LAUSR

The impact of neutron irradiation on the properties of second-generation REBaCuO tapes was studied. The main aim of the present study was to identify the fast neutrons irradiation fluence threshold, φ th, at which the high-field critical current at low temperatures, I c (10 K, 8 T), starts degrading. Following up on our previous publication for low irradiation fluences, two new irradiation steps were added. Up to the last but one irradiation step, the T c in all samples followed a linear dependence on the fast neutrons irradiation fluence, T c(φ) ≈ T c(0) − τφ (τ being a numerical constant in units of K/1022 m−2 and φ in 1022 m−2). In parallel, I c (10 K, 8 T) continuously grew with φ up to the threshold fluence, φ th ≈ 3× to 4.3 × 1022 m−2. The last gradual irradiation by φ≈ 1.83 × 1022 m−2 brought a severe degradation both in T c and I c (10 K, 8 T) in most samples, irrespective of their irradiation history. This effect was attributed to radiation overheating. Annealing of pristine tapes in dilute Ar confirmed this scenario. Two of the SuperPower tapes, doped by Zr, appeared to be exceptionally stable against both types of overheating. The tape doped with 7.5% Zr, T c(φ) followed the linear dependence up to the highest cumulative fluence φ =6.16 × 1022 m−2, while the I c (10 K, 8 T) drop was several orders of magnitude lower than in the samples without Zr. TEM study found that the Zr-doped tapes survived the overheating during the last irradiation step in a crystalline form, while all other samples were amorphized.