Conceptual Design of the Capture Superconducting Solenoid for Experimental Muon Source

The experimental muon source (EMuS) project foreseen for muon science and neutrino physics is utilizing a superconducting solenoid for muon and pion capture, and is proposed at the China Spallation Neutron Source (CSNS). For the optimal particles collection efficiencies, an adiabatic magnetic field from 5 to 2.2 T along the central axis of the solenoid is generated by the solenoid. The superconducting solenoid is composed of four windings and an iron yoke. The iron yoke is arranged for flux returning and magnetic field shielding. Two conductor options for the windings, the aluminum stabilized NbTi Rutherford cable and the NbTi monolith wire are compared from the mechanical structure and radiation performance. The results of the mechanical analysis from ANSYS show that the excitation stress is suitable. But the results of the radiation analysis from FLUKA Monte-Carlo show that the recovery of the Residual Resistivity Ratios (RRRs) is necessary for the stabilizers of the superconductor. The recovery cycle of the aluminum stabilizer and the monolith wire solenoids are three months and one year, respectively. However, the RRR of copper for the monolith wire solenoid will be less than 50, after 12 years continuous running, which is shorter than the EMuS lifetime of 30 years. Therefore, the aluminum stabilized NbTi Rutherford cables are chosen to fabricate the windings.