Construction and Commissioning Status of the Superconducting Magnets for COMET Phase-I Experiment at J-PARC

A new muon beamline is under construction for the COMET Phase-I experiment at J-PARC. The experiment requires a negative muon beam with the world-highest intensity to search for muon-electron conversion processes. The muon beamline consists of a series of superconducting solenoid magnets to generate muons by 8 GeV pulsed proton beam from MR of J-PARC, to transport muons to the detectors. A radiation-tolerant superconducting solenoid, the Pion Capture Solenoid, is developed to generate a high magnetic field on a production target to trap pions and muons efficiently. A long curved solenoid, the Muon Transport Solenoid, with correction dipole coils is utilized not only to transport muons but also to select low-momentum muons against unnecessary particles. A large detector solenoid is planned to connect to the muon beamline with a gradually reduced solenoidal field tuned by additional small solenoids. This paper reports the status of the construction and commissioning of the superconducting magnet system.