Onion skin model (OSM) analysis of EAST SOL plasmas

Two-dimensional maps of the Experimental Advanced Superconducting Tokamak (EAST) scrape-off layer (SOL) plasma conditions for ohmic, L-mode and H-mode discharges are reconstructed using an onion skin model (OSM) coupled in DIVIMP together with the Monte Carlo neutral transport code, EIRENE. The boundary conditions for OSM calculation are taken from the measurements of the Langmuir probe built into the divertor targets. The OSM-calculated values of the outboard mid-plane electron density, ne, and temperature, Te, are compared with the mid-plane measurements of ne and Te from a fast reciprocating probe. Some other characteristics of these SOL plasmas are also derived from the OSM solution, reflecting that the upstream plasma conditions are governed by the SOL collisionality to a large degree. Values of χ⊥SOL at the low-field side and the high-field side mid-plane are derived separately as a function of the distance to the separatrix for ohmic, L- and H-mode discharges, showing that χ⊥SOL increases with the distance to the separatrix at both sides and that the values of χ⊥SOL at the low-field side tends to be higher than that at the high-field side. χ⊥eSOL is found to be larger than χ⊥iSOL by a factor of 2–3 for all the discharges considered here. In addition, before the use of the OSM method of extracting χ⊥SOL and D⊥SOL for EAST discharges, the reliability of this method is assessed by taking SOLPS-generated target n, T profiles as boundary conditions and by comparing the OSM-extracted cross-field transport coefficients with those input in the SOLPS modelling. (paper)