Role of E x B Drift in Divertor Detachment Control via Boron Powder Injection on EAST

The effects of B powder injection on plasma detachment about EAST discharge were studied by using SOLPS-ITER code package with the effects of E x B drifts considered. The simulation results show that plasma detachment occurs at the inner target in favourable toroidal magnetic field (Bt) direction at a relatively low B powder flow rate, one order of magnitude lower than that at the outer target. In a similar scenario with unfavourable Bt, it is found that the detachment thresholds of B flow rate for both the inner and outer targets are close and of the same order as that for the outer target with favourable Bt. In favourable Bt direction at B powder flow rate of 1.2 x 1021 atoms/s, a localized, broadened high-density region is formed near the inner target benefitted by the injection location and the E x B drift, and a radiation-intensified zone, mostly contributed by B1+ and B2+, occurs there. The E x B drift facilitates plasma detachment at the inner target and simultaneously amplifies the in-out divertor asymmetry. In addition, the simulation results with three different injection locations show that the injection from outer strike point leads to the lowest Zeff inside the separatrix and has an intermediate flow rate for detachment at the outer target, comparing with the X-point and upstream locations.