Timescales for non-inductive current buildup in low aspect ratio toroidal geometry

The fundamental differences between inductive and non-inductive current buildup are clarified and the associated timescales and other implications are discussed. A simulation is presented whereby the plasma current in a low aspect ratio torus is increased primarily by self-generated bootstrap current, with only 10% coming from external current drive. The maximum obtainable plasma current from this process is shown to scale with toroidal field strength. The basic physics setting the timescales can be obtained from a 1-D analysis. Comparisons are made between the timescales found here and those reported in the experimental literature.