Simulation of 2D electrostatic presheath potential in FRC SOL

The electrostatic presheath potential in the scrape-off layer (SOL) of a field-reversed configuration (FRC) could affect the turbulent transport in the SOL and the penetration of divertor biasing to the FRC confinement region. Full-f gyrokinetic simulation is needed to find the SOL equilibrium including presheath potential, which is intrinsically 2D resulting from the balance between radial and parallel transport. We have formulated an electrostatic simulation model for the SOL pre-sheath and implemented in the GTC-X code. The model has first been verified in a 1D presheath simulation on a single flux surface by recovering the parallel force balance and continuity equation. To further construct a 2D presheath, different radial boundary conditions and simulation domain size have been tested. With the absence of radial coupling between flux surfaces such as radial current, the radial electric field profile is mainly determined by the boundary condition at the divertor. To capture the penetration of the divertor biasing, a resistive radial current model is proposed to determine a more realistic 2D structure of the presheath potential. By including the 2D presheath as background time-independent equilibrium, we have carried out microturbulence simulation in the FRC SOL and found that the radial electric field of the presheath can reduce the ITG instability by providing a considerable ExB shearing rate.