Installation of Lyman Alpha Pinhole Cameras on DIII-D and Initial Measurements of Main Chamber Neutrals*

A one dimensional hydrogen Lyman-alpha (Ly-$\alpha$) edge diagnostic was recently installed and commissioned on the DIII-D tokamak. The system consists of two cameras, one viewing the low field and the other the high field side of the tokamak, each providing a toroidal fan of twenty lines of sight covering the scrape off layer and pedestal region below the midplane. Each camera has an aperture, Ly-$\alpha$ reflective mirror, Ly-$\alpha$ transmission filter, and AXUV detector array providing a radial resolution of 8 mm with a total coverage of 214 mm. The system was aligned on the bench and its positioning verified in vessel using a coordinate measuring machine, accurately matching the design parameters without the need of in vessel laser alignment. The Ly-$\alpha$ camera began taking data early in the 2019 DIII-D experiment campaign, providing an improved characterization of neutrals by measuring the Ly-$\alpha$ brightness. Using standard rate coefficients and electron density and temperature profiles, brightness profiles can be inverted to obtain Ly-$\alpha$ emissivity profiles, which can yield atomic deuterium and ionization rate profiles. Installation, alignment, initial data analysis, and preliminary results will be discussed.