Low-temperature deuteron irradiation of differently reacted Nb 3Sn superconductors

Abstract

Irradiation measurements with 50 MeV deuterons at 18 K and subsequent annealing measurements were performed on Nb 3Sn single and multifilamentary superconductors at the Helium-Bath Irradiation Facility of the Karlsruhe Cyclotron. The critical current densities j c of Nb 3Sn bronze-reacted wire samples at various reaction temperatures ( T R = 650 , 700, 750, 800 and 850°C) with equal layer thickness were measured for integral deuteron fluxes up to Φt = 0.7 × 10 18 cm −2 . After a decrease in j c of 85% at maximum dose a relatively small annealing effect (4 to 10%) was observed at ambient temperatures. The maximum value of the normalized critical current density, j c/j c0 , at Φt ≅ 10 17 cm −2 increases with increasing reaction temperature. The difference in volume pinning forces before and after irradiation increases less than linear ( ~ √Φt) with the irradiation dose. An almost linear dependence between the inverse grain diameter ( d K −1 ) and volume pinning force is obtained both before and after irradiation.