Synergistic effects of E × B drifts and neutral recycling on upstream density shelf in HL-2A with a long leg closed divertor

Abstract In this paper, we found that the formation of an upstream density shelf, accompanied by double peaks in the target particle flux, as a potential physical mechanism for edge-localized mode suppression in HL-2A’s closed, long-leg divertor configuration with favorable B t . The density shelf is manifested as local flattening of the radial gradient of plasma density at the core-edge interface, potentially improving edge stability. SOLPS-ITER modeling results showed that the formation of density shelf results from the synergistic effects of divertor closure and E × B drifts: (i) the improved divertor closure to sufficiently reduce and even reverse the parallel plasma flow along B from the upstream plasma due to strong particle recycling inside the closed divertor; (ii) the drifts to redistribute particle fluxes at the divertor target with generation of a double-peak profile, leading to the reversal of the poloidal E × B flow near the separatrix. Such a density shelf is enhanced by increased heat power and decreased power decay length. Furthermore, during partial detachment, the density shelf could be sustained, attributed to the enhanced recycling ionization source facilitated by the long-leg closed divertor configuration.