Experimental Studies on low temperature Helium plasmas for investigations of Arc chamber failure on DIII-D Neutral Beam System*

The Neutral Beam Injection system of the DIII-D tokamak consists of eight ion sources based on the US Common Long Pulse Source (CLPS), with a total output power of 20 MW. During helium operation, desired for research regarding the ITER pre-nuclear phase, it has been observed that the ion source arc chamber performance steadily deteriorates. Also, the device eventually fails due to electrical breakdown in the insulation material that electrically separates the energized arc and filament plates from the body of the ion source. To address the cause of this failure, a table-top ion source analog with similar parameters was constructed. The Miniature Arc Chamber Experiment (MACE) is equipped with Langmuir probes, spectroscopes, thermocouples and infrared imaging. This work presents an overview of the MACE system, a comprehensive characterization of the plasma parameters within the operating space of the ion source and results of recent studies on alternate insulator designs.