Observation of high impurity ion temperatures in ECW/EBW sustained plasmas on LATE

Abstract

Carbon and oxygen impurity line emissions from LATE spherical tokamak plasmas were measured using a visible spectrometer. A plasma current of approximately 10 kA was sustained by ECW/EBW with a frequency of 5 GHz and a power of 130 kW. Emissions of CIII (464.7 nm), OV (278.1 nm) and CV (227.1 nm) were observed, and the ion temperatures calculated from the Doppler broadening reached 40 ± 8, 110 ± 10 and 130 ± 30 eV, respectively. The high ion temperatures cannot be explained by collisional heating from electrons, suggesting that the ions are directly heated via unidentified mechanisms.