1. Applied Superconductivity at UNIGE Overview of the activities Départment de Physique de la Matière Condensée & Départment de Physique Appliquée Université de Genève - Switzerland Carmine Senatore

2. MATERIAL SCIENCE PHYSICS ENGINEERING Applied Superconductivity @ UNIGE

3. fundamental understanding of the material properties material engineering development of technical superconductors

4. Applied Superconductivity @ UNIGE Unique facilities for material synthesis Sophisticated measurement techniques All the equipment for the development of superconducting wires 250t hydrostatic hot extrusion machine 2000 bar, 2000°C Hot Isostatic Press Various controlled atmosphere furnaces High magnetic fields: 21 Tesla Electromechanical properties under axial and transverse loads Specific heat and thermal conductivity Magnetic properties

5. Our collaboration with CERN 2004-2009K1151/AT/LHC Études et mesures des propriétés supraconductrices des matériaux développés pour les aimants supraconducteurs à champ très élevé 2009-2012K1629/TE Characterization of advanced superconductors for high field superconducting magnets Development of the Nb 3 Sn technology for the next generation of accelerator magnets 2013-… K- - - - Electromechanical and thermal properties of high performance superconducting wires in view of accelerator magnets above 10 T High field magnets for HL-LHC and HE-LHC Development of the HTS conductor technology

6. There is still to learn about Nb 3 Sn…

7. Powder-In-Tube Nb 3 Sn: Formation and Microstructure Large grains (> 1 µm) Fine grains (~ 200 nm) Temperature and duration of the heat treatment determine size and composition of the two A15 regions ~ 23 at.% Sn ~ 25 at.% Sn

8. B-T diagram for the two A15 regions B c2 T Large grains B c2 (0) = 25.7 T Fine grains B c2 (0) = 31.7 T Senatore and Flükiger APL 102 (2013)

9. Development of superconducting wires @ UNIGE

10. Nb 3 Sn wires: fabrication techniques Bronze Route Internal Sn Cu Nb Sn Bronze NbTa Ta Cu Made at UNIGE

11. Internal Sn wire development @ UNIGE Internal Sn Bronze route non-Cu J c @ 15 T = 1500 A/mm 2 non-Cu J c @ 12 T > 2500 A/mm 2

12. MgB 2 wires: fabrication by powder metallurgy SwagingDrawing MgB 2 powders or Mg + 2B powders ……

13. Cold High Pressure Densification A new industrial wire densification process developed in Geneva as drawn 1 mm densified @ p = 2 GPa Fe/MgB 2 wire MgB 2 wire development @ UNIGE

14. Enhancement of B c2 & Improvement of Connectivity Square wire without Densification after Cold High Pressure Densification Binary Malic doped in parallel field 10 4 A/cm 2 @ 13.4 T in perpendicular field 10 4 A/cm 2 @ 12.9 T + CHPD

15. horizontal 16 t hydraulic press 40 t precision press

16. … still voids in Nb 3 Sn, but different issues Electromechanical properties of technical superconductors

17. 3D high resolution synchrotron radiation tomography F. Buta, B.Seeber - UNIGE C. Scheuerlein - CERN M. di Michiel - ESRF Voids after heat treatment in Nb 3 Sn wires Irreversible damages under loads arise from the voids in the filaments formed during reaction

18. Hot Isostatic Press: up to 2 kbar/2000°C Hot isostatic pressing (HIP) was used to reduce the porosity and enhance the electromechanical properties

19. Critical current vs. axial strain after HIP Nb 3 Sn WASP After HIP the irreversible limit is raised from 0.62% to 0.88%

20. Cables and transverse loads Electromechanical properties of technical superconductors Short Model Coil dipole cable: 14 wires (Ø 1.25 mm) Fresca2 dipole cable: 40 wires (Ø 1.0 mm)

21. I c vs. transverse stress: the WASP concept Developed in the frame of the CERN-UNIGE collaboration

22. Pulling force Sample 4-WALL + impregnation Epoxy Radial freedom Significant shear and distortional stresses Wire impregnated with epoxy applied stress uniformly distributed Wire constrained in a groove I c vs. transverse stress: evolution of the concept Sample Pulling force 4-WALL2-WALL

23. PIT Nb 3 Sn wire: I c vs. transverse stress

24. Thermal properties of technical superconductors

25. New setup for thermal conductivity measurements Thermal conductivity Heat power Temperature difference Cernox distance Wire cross section ΔTΔT Thermal conductivity κ is a primary ingredient for modelling the quench behaviour of superconducting coils However data in literature are scarce…

26. PIT Nb 3 Sn wires: Thermal conductivity at B = 0 & 15T Theoretical prediction from electrical resistivity - RRR = 330

27. Perspectives How to improve the electromechanical properties Focus on the dynamics of the irreversible degradation under mechanical loads Also relevant for HTS and MgB 2 conductors How to improve the thermal properties Essential for HTS and MgB 2 conductors Gain fundamental understanding and think to new conductors

29. T c distribution from specific heat Large grains Fine grains

30. Field dependence of the T c distribution Fine grains, which have the lower Sn content, exhibit the higher B c2 !!

31. 0 T 7 T 3 T 14 T Field dependence of the T c distribution Standard Reaction : 675C/84h

32. Gun drilling, annealing and Sn insertion 1 st extrusion billet HIP + 2 nd extrusion Cold restack, 109 subelements straightening Internal Sn wire development @ UNIGE Internal Sn Bronze route non-Cu J c @ 15 T = 1500 A/mm 2 non-Cu J c @ 12 T > 2500 A/mm 2

33. Cold densification, grain connectivity & percolation Resistivity decreases, as a result of the increased connectivity (porosity reduction) Homogeneity is improved and thus the n value of I-V curve is increased The superconducting volume needed for percolation is strongly reduced After cold densification Hossain et al. SuST 22, 085002 (2009) Senatore et al. IEEE TAS 21, 2680 (2011)

34. Our collaboration with CERN 2004-2009K1151/AT/LHC Études et mesures des propriétés supraconductrices des matériaux développés pour les aimants supraconducteurs à champ très élevé 2009-2012K1629/TE Characterization of advanced superconductors for high field superconducting magnets Development of the Nb 3 Sn technology for the next generation of accelerator magnets 2013-… K- - - - Electromechanical and thermal properties of high performance superconducting wires in view of accelerator magnets above 10 T High field magnets for HL-LHC and HE-LHC Development of the HTS conductor technology