Design and Analysis of the Quench Protection System for the MICE Coupling Coils

Two identical MICE coupling coils have the largest diameter and stored energy, at 13 MJ each, of all coils in the Muon Ionization Cooling Experiment (MICE). The coils have an inner diameter of 1.5 m and radial and axial builds of 102.5 and 285 mm, respectively. The coils contain approximately 15 936 turns and are wound with a single rectangular NbTi strand with a copper-to-superconductor ratio of 3.9:1. Each coil is conduction cooled using three cryocoolers, which maintain an operating temperature at about 4.5 K. Each coil is powered through a pair of series-connected copper and 500 A HTS current leads. The quench protection analyses described here show that subdividing the winding into four or more, cold-diode-protected subsections maintain hot spot temperatures below 150 K and internal winding voltages below 300 V. The superconducting subdivision interconnect loops are protected by heat sinking them to the aluminum winding housing. Stabilizing the coil leads from the winding to HTS current leads minimizes the likelihood of lead quench. The first of three coils will be tested at Fermi Lab and the final two coils will be installed in MICE at Rutherford Laboratory.