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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 of3He 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 of3He into the flare acceleration region. The amount of heated3He that will be driven into the flare site is proportional to the wave energy. Using values from our simulations, we show that the abundance of3He driven into the acceleration region should approach that of4He in the corona. Therefore, waves driven by energetic ions produced in flares are a strong candidate to drive the enhancements of3He observed in impulsive flares.
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Ion beam instabilities during solar flare energy release
The linear stability of waves driven by ion beams produced during solar flare energy release are explored to assess their role in driving abundance enhancements in minority species such as 3He and in controlling, through pitch-angle scattering, proton/alpha confinement during energy release. The Arbitrary Linear Plasma Solver is used to solve the linear dispersion relation for a population of energetic, reconnection-accelerated protons streaming through a less energetic background plasma. We assume equal densities of the two populations, using an anisotropic (T∥/T⊥=10), one-sided kappa distribution for the energetic streaming population and a cold Maxwellian for the background. We find two unstable modes with parallel propagation: a right-handed wave with a frequency of the order of the proton cyclotron frequency (Ωcp) and a left-handed, lower frequency mode. We also find highly oblique modes with frequencies below Ωcp that are unstable for higher beam energies. Through resonant interactions, all three modes will contribute to the scattering of the high-energy protons, thereby limiting their transport out of the flare-acceleration region. The higher-frequency oblique mode, which can be characterized as a kinetic Alfvén wave, will preferentially heat 3He, making it a good candidate for the driver of the abundance enhancements commonly observed for this species in impulsive events.
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- Award ID(s):
- 2109083
- PAR ID:
- 10586287
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Physics of Plasmas
- Volume:
- 32
- Issue:
- 4
- ISSN:
- 1070-664X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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