Wave Generation by Flare-accelerated Ions and Implications for 3He Acceleration

Abstract

The waves generated by high-energy proton and alpha particles streaming from solar flares into regions of colder plasma are explored using particle-in-cell simulations. Initial distribution functions for the protons and alphas consist of two populations: an energetic, streaming population represented by an anisotropic ( T _∥ > T _⊥ ), one-sided kappa function and a cold, Maxwellian background population. The anisotropies and nonzero heat fluxes of these distributions destabilize oblique waves with a range of frequencies below the proton cyclotron frequency. These waves scatter particles out of the tails of the initial distributions along constant-energy surfaces in the wave frame. Overlap of the nonlinear resonance widths allows particles to scatter into near-isotropic distributions by the end of the simulations. The dynamics of ^3 He are explored using test particles. Their temperatures can increase by a factor of nearly 20. Propagation of such waves into regions above and below the flare site can lead to heating and transport of ^3 He into the flare acceleration region. The amount of heated ^3 He that will be driven into the flare site is proportional to the wave energy. Using values from our simulations, we show that the abundance of ^3 He driven into the acceleration region should approach that of ^4 He in the corona. Therefore, waves driven by energetic ions produced in flares are a strong candidate to drive the enhancements of ^3 He observed in impulsive flares.

Keywords

• Solar energetic particles
• Solar physics
• Solar flares
• Space plasmas