Design of combined system of helium charge exchange spectroscopy and hydrogen beam emission spectroscopy in VEST

Abstract A 468.6-nm HeII charge exchange spectroscopy (CES) system combined with 656.3-nm H beam emission spectroscopy (BES) system is designed to measure helium impurity density as well as toroidal rotation and ion temperature in Versatile Experiment Spherical Torus (VEST). A dichroic beam splitter is used to measure CES and BES spectra simultaneously with sharing the same observation and transmission components which include the line of sight, lenses, and fiber bundles. In the combined system, we employ the transmission gratings with high diffraction efficiency for CES and BES in order to obtain high throughput and spectral resolution. Spectra simulation results show that the signal to noise ratio (SNR) of this diagnostic system is no less than 10 with the injection of a diagnostic neutral hydrogen (beam energy and current are 40 keV and 0.4 A, respectively).