Studies in DIII-D of High Beta Discharge Scenarios Appropriate for Steady-state Tokamak Operation With Burning Plasmas
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.