Thermo-magnetic instabilities in MgB2 bulk magnets: A combined experimental and numerical investigation

The ability of MgB2 polycrystalline samples to carry strong current densities even across high-angle grain boundaries has boosted the fabrication of large bulk superconductors. However, the occurrence of thermomagnetic instabilities, such as flux-jumps, compromises the use of this compound at low working temperatures. Investigating and mitigating these phenomena are then crucial for future applications, as for instance permanent bulk magnets. In this paper, starting from the experimental evidence of flux-jump occurrence in a MgB2 disc-shaped magnet prototype, we numerically investigated this phenomenon coupling the electromagnetic equations (formulated using the magnetic vector potential) to the heat diffusion equation. This numerical approach – validated via the comparison between computed and experimental results – provided us with the evolution of the local magnetic field and temperature in correspondence to a flux-jump. Based on this information, we finally investigated possible solutions to prevent flux-jump occurrence through the improvement of the thermal exchange between the sample and the cooling stage.