R&D updates from the DIII-D neutral beam Radiofrequency Ion Source Experiment (RISE)

RF-driven ion sources for tokamak neutral beam injection (NBI) have lower costs and maintenance requirements than traditional filament-driven sources. However, optimizing power transfer in RF-driven sources requires understanding a new set of systems on the source, including an impedance-matching network and an RF antenna. We present updates and results from the DIII-D National Fusion Facility's neutral beam Radiofrequency Ion Source Experiment (RISE), an argon-based table-top ion source capable of producing similar plasma densities and temperatures as a full-scale source and equipped with a Langmuir probe and spectrometer. An in-house collisional radiative model calculated plasma parameters consistent with Langmuir analysis, and preliminary results show electron and ion number density to depend on all three of our control inputs: chamber pressure, RF power supply driving frequency, and RF power supply voltage. A simple circuit transformer model that also accounts for plasma skin depth demonstrates an ability to describe these dependencies. These experimental and model results provide guidance for the development of a full-scale RF-driven ion source for the DIII-D neutral beam injectors.