Particle motion in the tail current sheet

Abstract

Theory of particle motion in current sheets is reviewed. For small, approximately constant normal magnetic field, B z , particles oscillate about the current sheet and “live” within the sheet for one-half gyroperiod based on B z . This lifetime replaces the mean collision time in the Lorentzian conductivity and thus gives rise to the concept of an inertial (or gyro-) conductivity. A substorm model by Coroniti /2/ utilizes this conductivity to allow reconnection to proceed without anomalous processes, due to wave-particle interactions. Chaotic particle orbits may at times be important to the dynamics, depending on parameters such as particle energy, current sheet thickness, and field line curvature. A current sheet model with neutral line predicts a ridge structure and asymmetries in the distribution function. Ion distributions near the plasma sheet boundary layer, during the CDAW 6 interval, are consistent with the model predictions. In recent studies by Mitchell et al. /27/ and Williams et al. /26/, the major current carriers during the growth phase of a substorm were found to be adiabatic electrons ≤ 1 keV, but just before a current disruption event, the tail current was mainly carried by energetic ions undergoing current sheet oscillation.