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Title: Steady state scenario development with elevated minimum safety factor on DIII-D

Abstract

On DIII-D, a high β scenario with minimum safety factor (q min) near 1.4 has been optimized with new tools and shown to be a favourable candidate for long pulse or steady state operation in future devices. Furthermore, the new capability to redirect up to 5 MW of neutral beam injection (NBI) from on- to off-axis improves the ability to sustain elevated q min with a less peaked pressure profile. The observed changes increase the ideal magnetohydrodynamics (MHD) n = 1 mode β N limit thus providing a path forward for increasing the noninductive current drive fraction by operating at high β N. Quasi-stationary discharges free of tearing modes have been sustained at βN = 3.5 and β T = 3.6% for two current profile diffusion timescales (about 3 s) limited by neutral beam duration. The discharge performance has normalized fusion performance expected to give fusion gain Q ≈ 5 in a device the size of ITER. Analysis of the poloidal flux evolution and current drive balance show that the loop voltage profile is almost relaxed even with 25% of the current driven inductively, and q min remains elevated near 1.4. Our observations increase confidence that the current profile willmore » not evolve to one unstable to a tearing mode. In preliminary tests a divertor heat flux reduction technique based on producing a radiating mantle with neon injection appears compatible with this operating scenario. 0D model extrapolations suggest it may be possible to push this scenario up to 100% noninductive current drive by raising β N. Similar discharges with q min = 1.5–2 were susceptible to tearing modes and off-axis fishbones, and with q min > 2 lower normalized global energy confinement time is observed.« less

Authors:
 [1];  [2];  [2];  [2];  [3];  [4];  [2];  [5];  [1];  [4];  [2];  [6];  [2];  [2];  [2]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Columbia Univ., New York, NY (United States)
  5. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  6. FAR-TECH Inc., San Diego, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); US Department of Energy
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1343029
Alternate Identifier(s):
OSTI ID: 1352312
Report Number(s):
LLNL-JRNL-647501
Journal ID: ISSN 0029-5515
Grant/Contract Number:
AC52-07NA27344; FC02-04ER54698; AC05-00OR22725; FG02-04ER54761; AC02-09CH11466; FG02-08ER85195
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 54; Journal Issue: 9; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; steady state scenarios; high beta; non-inductive current drive; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Holcomb, Christopher T., Ferron, John R., Luce, Timothy C., Petrie, Thomas W., Park, J. M., Turco, Francesco, Van Zeeland, Michael A., Okabayashi, Michio, Lasnier, Charles T., Hanson, Jeremy M., Politzter, P. A., In, Y., Hyatt, A. W., La Haye, R. J., and Lanctot, M. J.. Steady state scenario development with elevated minimum safety factor on DIII-D. United States: N. p., 2014. Web. doi:10.1088/0029-5515/54/9/093009.
Holcomb, Christopher T., Ferron, John R., Luce, Timothy C., Petrie, Thomas W., Park, J. M., Turco, Francesco, Van Zeeland, Michael A., Okabayashi, Michio, Lasnier, Charles T., Hanson, Jeremy M., Politzter, P. A., In, Y., Hyatt, A. W., La Haye, R. J., & Lanctot, M. J.. Steady state scenario development with elevated minimum safety factor on DIII-D. United States. doi:10.1088/0029-5515/54/9/093009.
Holcomb, Christopher T., Ferron, John R., Luce, Timothy C., Petrie, Thomas W., Park, J. M., Turco, Francesco, Van Zeeland, Michael A., Okabayashi, Michio, Lasnier, Charles T., Hanson, Jeremy M., Politzter, P. A., In, Y., Hyatt, A. W., La Haye, R. J., and Lanctot, M. J.. Fri . "Steady state scenario development with elevated minimum safety factor on DIII-D". United States. doi:10.1088/0029-5515/54/9/093009. https://www.osti.gov/servlets/purl/1343029.
@article{osti_1343029,
title = {Steady state scenario development with elevated minimum safety factor on DIII-D},
author = {Holcomb, Christopher T. and Ferron, John R. and Luce, Timothy C. and Petrie, Thomas W. and Park, J. M. and Turco, Francesco and Van Zeeland, Michael A. and Okabayashi, Michio and Lasnier, Charles T. and Hanson, Jeremy M. and Politzter, P. A. and In, Y. and Hyatt, A. W. and La Haye, R. J. and Lanctot, M. J.},
abstractNote = {On DIII-D, a high β scenario with minimum safety factor (qmin) near 1.4 has been optimized with new tools and shown to be a favourable candidate for long pulse or steady state operation in future devices. Furthermore, the new capability to redirect up to 5 MW of neutral beam injection (NBI) from on- to off-axis improves the ability to sustain elevated qmin with a less peaked pressure profile. The observed changes increase the ideal magnetohydrodynamics (MHD) n = 1 mode βN limit thus providing a path forward for increasing the noninductive current drive fraction by operating at high βN. Quasi-stationary discharges free of tearing modes have been sustained at βN = 3.5 and βT = 3.6% for two current profile diffusion timescales (about 3 s) limited by neutral beam duration. The discharge performance has normalized fusion performance expected to give fusion gain Q ≈ 5 in a device the size of ITER. Analysis of the poloidal flux evolution and current drive balance show that the loop voltage profile is almost relaxed even with 25% of the current driven inductively, and qmin remains elevated near 1.4. Our observations increase confidence that the current profile will not evolve to one unstable to a tearing mode. In preliminary tests a divertor heat flux reduction technique based on producing a radiating mantle with neon injection appears compatible with this operating scenario. 0D model extrapolations suggest it may be possible to push this scenario up to 100% noninductive current drive by raising βN. Similar discharges with qmin = 1.5–2 were susceptible to tearing modes and off-axis fishbones, and with qmin > 2 lower normalized global energy confinement time is observed.},
doi = {10.1088/0029-5515/54/9/093009},
journal = {Nuclear Fusion},
number = 9,
volume = 54,
place = {United States},
year = {Fri Aug 15 00:00:00 EDT 2014},
month = {Fri Aug 15 00:00:00 EDT 2014}
}

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