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Magnetohydrodynamic (MHD) stability analyses of Negative Central Shear (NCS) equilibria have revealed a new understanding of the limiting MHD instabilities in NCS experiments. Ideal stability calculations show a synergistic effect between cross-section shape and pressure profile optimization; strong shaping and a broader pressure profile independently lead to moderately higher beta limits, but broadening of the pressure profile in a strongly dee-shaped cross-section leads to a dramatic increase in the ideal beta limit. Localized resistive interchange (RI) modes can be unstable in the negative shear region and are most restrictive for peaked pressure profiles. Resistive global modes can also be destabilized significantly below the ideal beta limit. Experiments largely confirm the general trends, and diagnostic measurements and numerical stability calculations are found to be in good qualitative agreement. Observed disruptions in NCS discharges with L mode edge and strongly peaked pressure appear to be initiated by interactions between the RI and the global ideal and resistive modes.

Additional information

Authors: TURNBULL A D ET AL, General Atomics, San Diego (US);CASPER T A ET AL, Lawrence Livermore National Laboratory (US);LEE B J, University of San Diego (US);REN C ET AL, University of Wisconsin, Madison (US);RETTIG C L ET AL, University of California, Los Angeles (US);SAUTER O, CRPP-EPFL, Lausanne (CH)
Bibliographic Reference: Article: 16th IAEA Fusion Energy Conference, Montreal (CA), October 7-11, 1996
Record Number: 199811286 / Last updated on: 1998-10-27
Original language: en
Available languages: en