Evolution of bulk ion temperature and velocity distributions in the C-2W FRC plasma device using a high-throughput grism spectrometer

The C-2W experiment at TAE Technologies is a cutting-edge fusion device that generates beam-driven field-reversed configuration (FRC) plasmas within a magnetic mirror environment [1]. Accurate measurements of key parameters aimed at elucidating plasma dynamics and guiding machine optimization requires advanced diagnostic tools. This study presents initial results obtained using a novel high-throughput grism spectrometer designed to extract high-fidelity temperature and velocity profiles of bulk ions in C-2W plasmas. The diagnostic technique utilizes active charge-exchange recombination spectroscopy, employing a 40 keV hydrogen Diagnostic Neutral Beam (DNB) for localized measurements. The newly developed spectrometer incorporates a linear multi-fiber array, fast collimating and focusing lenses, a volume phase holographic transmission grating-based grism (2800 lines/mm centered at 656 nm), a fast-readout CMOS camera, and an automated slit mechanism for precise control of incoming light and excellent spectral resolution. The versatility of the system permits operation under various DNB modulation schemes and variable data-acquisition speeds of up to 10 kHz, enabling comprehensive investigations into the rapid and transient heating and rotational dynamics of bulk ions in C-2W plasmas. This work outlines the experimental technique, data analysis methodology, and discussion of obtained results from a recent experimental campaign.

[1] H. Gota, et al., Nuclear Fusion 61, 106039 (2021)