Field-guided proton acceleration at reconnecting X-points in flares

Abstract

An explicitly energy-conserving full orbit code CUEBIT, developed originally to describe energetic particle effects in laboratory fusion experiments, has been applied to the problem of proton acceleration in solar flares. The model fields are obtained from solutions of the linearised MHD equations for reconnecting modes at an X-type neutral point, with the additional ingredient of a longitudinal magnetic field component. To accelerate protons to the highest observed energies on flare timescales, it is necessary to invoke anomalous resistivity in the MHD solution. It is shown that the addition of a longitudinal field component greatly increases the efficiency of ion acceleration, essentially because it greatly reduces the magnitude of drift motions away from the vicinity of the X-point, where the accelerating component of the electric field is largest. Using plasma parameters consistent with flare observations, we obtain proton distributions extending up to gamma-ray-emitting energies (>1MeV). In some cases the energy distributions exhibit a bump-on-tail in the MeV range. In general, the shape of the distribution is sensitive to the model parameters.

14 pages, 4 figures, accepted for publication in Solar Physics

Cited by in corpus (6)

• Effects of the non-uniform initial environment and the guide field on the plasmoid instability
• Particle acceleration by fluctuating electric fields at a magnetic field null point
• Alfvèn wave phase-mixing and damping in the ion cyclotron range of frequencies
• Numerical Simulation of Superhalo Electrons Generated by Magnetic Reconnection in the Solar Wind Source Region
• Simultaneous Observation of Solar Neutrons from the ISS and High Mountain Observatories in association with a flare on July 8, 2014
• Particle interactions with single or multiple 3D solar reconnecting current sheets