Ion Irradiation and Flux Pinning in Type II Superconductors
Niobium foils containing 10 and 900 wt ppm oxygen were irradiated with 3.5 MeV 58Ni +to between 50 and 100 displacements per atom. The irradiation at 900°C produced a bimodal void distribution with a large number of small voids and with large diameter voids that act as strong pinning centers for fluxoids in type II superconductors. Transverse critical current measurements showed a substantial increase in both the upper critical field Hc2 and the critical current density Jc. Jc was anisotropic and exhibited a maximum for fluxoids parallel to the irradiated surface. From the void size and number densities, determined by transmission electron microscopy, interaction forces between fluxoids and voids as well as volume pinning forces are estimated and compared with the experimental results.
KeywordsCritical Current Density Dislocation Loop Void Size flUX Pinning Pure Niobium
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