VERY HIGH-CONFINEMENT AND HIGH-CONFINEMENT MODE LIMITED DISCHARGES INDIII-D

The first observations of marginally limited very high confinement mod e (VH-mode) discharges have been achieved in DIII-D [Nucl. Fusion Spec ial Supplement: World Survey of Activities in Controlled Fusion Resear ch (International Atomic Energy Agency, Vienna, 1990)] with significan t reductions in peak heat flux conducted to plasma facing surfaces. In addition, quasistationary well limited high confinement-mode (H-mode) discharges have been obtained in DIII-D, also with reduced peak heat flux. This demonstration of reduced peak heat flux while maintaining h igh performance, i.e., high energy confinement time, can be important for the design of fusion ignition devices. Energy confinement enhancem ents in these high triangularity discharges are comparable to diverted discharges with similar parameters: tau(E)/tau(ITER-89P)=2.9 for VH-m ode and tau(E)/tau(ITER-89P)=1.8 for quasistationary high confinement mode (H mode), where tau(ITER-89P) is the empirically derived low conf inement mode (L-mode) energy confinement scaling relation [Nucl. Fusio n 30, 1999 (1990)]. Comparisons of the conducted heat flux, particle f lux, and radiated power profiles show a shift toward the inner wall as the discharge configuration becomes more limited. In addition to the advantage of reduced peak heat flux in these limiter discharges, such configurations also allow more effective use of the internal vessel vo lume, providing the potential for higher performance, i.e., higher pla sma current at a fixed safety factor, q(95). (C) 1996 American Institu te of Physics.