Implementation of a Thomson Scattering Diagnostic on Pegasus*

The multipoint Thomson scattering system on \textsc{Pegasus} will diagnose point-source helicity-driven plasmas, including dominant particle transport mechanisms and sources of helicity dissipation. Helicity-driven plasmas are estimated to have $\left\langle {T_e } \right\rangle \sim 50$ eV for stochastic field line confinement and $\sim $200 eV for standard Ohmic closed flux surface confinement. To accurately characterize these regimes, a novel system is being designed, installed, and calibrated. A Nd:YAG laser is frequency doubled to provide a 9 ns, 2 J pulse radially across the plasma. Remote alignment of steering mirrors can be performed between shots along the 6 m length of the external laser beam-line. The 532 nm laser beam is focused to a $\le $ 3 mm diameter beam within the plasma. Plasma background measurements are made simultaneously with data collection. A custom optical system collects signal from $>$70{\%} of the plasma cross-section with 1.4 cm radial resolution. Optical fibers relay light to a high-efficiency volume phase holographic grating spectrometer coupled to a high quantum efficiency image intensified CCD camera, gated at $\ge $ 2 ns. Signal levels for plasmas with $n_e >10^{18}$ m$^{-3}$ and 10 eV $< T_e <$ 1 keV are predicted at 10$^{3}$ photons/pulse before background subtraction.