Neutron irradiation of NbTi-superconductors

The present study is aimed at a thorough investigation of neutron irradiation effects on critical currents in NbTi of widely differing metallurgical starting conditions. The analysis of data prior to irradiation shows a predominance of cell pinning in Nb-42 wt% Ti and of precipitate pinning in Nb-49; 54 wt% Ti, respectively. The first series of irradiation experiments was made at the ambient pool water temperature in the reactor core. The results obtained up to a fluence of 9 × 10²²m^-2(E > 1 MeV) show decreasing degradations of jcwith increasing Ti-concentration indicating significantly different effects of neutron irradiation on cell and precipitate pinning. Furthermore, we find that the deterioration of jcis, in general, smaller than the improvements of jcachievable by an optimized metallurgical treatment prior to irradiation. The second series of experiments involves low temperature neutron irradiation (T = 77 k) on a selected number of the same conductors with and without a thermal cycle to room temperature. The results obtained so far show comparable, but in general smaller, jc-degradations with neutron fluence.