Kinetic simulation of DIII-D pedestal fueling asymmetry with synthetic diagnostics

It has been observed on the DIII-D tokamak that ionization is much higher at the high-field side of discharges with counter-current magnetic field and this asymmetry reverses upon swapping the direction of the toroidal magnetic field. This was revealed by the LLAMA diagnostic, which measures hydrogenic Lyman-alpha radiation emitted along several dozen lines of sight that straddle the separatrix. A synthetic version of this diagnostic was incorporated into the DEGAS2 neutral transport solver, and results are sensitive to both the plasma background and the neutral source. Kinetic neutral simulations were thereby performed as a validation mechanism for total-f XGC simulations of the edge plasma turbulence including neoclassical physics, turbulence, and neutral recycling.



General agreement is observed between the LLAMA measurements and the synthetic diagnostic, including the characteristic asymmetry, trends, and order-of-magnitude. Turbulence plays an important role in transporting particles out of the confined region, which propagates via neoclassical effects in one direction or the other along the magnetic field to provide an asymmetric source of recycled neutrals.