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Title: Strain control of composite superconductors to prevent degradation of superconducting magnets due to a quench: I. Ag/Bi 2Sr 2CaCu 2O x multifilament round wires

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 Bi 2Sr 2CaCu 2O x 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 allowable(σ a) is shown to be nonlinear and independent of magnetic field from 15 to 30 T. T allowable(σ a) dictates the balance between magnetic field generation, which increases withmore » the magnet operating current and stress, and the safety margin, which decreases with decreasing T allowable, and therefore has important engineering value. Lastly, 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.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering
  2. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  3. Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab)
  4. North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering
  5. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Report Number(s):
FERMILAB-PUB-17-642-TD
Journal ID: ISSN 0953-2048; 1512387
Grant/Contract Number:
AC02-07CH11359
Type:
Accepted Manuscript
Journal Name:
Superconductor Science and Technology
Additional Journal Information:
Journal Volume: 30; Journal Issue: 2; Journal ID: ISSN 0953-2048
Publisher:
IOP Publishing
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; superconducting magnet; quench protection; Bi-2212
OSTI Identifier:
1423259
Alternate Identifier(s):
OSTI ID: 1334196