Development of Spatial Heterodyne Spectroscopy for ion temperature and rotation measurements during transient events in DIII-D

To validate models that describe the transition from the low to the high confinement mode in tokamaks, as well as the evolution of edge localized modes [Cathey et al (2020)] [Snyder et al (2002)], high speed measurements of ion temperature/rotation and plasma current profiles are of particular interest. At the DIII-D tokamak, the Spatial Heterodyne Spectroscopy (SHS) technique has been applied successfully to investigate fast changes of the edge-localized magnetic field which contains information on the current profiles. Here, we present an upgraded SHS system with replaced optics, a new low-noise CCD detector, and a modified optical filter, which can be additionally used to study ion temperatures and plasma rotation by observing charge-exchange emission of C⁶⁺ ions. Thanks to the interferometric method utilized, both the required high spectral resolution (0.1 nm) and high photon throughput (etendue of 0.64 mm²sr) can be achieved, allowing for high quality measurements with sub-ms time resolution. The modified device will be optimized for 1-10 kHz low-uncertainty measurements for comparison with previous SHS edge current analysis, as well as with the upcoming installation of 4 new beam-emission spectrometers designed to improve on the previous edge-current data.