Ion source studies for application to the DIII-D neutral beam system.

Neutral beam systems for plasma heating in fusion devices require a source of plasma from which to extract ions. These ions are then accelerated by a series of grids at high potentials before they pass through a neutralizer and are recombined through collisions with a gas and injected into a device to impart their energy into the plasma. The DIII-D facility currently uses neutral beam systems with ions supplied by a tungsten filament driven plasma. As in incandescent lightbulbs, these filaments have a very finite lifespan and they produce a stable plasma with a limited range of parameters. It is for this reason that this study investigates alternative plasma sources for use in neutral beams. In a tabletop scale apparatus the plasma produced by a tungsten filament source is characterized via Langmuir probe and spectroscopy. This data is used as a foundation to design an RF driven plasma source outputting a similarly characterized plasma which should provide a decreased failure rate, an increased possible parameter space and other engineering improvements. Additionally an alternative filament material, lanthanum hexaboride, is investigated with respect to its fabrication considerations and failure modes as compared to the tungsten and RF driven sources.

Work supported by US DoE under the Science Undergraduate Laboratory Internship (SULI) program and under DE-FC02-04ER54698.