Initial measurement of ultrafast charge exchange recombination spectroscopy on the EAST tokamak

Ultrafast charge exchange recombination spectroscopy (UF-CXRS) has been developed on the EAST tokamak (Yingying Li et al 2019 Fusion Eng. Des. 146 522) to measure fast evolutions of ion temperature and toroidal velocity. Here, we report the preliminary diagnostic measurements after relative sensitivity calibration. The measurement results show a much higher temporal resolution compared with conventional CXRS, benefiting from the usage of a prism-coupled, high-dispersion volume-phase holographic transmission grating and a high quantum efficiency, high-gain detector array. Utilizing the UF-CXRS diagnostic, the fast evolutions of the ion temperature and rotation velocity during a set of high-frequency small-amplitude edge-localized modes (ELMs) are obtained on the EAST tokamak, which are then compared with the case of large-amplitude ELMs.