Showing papers by "John (Jack) W. Ekin published in 1979"

Strain dependence of the critical current and critical field in multifilamentary Nb 3 Sn composites

Abstract: High-J c multifilamentary Nb 3 Sn superconductors with widely varying amounts of prestrain and critical field values can be characterized fairly accurately by a single normalized critical field-strain relationship. Such a relationship permits first order prediction of critical-current degradation at arbitrary magnetic field magnitudes knowing only two parameters for any conductor, the prestrain and the maximum critical field. Some of the conductor-fabrication factors affecting the parameters are considered.

Effect of Strain on Epoxy-Impregnated Superconducting Composites

Abstract: Flux-jump stabilized superconducting magnets are usually impregnated with epoxy to prevent wire movement and enhance stability. Hoop stress experienced by the windings when the magnet is energized would otherwise cause wire movement, leading to localized heating and, quite probably, thermal runaway.

The development of standards for practical superconductors

Abstract: The program to develop standard measurement practices for practical superconductors includes the generation of uniform definitions of terms, the development of standard measurement techniques, and comparisons of these measurements using standard reference materials. The initial sets of definitions have been published and their development will be described. Responses will be solicited on terms whose definitions are still in development or are controversial. The progress in the development of standard measurement techniques for critical current, transient losses and critical temperature will be discussed. The different techniques will be compared and the experimental parameters which must be carefully controlled will be enumerated.

Effect of strain on the critical current of Nb 3 Ge

Abstract: The strain dependence of the critical-current density has been determined for composite tapes of Nb 3 Ge prepared by chemical vapor deposition. For Nb 3 Ge layers 3-4 μm thick deposited on a nickel-molybdenum-iron alloy substrate, the critical current monotonically increases when uniaxially strained to about 0.6%. This strain corresponds almost exactly to the compressive strain that would be introduced into the Nb 3 Ge by the substrate due to thermal contraction during cooldown after reaction. The increase in critical current was relatively small, about 6½% at 7T and 5½% at 4T. At higher strain, the critical current decreased rapidly, falling by more than 50% at a strain of 0.9%, for example. For Nb 3 Ge deposited on a tantalum substrate, however, the critical current monotonically decreased, falling by more than 50% at a strain of 0.4%. The results indicate that Nb 3 Ge can withstand considerable compressive strain (at least 0.6%), but fractures at tensile strains of only 0.1 to 0.2%.