Acceleration and Enrichment of 3He in Impulsive Solar Flares by Electron Firehose Waves
Gunnar Paesold Submitted: 2002-09-08 10:55
A new mechanism for acceleration and enrichment of 3He
during impulsive solar flares is presented. Low-frequency
electromagnetic plasma waves excited by the Electron
Firehose Instability (EFI) can account for the acceleration
of ions up to 1 MeV/amu energies as a single stage process.
The EFI arises as a direct consequence of the free energy
stored in a temperature anisotropy (T_parallel>T_perp) of
the bulk energized electron population during the
acceleration process. In contrast to other mechanisms which
require special plasma properties, the EFI is an intrinsic
feature of the acceleration process of the bulk electrons.
Being present as a side effect in the flaring plasma, these
waves can account for the acceleration of 3He and 4He
while selectively enhancing 3He due to the spectral energy
density built up from linear growth. Linearized kinetic
theory, analytic models and test-particle simulations have
been applied to investigate the ability of the waves to
accelerate and fractionate. As waves grow in both directions
parallel to the magnetic field, they can trap resonant ions
and efficiently accelerate them to the highest energies.
Plausible models have been found that can explain the
observed energies, spectra and abundances of 3He and 4He.
Authors: G. Paesold, R. Kallenbach and A.O. Benz
Publication Status: Astrophysical Journal, in Press
Last Modified: 2002-09-08 10:55