Modeling the formation of current sheets in symmetric and asymmetric reconnection

Abstract

In this thesis we investigate the nature of magnetic reconnection using analytic and numerical methods. We consider configurations which are symmetric across the reconnection layer relevant to the Earth magnetotail, as well as configurations asymmetric in density and temperature across the reconnection layer, important to reconnection in Earth's dayside magnetopause. We develop an analytic model for the evolution of the electron phase space distribution function based on adiabatic invariants. We then apply this two model problems-Fermi acceleration and electron trapping-to extend previous results in these areas and model their effects on parallel heating. Following this, we run a battery of simulations of reconnection using particle in cell (PIC) codes at several different values of density asymmetry and guide field. These simulations reveal a number of regimes of current sheet formation, all of which are associated with significant anisotropic heating. Finally, we take a closer look at the case of antiparallel reconnection, where small levels of asymmetry cause significant shortening in the current sheet that develops at the midplane. Analysis of the data suggests an asymmetry in the firehose condition is the cause. Running another battery of simulations that adds a temperature asymmetry, we find that elongated current sheets will again form when the temperature asymmetry is large enough to restore balance in the firehose condition across the layer.