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.
Original language | English |
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Article number | 092504 |
Journal | Physics of Plasmas |
Volume | 20 |
Issue number | 9 |
DOIs | |
State | Published - Sep 2013 |
Funding
This work was supported in part by the US Department of Energy under DE-FC02-04ER54698, DE-AC52-07NA27344, DE-AC05-00OR22725, DE-FG02-04ER54761, SC-G903402, DE-FG02-08ER54984, DE-FG02-06ER84442, and DE-AC02-09CH11466.