Experimental study on the effect of nonuniform magnetic fields on the behavior of a cylindrical scrape-off layer plasma

Abstract

A boundary plasma fluid model that takes into account nonuniform magnetic fields in the previous study [T. Ohira et al., Phys. Fluids B 3, 2010 (1991)] is presented. From the numerical simulations based on the model, it was observed that cross-field particle fluxes in a cylindrical scrape-off layer (SOL) plasma are dramatically influenced by azimuthal (poloidal) changes in applied axial magnetic fields. In this study, experiments to confirm the numerical results and the phenomenon have been made. Two-dimensional (r,θ) distributions of plasma density, electron temperature, floating potential, and plasma potential in the cylindrical SOL plasma with and without nonuniform magnetic fields have been measured by 12 single probes located every 30° azimuthally. The nonuniform magnetic fields were produced by ferromagnetic amorphous shells. It was observed that the densities in the SOL plasma decrease where the axial magnetic fields have positive gradient azimuthally and increase where negative in the real experiment. In addition, the phenomenon could be simulated by the two-dimensional SOL plasma code developed in the previous study. It is thought that this might be due to azimuthal mobility flows and cross-field E×B flows which are influenced by nonuniform magnetic fields.