Ultraviolet Spectroscopy of Near-Neutral Tungsten Emission for Improved Re-deposition Measurements

To investigate tungsten (W) impurity erosion and re-deposition, a high-resolution UV spectrometer with improved throughput has been installed on the Compact Toroidal Hybrid (CTH) experiment. Time resolved erosion rates from plasma facing materials can be quantified from spectroscopic measurements of emission intensity combined with S/XB coefficients provided by collisional-radiative models. Accurately estimating re-deposition requires spectroscopic observation of several near-neutral charge states, which for W emit at ultraviolet wavelengths. As such, a 1.33-meter spectrometer with a high-resolution diffraction grating, UV optimized CCD camera, and improved optical throughput has been developed, providing ~4 pm resolution down to 200 nm. Tungsten emission is produced by plasma interaction with a W sample at end of a translatable probe. At the W sample surface, a single tip, swept Langmuir probe measures the plasma electron temperature and density. W III emission produced in CTH will be measured with improved sensitivity and presented to assess the feasibility of improved W redeposition measurements.