Hybrid copper-superconductor transformer impedance behavior at cryogenic temperatures with a novel liquid cryogen level sensor example

The complex impedance across copper primary windings of a conduction cooled hybrid copper-superconducting transformer is measured at different temperatures. This was motivated by advances in superconducting power supply research where abrupt transitions through the flux creep temperature are common. It is shown that changes in the measured complex impedance of the primary windings are a result of the superconductor secondary transitioning between the superconducting and normal states. These two states have a large difference in resistance leading to changes in the reflected secondary impedance, measured as sharp changes in the complex impedance across the primary. These findings will help to inform future superconducting power supply system design. These findings are also used to create a novel, compact and low power liquid cryogen level sensor using a jointless superconducting secondary, demonstrated with a bath of liquid nitrogen. Suggestions on how to optimise such a sensor are outlined. This simple sensor concept in combination with different superconducting materials can safely be used for leak detection and to monitor the fill levels of volatile cryogenic liquids such as oxygen or hydrogen. • A novel single point temperature sensor suitable for volatile liquid cryogens used to detect levels and/or leaks. • Resistance measurements below and above the critical temperature of a commercially available copper coated high temperature superconductor. • Hybrid copper-superconductor transformer impedance changes as a function of temperature around the critical temperature of the superconducting material used. • Reflected secondary impedance from a superconducting transformer secondary and its implications for transformer rectifier flux pump design.