Development of a Multichannel Spectrometer for the Thomson Scattering Diagnostic on Pegasus

To explore electron transport in helicity-driven discharges and investigate edge stability, a multi-point Thomson scattering diagnostic is being developed. Red-shifted scattered light from the Nd:YAG laser, 532-632 nm, is imaged using a custom lens coupled to fiber optic cables capable of imaging 1.4 cm along the length of the laser beam. Initially 1 spectrometer, containing up to 8 radial spatial points will be available for detection, with an upgrade to 3 spectrometers planned in the near future. New high efficiency volume phase holographic gratings, with $>$ 75{\%} transmission, allow for a simplified spectrometer design. This provides high optical throughput and readily couples to new high quantum efficiency ($\sim $45{\%}) image intensified CCD cameras for multichannel design. These cameras can be gated to as low as 2 ns. The two gratings fabricated for this system (2971 lines/mm and 2072 lines/mm) cover the design temperature range of 10 eV to 1 keV. Completing the spectrometer are high quality lenses with focal lengths of 130 cm on the collimating lens and 85 cm on the exit lens. This design has a spectral range compatible with the blue shift from a conventional ruby laser and allows for a compact, simplified system.