Numerical analysis of thermal stability and mechanical response in a no-insulation high-temperature superconducting layer-wound coil

Abstract

To achieve magnetic field spatial homogeneity and reduce resistive joints, no-insulation (NI) high-temperature superconducting layer-wound coils are highly desirable for nuclear magnetic resonance and magnetic resonance imaging. A multiphysics quench model is built to study the thermal stability and mechanical behaviors in an NI layer-wound coil. The numerical results show that when an NI layer-wound coil is subjected to heat disturbance, the transport current will be redistributed owing to the low turn-to-turn contact resistance, and thus the coil can achieve post-quench recovery. Although the layer-wound coil can rapidly return to its initial temperature after a quench, the current diffusion process within the coil leads to a long characteristic field delay time, which means that the circumferential current needs more time to recover. The increase of the peak temperature for coils with high turn-to-turn contact resistivity is not significant, which indicates that the temperature rise is mainly caused by the heat disturbance. Additionally, the recovery time of the central field is dramatically shortened. Thus, it is feasible to reduce the field delay time without sacrificing high thermal stability by designing a layer-wound coil with high turn-to-turn contact resistivity. Moreover, owing to the fast temperature rise during a heat disturbance, the coil undergoes remarkable deformation. The hoop and axial stresses exhibit larger changes than the radial and shear stresses. It can be also found that the mechanical behaviors are mainly affected by the heat disturbance rather than the electromagnetic force in the self-field.