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Progress toward fully noninductive discharge operation in DIII-D using off-axis neutral beam injection

  • Author(s): Ferron, JR
  • Holcomb, CT
  • Luce, TC
  • Park, JM
  • Politzer, PA
  • Turco, F
  • Heidbrink, WW
  • Doyle, EJ
  • Hanson, JM
  • Hyatt, AW
  • In, Y
  • La Haye, RJ
  • Lanctot, MJ
  • Okabayashi, M
  • Petrie, TW
  • Petty, CC
  • Zeng, L
  • et al.

Published Web Location

https://doi.org/10.1063/1.4821072Creative Commons 'BY' version 4.0 license
Abstract

The initial experiments on off-axis neutral beam injection into high noninductive current fraction (f NI), high normalized pressure (β N) discharges in DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] have demonstrated changes in the plasma profiles that increase the limits to plasma pressure from ideal low-n instabilities. The current profile is broadened and the minimum value of the safety factor (q min) can be maintained above 2 where the profile of the thermal component of the plasma pressure is found to be broader. The off-axis neutral beam injection results in a broadening of the fast-ion pressure profile. Confinement of the thermal component of the plasma is consistent with the IPB98(y,2) scaling, but global confinement with q min > 2 is below the ITER-89P scaling, apparently as a result of enhanced transport of fast ions. A 0-D model is used to examine the parameter space for f NI = 1 operation and project the requirements for high performance steady-state discharges. Fully noninductive solutions are found with 4 < β N < 5 and bootstrap current fraction near 0.5 for a weak shear safety factor profile. A 1-D model is used to show that a f NI = 1 discharge at the top of this range of β N that is predicted stable to n = 1, 2, and 3 ideal MHD instabilities is accessible through further broadening of the current and pressure profiles with off-axis neutral beam injection and electron cyclotron current drive. © 2013 AIP Publishing LLC.

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