Thermally controlled flux avalanche dynamics in the bulk superconductor NbTi
Phys. Rev. B 113, 104511 – Published 16 March, 2026
DOI: https://doi.org/10.1103/lq5f-lvh7
Abstract
We report spatiotemporally resolved measurements of flux avalanche dynamics in bulk superconducting NbTi using high-speed magneto-optical imaging. Tracking individual avalanche events reveals propagation velocities of 15–25 m/s, which are orders of magnitude slower than the km/s speeds observed in thin films. Analysis of characteristic time scales reveals that these avalanches are governed by local heating and limited heat dissipation through the adhesive layer, establishing a fundamentally different, thermally limited propagation regime. The threshold field for avalanche nucleation decreases with temperature, contrary to the increasing trend in thin films with efficient cooling—a behavior consistent with slow heat removal and thermal runaway in our system. All observed avalanches exhibit universal normalized velocity-distance scaling despite varying morphologies, confirming the robustness of thermal control. These findings reveal that bulk superconductors with poor thermal coupling operate in a previously uncharacterized avalanche regime, with direct implications for flux stability and quench protection in NbTi-based magnets, as well as a broader understanding of thermomagnetic instabilities in technological superconductors.