Large experiment data analysis collaboration. Annual progress report for period November 15, 1998 - November 14, 1999

Studies of neoclassical tearing modes have remained the dominant area of research on this grant. This year articles and reports on our previous research projects in collaboration with GA colleagues on a new nonlinear tearing mode model, seed island excitation from geometrically coupled perturbations, the combination of flow shear and viscosity on magnetic islands, and ITER projections got published. A major new theoretical achievement by our group was the development of generalized reduced MHD equations that include flow shear effects. The potential importance of this work was recognized by its having been selected for an invited oral talk at the most recent Sherwood Theory Conference. These new equations facilitate a self-consistent treatment of the effects of flow shear on neoclassical tearing modes, the study of which is just beginning. It is anticipated that the subcontract sublet to S.E. Kruger will allow him to continue this research work in close collaboration with C.C. Hegna and GA colleagues, and in particular to apply the resultant theory to DIII-D data on such effects. In addition, seed island formation induced by geometrically coupled perturbations was simulated using the neofar code, and the neoclassical tearing mode in DIII-D shot 86144.02250 was simulated using the NIMROD code. Also, RF stabilization of tearing modes was modeled. Finally, a couple of summary-type talks were given in Japan on the status of neoclassical tearing mode studies. The model we have constructed in collaboration with DIII-D colleagues for the temporal development of disruption precursors in NSC L-mode DIII-D plasmas has been published as a General Atomics report and is in the process of being published in the Physics of Plasmas. This simple model is based on the temporal development of an ideal MHD instability as its beta is driven slowly through the instability threshold. Unfortunately, rather than being ''the'' mechanism for disruptions, it seems to be just one of many such mechanisms. In order to explore the topology of the magnetic flux surfaces just before the major disruption for our model, we have begun to use a signal analysis code developed previously to compare ECE signals with theoretical predictions for these disruption precursors--in particular their radial dependence, and the implications for the flux surface geometry and topology