Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390702
Title: Temperature and strain scaling laws for the critical current density in Nb(_3)Sn and Nb(_3)Al conductors in high magnetic fields
Author: Keys, Simon Alastair
ISNI:       0000 0001 3597 9229
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 2001
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Abstract:
Detailed, accurate measurements of critical current density and resistivity to determine the upper critical field have been made on a technological NbsAl conductor in magnetic fields up to 15 T, temperatures from 4.2 K up to the critical temperature and in the strain range from -1.8% to 0.7%. The uncertainty in temperature above 4.2 K was equivalent to ± 100 mK with a stability during the measurements of < 5 mK up to a limiting current of 80 A and a typical noise level of 1 µ Vm(^-1).When B(_c2){T,ε) is defined at 5%pn, 50%pn or 95%/%pn, an empirical relation is found where and an approximate relation, holds. The Jε data were parameterised using F(_p) = J(_E)B = A(ε)[Bc(_2)](^n)b(^p)(1-b)(^9) where b = B/B(_c2)(T,ε). When B(_c2)(T,ε) is constrained to be the value at 50%pn or 95%pn, the scaling law for F(_p) breaks down such that p and q are strong functions of temperature and q is also a strong function of strain. However, when B(_c2)(T,ε) is defined at 5%pn, there is good scaling where p and q are constants independent of temperature and strain. F(_p) can also be approximated by a Kramer form where the Ginzburg-Landau constant is γ is the electronic density of states and is interpreted as the average B(_c2) for the bulk where percolative current flow occurs. The critical current density of Hot Isostatic Pressed (HIP'ed) and unHIP'ed Nb(_3)Sn Modified Jelly Roll wires has also been measured at 4.2 K. The critical current and upper critical field were decreased for the HIP'ed sample. The reduced upper critical field of the HIP'ed wire was found to be less sensitive to strain than the unHIP'ed wire. The exponent of B(_c2) in the flux pinning scaling law increased from 0.86 to 2.14 as a result of the HIP processing.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.390702  DOI: Not available
Keywords: MAGNETIC FLUX; CURRENT DENSITY; MAGNETIC FIELDS; CRITICAL CURRENT; ELECTRIC CONDUCTIVITY; TEMPERATURE DEPENDENCE; STRAINS; SCALING LAWS; NIOBIUM; TIN; INTERMETALLIC COMPOUNDS; SUPERCONDUCTORS Solid state physics
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