Gyrokinetic full-f study on the role of the X-point height on pedestal structure and L-H transition in tokamak

The change in the X-point height can alter the location where the outer strike point hits the divertor. It may even change the strike point from the horizontal to the vertical divertor plates. Such an event may influence the neutral particle penetration into the pedestal region which in turn can change the pedestal physics in H-mode. We investigate the X-point height effect on EXB flow profile in the presence of neutral recycling, without however modeling the vacuum pump. For this purpose we use the total-f global gyrokinetic neoclassical code XGCa. Results show that the neoclassical Er profile is sensitive to the vertical X-point location, which implies that the ExB profile could cause a difference in the pedestal physics such as the ELM stability and turbulent/neoclassical transport.