Hybrid Scenario Development in DIII-D

Abstract

Experiments in the DIII-D tokamak have demonstrated the ability to sustain ELMing H-mode discharges with high beta and good confinement quality under stationary conditions. These experiments have shown the ability to sustain normalized fusion performance (in terms of β_NH_89P /q₉₅²) at or above that projected for Q_fus = 10 operation in the International Thermonuclear Experimental Reactor (ITER) design over a wide range in operating parameters. In the best cases, operation is maintained at the free boundary, n = 1 stability limit. Confinement is found to be better than standard H-mode confinement scalings over a wide range in operation space, and experimentally measured transport is consistent with predictions from the GLF23 transport code. Projections using the standard ITER H-mode scaling laws based on these discharges indicate that Q_fus = 5 can be maintained for >5400 s in ITER at q₉₅ = 4.5 while Q_fus = 40 can be obtained for ~2400 s at q₉₅ = 3.2. These projected performance levels further validate the ITER design and suggest that long-pulse, high neutron fluence operation as well as very high fusion gain operation may be possible in next-generation tokamaks.