TFTR experimental data analysis collaboration. Final progress report for period November 15, 1994 - November 14, 1995

Abstract

Studies of neoclassical tearing modes have remained the dominant area of research on this grant. Our major role in their development was recognized through an invited paper at the 1998 Pittsburgh DPP-APS meeting and through our inclusion as coauthors on some major TFTR and DIII-D papers. During this past year, prior work has been published on DIII-D experiment-motivated theories of stabilization of tearing modes via localized current-drive and heating and on effects of geometry on these modes (elongation and triangularity effects should be small in DIII-D), and on experimental studies of the imposed beta limits and direct, internal measurements of the critical classical tearing mode stability parameter (delta-prime). Also, linear and nonlinear theory and computation studies of classical tearing modes via the ''almost ideal MHD'' constraint has been the subject of a number of meeting presentations and has recently been published. Recent work has been concerned with developing a theoretical model for the magnitude of seed island perturbations due to, geometrically coupled magnetic perturbations (e.g., ELMS or sawtooth crashes) and simulations thereof, exploring the effects of external perturbations, development of a simulation model for flow shear effects, studies of the effect of the combination of flow shear and perpendicular viscosity in distorting the magnetic island structure and producing the phase shift in ECE signals across a magnetic island, simulations of feedback stabilization of tearing mode islands, and exploring what aspects of tearing modes need to be calculated for DIII-D. Our continuing role in transient transport and nonlocal electron heat transport was recognized by an invited paper at the June 1997 EPS Berchtesgaden meeting which was published this past year. In addition, further details of nonlocal electron heat transport, primarily on TFTR, have been the subject of meeting presentations and are being published. Since Dr. Kissick left this research group for UCLA in April 1998 and Prof. Callen is in the process of transferring leadership of the TTF Transient Transport Working Group to Prof. Gentle (U. Texas), it is anticipated that this grant research area will be substantially diminished in the future. Stimulated in large part by the excellent internal fluctuation diagnostics (primarily ECE and BES) for studying MHD modes in the interior of DIII-D, we have begun work in a new area: disruption precursors induced by MHD modes being driven slowly through their ideal stability boundaries. In particular, we have constructed a new model for the temporal development of such precursors and shown that it provides a very good fit to DIII-D data. Also, we are in the process of developing codes for comparing the spatial profile of the disruption precursors with those predicted from the GATO ideal MHD instability code.