PROTON DAMAGE ON NB-BASED JOSEPHSON-JUNCTIONS

The effects of proton irradiation on Nb-based Josephson junctions have been investigated. The fabrication technology employed is essentially the same of Josephson digital circuit designs, the main difference be ing a much lower Josephson critical current density. We have analysed in detail the magnetic field dependence of the junction critical curre nt, and the quasiparticle tunnelling cur rent, in order to observe pos sible occurrence of permanent changes produced by the ionizing particl es. No evidence of radiation induced damage on the properties of the j unctions has been found. The profile of the energy lost by protons wit hin the Nb-targets and the dose is calculated by means of Monte Carlo simulations. A schematic description of the vacuum scattering chamber used for proton irradiation is also reported.