Lawrence Berkeley National Laboratory

The MICE coupling coil is fabricated from Nb-Ti, which has high quench propagation velocities within the coil in all directions compared to coils fabricated with other superconductors such as niobium tin. The time for the MICE coupling coil to become fully normal through normal region propagation in the coil is shorter than the time needed for a safe quench (as defined by a hot-spot temperature that is less than 300 K). A MICE coupling coil quench was simulated using a code written at the Institute of Cryogenics and Superconductive Technology (ICST) at the Harbin Institute of Technology (HIT). This code simulates quench back from the mandrel as well as normal region propagation within the coil. The simulations included sub-division of the coil. Each sub-division has a back to back diodes and resistor across the coil. Current flows in the resistor when there is enough voltage across the coil to cause current to flow through the diodes in the forward direction. The effects of the number of coil sub-divisions and the value of the resistor across the sub-division on the quench were calculated with and without quench back. Sub-division of the coupling coil reduces the peak voltage to ground, the layer-to-layer voltage and the magnet hot-spot temperature. Quench back reduces the magnet hot-spot temperature, but the peak voltage to ground and layer-to-layer voltage are increased, because the magnet quenches faster. The resistance across the coil sub-division affects both the hot-spot temperature and the peak voltage to ground.