A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1

A fast edge turbulence suppression event has been simulated in the electrostatic version of the gyrokinetic particle-in-cell code XGC1 in a realistic diverted tokamak edge geometry under neutral particle recycling. The results show that the sequence of turbulent Reynolds stress followed by neoclassical ion orbit-loss driven together conspire to form the sustaining radial electric field shear and to quench turbulent transport just inside the last closed magnetic flux surface. The main suppression action is located in a thin radial layer around ψN ≅ 0.96–0.98, where ψN is the normalized poloidal flux, with the time scale ~0.1 ms.