Diagnostic Neutral Beam and Charge Exchange Recombination Spectroscopy Diagnostic for Studying Non-Solenoidal Tokamak Plasma Startup in Pegasus-III

Localized measurements facilitated by a diagnostic neutral beam are essential for characterization of tokamak plasmas produced by non-solenoidal startup methods. Beam-based diagnostics provide constraints on kinetic equilibrium reconstructions, enable the measurement of impurity densities, and allow for indirect measurement of current density profiles. A 60–80 kV, ≤ 4A, H⁰ beam is being developed for evaluating plasmas in the Pegasus-III spherical tokamak. Ion heating from magnetic reconnection during helicity injection (HI) contributes significant pressure to the equilibrium, and edge biasing induces flows that can affect transport. Understanding the impact of reconnection heating and flows on HI plasmas is needed to inform the performance scaling and optimization of the technique. A new charge-exchange recombination spectroscopy diagnostic will measure ion temperature and flow velocity profiles to explore the impact of anomalous ion heating on power balance, impurity transport, and equilibrium parameters in HI plasmas. Initial tests of the uninsulated high-voltage beam power supply have produced 5 kV pulses with less than 0.2% RMS ripple.