Studies in DIII-D of High Beta Discharge Scenarios Appropriate for Steady-state Tokamak Operation With Burning Plasmas
J.R. Ferron, J.C. DeBoo, T.C. Luce, T.W. Petrie, C.C. Petty, P.A. Politzer, H. Reimerdes, M. Schneider, T.A. Casper, C.T. Holcomb, J.M. Park, M. Murakami, Y. Ou, E. Schuster, E.J. Doyle
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Dallas, Texas, November 17-21, 2008
Abstract
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In the DIII-D steady-state scenario with qmin = 1.5-2.0, the duration
with the noninductive current fraction (fNI) near 1 has been extended
to 70% of the resistive time. To extend duration, ECCD is deposited
with a broad profile in order to avoid the 2/1 tearing mode, enabling
reliable operation at βN = 3.6-3.7. These discharges have double-null
shape biased in the direction opposite the ∇B drift, in order to
simultaneously optimize confinement and divertor pumping, and ECCD
power up to 3 MW. An alternate scenario with internal inductance
increased to 1.1-1.4 is under study, motivated by the pos- sibility
of steady-state operation at βN =4-5 without wall stabilization. Thus
far, βN =4.6, just below the calculated n = 1 and n = ∞ stability limits,
has been achieved transiently with fNI = 0.85.