Far scrape-off layer particle and heat fluxes in high density – High power scenarios

Abstract

The far scrape-off layer transport is studied in ASDEX Upgrade H-mode discharges with high divertor neutral density N0,div, high power across the separatrix Psep and nitrogen seeding to control the divertor temperature. Such conditions are expected for ITER but usually not investigated in terms of turbulent SOL transport. At high N0,div and Psep the H-mode discharges enter a regime of high cross-field particle and power transport in the SOL which is accompanied by a significant change of the turbulence characteristic analogous to the transition from conductive to convective transport in L-mode. Parallel particle and power flux densities of several 1023m−2s−1 and 10MWm−2 have been detected about ∼40 to 45mm outside the separatrix mapped to the outer mid-plane. The particle flux fall-off length reached up to 45mm. This paper presents for the first time an empirical condition to enter the high transport regime in H-mode and the relation of this regime to changes in the filamentary transport.