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is aimed at the development of a large-aperture

Magnetization measurements as a tool for investigating the potential electrical transport properties of Nb 3 Sn superconducting wires. Michela Greco, INFN-Genova. Intro. m(T, B). m(B). c (B,T). samples. Nb?. …. is aimed at the development of a large-aperture

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is aimed at the development of a large-aperture

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  1. Magnetization measurements as a tool for investigating the potential electrical transport properties of Nb3Sn superconducting wires. Michela Greco, INFN-Genova

  2. Intro m(T, B) m(B) c(B,T) samples Nb? … is aimed at the development of a large-aperture high field (up to 15 T) superconducting dipole magnet that will serve as a technology test bed for LHC luminosity upgrade Development of a high-performance Nb3Sn wire (aiming at a non-copper critical current density of 1500 A/mm2 at 4.2 K and 15 T) is carried out. A Working Group on Conductor Characterization (WGCC) CEA, CERN, INFN-Genova, INFN-Milano, University of Twente is aimed to define and carry out reliable, reproducible methods for the measurement of electromagnetic properties. M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  3. Intro m(T, B) m(B) c(B,T) samples Nb? … Genova coordinates three groups, having at disposal three facilities: a Vibrating Sample Magnetometer (VSM) in Frascati, a DC-SQUID magnetometer and an AC susceptibility apparatus in Genova. Pasquale Fabbricatore, INFN-Genova; Carlo Ferdeghini, CNR-INFM; Umberto Gambardella, INFN-Frascati M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  4. Intro m(T) • Tc(B) • Nb shielded volume • Nb3Sn shielded volume Bdc=10 G, parallel field m(T) m(B) m= c0 ×Applied Field ×Sample Volume [Wb m] Conversion from cgs to SI units 1 emu=10-10/4p [Wb m] Susceptibility c0 can be calculated using FEM. The samples measured can be assumed as cylinders Parallel field, c0 ~1; Transverse field, c0~2 c(B,T) samples From the comparison of measurements in parallel and transverse field it is possible to evaluate demagnetizing value N [Beff=B/(1-N)] and compare with FEM calculation. Nb? … M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  5. Intro m(T) m(B) c(B,T) samples Nb? Dm … m(B) • Parallel and transverse field • indication of shielding • flux jumps at low fields • Estimation of Jc(B) from Dm from meas in transverse field comparison with Ic results M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  6. Intro m(T) reference m(B) dual phase lock-in amplifier • external susceptibility under conditions of perfect screening (Meissner state) c(B,T)   s2 primary coil • stored energy samples secondary coils • dissipated energy s1 Nb? … c(B,T) The signal U at the pick-up coils s1 and s2 gives relevant information: DU=Us1-Us2=N2pn/G m N= Turns in the pick-up coils, n= frequency G= geometrical factor m= magnetic moment normal stateB=0H, so c’=c’’=0 perfect screeningc”=0, c0=-M/B0 M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  7. Intro m(T) m(B) c(B,T) samples Jc Ic c(B,T) • Tc(B) • Nb shielding volume • Nb3Sn shielded volume • Sharp transition homogeneous material • Smooth transition key of dishomogeneity The peak becomes lower and smoother M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  8. Intro m(T) m(B) c(B,T) samples Nb? … • First phase: • Preliminary measurements on Internal TIN and “old” PIT samples • Calibrated the DCsquid /VSM/AC apparata and understand “different” results, if any • Verified the info that can be derived from different meas M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  9. Intro m(T) m(B) c(B,T) Int TIN -3c” Nb? c’ … Comparison of m-B measurements at 4.2 K with SQUID and VSM on two different samples differing by 7.5% in length Courtesy A. Devred, CEA/CERN INTERNALTIN sample Extremely smooth Nb3Sn transition presence of several phases. • Absence of flux-jumps at low field • 20% difference between Nb3Sn geometrical and shielded volume values..hint of filament interconnection? M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  10. Intro m(T) m(B) c(B,T) PIT Nb? … Critical current measurements show high values of Jc for this kind of Nb3Sn wires..but, unfortunately, all the samples measured up-to-now show instabilities at low fields. POWDER-in-TUBE samples Samples: courtesy of A. Den Ouden & S. Wessel, UTwente Micrograph:courtesy of Carlo Ferdeghini, CNR-INFM LAMIA M. Greco, CARE05

  11. Intro Powder-in-Tube sample m(T) m(B) c(B,T) PIT Nb? … 7 K 4.5 K 6 K 9 K 8 K 10 K M. Greco, CARE05

  12. Intro POWDER-in-TUBE sample m(T) m(B) c(B,T) PIT Nb? … 4.5 K 8 K Reliability of repeated measurements in parallel field with SQUID M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  13. Intro m(T) m(B) c(B,T) samples Nb? … Second phase: • Measurements in parallel to the critical current • cross-check program: •  cross-check “different” results, if any of CEA, TWENTE and INFN-Milano •  evaluation of wire degradation •  why flux jumps? M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  14. Intro m(T) m(B) c(B,T) wire degr Nb? … Courtesy of Thierry Boutboul, CERN M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  15. Intro m(T) m(B) c(B,T) wire degr. Nb? … First results.. M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  16. Intro m(T) m(B) c(B,T) PIT Nb? … There is a large amount of Nb in the conductor m=c0BaV m=3*10-3 emu=3.77*10-12 Wb m 1emu=4p 10-10 Wb m Ba=10 G VshieldedNb=3.77 mm3 VshieldedNb3Sn=1.83 mm3 FNb3Sn=44mm VNb3Sn=0.98 mm3 Parallel field Why flux-jumps? FNb=65 mm M. Greco, CARE05

  17. Intro m(T) m(B) c(B,T) PIT Nb? … Enquire the role of Nb in the conductor FNb=65 mm, FNb3Sn=44mm B is the Nb3Sn area, corresponding to F=50 mm M. Greco, CARE05

  18. Intro m(T) m(B) c(B,T) PIT Nb? … VSM meas at 6.6 K Is this a single flux-jump or rather the transition of the pure Nb phase? May this phase quench at 0.7 T? M. Greco, CARE05

  19. Intro ac measurements in normal field m(T) m(B) c(B,T) PIT According to this extrapolation, at 4.2 K we can have strong effects on magnetization due to this dirty Nb phase Nb? Ic M. Greco, CARE05

  20. Intro m(T) m(B) c(B,T) PIT Nb? … M(B) on a not-reacted PIT sample in transverse field Flux jumps… M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

  21. Intro m(T) m(B) c(B,T) PIT Nb? … Magnetization measurements are a powerful tool correlation with Jc meas study of degradation flux jumps [..the presence of instabilities at low field is a strong limitation of application of Nb3Sn.. Modelization with FEM is in progress No concluding word, for sure, but a warning on the importance of Nb in PIT Nb3Sn wires.]

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