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

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.