Develop advanced calibration techniques for the LLAMA diagnostic to measure fueling properties of fusion plasmas on DIII-D

Responsivity measurements of new and degraded absolute extreme ultraviolet (AXUV) photodiodes are presented with the aim to improve the calibration of DIII-D's Lyman-Alpha Measurement Apparatus (LLAMA). The LLAMA diagnostic measures Lyman-alpha (Ly-α) emission to infer the density of atomic deuterium neutrals and quantify the particle source at the plasma edge [1,2]. Over campaigns, the responsivity of the LLAMA AXUV detectors are degraded by neutron, gamma, and X-ray fluxes. To assess degradation, the AXUV photodiode arrays are calibrated using a commercially available Krypton plasma source with an emission line at 123.6 nm, providing a good proxy for the detector response at Ly-α (121.6 nm). The measurement is set up in a vacuum chamber to avoid the absorption of vacuum UV light. The setup also includes a narrow band interference filter optimized for 124 nm, therefore the detector sensitivity is tested only for Ly-α relevant wavelengths. Each channel on the photodiode arrays is analyzed individually to isolate and identify specific degradation. Calibration factors are determined from this data and used to improve the accuracy of LLAMA measurements from recent DIII-D experimental campaigns.