Effects of internal and external magnetic fields on the characteristics of a magnetic multipole plasma source

Abstract

Influences of an externally produced axial magnetic field and the field produced by the filament current on the performance of a magnetic multipole plasma source were experimentally studied using a high-proton-yield ion source developed for the JT-60 NBI. It was shown that both of the fields give significant effects on the arc discharge characteristics, the arc efficiency, and the plasma uniformity. The probe measurement showed that the change of the arc efficiency caused by the field is closely related to the change of the ion saturation current density distribution on the extraction grid. The change of the distribution can be explained by the effect of the magnetic field on the orbits of the primary electrons emitted from the filaments. On the basis of the experimental results, a permissible level of the external field in the source was evaluated to be ±5 G.