Numerical Simulation of Quench of MgB2 Superconducting Magnet in 0.3 T MRI System

In this article, the quench characteristics of the magnesium diboride (MgB₂) superconducting magnet in a magnetic resonance imaging system are studied. The magnet generates a central magnetic field of 0.3 T, operates at 20 K with a current of 90 A, and stores an energy of 26.25 kJ. A coupled electromagnetic-thermal multiphysics quench model for the MgB₂ magnet was established based on the finite difference method. To accurately represent magnet quench behavior, a current-sharing model applicable for low n-values was employed. Computational efficiency was enhanced by utilizing a modified integral method for solving the magnetic field equations. To explore the self-protection characteristics of a magnet operating in persistent current mode, the influence of copper (Cu) content and Cu purity grade within the MgB₂ wire on the quench characteristics of the magnet was studied. The results reveal that both the peak temperature and peak voltage during a quench event decrease with increasing Cu content within the MgB₂ wire. Crucially, self-protection capability was achieved for this magnet when the Cu content exceeded a specific threshold. At the same time, increasing the purity of the Cu stabilizer was found to elevate the peak quench temperature and reduce the peak voltage. This occurs because high-purity Cu tends to confine the quench process within a smaller spatial region. Furthermore, a quench protection scheme based on a dump resistor was specifically designed for the MgB₂ superconducting magnet operating in driven mode. Simulation results confirm that this protection scheme effectively prevents damage to the magnet during quench.