Development of a Radiation Resistant Superconducting Solenoid Magnet for mu-e Conversion Experiments

A radiation-resistant superconducting magnet is mandatory to generate intense negative-charged muon beams in the next-generation mu-e conversion experiments, COMET at J-PARC and Mu2e at FNAL. Expected neutron fluence on the superconducting coils in the projects reaches 10²¹ n/m². Therefore, irradiation effects in superconducting magnet material are considered in a design of the superconducting magnet system. The pion capture solenoid magnet is designed to utilize aluminum-stabilized superconducting cable to reduce the nuclear heating by radiation from the pion production target enclosed in the magnet. To achieve higher magnetic field on the target, the coil has multiple layers of thick conductor, and need pure aluminum strips in between the coil layers for heat removal. Prototyping of the coil with aluminum stabilized conductor, heat removal strips, and radiation-hard insulator is performed to check the feasibility of the coil winding and basic properties. The conceptual design of the COMET magnet and the prototype coil are reported.