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

Journal Article · Thu Oct 15 00:00:00 EDT 2015 · Nuclear Fusion

DOI:https://doi.org/10.1088/0029-5515/55/11/113034· OSTI ID:1345398

Turco, Francesca ^[1]; Turnbull, Alan D. ^[2]; Hanson, Jeremy M. ^[1]; Navratil, Gerald A. ^[1]

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1. Columbia Univ., New York, NY (United States)
2. General Atomics, San Diego, CA (United States)

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 β_N limit is reached. In a β_N scan, the MARS-K model with thermal and fast-ions, reproduces the experimental measurements above the no-wall limit, except at the highest β_N 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 β_N, and recovers the measured response even when fast-ions are neglected, reversing the effect found in lower β_N cases, but consistent with the higher β_N 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: the 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 q_edge~2. This suggests that previously developed RWM feedback techniques together with the additional optimizations that enabled q_edge~2 operation, can be applied to control of both current-driven and pressure-driven modes at high β_N.

• Research Organization: Columbia Univ., New York, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE Advanced Research Projects Agency - Energy (ARPA-E)
• Grant/Contract Number: FC02-04ER54698; FG02-04ER54761
• OSTI ID: 1345398
• Alternate ID(s): OSTI ID: 1238959
• Journal Information: Nuclear Fusion, Vol. 55, Issue 11; ISSN 0029-5515
• Publisher: IOP Science
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
MHD stability
RWM
fast-ions
drift-kinetic damping