A Mechanism for Helium-3 Abundance Enhancements in Solar Flares

Abstract:

A new mechanism for abundance enhancements of high-energy Helium-3 produced by impulsive flares is explored. Observations have shown a 10³-10⁴ increase in the high-energy Helium-3 abundance following impulsive solar flares. A likely mechanism is the resonant heating of Helium-3 in the corona by Alfvén-Cyclotron waves. While electron beams have been proposed as a source of these waves, this mechanism has not been firmly established in the impulsive flare context. We propose instead that the proton temperature anisotropy produced during magnetic reconnection drives these waves. We have shown, through 2-dimensional PIC simulations of magnetized plasmas, that low-beta magnetic reconnection produces strong temperature anisotropy in reconnection exhausts, with a higher temperature perpendicular to the magnetic field. Simulations further reveal that this temperature anisotropy drives Alfvén-Cyclotron waves whose frequency falls directly at the Helium-3 cyclotron frequency. The resulting resonant heating of Helium-3 leads to an increase in the temperature by a factor of 3-7. These simulations establish the potential viability of this mechanism. Ongoing simulations are being carried out to explore whether the resonant heating by these waves can drive Helium-3 to the MeV/nucleon range seen in the observational data.