Confinement improvement in the high poloidal beta regime on DIII-D and application to steady-state H-mode on EAST

摘要

Systematic experimental and modeling investigations on DIII-D show attractive transport properties of fully non-inductive high β_p plasmas. Experiments on DIII-D show that the large-radius internal transport barrier (ITB), a key feature providing excellent confinement in the high β_p regime, is maintained when the scenario is extended from q_(95) ~ 12 to 7 and from rapid to near-zero toroidal rotation. The robustness of confinement versus rotation was predicted by gyrofluid modeling showing dominant neoclassical ion energy transport even without the E×B shear effect. The physics mechanism of turbulence suppression, we found, is the Shafranov shift, which is essential and sets a bp threshold for large-radius ITB formation in the high β_p scenario on DIII-D. This is confirmed by two different parameter-scan experiments, one for a β_N scan and the other for a q_(95) scan. They both give the same β_p threshold at 1.9 in the experiment. The experimental trend of increasing thermal transport with decreasing β_p is consistent with transport modeling. The progress toward the high bp scenario on Experimental Advanced Superconducting Tokamak (EAST) is reported. The very first step of extending the high β_p scenario on DIII-D to long pulse on EAST is to establish a long pulse H-mode with ITB on EAST. This paper shows the first 61 s fully non-inductive H-mode with stationary ITB feature and actively cooled ITER-like tungsten divertor in the very recent EAST experiment. The successful use of lower hybrid wave as a key tool to optimize the current profile in the EAST experiment is also introduced. Results show that as the electron density is increased, the fully non-inductive current profile broadens on EAST. The improved understanding and modeling capability are also used to develop advanced scenarios for the China Fusion Engineering Test Reactor. Overall, these results provide encouragement that the high β_p regime can be extended to a lower safety factor and very low