A 1 kA-class cryogen-free critical current characterization system for superconducting coated conductors

A cryogenic electrical transport measurement system is described that is particularly designed to meet the requirements for routine and effective characterization of commercial second generation high-temperature superconducting (HTS) wires in the form of coated conductors based on YBa2Cu3O7. Specific design parameters include a base temperature of 20 K, an applied magnetic field capability of 8 T (provided by a HTS split-coil magnet), and a measurement current capacity approaching 1 kA. The system accommodates samples up to 12 mm in width (the widest conductor size presently commercially available) and 40 mm long, although this is not a limiting size. The sample is able to be rotated freely with respect to the magnetic field direction about an axis parallel to the current flow, producing field angle variations in the standard maximum Lorentz force configuration. The system is completely free of liquid cryogens for both sample cooling and magnet cool-down and operation. Software enables the system to conduct a full characterization of the temperature, magnetic field, and field angle dependence of the critical current of a sample without any user interaction. The system has successfully been used to measure a wide range of experimental and commercially-available superconducting wire samples sourced from different manufacturers across the full range of operating conditions. The system encapsulates significant advances in HTS magnet design and efficient cryogen-free cooling technologies together with the capability for routine and automated high-current electrical transport measurements at cryogenic temperatures. It will be of interest to both research scientists investigating superconductor behavior and commercial wire manufacturers seeking to accurately characterize the performance of their product under all desired operating conditions.