Inductively Coupled Ion Source Studies for Application to the DIII-D Neutral Beam System.

Neutral beam injection (NBI) is a tool primarily used for heating and current drive in a tokamak. NBI requires a source of ions that are then accelerated and neutralized to produce the beam that is injected into the plasma. At DIII-D, the current plasma source utilized is the Common Long Pulse Source. This is an arc discharge plasma source that, when operated at higher powers and ion densities, is prone to failures of plate-to-plate insulating gaskets and tungsten filaments. As part of the DIII-D five year plan, available neutral beam power will be increased, but reliability must also remain high. For this reason, the prospect of an inductively coupled plasma source is being investigated using a small tabletop sized device. This new device operates with 1 kilowatt of injected power. Axial ion density and electron temperature measurements are taken as well as radial measurements at key locations. Engineering considerations such as antenna coupling and thermal properties of chosen materials are also investigated to inform future engineering models for a possible future full-sized ion source.