Single particle finite orbit width effects and the H-mode edge transport barrier

Full-orbit single particle simulations using the SPIRAL code [1] have been performed to study the effects of finite orbit widths on the steep edge gradient region of H-mode plasmas.  It was found that finite orbit width effects of the thermal ions create an edge parallel current in the plasma current direction and a surface current perpendicular to the magnetic field lines. These edge ion-currents cannot be canceled by equivalent electron currents because of the large difference between ion and electron orbit widths. The surface current is equivalent with a poloidal flow that creates an inwardly directed electric field. After including scattering of test particles inside and charge exchange effects outside the plasma, simulation results are compared with experimental result showing that finite ion orbit width effects create the edge radial electric field which is important for the H-mode transport barrier.

[1] G.J. Kramer et al. Plasma Phys. Control.Fusion 55 (2013) 025013