Coronal Electron Acceleration by Double Layer Confinement

Abstract:

Observations show that hot electrons above solar flare looptops can reach tens of kev, but the specific heating mechanism remains unclear. When an electron passes through a reconnection exhaust region, its speed increases by an amount on the order of the Alfven speed. Due to the small mass and thus high thermal speed (on the order of 10 times the Alfven speed) of hot electrons, a single pass does not heat electrons effectively. However, if electrons are confined in the exhaust region by double layers (localized regions of electrostatic field) [1], so that they can pass this region multiple times, the speed of electrons may increase multiple times as well. So we perform particle-in-cell simulations of the related model system known as the Riemann problem [2] in order to test whether trapping via double layers can result in more effective electron heating. Preliminary results suggest that this mechanism does not produce sufficient heating to account for solar observations. [1] Li, T. C., Drake, J. F., & Swisdak, M. 2012, ApJ, 757, 20 [2] Yi-Hsin Liu, J. F. Drake, and M. Swisdak 2011, Phys. Plasmas, 18, 062110