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

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.

doi:10.1088/0029-5515/54/9/093009

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

Journal Article · Fri Aug 15 00:00:00 EDT 2014 · Nuclear Fusion

DOI:https://doi.org/10.1088/0029-5515/54/9/093009· OSTI ID:1343029

Holcomb, Christopher T. ^[1]; Ferron, John R. ^[2]; Luce, Timothy C. ^[2]; Petrie, Thomas W. ^[2]; Park, J. M. ^[3]; Turco, Francesco ^[4]; Van Zeeland, Michael A. ^[2]; Okabayashi, Michio ^[5]; Lasnier, Charles T. ^[1]; Hanson, Jeremy M. ^[4]; Politzter, P. A. ^[2]; In, Y. ^[6]; Hyatt, A. W. ^[2]; La Haye, R. J. ^[2]; Lanctot, M. J. ^[2]

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
General Atomics, San Diego, CA (United States)
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Columbia Univ., New York, NY (United States)
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
FAR-TECH Inc., San Diego, CA (United States)

On DIII-D [J.L. Luxon, 2005 Fusion Sci. Tech. 48 828], a high β scenario with minimum safety factor ( qmin ) near 1.4 has been optimized with new tools and shown to be a favorable candidate for long pulse or steady state operation in future devices. 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. These changes increase the ideal 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 seconds) 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. These 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. 0-D 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.

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Research Organization:: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); General Atomics, San Diego, CA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: AC52-07NA27344; FC02-04ER54698; AC05-00OR22725; FG02-04ER54761; AC02-09CH11466; FG02-08ER85195

OSTI ID:: 1343029

Alternate ID(s):: OSTI ID: 1352312

Report Number(s):: LLNL-JRNL-647501

Journal Information:: Nuclear Fusion, Vol. 54, Issue 9; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 14 works

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