A 2D presheath potential model for turbulence transport study in FRC SOL*

The electrostatic presheath potential in the Scrape-off layer (SOL) of the Field-reversed configuration (FRC) could affect the turbulent transport in the SOL and the penetration of divertor biasing to the FRC confinement region. A full-f gyrokinetic simulation is used 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 it 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 capture the penetration of the divertor biasing, a radial current model is proposed to determine a more realistic 2D structure of the presheath potential. The current distribution with a biasing potential at the divertor ends can be obtained by using this fluid electron model, and the 2D electrostatic potential in the SOL region can be determined through interplay between the parallel resistivity and toroidal flow damping. The full-f scheme was also used to successfully replicate the slab ion temperature gradient (ITG) instability observed in previous delta-f simulations. This comprehensive full-f scheme holds potential for future investigations into turbulence transport in the FRC SOL, where non-Maxwellian distributions and open boundary conditions can be involved.