Concept design of ultrafast charge exchange recombination spectroscopy on EAST tokamak

An ultrafast charge exchange recombination spectroscopy (CXRS) has been constructing for the measurement of the plasma ion temperature and rotation velocity fluctuations on EAST tokamak. The system shares the collection optics with the existing BES. The designed spectrometer operates at the spectral range of 527.5 ± 5 nm, then the emission lines from C VI at 529.059 nm and Ne X at 524.897 nm can be observed simultaneously. The collimating and focusing lenses are specially designed to realize the maximized transmission (˜95% for each lenses) and the optimized image quality. One customized transmission grating sandwiched by two identical BK7 prisms from Wasatch Photonics is used. The clear size of the grating is ˜205 × 100 mm and the grating has very high diffraction efficiency of > 80% for unpolarized light. The Simulation of Spectra code is used to guide the design and evaluate the diagnostic performance. In this paper, an overview of the status and performance of the ultrafast CXRS system will be presented.