Investigation of the magnetic field influence on the plasma parameter homogeneity in a large H− / D− RF ion source relevant for ITER

Abstract

A study was conducted on the large half-size ITER source RADI testbed in order to determine the influence of the magnetic field strength on the plasma parameters in the neighbourhood of the grid. The magnetic field at RADI is created by a current flowing in the plasma grid, in contrast to the small IPP prototype source where permanent magnets are used. The investigations show a plasma homogeneity within 10% near the grid along the direction of the magnetic field lines as well as a reduction of the electron temperature. In the direction perpendicular to the magnetic field lines, and for field strengths higher than 2.4 mT, the density shows a minimum due to the reduced transport coefficient across a perpendicular magnetic field. A form of effective enhanced confinement is achieved for low magnetic field intensity.