Effect of irradiation on the critical currents of alloy and compound superconductors

Abstract

The effects of irradiation on the critical current density J c(H) of several superconducting compounds and Nb-Ti alloys have been examined by a number of workers. The irradiations in the studies include electrons, fast neutrons, ions and fission fragments. In alloys, changes in J c(H) on irradiation depend on the metallurgical history of the material and indicate that radiation defects modify the interaction between the fluxoid array and the sample microstructure. Radiation defects in alloys can also affect J c(H) through small decreases in T c , the transition temperature and ρ, the normal state resistivity. Irradiations of A15 compounds to moderate fluences (dependent on the type and energy of irradiating particle) lead to decreases in T c of ∼1 K and increases in J c(H) with dose for most of the samples investigated and can be qualitatively understood as resulting from changes in ρ and the pinning force acting on the fluxoids. At higher dose levels, larger depressions of T c and possibly γ, the electronic specific heat coefficient, lead to drastic reductions J c(H) . The effect of various energetic particles and irradiation temperature on J c(H) are discussed.