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Title: Modeling of fast neutral-beam-generated ions and rotation effects on RWM stability in DIII-D plasmas

Here, validation results for the MARS-K code for DIII-D equilibria, predict that the absence of fast Neutral Beam (NB) generated ions leads to a plasma response ~40–60% higher than in NB-sustained H-mode plasmas when the no-wall βN limit is reached. In a βN scan, the MARS-K model with thermal and fast-ions, reproduces the experimental measurements above the no-wall limit, except at the highest βN where the phase of the plasma response is overestimated. The dependencies extrapolate unfavorably to machines such as ITER with smaller fast ion fractions since elevated responses in the absence of fast ions indicate the potential onset of a resistive wall mode (RWM). The model was also tested for the effects of rotation at high βN, and recovers the measured response even when fast-ions are neglected, reversing the effect found in lower βN cases, but consistent with the higher βN results above the no-wall limit. The agreement in the response amplitude and phase for the rotation scan is not as good, and additional work will be needed to reproduce the experimental trends. In the case of current-driven instabilities, the magnetohydrodynamic spectroscopy system used to measure the plasma response reacts differently from that for pressure driven instabilities: themore » response amplitude remains low up to ~93% of the current limit, showing an abrupt increase only in the last ~5% of the current ramp. This makes it much less effective as a diagnostic for the approach to an ideal limit. However, the mode structure of the current driven RWM extends radially inwards, consistent with that in the pressure driven case for plasmas with qedge~2. This suggests that previously developed RWM feedback techniques together with the additional optimizations that enabled qedge~2 operation, can be applied to control of both current-driven and pressure-driven modes at high βN.« less
 [1] ;  [2] ;  [1] ;  [1]
  1. Columbia Univ., New York, NY (United States)
  2. General Atomics, San Diego, CA (United States)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
FC02-04ER54698; FG02-04ER54761
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 55; Journal Issue: 11; Journal ID: ISSN 0029-5515
IOP Science
Research Org:
U.S. Dept. of Energy, Washington, D.C. (United States)
Sponsoring Org:
USDOE Advanced Research Projects Agency - Energy (ARPA-E)
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; MHD stability; RWM; fast-ions; drift-kinetic damping