The DIII-D National Fusion Facility aims to increase the auxiliary heating power for the tokamak by upgrading the neutral beam injection (NBI) system. In collaboration with North Carolina State University, the conventional arc-and-filament NBI ion sources will be converted to inductively coupled plasma (ICP) sources that utilize radiofrequency (RF) coupling to maximize reliability for high-power operation. In support of this initiative, a full-scale test device, Superior Radiofrequency Ion Source Experiment (SupRISE,) is currently under construction at the DIII-D facility.

In preparation for the construction of a full-scale prototype that can be installed on the DIII-D NBI system, experiments on SupRISE have been conducted to determine the optimal RF frequency for high-power coupling, the Faraday shield slit configuration, and the ICP chamber length. SupRISE is comprised of an approximately 30 × 70 cm quartz dielectric vessel with an internal Faraday shield enclosed in a secondary vacuum chamber to ensure structural stability of the dielectric. Actively cooled front and back plates are designed to reduce the thermal stresses on the plasma-facing components and mate with the existing accelerator used by the NBI system at DIII-D.

A total of 50 kW of RF power will be coupled to the plasma through the quartz over a variable frequency range of 4 to 8 MHz to sustain a plasma density of ~1018 m for a 10-s ON, 210-s OFF duty cycle. Various modeling efforts have been employed to simulate the thermal and stress profiles over the primary components of the SupRISE device, as well as the inductance behavior of the RF antenna.

These simulation results and the final design for SupRISE are presented. An additional reduced-scale predecessor ICP source (called RISE) has been used to develop a predictive match model that will be applied to frequency optimization studies on SupRISE. The outcomes of this research and complementary efforts at North Carolina State University are essential for the incorporation of ICP NBI positive ion sources at the DIII-D facility.