Effect of Proximity Length on Flux Pinning in APC Composites: An Overview of APC

  • Lance D. Cooley
Part of the Advances in Cryogenic Engineering Materials book series (ACRE, volume 42)


The lack of adequate high-field pinning in APC composites is an intrinsic property of a dominant magnetic pinning mechanism and the long proximity length of Nb pins. Recent work on APC composites has uncovered trends in the flux-pinning and microstructural data, which hold despite the variety of their designs. By comparing these trends to those of conventional Nb-Ti composites, evidence for magnetic pinning being the dominant flux-pinning mechanism is found. This model departs from the widely accepted view that core-pinning is the dominant pinning mechanism. The parameter that controls the optimization of flux-pinning in the microstructure is the proximity length ξ n instead of the diameter of the fluxon core. The optimum bulk pinning force occurs for the best balance of a strong elementary pinning force f p and a high number density of pins. However, since f p is maximum when the pin thickness tξ n , the number density of pins can be made to be on the order of the fluxon number density by using artificial pins which have very short proximity lengths. Such pins are most desirable to achieve high J c at high fields.


High Field United States Patent Filament Diameter High Number Density Conventional Composite 
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Copyright information

© Springer Science+Business Media New York 1996

Authors and Affiliations

  • Lance D. Cooley
    • 1
  1. 1.Electromagnetic Technology DivisionNISTBoulderUSA

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