Quench Development at Supercritical Currents in Low $n$ -Value Superconductors

Superconducting magnets consisting of conductor having a low n-value can be operated shortly at supercritical currents without quenching the magnet. This applies also to epoxy impregnated coils. However, when sufficiently high disturbance occurs at a supercritical current a magnet quenches. Traditional approaches on minimum quench energy (MQE) do not consider the supercritical region. In this study we measured MQE at sub- and supercritical currents for MgB₂ and Bi-2223/Ag conductors having low n -values, i.e. below 15. Simulation results from a Finite Element Method model were compared with the measurement results and the differences in MQE between the sub- and supercritical regime were scrutinized.