Upgraded main ion charge exchange recombination spectroscopy on the C-2W field reversed configuration (FRC) plasma

Abstract

A prototype main-ion CHarge Exchange Recombination Spectroscopy (mCHERS) diagnostic is providing measurements of the main-ion (hydrogen or deuterium) temperature and velocity in the C-2W field reversed configuration plasma using charge exchange Balmer-alpha emission at five different radial locations with 500 Hz frequency and a per-pixel velocity resolution of 15 km/s. Measurement along the entire plasma radius of C-2W is enabled by a diagnostic neutral beam (DNB) that passes through the center of plasma, unlike the larger diameter heating neutral beams that have impact parameters of 20 cm. DNB provides high time resolution via beam modulation and spatial resolution via its small cross section. The goals of the current mCHERS upgrade are to double the number of spatial channels, improve the per-pixel velocity resolution by three times, and increase the measurement frequency to match the maximum modulation frequency of the diagnostic neutral beam (∼10 kHz). To accomplish these goals, a new astigmatism-free Isoplane spectrometer has been commissioned. Progress and results from the newly upgraded mCHERS system are detailed.