Ion-Scale Wave Generation by Flare-Accelerated Ions

Authors: Anna Fitzmaurice (University of Maryland), James Drake (University of Maryland), Marc Swisdak (University of Maryland)

We employ particle-in-cell plasma simulations to study the waves generated by high-energy proton and alpha particles streaming out from solar flares. Ions accelerated by flares exhibit non-thermal power-law tails which can be modeled by a one-sided kappa function. The non-zero heat flux from these distributions induce waves which can have important effects on particle scattering and heating of secondary ion species, including helium-3. Initial distribution functions for the protons and alphas consist of two populations of equal density: a hot, streaming population represented by a one-sided kappa function (κ = 2.5) and a cold, Maxwellian background population. This set of initial conditions produces oblique, right-handed waves with frequencies below the proton cyclotron frequency. The waves scatter particles out of the tails of the distributions along constant energy surfaces in the wave frame, thereby decreasing the total energy in the observer frame. Overlap of the nonlinear resonance widths allow particles to scatter into near isotropic distributions by the end of the simulations. Helium-3 ions experience heating initially through the n = -1 resonance and later through the n = +1 and n = 0 (Landau) resonances. Raising the initial energy of the proton and alpha populations results in significantly increased helium-3 heating and proton scattering, along with both left- and right-handed waves, while lowering the energy results in predominantly parallel waves and a significant decrease in helium-3 heating.