ION-ACCELERATION AND ABUNDANCE ENHANCEMENTS BY ELECTRON-BEAM INSTABILITIES IN IMPULSIVE SOLAR-FLARES

We show that a nonrelativistic electron beam in a hydrogen-helium solar flare plasma will excite H+ electromagnetic ion cyclotron, shear Alfven, and R-X waves, in addition to waves resulting from the two-stream instability. The H+ electromagnetic ion cyclotron and shear Alfven waves are able to selectively accelerate ambient He-3 and Fe, respectively, to MeV energies through first harmonic gyroresonance, and thereby account for the large He-3/He-4 and Fe/C ratios seen in the energetic particles from impulsive solar flares. In this model, separate heating and acceleration mechanisms for either He-3 or Fe are not required, and Fe acceleration is quite efficient since it does not need to occur by second harmonic gyroresonance. The combination of the other two unstable modes is able to accelerate ions to hundreds of MeV if the particles become trapped in an electrostatic potential well of a two-stream wave.