The pinch of cold ions from recycling in the tokamak edge pedestal

Abstract

We apply the “natural fueling mechanism” [W. Wan, S. E. Parker, Y. Chen, and F. W. Perkins, Phys. Plasmas 17, 040701 (2010)] to the edge pedestal. The natural fueling mechanism is where cold ions naturally pinch radially inward for a heat-flux dominated plasma. It is shown from neoclassical-neutral transport coupled simulations that the recycling neutrals and the associated source ions are colder than the main ions in the edge pedestal. These recycling source ions will pinch radially inward due to microturbulence. Gyrokinetic turbulence simulations indicate that near the top of the pedestal, the pinch velocity of the recycling source ions is much higher than the main ion outgoing flow velocity. The turbulent pinch of the recycling source ions may play a role in the edge pedestal transport and dynamics. The cold ion temperature significantly enhances the pinch velocity of the recycling source ions near to the pedestal top. Neoclassical calculations show a cold ion pinch in the pedestal as well.