Cross campaign database comparison of the absolute calibration of the LLAMA diagnostic on DIII-D

High temperature plasma diagnostics in tokamak reactors face several deteriorating agents, such as neutron fluxes, throughout operation campaigns. This can lead to signal degradation, which in turn affects the accuracy and precision of the measurements. The LLAMA (Lyman-α Measurement Apparatus) diagnostic at DIII-D measures the Lyman-α brightness across the plasma boundary to infer neutral deuterium density and ionization rate profiles. LLAMA uses absolute extreme ultraviolet (AXUV) photodiode arrays, which are prone to responsivity degradation when exposed to ultraviolet radiation and neutrons. In order to account for this degradation, LLAMA undergoes an absolute calibration both before and after a run campaign to maintain accuracy. For a better estimation of the calibration factor throughout the campaign, a cross campaign database of plasma parameters (electron density and temperature) and LLAMA raw signals has been assembled and correlated. The database enables tracking of AXUV detector degradation by analyzing LLAMA signal changes across similar plasma discharge conditions. Relative changes of the calibration factor can be studied by applying this method after every DIII-D experimental campaign.