Phenomenology of Internal Reconnections in NSTX
Authors: I. Semenov, S. Mirnov, D. Darrow, L. Roquemore, E.D. Fredrickson, J. Menard, D. Stutman, and A. Belov
Date of PPPL Report: June 2002
Published in: Physics of Plasmas 10 (March 2003) 664-670.
The behavior of large-scale MHD modes was investigated in the National Spherical Torus Experiment (NSTX) during Reconnection Events (RE) using combined analysis of magnetic probe signals, and soft X-ray (SXR) data. The comparison of mode dynamics during precursor and disruption stages in T-11M (small circular plasma), TFTR (large circular plasma), and NSTX (large spherical plasma) was done. The analysis shows that the sequence of events of minor and major IREs (internal reconnection events) in NSTX is essentially similar to that for disruptions in moderate aspect ratio tokamaks. The main feature of disruption dynamics apparently affected by small aspect ratio in NSTX appears in the relatively slow thermal quench event (5-10 times longer compared to ordinary tokamaks), which precedes the major IRE. The coincidence of the electron and neutron quench times during the major IRE leads us to the conclusion that the fast ions and hot electrons leave the center of a plasma column simultaneously, i.e., convectively.