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(TH3/6) Predictive Capability of MHD Stability Limits in High Performance DIII-D Discharges

A. D. Turnbull¹⁾, D. Brennan^2)*, M. S. Chu¹⁾, L. L. Lao¹⁾, J. R. Ferron¹⁾, A. M. Garofalo^3)*, P. B. Snyder¹⁾, J. Bialek³⁾, I. N. Bogatu⁴⁾, J. D. Callen⁵⁾, M. S. Chance^6)*, K. Comer⁵⁾, D. H. Edgell⁴⁾, S. A. Galkin⁷⁾, D. A. Humphreys¹⁾, J. S. Kim⁴⁾, R. J. La Haye¹⁾, T. C. Luce¹⁾, M. Okabayashi⁶⁾, B. W. Rice⁸⁾, E. J. Strait¹⁾, T. S. Taylor¹⁾, and H. R. Wilson^9)
 
1) General Atomics, P.O. Box 85608, San Diego, California USA
²⁾ Oak Ridge Institute for Science Education, Oak Ridge, Tennessee
³⁾ Columbia University, New York, New York
⁴⁾ FARTECH, P.O. Box 221053, San Diego, California USA
⁵⁾ University of Wisconsin-Madison, Madison, Wisconsin USA
⁶⁾ Princeton Plasma Physics Laboratory, Princeton, New Jersey USA
⁷⁾ University of California-San Diego, La Jolla, California USA
⁸⁾ Lawrence Livermore National Laboratory (present address: Xenogen, 860 Atlantic, Alameda, California USA
⁹⁾ Culham Laboratory, UKAEA, Abingdon, Oxfordshire OX14 3DB, UK
^* Present address: General Atomics, P.O. Box 85608, San Diego, California USA

Abstract.  Results from an array of theoretical and computational tools developed to treat the instabilities of most interest for high performance tokamak discharges are described. The theory and experimental diagnostic capabilities have now been developed to the point where detailed predictions can be productively tested so that competing effects can be isolated and either eliminated or confirmed. The predictions using high quality discharge equilibrium reconstructions are tested against the observations for the principal limiting phenomena in DIII-D: L-mode negative central shear (NCS) disruptions, H-mode NCS edge instabilities, and tearing and resistive wall modes (RWMs) in long pulse discharges. In the case of predominantly ideal MHD instabilities, agreement between the code predictions and experimentally observed stability limits and thresholds can now be obtained to within several percent, and the predicted fluctuations and growth rates to within the estimated experimental errors. Edge instabilities can be explained by a new model for edge localized modes as predominantly ideal low to intermediate n modes. Accurate ideal calculations are critical to demonstrating RWM stabilization by plasma rotation and the ideal eigenfunctions provide a good representation of the RWM structure when the rotation slows. Ideal eigenfunctions can then be used to predict stabilization using active feedback. For non-ideal modes, the agreement is approaching levels similar to that for the ideal comparisons; $\Delta{^\prime}$ calculations, for example, indicate that some discharges are linearly unstable to classical tearing modes, consistent with the observed growth of islands in those discharges.

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