Strain control of composite superconductors to prevent degradation of superconducting magnets due to a quench: I. Ag/Bi2Sr2CaCu2Ox multifilament round wires

Liyang Ye, Pei Li, Jan Jaroszynski, Justin Schwartz, Tengming Shen

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Abstract

The critical current of many practical superconductors is sensitive to strain, and this sensitivity is exacerbated during a quench that induces a peak local strain which can be fatal to superconducting magnets. Here, a new method is introduced to quantify the influence of the conductor stress and strain state during normal operation on the margin to degradation during a quench, as measured by the maximum allowable hot spot temperature T allowable, for composite wires within superconducting magnets. The first conductor examined is Ag-sheathed Bi2Sr2CaCu2Ox round wire carrying high engineering critical current density, J E, of 550 A mm-2 at 4.2 K and 15 T. The critical axial tensile stress of this conductor is determined to be 150 MPa and, in the absence of Lorentz forces, T allowable is greater than 450 K. With increasing axial tensile stress, σ a, however, T allowable decreases nonlinearly, dropping to 280 K for σ a = 120 MPa and to 160 K for σ a = 145 MPa. T allowablea) is shown to be nonlinear and independent of magnetic field from 15 to 30 T. T allowablea) dictates the balance between magnetic field generation, which increases with the magnet operating current and stress, and the safety margin, which decreases with decreasing T allowable, and therefore has important engineering value. It is also shown that T allowablea) can be predicted accurately by a general strain model, showing that strain control is the key to preventing degradation of superconductors during a quench.

Original languageEnglish (US)
Article number025005
JournalSuperconductor Science and Technology
Volume30
Issue number2
DOIs
StatePublished - Feb 2017

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All Science Journal Classification (ASJC) codes

  • Ceramics and Composites
  • Condensed Matter Physics
  • Metals and Alloys
  • Electrical and Electronic Engineering
  • Materials Chemistry

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