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

2. is aimed at the development of a large-aperture …
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.
This work was carried out in the framework of NED. As you know, NED
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.
Field orientation
Meas type
Applied Field
Info
Parallel
m(T)
Bdc=10 G,
Bdc=100 G
Nb3Sn shielded volume
Tc(B)
c(T)
Sample geometry,
Nb3Sn homogeneity
Transverse
Demagnetizing factor evaluation
c (T)
m(B)
0-3T, 0-8T
Surface shielding, flux jumps, Jc
Set-up
Pasquale Fabbricatore, INFN-Genova;
Carlo Ferdeghini, CNR-INFM; Umberto Gambardella, INFN-Frascati
M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

4. m(T) Intro Tc(B) Nb shielded volume Nb3Sn shielded volume m(T)
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.
It is better to measure in parallel field, in order to have a direct evaluation of the shielded volumes..
Nb? …
M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

5. m(B) Intro Parallel and transverse field indication of shielding
m(T)
m(B)
c(B,T)
samples
Nb? …
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 Dm
wire with tubular filaments
comparison with Ic results
M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

6. dual phase lock-in amplifier
Intro
m(T)
m(B)
c(B,T)
samples
Nb? …
c(B,T)
primary coil
dual phase lock-in amplifier
reference 

secondary coils s1 s2
external susceptibility under
conditions of perfect screening
(Meissner state)
stored energy
Manca quando si annullano
dissipated energy
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. c(B,T) Intro Tc(B) m(T) Nb shielding volume Nb3Sn shielded volume m(B)
samples Jc Ic
c(B,T)
Tc(B)
Nb shielding volume
Nb3Sn shielded volume
Sharp transition  homogeneous material
Smooth transition key of dishomogeneity
Eg in this case you can note the sharp transition of Nb and then the presence of a dirty phase
The peak becomes lower and smoother
M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

8. Preliminary measurements on Internal TIN and “old” PIT samples
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
Questo e’ il volume che si puo’ trasfrmare in NbSn, con un ulteriore incremento del 20%
Il volume del Nb e’ quello ottenuto sottraendo il buco dello Sn interno!
Il raggio e’ 15 um
M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

9. Intro
m(T)
m(B)
c(B,T)
Int TIN
Nb? …
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
INTERNAL TIN
sample
Extremely smooth Nb3Sn transition
presence of several phases. c’
-3c”
Questo e’ il volume che si puo’ trasfrmare in NbSn, con un ulteriore incremento del 20%
Il volume del Nb e’ quello ottenuto sottraendo il buco dello Sn interno!
Il raggio e’ 15 um
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. POWDER-in-TUBE samples 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
Questo e’ il volume che si puo’ trasfrmare in NbSn, con un ulteriore incremento del 20%
Il volume del Nb e’ quello ottenuto sottraendo il buco dello Sn interno!
Il raggio e’ 15 um
Samples: courtesy of A. Den Ouden & S. Wessel, UTwente
Micrograph:courtesy of Carlo Ferdeghini, CNR-INFM LAMIA
M. Greco, CARE05

11. Powder-in-Tube sample
Intro
m(T)
m(B)
c(B,T)
PIT
Nb? …
7 K
4.5 K
6 K
9 K
8 K
10 K
Questo e’ il volume che si puo’ trasfrmare in NbSn, con un ulteriore incremento del 20%
Il volume del Nb e’ quello ottenuto sottraendo il buco dello Sn interno!
Il raggio e’ 15 um
M. Greco, CARE05

12. 4.5 K 8 K POWDER-in-TUBE sample
Intro
m(T)
m(B)
c(B,T)
PIT
Nb? …
4.5 K
8 K
Questo e’ il volume che si puo’ trasfrmare in NbSn, con un ulteriore incremento del 20%
Il volume del Nb e’ quello ottenuto sottraendo il buco dello Sn interno!
Il raggio e’ 15 um
Reliability of repeated measurements in parallel field
with SQUID
M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

13. Measurements in parallel to the critical current cross-check program:
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?
Questo e’ il volume che si puo’ trasfrmare in NbSn, con un ulteriore incremento del 20%
Il volume del Nb e’ quello ottenuto sottraendo il buco dello Sn interno!
Il raggio e’ 15 um
M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

14. Intro m(T) m(B) c(B,T) wire degr Nb? … 0.35 mm deformation
Courtesy of Thierry Boutboul, CERN
0.35 mm deformation
M. Greco, INFN-Genova/ CARE05, CERN November 23, 2005

15. First results.. Intro m(T) m(B) c(B,T) wire degr. Nb? …
Questo e’ il volume che si puo’ trasfrmare in NbSn, con un ulteriore incremento del 20%
Il volume del Nb e’ quello ottenuto sottraendo il buco dello Sn interno!
Il raggio e’ 15 um
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 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. B is the Nb3Sn area, corresponding to F=50 mm
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. ac measurements in normal field
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. M(B) on a not-reacted PIT sample in transverse field
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. Magnetization measurements are a powerful tool
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.]