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NIMROD Modeling of Sawtooth Modes Using Continuum and Hot-Particle Closures

Author: Thomas G. Jenkins
Requested Type: Poster Only
Submitted: 2015-01-16 13:23:46

Co-authors: E. D. Held, J. R. King, S. E. Kruger

Contact Info:
Tech-X Corporation
5621 Arapahoe Avenue
Boulder, Colorado   80303
USA

Abstract Text:
We summarize ongoing efforts to model giant sawtooth onset and growth in DIII-D shot 96043 using NIMROD. The RF heating used in this discharge gives rise to an energetic ion population that alters the sawtooth stability boundary; the conventional sawtooth cycle is replaced by longer-period `giant sawtooth’ oscillations of much larger amplitude. We explore the use of both continuum kinetic and particle-in-cell closures to numerically represent the RF-induced hot-particle distribution, and investigate the role played by the form of this distribution, including a possible high-energy tail drawn out by the RF, in determining the altered mode onset threshold and subsequent nonlinear evolution. Equilibrium reconstructions from the experimental data are used to enable these detailed validation studies. Effects of other parameters on the sawtooth behavior, such as the plasma Lundquist number and hot-particle beta-fraction, are also considered. Ultimately, we hope to assess the degree to which NIMROD’s extended MHD model correctly simulates the observed linear onset and nonlinear behavior of the giant sawtooth, and to establish its reliability as a predictive modeling tool for these modes.

Supported by US DoE via the SciDAC Center for Extended MHD Modeling (CEMM).

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