Study on the Mechanical Instability of MICE Coupling Magnets

The superconducting coupling solenoid magnet is one of the key equipment in the Muon Ionization Cooling Experiment (MICE). The coil has an inner radius of 750 mm, length of 281 mm and thickness of 104 mm at room temperature. The peak induction in the coil is about 7.3 T with a full current of 210 A. The mechanical disturbances which might cause the instability of the impregnated superconducting magnet involve the frictional motion between conductors and the cracking of impregnated materials. In this paper, the mechanical instability of the superconducting coupling magnet was studied. This paper presents the numerical calculation results of the minimum quench energy (MQE) of the coupling magnet, as well as the dissipated strain energy in the stress concentration region when the epoxy cracks and the frictional energy caused by “stick-slip” of the conductor based on the bending theory of beam happens. Slip planes are used in the coupling coil and the frictional energy due to “slow slip” at the interface of the slip planes was also investigated. The dissipated energy was compared with MQE, and the results show that the cracking of epoxy resin in the region of shear stress concentration is the main factor for premature quench of the coil.