JOSEPHSON JUNCTION NETWORK AS A TOOL TO SIMULATE INTERGRAIN SUPERCONDUCTING CHANNELS IN YBCO FILMS

Recent considerations on the physics of YBa 2 Cu 3 O 7-δ films made possible explaining their transport properties as flow of supercurrents through links between the granular structure of the film. The present work deals with the analysis of the Josephson junction network as a discrete set of parallel junctions (1D array) in quasi-static conditions and is aimed to compare the results of the simulations with the experimental findings, in particular with the plateau-like features in the critical current dependence on the magnetic field. Different regimes and vortex phases have been individuated and discussed

Expected radiation environment and damage for YBCO tapes in compact fusion reactors

We investigate the neutron damage expected in high-temperature superconducting tapes that will be employed in compact fusion reactors. Monte Carlo simulations yield the expected neutron spectrum and fluence at the magnet position, from which the primary knock-on atom energy distributions can be computed for each atomic species comprising the superconductor. This information is then employed to characterize the displacement cascades, in terms of size and morphology, through molecular dynamics simulations. The expected radiation environment is then compared with the neutron spectrum and fluences achievable at the facilities currently available for experimental investigation in order to highlight similarities and differences that could be relevant to the understanding of the radiation hardness of these materials in real fusion conditions. We find that the different neutron spectra result in different damage regimes, the irradiation temperature influences the number of generated defects, and the interaction of the neutrons with the superconductor results in a local increase in temperature. These observations suggest that further experimental investigations are needed in different regimes and that some neutron shielding will be necessary in compact fusion reactors.Funding Agencies|Italian Ministry of Education, University, and Research through Project PRIN HIBiSCUS [201785KWLE]; Programma Operativo Nazionale (PON) Ricerca e Innovazione 2014-2020; Swedish Research Council [2018-05973]; European Cooperation in Science and Technology, COST Action [CA19108]</p

Confinement of fluxons by surface columnar defects in Bi1.8Pb0.33Sr1.87Ca2Cu3Oy tapes

We study the effects of surface columnar defects created along about 5% of the sample thickness by means of 0.25 GeV Au ions at different doses on Bi1.8Pb0.33Sr1.87Ca2Cu3Oy high-quality tapes on the vortex dynamics in the sample bulk. Strong phenomena of vortex localization inside the bulk are revealed by shifts of the irreversibility lines (IL's) as well as by their after-irradiation shape. The enhanced IL's exhibit specific characteristics, such as a Bose-glass-like behavior up to quite high fields, with a dose-dependent onset point. Moreover, the irreversible regime expands with decreasing defect density. Such results are consistent with the setting up of confined vortices morphologies. Experimental data concerning the IL with the field orthogonal to the columnar defect direction as well as critical current density enhancements are also reported and discussed

Study of the thermal distribution for YBCO based Transition Edge Bolometers working above 77 K

ransition Edge Bolometers (TEB) are among the simplest radiation detectors. The straightforward operation mode provides good results only if it is combined with a careful thermal optimization.In a TEB, the strong dependence of the electrical resistivity on the temperature in its transition zone enables the detection of a variation of the local temperature which can reach tens of µK. For this reason, it is essential to study the thermal profile of the superconducting active part of the detector, hence its substrate, to make it as homogeneous as possible.Irradiated YBa 2 Cu 3 O 7-x (YBCO) films can be used for position sensitive detection of infrared radiation. A TEB with a double meander pattern, one of which with a reduced critical temperature due to irradiation with high-energy heavy ions, was designed to work in a portable cryostat at a temperature above the liquid nitrogen (LN 2 ) point.In this work, we present a series of Finite Element Method simulations (using COMSOL Multiphysics ® ) aimed at the optimization of the thermal distribution above the YBCO film. Once the optimal working point for the device is found, various materials for the bolometer hosting are tested to identify the combination that provides the most homogeneous temperature distribution. The optimal configurations are then analyzed in response to a sudden change in the PID current to determine the one which presents the best behavior in a transient situation

Microwave analysis of the interplay between magnetism and superconductivity in EuFe 2 (As 1 -x P x ) 2 single crystals

This paper presents a microwave analysis of the interplay between magnetism and superconductivity in an iron-based ferromagnetic superconductor. By comparing the complex rf susceptibility with magnetic force images, the authors discuss the nature of the observed phase transitions and the possible presence of a quantum critical point

Screening magnetic fields by superconductors: A simple model

We introduce a simple approach to evaluate the magnetic field distribution around superconducting samples, based on the London equations; the elementary variable is the vector potential. This procedure has no adjustable parameters, only the sample geometry and the London length determine the solution. This approach was validated by comparing the induction field calculated to the one measured above MgB2 disks of different diameters, at 20K and for applied fields lower than 0.4T. The model can be applied if the flux line penetration inside the sample can be neglected when calculating the induction field distribution outside the superconductor. We conclude by showing on a cup-shape geometry how one can design a magnetic shield satisfying a specific constraint