Electron equations of state during magnetic reconnection

Abstract

Magnetic reconnection is a rapid reconfiguration of the magnetic field lines in a plasma that converts stored magnetic energy into particle energy in a wide range of environments. It is a source of energetic particles in the solar corona and wind, and in planetary magnetospheres. Disruptive reconnection in laboratory fusion experiments rapidly deconfines the plasma. While reconnection alters the global magnetic field and plasma properties, it depends on small-scale local electron dynamics. Particularly in collisionless plasmas, velocity-space anisotropy of the electrons plays a leading role in governing the energy exchanges and shaping the currents that develop during reconnection. The anisotropy results from an electric field parallel to the magnetic field that tends to accelerate electrons towards the site of reconnection. In this thesis, the equations of state that describe the main anisotropy of the electrons during collisionless reconnection are derived. The equations of state give the components of the electron pressure tensor parallel and perpendicular to the magnetic field as functions of the plasma density and magnetic field strength. Through comparison to numerical solutions of the kinetic plasma equations of motion starting from a variety of initial conditions, several predictions and consequences of the equations of state are tested. The electron pressure anisotropy feeds back on the magnetic geometry of the reconnection region and drives narrow current layers. The dynamics depend on the plasma parameters, and electron heating is most extreme when the electron pressure is much smaller than the magnetic field pressure.