LAUSR

High-energy-resolution X-ray spectroscopy using X-ray microcalorimeters has been widely adopted for high-precision experiments on fundamental science. The technical difficulties come from its use at low temperatures and its high sensitivity to the external environment, though many countermeasures have been proposed through the experience of space applications. The limit of the number of pixels of the semiconductor-type X-ray microcalorimeters can be solved by using the transition-edge sensor (TES) superconducting detector. Recently, a study of the strong nuclear force via high-energy-resolution X-ray spectroscopy of kaonic atoms using TES at the J-PARC accelerator facility was successfully performed by the HEATES collaboration. Furthermore, muonic-atom spectroscopy using TES has been demonstrated at the J-PARC muon facility, and a physical experiment to test the electromagnetic force under a strong electric field is ready for commissioning. Material diagnostics at a hard X-ray synchrotron facility have been tested at SPring-8 and resulted in a successful operation for the first time. Other than X-rays, TES has been used as a mass spectrometer for neutral molecules in a cryogenic electrostatic ion ring. The entire design of the experiment is carefully considered to meet the science-specific requirement. We will summarize the latest and future applications of the microcalorimeter and present key technologies, such as digital electronics, data acquisition software, aperture, collimator, mechanical, and electrical interface. Our results will be helpful for other users to design new experiments for fundamental science.