Quench protection design of a 9.4 T whole-body MRI superconducting magnet

A 9.4 T MRI superconducting magnet with a 800mm clear warm bore in diameter is designed and fabricated for bioscience research. The superconducting magnet consisting of five coaxial solenoid coils is fabricated with NbTi Wire-in-Channel (WIC) conductor where the ratios of copper to non-copper are from 5 to 10. The four compensation solenoid coils are with rectangular NbTi/Cu strand wires. The magnet will be operated in a relative low nominal current of 224.5A with a high level of stored energy, about 138MJ. A protection method with the cold diodes and resistors in series across the subdivided sections and active trigger heater to accelerate quench is adopted to avoid the damage of the magnet. In the paper, the quench simulation results of currents, voltages and hot-spot temperatures based on the protection scheme are analyzed in details.