Abstract
A method for calculating stored magnetic energy in a thin superconducting film based on quantitative magneto-optical imaging is developed. Energy and magnetic moment are determined with these calculations for full hysteresis loops in a thin film of the superconductor NbN. Huge losses in energy are observed when dendritic avalanches occur. Magnetic energy, magnetic moment, sheet current and magnetic flux distributions, all extracted from the same calibrated magneto-optical images, are analyzed and discussed. Dissipated energy and the loss in moment when dendritic avalanches occur are related to each other. Calculating these losses for specific spatially-resolved flux avalanches is a great advantage, because of their unpredictable and non-reproducible nature. The relative losses in energy are much higher than the relative losses in moment.
Highlights
When exposed to an external magnetic field, type-II superconductors are susceptible to flux jumps caused by a thermomagnetic instability.[1]
Overheating and destruction of superconductors caused by thermomagnetic avalanches is a result of sudden release of large amounts of energy stored in the magnetic field
Iwasa et al.[31] have measured the energy released when flux jumps occur in Nb-Ti superconducting wires by observing the volume of evaporated liquid helium during the jump event
Summary
When exposed to an external magnetic field, type-II superconductors are susceptible to flux jumps caused by a thermomagnetic instability.[1]. Germany 6Nanoscience Center, Department of Physics, P.O. Box 35, University of Jyvaskyla, FIN-40014 Jyvaskyla, Finland 7Institute for Superconducting and Electronic Materials, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia (Received June 2018; accepted August 2018; published online 30 August 2018) In the present work we use magneto-optical imaging (MOI) to measure both the energy built up during a field ramp, and the amount of magnetic energy released when dendritic avalanches occur in a thin superconducting NbN
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