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Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors.
L F Goodrich1, N Cheggour1, T C Stauffer2
1Department of Physics, University of Colorado, Boulder, CO 80309 ; National Institute of Standards and Technology, Boulder, CO 80305.
Journal of Research of the National Institute of Standards and Technology
|September 25, 2015
Summary
Researchers developed advanced variable-temperature systems for precise superconductor critical-current (Ic) measurements. Their innovative helium gas pre-regulation minimizes temperature errors to ±0.05 K, ensuring accurate Ic data for various superconducting materials.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Electrical Engineering
Background:
- Accurate measurement of critical-current (Ic) in superconductors is crucial for their technological applications.
- Variable-temperature measurements present challenges due to heat generation from high currents, impacting temperature stability.
- Existing measurement systems require refinement to achieve high precision under varying conditions.
Purpose of the Study:
- To review and present developed variable-temperature systems for transport critical-current measurements on commercial superconductors.
- To detail methods for achieving high temperature stability (±0.05 K) during high-current measurements.
- To analyze the generalizability of measurement protocols across different laboratories and systems.
Main Methods:
- Development and utilization of specialized variable-temperature probes with coil sample geometries.
- Implementation of a helium gas pre-regulator system to control sample temperature stability.
- Comparison of critical-current measurements in liquid helium versus flowing helium gas to validate temperature control accuracy.
- Calibration of magnetoresistance effects for resistive thermometers in varying magnetic fields (0-16 T) and temperatures (4-35 K).
Main Results:
- Achieved temperature stability of less than ±0.05 K, crucial for accurate critical-current measurements.
- Demonstrated effective temperature control over the superconducting wire length, validated across Nb-Ti, Nb3Sn, and MgB2 wires.
- Established that liquid/gas comparisons accurately reflect the true critical current, confirming the reliability of the measurement protocol.
Conclusions:
- The developed variable-temperature measurement systems and protocols provide highly accurate critical-current data for superconductors.
- The helium gas pre-regulation technique is effective in mitigating temperature errors, enhancing measurement reliability.
- The study offers insights into generalizing measurement protocols and system design choices for broader laboratory application.
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