Progress toward long-pulse high-performance Advanced Tokamak discharges on the DIII-D tokamak

Significant progress has been made in obtaining high-performance discharges for many energy confinement times in the DIII-D tokamak [J. L. Luxon , Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159]. Normalized performance (measured by the product of beta H-N(89) and indicative of the proximity to both conventional beta limits and energy confinement quality, respectively) similar to 10 has been sustained for >5 tau (E) with q(min)>1.5. These edge localized modes (ELMing) H-mode discharges have beta similar to5%, which is limited by the onset of resistive wall modes slightly above the ideal no-wall n=1 limit, with approximately 75% of the current driven noninductively. The remaining Ohmic current is localized near the half-radius. The DIII-D electron cyclotron heating system is being upgraded to replace this inductively driven current with localized electron cyclotron current drive (ECCD). Density control, which is required for effective ECCD, has been successfully demonstrated in long-pulse high-performance ELMing H-mode discharges with beta (N)H(89)similar to7 for up to 6.3 s. In plasma shapes compatible with good density control in the present divertor configuration, the achieved beta (N) is somewhat less than that in the high beta H-N(89)=10 discharges. (C) 2001 American Institute of Physics.