Construction Status of the Superconducting Magnet System for the COMET Experiment

The COMET experiment, which is being prepared at the Japan Proton Accelerator Research Complex (J-PARC), aims to explore the rare decay phenomenon of muons. This phenomenon is not allowed in the Standard Model of elementary particles but is expected to occur due to new physics beyond the Standard Model. In the COMET experiment, superconducting magnets are used throughout the muon beamline. The Pion Capture Solenoid concentrates the pions generated by the injection of proton beams into the target. Since this magnet surrounds the target, it is designed to operate in a high radiation environment. The Muon Transport Solenoid guides the muons generated by the decay of pions. This magnet maximizes the muon yield and reduces the other background particles. The Detector Solenoid acts as a spectrometer of the electrons generated by the decay of muons. These low-temperature superconducting magnets are now being developed and constructed. The current lead box is also constructed to supply high currents to the magnets. It provides a thermal gradient from the room-temperature part of the power supply to the low-temperature part of the coil. It is designed to provide a large thermal gradient over a short distance using high-temperature superconductors. Using the current lead box, all magnets, including the high-temperature superconducting leads, are cooled by conduction cooling. In this paper, the construction status of the COMET superconducting magnet system is reported.