CRITICAL CURRENT-DENSITY CHANGES IN IRRADIATED NB3SN

Söll recently modeled changes in the current-carrying capacity of superconducting Nb3Sn after irradiation. As the dose increases, the critical current density (Jc) generally increases, reaches a maximum, and decreases. The model relates the maximum Jc for different types of irradiations to the integrated damage energy (ED) that the irradiating particles transfer to the lattice. Earlier, Söll et al. related cirtical-temperature (Tc) decreases in irradiated Nb3Sn to Ed, which appears more reasonable since Tc is a measure of disorder (or replacements) accompanying defect production, and the final defect configuration (or displacements) are less important. The annealing temperature for the disorder (~700°C) exceeds any of the irradiation temperatures (TIRR); therefore, TIRR is unimportant in the Tc experiments. However, different defect structures exhibit considerably different flux pinning and the Jc model does not consider different spatial variations of the defects during production or migration and agglomeration of the defects during high-TIRR experiments, both of which affect flux pinning. The lack of the model to take into account the physics of the damage is the subject of this paper. Arguments are presented why the defect configurations should be considered, and recently published data is presented that conflict with the conclusions of this damage-energy model. © 1979.