Preparation of high field Nb3Al and Nb3(Al,Ge) superconducting tapes by an electron beam annealing

Nb3Al and Nb3(Al,Ge) tape superconductors with excellent high-field properties have been successfully prepared by an electron beam annealing. The electron beam irradiation was performed on Nb-25at.%Al and Nb- 20at.%Al-5at.%Ge composite tapes moved at a velocity of 6m/min.. The accelerate voltage, current and diameter of the electron beam were 20kv, 5-20mA and 0.5-3mm, respectively. During the irradiation, the Al fibers reacted at a high temperature with surrounding Nb matrix to form A15 phase with stoichiometric composition. Tc´s above 17K have been easily obtained after the electron beam irradiation, which can be increased by 1-2K by the following low temperature annealing at 700-800°C. Maximum Tc´s attained for Nb-Al and Nb-Al-Ge tapes are 18.4K and 19.8K(midpoint), respectively. The Jc-H curves show no degradation in high magnetic fields up to 23T, exceeding 10⁴A/cm². The highest overall Jc(for irradiated area) at 23T and 4.2K is 3×104A/cm²obtained for the Nb-Al-Ge tape. A new continuous irradiation system has been developed to fabricate longer tape of 10-100m.