Dynamic Stabilization against Flux Jumps for Structures Wound from Composite Superconductor-Normal-Metal Tapes

Abstract

Magnetic instabilities or flux jumps are responsible for many of the difficulties which have accompanied attempts to realize the full potential of high-field superconductors in magnet construction. Superconducting windings will be dynamically stable1 against flux jumps if the flux motion following a disturbance is sufficiently damped by a pure normal metal and if the superconductor is cooled well enough. The critical-state model has been used in developing the criteria for dynamic stability for a geometry approximating a magnet winding formed of a composite superconductor-normal-metal tape. It is found that there are two classes of dynamic stability requirements; both must be met: (i) The thickness of the superconducting layer in the composite tape must be smaller than a critical value which is derived.2 (ii) The winding formed from layers of a wide composite tape tends to exclude (and trap) the component of magnetic field which is perpendicular to the plane of the tape. The winding thus acts much like an anisotropic bulk high field superconductor and is likewise subject to flux jumps. The dynamic stability requirements for this composite structure are derived and discussed.2 Experimental results obtained with simple geometries are used to illustrate the main conclusions.