X-point ion orbit physics in scrape-off layer and generation of a localized electrostatic potential perturbation around X-point

Abstract

It has been well known that the logarithmically vanishing poloidal magnetic field strength Bθ near the magnetic X-point in a tokamak plasma yields the so-called ion X-loss or X-transport of ions when the ion temperature is high enough [Chang et al., Phys. Plasmas 9, 3884 (2002)], which has a notable impact on the physics just inside the magnetic separatrix surface, e.g., most prominently, to force a well-like structure in the global negative radial electric field and hence a pressure pedestal buildup. In this brief communication, we show that a similar effect exists in the scrape-off (SOL) layer near the X-point that can create a localized electrostatic potential structure around the X-point and have a significant impact on the near-SOL physics.