Evaluation of the resistance to quantum efficiency degradation of cesium iodide-coated microchannel plates for extreme ultraviolet detection

In this study, we experimentally evaluated the quantum efficiency (QE) enhancement and storage stability of cesium iodide (CsI) coated microchannel plates (MCPs), which are widely used as high-sensitivity detectors for extreme ultraviolet (EUV) observations. A 42 mm diameter MCP was partially coated with CsI and irradiated with a common EUV light source to directly compare the relative QE and gain between the CsI-coated and uncoated (bare) regions. To simulate pre-launch storage conditions, we also investigated QE variations after storing the MCP in low-vacuum (10-1000 Pa) and dry nitrogen environments for up to 30 days. The results demonstrated that the CsI coating yielded an increase by a factor of 100 in QE at wavelengths above 100 nm, with no significant degradation observed during vacuum-sealed storage. Furthermore, the observed reduction in gain over time could be compensated by fine-tuning the applied high voltage, posing no operational issue. These findings demonstrate that CsI-coated MCPs maintain high QE during extended storage and are, therefore, suitable for future small-scale space missions.