A computational model for exploring particle acceleration during macroscale magnetic reconnection

A novel computational model for describing energetic electrons produced by magnetic reconnection in macroscale systems is developed and explored. It has long been known that magnetic reconnection in the solar corona produces a power law for high energy electrons (Lin & Hudson 1971; Emslie et al. 2004; Emslie et al. 2005). However, due to the extreme separation of scales, it is difficult to produce a model that can resolve the small scale structures near the x-line during reconnection and include the evolution of the global system. Fortunately, recent research suggests that large scale Fermi reflection is primarily responsible for the production of these electrons (Dahlin et al. 2015; 2016). By taking advantage of this discovery, we can order out the small scales, neglecting the parallel electric field around the x-line and separatrices, but keeping the large scale parallel electric field due to gradients in the electron pressure (Haggerty et al. 2016). The resulting model has a magnetohydrodynamic (MHD) backbone with energetic electrons represented as macro-particles. These particles feed back onto the MHD equations ensuring overall energy conservation and, importantly, the equations correctly describe the firehose instability, which plays a crucial role in both throttling reconnection (Drake et al. 2006, Drake et al. 2010) and in controlling the spectral index of the energetic electrons (Drake et al. 2013). Tests of the model are presented in addition to preliminary results from magnetic reconnection simulations.