Instability of superconducting racetrack magnets

The training and degradation behavior of superconducting racetrack-shaped magnets were studied for use in a high-performance superconducting wiggler. Several small magnets that were fabricated with NbTi multifilamentary superconductor and impregnated with epoxy resin were tested by changing the winding tension, aspect ratio of the magnets, and copper ratio of the superconductor. The acoustic emission signals were monitored during the tests. The correlation between training/degradation behavior and fabrication condition of the magnets was studied. The test magnets that had the smaller aspect ratio, a low winding tension, and a high copper ratio and were impregnated with epoxy resin showed no premature quenches and reached critical current at first charging.