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Title: Optimisation, characterisation and synthesis of low temperature superconductors by current-voltage techniques
Author: Hopkins, S. C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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The reaction-diffusion behaviour of bronze process Nb3Sn wires has been modelled, and good agreement has been obtained between predicted and measured compositions and Nb3Sn layer thicknesses for a wide range of isothermal heat treatments. Isothermal and two-stage heat treatments have been assessed for uniformity of Nb3Sn layer thicknesses and predicted critical current behaviour, and suggestions for optimising heat treatments and wire designs have been made. The electrical resistivity of bronze as a function of temperature and composition has been measured, and its annealing behaviour investigated. These results have been used with the diffusion model to calculate the electrical resistivity during isothermal heat treatment. Most features are in good agreement with experiment results, suggesting that this technique has potential for the monitoring and control of bronze process wire heat treatments. Discrepancies and areas for improving in the calculations have been identified, and these will form the subject of future work. A critical current characterisation system using pulsed currents and pulsed magnetic fields, Cryo-BI-Pulse, has been developed with Metis Instruments and Equipment. Excellent agreement with DC measurements has been obtained for a copper-matrix NbTi wire and a nickel-matrix MgB2 tape, but discrepancies have been found for materials with resistive matrix materials. These discrepancies are mostly caused by current transfer effects when testing very short samples, and can be addressed by testing longer samples and improving the analysis of the measured sample voltages.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available