Large experiment data analysis collaboration. Final annual progress report for period November 15, 2000 - April 30, 2002

Abstract

Because of the good agreement between theory and experiment (on a number of tokamak experiments) on the nonlinear development, saturation of neoclassical tearing modes (NTMs), the study of NTMs is becoming a mature subject. Thus, our contributions to studies of neoclassical (and regular classical) tearing modes over the past year have focused on a number of particular, more detailed issues: flow shear effects on linear tearing modes, exploring the possibility of NTMs in spherical tokamaks such as NSTX, assisting with classical tearing mode explorations in DIII-D, and fast ion effects on NTMs. In addition, a collaboration with the Institute for Plasma Research group in India was initiated due to their interest in using the NEAR code (developed in part under this grant) to explore neoclassical tearing modes. Finally, a number of talks have been given on basic, current frontier and future extensions of neoclassical tearing mode theory. Our previous identification of the disruption precursor in DIII-D shot 87009 as being due to a global ideal MHD interchange-type instability being driven slowly though its threshold was featured prominently in the DIII-D MHD theory paper at the 2000 IAEA Sorrento meeting. We have also stimulated the application of the NIMROD code to this particular DIII-D disruption precursor and continued to support this code exploration of it. To facilitate quicker evaluations of global-type ideal MHD growth rates and eigenmodes, we have continued our development of a new method for using perturbed equilibria to ''maneuver in delta-W'' space. Since this basic concept for efficiently finding trends in ideal MHD stability using perturbed equilibria has been proven using a screw-pinch geometry, we are now beginning to implement and test the procedure in the GAT0 code for specific DIII-D high beta equilibria. In addition, to analytically explore the ultimate nonlinear evolution of these types of modes, we have begun (primarily on our DOE ''Nonlinear and Nonideal MHD'' theory grant) exploring the growth rate and eigenmode structure of localized interchange instabilities. A surprising aspect of that work is that robust, ideal MHD-like growth rates and radially spread eigenmodes are only obtained when the Suydam/Mercier criteria are exceeded by about a factor of two (D{sub I} > 0.45). A new issue we have begun exploring is how ''thin, isolated'' magnetic islands and their effects can be incorporated into MHD equilibria and hence the EFIT code. In addition, we have given presentations on more general fusion, and MHD topics, which have included some of the results developed under this research grant.