Development of AXUV diagnostic system on the EXL-50U spherical torus

An absolute extreme ultraviolet (AXUV) photodiode array system has been developed and successfully tested on the EXL-50U spherical torus for radiated power measurement. Double-layer shielding combined with single-point series grounding successfully suppresses electromagnetic interference and oscillation in multi-channel detection circuit. To enhance mechanical precision and thermal stability, a monolithic 3D-printed camera housing integrated with cooling pipes and support structures was fabricated. A nanotube-carbon absorber was deposited on the inner surface to suppress stray light. A foil bolometer was co-installed with the AXUV array at the same port for cross-comparison. In general, the two systems show consistent measurements of the radiated power, while the AXUV system exhibits relatively low amplitudes due to its narrow spectral response. They provide an effective tool for estimating the radiated power and analysis of MHD instabilities and sawtooth oscillations. Radiated power under typical discharge conditions has been estimated using a weighted summation approach.