Observation of Instability-induced Current Redistribution in a Spherical Torus Plasma
Authors: J.E. Menard, R.E. Bell, S.M. Kaye, B.P. LeBlanc, F.M. Levinton, S.S. Medley, D. Stutman, K. Tritz, and H. Yuh
Date of PPPL Report: May 2006
A novel Motional Stark Effect diagnostic has been utilized to reconstruct the parallel current density profile in a spherical torus plasma for the first time. The measured current profile compares favorably with neoclassical theory when no large-scale MHD instabilities are present in the plasma. However, in discharges with sustained high fraction of non-inductive current drive, a current profile anomaly is observed during saturated interchange instability activity. Neutral beam injection current drive redistribution can account for the apparent anomaly and contributes to sustaining the central safety factor above unity for over five current redistribution times.