavy ions Ne, Mg, Si and Fe in impulsive solar energetic particle (SEP) events are explained by a plasma acceleration mechanism. In consideration of the fact that the coronal plasma is mainly composed of hydrogen and helium ions, the authors think that the ion-ion hybrid wave and quasi-perpendicular wave can be excited by the energetic electron beam in impulsive solar flares. These waves may resonantly be absorbed by heavy ions when the frequencies of these waves are close to the second-harmonic gyrofrequencies of these heavy ions. This requires the coronal plasma temperature to be located in the range of T∼(5-9) x 106 K in impulsive solar flares and makes the average ionic charge state of these heavy ions in impulsive SEP events higher than the average ionic charge state of these heavy ions in gradual SEP events. These pre-heated and enhanced heavy ions can successively and stochastically be accelerated by Alfven turbulence and then form a power-law distribution in impulsive SEP events