The effect of an axial current on particle loss cone in an axially symmetric mirror

Recent research in the Current Drive Experiment-Upgrade (CDX-U), low-aspect-ratio tokamak, has been concentrated on non-inductive current drive experiments for future steady-state tokamaks. To understand the observed current level in these experiments, the authors first carry out particle orbit studies using a simple mirror configuration with an axial current. Particles are confined by mirroring forces and by conservation of angular momentum. This distorts the loss cones and can result in current generation through preferential losses. The equation of motion for a single particle in this magnetic configuration is solved numerically, and modification to the usual mirror loss-cone is studied. Particles having a preferred azimuthal velocity component tend to be lost at one end or the other. The results of PIC code studies and analysis are presented and implications on the mechanism for bootstrap current are discussed