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

In this paper, the quench characteristics of magnesium diboride (MgB<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) superconducting magnet in MRI 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 multi-physics quench model for the MgB<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> magnet was established based on the finite difference method (FDM). 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 magnet operating in persistent current mode, the influence of copper (Cu) content and copper purity grade within the MgB<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire on quench characteristics of magnet was studied. The results reveal that both the peak temperature and peak voltage during a quench event decrease with increasing copper content within the MgB<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire. Crucially, self-protection capability was achieved for this magnet when the copper content exceeded a specific threshold. At the same time, increasing the purity of the copper stabilizer was found to elevate the peak quench temperature and reduce the peak voltage, this occurs because high-purity copper 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 MgB<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconducting magnet operating in driven mode. Simulation results confirm that this protection scheme effectively prevents damage to the magnet during quench.