Development and Testing of LUPIN: A High-Density RF Ion Source for Enhanced NBI on DIII-D

The Large, Uniform Plasma for Ionizing Neutrals (LUPIN) is an RF inductively coupled plasma (ICP) ion source for the DIII-D Neutral Beam Injection (NBI) system. LUPIN drives 20 kW RF power at 2 MHz in a 20 cm long, 10 cm radius quartz vessel to create hydrogen plasmas with electron densities of 10¹⁸ m^-3 over 10 s, yielding an extracted ion current of 85 A which matches power density requirements for a full-scale ion source. Vacuum conductance and gas flow calculations predict a maximum neutral flow rate of 7.5 Torr L/s at 2.5 Pa. Designs and thermomechanical simulations have been developed for an internal Faraday shield to mitigate heat flux and ion sputtering on the dielectric vessel. LUPIN will investigate ion source physics, including neutral gas dynamics, plasma density uniformity, interactions with magnetic cusp fields, Faraday shielding, and power coupling to novel RF antenna designs. Development of an RF ICP ion source for DIII-D will help increase both power and reliability currently limited by electrical failures of existing arc-and-filament ion sources at higher power. Results of experimental investigations on LUPIN will guide the design of a full-scale prototype for DIII-D integration.