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Description
The development of Nb3Sn wires doped with artificial pinning centres (APC) from binary to ternary compounds is reported. ZrO2-doped tube-type (TT) and powder-in-tube (PIT) were manufactured by Hyper Tech Research Inc. with the aim of reaching the FCC requirements (non-Cu Jc=1500 A mm-2 at 16T and 4.2K). Short pieces of the wires were characterized by means of SQUID magnetometry in order to evaluate their critical temperature and critical current. The upper critical field was determined via resistivity measurements in a 17 T cryostat. The layer-Jc (at 12 T and 4,2 K) is significantly higher than in commercial state-of-the-art wires (Ta or Ti-doped), which can be explained by a grain refinement, as inferred from by high-resolution transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD) analysis. An average grain size of 63 nm (in the best binary sample) was derived, resulting in a high grain boundary density which increases the pinning force. In this sense, a pinning force scaling analysis was carried out, showing a shift of the peak position close to a reduced field of 0.3. Scanning Hall probe microscopy (SHPM) was used to map the field above the wires cross-section in the Meissner and remnant-field state: a magnetization map of the individual sub-elements was obtained from the latter, and the critical currents were calculated from the field profiles at different temperatures. Meissner-state scans were used to assess the effective A-15 superconducting cross-section of the sub-elements together with the radial distribution of the transition temperature. These local properties were related to SEM-EDX data, which assessed stoichiometry variations.
Aknowledgments: This Marie Sklodowska-Curie Action (MSCA) Innovative Training Networks (ITN) receives funding from the European Union’s H2020 Framework Programme under grant agreement no. 764879.
