Magnetic Field Measurement of Superconducting Transport Solenoid for COMET

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Abstract
The COMET experiment, currently under construction at J-PARC, aims to explore the process of muon-to-electron conversion in a nucleus. This phenomenon, known as charged-lepton flavor violation, is an elementary process beyond the Standard Model. The muon beam is produced from pion decays generated by bombarding a proton beam on a target and corrected and transported from the production target to a stopping target in a detector with superconducting solenoid magnets. Their momentum is selected by a curved solenoid field (3 T) and dipole field (0.05 T) in the Muon Transport Solenoid (MTS), which has a diameter of 468 mm and a curvature radius of 3 m with a bending angle of 90 degrees. We energized the solenoid up to 105 A and the dipole to $\pm$ 175 A in the summer of 2022. Although the solenoid was operated at a half of its design value (210 A) due to the limitation of the support structure, this commissioning provided a sufficient current for the subsequent engineering beam operation (Phase- $\alpha$ ) to be conducted successfully. We performed in-situ magnetic measurements of the curved solenoid with Hall probes and compared them to 3D calculations. The paper describes the scheme and results of the magnetic filed measurement in MTS.
Funding Information
  • U.S.-Japan Science and Technology Cooperation

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