Electron Acceleration by Multi-Island Coalescence

TL;DR

This paper demonstrates through 2D particle-in-cell simulations that magnetic island coalescence, especially secondary anti-reconnection, efficiently accelerates electrons, providing insights into solar flare energetic electron generation.

Contribution

The study reveals that secondary magnetic reconnection during island coalescence is a key electron acceleration mechanism, advancing understanding of particle energization in solar phenomena.

Findings

Anti-reconnection is the dominant acceleration process.

Multiple acceleration mechanisms are identified.

Results support magnetic reconnection's role in solar energetic electrons.

Abstract

Energetic electrons of up to tens of MeV are created during explosive phenomena in the solar corona. While many theoretical models consider magnetic reconnection as a possible way of generating energetic electrons, the precise roles of magnetic reconnection during acceleration and heating of electrons still remain unclear. Here we show from 2D particle-in-cell simulations that coalescence of magnetic islands that naturally form as a consequence of tearing mode instability and associated magnetic reconnection leads to efficient energization of electrons. The key process is the secondary magnetic reconnection at the merging points, or the `anti-reconnection', which is, in a sense, driven by the converging outflows from the initial magnetic reconnection regions. By following the trajectories of the most energetic electrons, we found a variety of different acceleration mechanisms but the energization at the anti-reconnection is found to be the most important process. We discuss possible applications to the energetic electrons observed in the solar flares. We anticipate our results to be a starting point for more sophisticated models of particle acceleration during the explosive energy release phenomena.