Advanced Large Volume Surface Plasma H-/D- Source Neutral Beam Injectors

Abstract The design of an Advanced Large Volume Surface Plasma Source (LV SPS) for Neutral Beam Injectors is presented and discussed. The LV SPS will be assembled from a set of modules. Every module consists of a plasma generator with an RF saddle antenna injecting plasma and hyperthermal atoms into the expander chamber. The plasma electrode with multi-slit extraction system and localized magnetic filter is attached to the bottom flange of the expander chamber. The plasma will be generated by an RF discharge using a saddle antenna in an optimized longitudinal magnetic field. This type of discharge is very efficient for dense plasma generation. The magnetic field is used to suppress plasma diffusion to the wall, improve the efficiency of plasma generation and decrease the thermal flux to the plasma generator wall. The expanded flux of ions and hyperthermal atoms bombards uniformly the plasma electrodes of the extraction system and produces an intense beam of negative ions. With improved cooling, the average discharge power can be increased significantly above that of any existing SPS. With smaller slit emission apertures, it is possible to suppress H- stripping after extraction. These conditions are promising for reliable production of higher emission current density up to ~40-50 mA/cm2 with corresponding decrease of SPS dimensions and cost.