Advances in Plasma-Wall Interaction Control for H-Mode Operation over 100 s with ITER-like Tungsten Divertor on EAST

Full text: Managing excessively high divertor power and particle fluxes and related plasma-wall interactions (PWI) is one of the most critical issues for the steady-state operation of the EAST superconducting tokamak and future fusion devices, such as ITER and CFETR. A world record long pulse H-mode operation of 101.2 s with H₉₈ = 1.1 and total power injection of 0.3 GJ has been successfully achieved in EAST with ITER-like top tungsten (W) divertor, which has steady-state power exhaust capability of 10MW/m² . The peak temperature of the Wtarget of T ≈ 500°C and a heat flux ≈3MW/m² was maintained stably. Great efforts have been made to simultaneously control peak heat flux and particle/impurity exhaust towards the long pulse of 100 s time scale. Particle exhaust was optimized by preferentially directing the plasma flow toward the outer target with the ion B x ∇B drift away from theWdivertor and improving divertor pumping with the top cryo-pump. Effective power dispersal was achieved by tailoring the 3D divertor plasma footprint using lower hybrid wave (LHW) through induced edge magnetic topology change and broadened plasma wetted area, thus reducing peak heat flux andWsputtering. Extensive lithium coating was employed to lower edge recycling, low-Z impurity content andWsputtering. In addition, divertor detachment in H-mode for PWI handling was achieved for the first time with a W divertor in EAST. Compared with previous L-mode in EAST, in H-mode the detachment has a higher density threshold with n_e/n_G ∼ 0.65. Active feedback control of radiative divertor with neon impurity seeding was successfully achieved with f_rad ∼ 18-36%, and a slight loss of plasma stored energy ∼ 7-11%, offering a promising technique for steady-state divertor radiation and heat flux control. The upgrade plan and status of EAST bottom divertor from graphite to water-cooledWto accommodate more challenging PWI for steady-state H-mode over 400 s and L-mode operation over 1000 s will also be presented. (author)