Evidence for quantized vortex entry in Nb3Sn under the influence of RF fields

Abstract

Evidence for quantized magnetic vortex entry at a defect into a Type-II superconductor operating in the metastable state above Bc1 while under the influence of RF electromagnetic fields has been observed in a polycrystalline coating of Nb3Sn. The measurement was made using a 1.3 GHz microwave cavity for use in particle accelerator R&D and equipped with a temperature mapping system for precision measurements of local heating. At peak RF fields near the quench field of the cavity, discrete jumps in local heating at the quench origin were observed. A number of these jumps were found to be identical in height within measurement error. This suggests entry of a limited number of vortices at a defect. The behavior observed appears to be consistent with recent theoretical predictions regarding vortex entry at grain boundaries in the material.