SOL Density Variations During ICRF Heating and Gas Injection
In this paper, we present modeling results of the effect of gas injection on the SOL (Scrape-off-layer) density profiles (neSOL) during ICRF (Ion Cyclotron Resonance Frequency) heating. Gas injection during ICRF has been tested in several tokamaks with the goal of improving the coupling by modifying the density profile in front of the antenna, thus facilitating the fast wave propagation through the evanescent layer. The EDGE2D/NIMBUS code was adapted to model the presence of a wide SOL and a magnetic geometry with a 2nd X-point near to the top of the wall (as in JET Pulse No's: 68109-13). In contrast to the computational grid for the configurations considered in that have a SOL width of about 10cm at the Outer Mid-Plane (OMP), EDGE2D simulations with the 2nd X point at the top are only carried out considering about 4cm of SOL in the OMP. This is because the EDGE2D computational grid is restricted to a rather narrow OMP SOL layer in these ITER relevant configurations. One possibility is then to continue into the far SOL with "ad hoc" assumptions about transport with essentially 1D model.