In Situ Measurements of Neutral Beam Energy Components and Divergence with Doppler Shift Spectroscopy on C-2W

In TAE Technologies’ current experimental device C-2W (also known as “Norman”), steady-state beam-driven field reversed configuration (FRC) plasmas are sustained by neutral beam injection (NBI), edge biasing, and a robust real-time plasma control system [1]. C-2W's ensemble of neutral beams includes four static energy 15 keV H/D beams, four tunable energy 15-40 keV H/D beams, and one 40 keV diagnostic beam. On C-2W, the static and tunable energy beams provide heating, current drive, fueling, and added stability to the plasma. Optimizing important beam parameters such as beam divergence and energy composition is necessary to reduce power losses during beam injection and prevent damage to beamline components. Doppler Shift Spectroscopy (DSS) is a nonintrusive method of measuring the angular divergence and energy component fractions of the injected beam that can be used to supplement and contextualize traditional calorimetric measurements of beam divergence and injected power. Although previous DSS measurements of beam divergence and energy composition were carried out prior to the installation of the beams on C-2W, an in situ DSS diagnostic would allow for continuous monitoring and optimization of beam parameters after installation, with significant implications for device performance. Here, we report on preliminary in situ beam divergence and energy composition results obtained via DSS on C-2W.

1. H. Gota et al., Nucl. Fusion 61,106039 (2021)