Development of the High-Throughput Transmission Grating Spectrograph for the TV Thomson Scattering Diagnostics on EAST Tokamak

摘要

High-throughput spectrograph employing the transmission grating was developed in order to apply to the laser Thomson scattering (LTS) system for EAST tokamak. Photographic lens 1.4 in F-number (F/#) for a collimator optics can collect all photons from the input optical fiber 0.3 in numerical aperture located on the optical axis. An F/1.2 camera optics enabled the complete collection over the visible diffracted component. We recognized that the optical arrangement using transmission grating gave rise to multiple reflection ghost (MRG) spectra, and formulated the principle of MRG. Then, the possible countermeasures against MRG were implemented. In order to reject the stray light at the laser wavelength of 532 nm, holographic notch filter was installed inside the spectrograph. The dispersion of the spectrograph was deduced and compared with that obtained from the He I line spectra measured for the helium glow discharge cleaning plasmas of the EAST tokamak.