Modifying superconducting properties by fast neutron irradiation

by Michael EISTERER (Atominstitut TU Wien)

Wednesday 10 Jun 2015, 10:00 → 11:00 Europe/Zurich

30/7-010 (CERN)

The influence of fast neutron irradiation on the superconducting properties of various superconducting compounds will be compared. Fast neutrons create a large variety of defects, ranging from single displaced atoms to collision cascades of a few nanometers in diameter. Neutron capture reactions can lead to additional defects, for instance in magnesium diboride (MgB2) or gadolinium barium copper oxide (Gd-123). Fast neutron irradiation generally reduces the transition temperature but can enhance the upper critical field by reducing the mean free path of the charge carriers, e.g. in MgB2. The introduced defects serve as efficient pinning centers, if the coherence length fits the defect radius. The resulting currents are non-monotonous with magnetic field (“fishtail”-effect) in MgB2. In contrast, the “fishtail” disappears after irradiation in the cuprates or in some iron based superconductors. Fast neutron irradiation can be used to study anisotropy and granularity effects in high temperature superconductors, as will be demonstrated by topical results. Pinning can be enhanced significantly by neutron irradiation. Recently we obtained record values for the critical current densities in Nb3Sn wires. However, at very high neutron fluences the superconducting properties severely degrade, which is important in view of application in radiation environments, such us fusion or accelerator magnets. The radiation robustness of high temperature superconductors and Nb3Sn will be compared.