Numerical analysis of the coupling loss induced quench protection for a 1.5 T whole-body MgB2 MRI magnet

Abstract

Numerical simulations of a quench protection system using coupling loss induced quench (CLIQ) were performed on a conduction-cooled persistent mode ten coil 1.5 T MRI main magnet design with MgB2 wire. The temperature rise and currents through the coils were simulated in MATLAB to solve for the heat equation and the circuit equations associated with CLIQ. Many different parameters of the system can be varied to determine their impact on the quench protection performance: the number of CLIQ units, the capacitance and initial voltage of the CLIQ unit, the number of subdivisions per coil, and the wire’s twist pitch. While keeping the total stored energy in the CLIQ system constant, simulations were performed on varying the number of CLIQ units with a 10 mF capacitor and varying the CLIQ capacitor with 2 CLIQ units present. As the number of CLIQ units increased, the peak temperature and the charging voltage decreased, but the voltage across the coil increased. As the CLIQ unit capacitance increased, the peak temperature increased but the charging voltage and voltage across the coil decreased. The optimal twist of the wire increased as the CLIQ capacitance increased. From these simulations, a possible optimal design was obtained where each coil is divided into two subsections consisting of two CLIQ units, each with a capacitance of 15 mF and a 1.5 kV initial voltage and a wire with a twist pitch of 5.0 cm. Using these parameters, the simulated peak temperature was found to be 178 K, which is comparable to results from simulations on the same magnet design with the same wire using an external protection heater.