Critical current density and microstructural state of an internal tin multifilamentary superconducting wire
The critical current density (J/sub c/) of internal tin wires is increased when low-temperature diffusion heat treatments are performed prior to a high temperature reaction. To determine the variation of J/sub c/ with pre-reaction heat treatments a copper-stabilized IGC internal tin wire with an outside diameter of 0.267mm was studied. The wire has 2 to 2.5..mu..m diameter filaments, and within the Ta barrier, the area ratio of the copper matrix and Sn core to Nb is about 2.2. Due to the character of the Cu-Sn phase diagram, heat treatments at a series of temperatures below the Nb/sub 3/Sn reaction temperature affect the local Sn concentration in the matrix about the Nb filaments. The variation in J/sub c/ resulting from these heat treatments is a consequence of the microstructural state of the conductor and the morphology of the Nb/sub 3/Sn layer produced. The results of this work show that the internal tin and bronze-processed wires have diffenent J/sub c/(H) characteristics. The two processes have comparable critical currents at high fields, suggesting the same H/sub c2/, while at low fields the internal tin wire is superior, suggesting a better grain morphology.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5847025
- Report Number(s):
- LBL-18654; CONF-840937-29; ON: DE85009966
- Country of Publication:
- United States
- Language:
- English
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