Divertor asymmetry and scrape-off layer flow in various divertor configurations in Experimental Advanced Superconducting Tokamak

Divertor asymmetry and its dependence on the ion del B direction has been investigated in the Experimental Advanced Superconducting Tokamak by changing the divertor configuration from lower single null (LSN), via double null (DN), to upper single null (USN) during one single discharge. Divertor plasmas exhibit the usual in-out asymmetry in particle and heat fluxes in LSN with the ion del B direction toward the lower X-point, favoring the outer divertor, especially at high density. The in-out asymmetry is reversed when changing the divertor configuration from LSN to USN, thus clearly demonstrating the effect of classical drifts. DN exhibits an even stronger in-out divertor asymmetry, favoring the outer divertor. A significant top-down asymmetry is also seen for DN, with greater particle and heat fluxes to the bottom divertor. In addition, the parallel plasma flow has been measured by a fast moving Mach probe at the outer midplane, which shows similar magnitude to the Pfirsch-Schluter flow. Its contribution to the poloidal particle flux is also assessed and comparison is made with that from the poloidal E x B drift. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4707396]