Effects of heating power on divertor in-out asymmetry and scrape-off layer flow in reversed field on Experimental Advanced Superconducting Tokamak

Abstract

The dependence of divertor asymmetry and scrape-off layer (SOL) flow on heating power has been investigated in the Experimental Advanced Superconducting Tokamak (EAST). Divertor plasma exhibits an outboard-enhanced in-out asymmetry in heat flux in lower single null configuration for in reversed (ion ∇B drift direction toward the upper X-point) field directions. Upper single null exhibits an inboard-favored asymmetry in low heating power condition, while exhibits an outboard-favored asymmetry when increasing the heating power. Double null has the strongest in-out asymmetry in heat flux, favoring the outer divertor. The in-out asymmetry ratios of qt,out/qt,in and Pout/Ptotal increase with the power across the separatrix Ploss, which is probably induced by the enhanced radial particle transport due to a large pressure gradient. The characteristics of the measured SOL parallel flow under various discharge conditions are consistent with the Pfirsch-Schlüter (PS) flow with the parallel Mach number M∥ decreasing with the line averaged density but increasing with Ploss, in the same direction as the PS flow. The contributions of both poloidal E×B drift and parallel flow on poloidal particle transport in SOL on EAST are also assessed.