The hybrid scenario for high power, zero torque reactor operation

Operation at high density with off-axis EC power injection has been achieved in the high betaN hybrid scenario in DIII-D, expanding the parameter space to regimes compatible with a radiating divertor, for steady-state reactor relevant regimes. A variation on the high-betaN hybrid scenario has been found, that remains stable to the deleterious 2/1 mode without central CD deposition. Off axis EC heating leads to core impurity accumulation and lower confinement, but this effect is offset by the density increase, which leads to an enhanced pedestal and lower fast-ion losses. A second ingredient of a reactor-like scenario has been explored separately, obtaining passively stable hybrid plasmas at zero torque with and without ECCD. The lower torque discharges exhibit lower confinement. However, with reduced EC power (0.5 MW), tauE is found to increase (although H98y2 does not change significantly), such that the same betaN~2.3 can be reached with 2.3 MW less power.