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

Abstract

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

Authors:
 [1];  [2];  [1];  [1]
  1. Columbia Univ., New York, NY (United States)
  2. General Atomics, San Diego, CA (United States)
Publication Date:
Research Org.:
Columbia Univ., New York, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE Advanced Research Projects Agency - Energy (ARPA-E)
OSTI Identifier:
1345398
Alternate Identifier(s):
OSTI ID: 1238959
Grant/Contract Number:  
FC02-04ER54698; FG02-04ER54761
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 55; Journal Issue: 11; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; MHD stability; RWM; fast-ions; drift-kinetic damping

Citation Formats

Turco, Francesca, Turnbull, Alan D., Hanson, Jeremy M., and Navratil, Gerald A. Modeling of fast neutral-beam-generated ions and rotation effects on RWM stability in DIII-D plasmas. United States: N. p., 2015. Web. doi:10.1088/0029-5515/55/11/113034.
Turco, Francesca, Turnbull, Alan D., Hanson, Jeremy M., & Navratil, Gerald A. Modeling of fast neutral-beam-generated ions and rotation effects on RWM stability in DIII-D plasmas. United States. https://doi.org/10.1088/0029-5515/55/11/113034
Turco, Francesca, Turnbull, Alan D., Hanson, Jeremy M., and Navratil, Gerald A. 2015. "Modeling of fast neutral-beam-generated ions and rotation effects on RWM stability in DIII-D plasmas". United States. https://doi.org/10.1088/0029-5515/55/11/113034. https://www.osti.gov/servlets/purl/1345398.
@article{osti_1345398,
title = {Modeling of fast neutral-beam-generated ions and rotation effects on RWM stability in DIII-D plasmas},
author = {Turco, Francesca and Turnbull, Alan D. and Hanson, Jeremy M. and Navratil, Gerald A.},
abstractNote = {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: 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 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.},
doi = {10.1088/0029-5515/55/11/113034},
url = {https://www.osti.gov/biblio/1345398}, journal = {Nuclear Fusion},
issn = {0029-5515},
number = 11,
volume = 55,
place = {United States},
year = {Thu Oct 15 00:00:00 EDT 2015},
month = {Thu Oct 15 00:00:00 EDT 2015}
}

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Works referenced in this record:

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