Typical insulations for Rutherford cables Heat transfer model

1. Typical insulations for Rutherford cables Heat transfer model Heat flux comparison same operating conditions specific operating conditions Potential for enhanced insulation for NbTi Porosity checker Preliminary results Conclusions Nb3Sn vs NbTi in HeII

2. Typical Cable Insulations • The first barrier to the removal of the heat generated in a coil is the electrical insulation: • ~100-200 V between adjacent turns • ~5 kV to ground • up to 200 MPa Nb-Ti: All polyimide insulation: semi-permeable to He II Nb3Sn (wind & react):mineral fiber cloth wrapping & Epoxy resin impregnation: impermeable to He II Courtesy of F. Rondeaux (CEA)

3. NbTi : all PI

4. Nb3Sn : S2 glass +resin G.Dambrosio & D.Chichili

5. Heat Transfer Model Nb-Ti (porous insulation) He II is in direct contact with the strands Heat flux is shared by two parallel paths (a & b). Tb R InsulationKapton R Kapitza Kapt.-He II. a TC He II channels 1) Qa Vs Qb depends on insulation porosity 2)Qa & Qb are non linear 3)Qb has saturation level Qa Qa: Solid Conduction Qb He II bath, Tb=1.9 Cable, Tc=Tb+DT b R Kapitza Cu-He II R He II Channel Qb:Superfluid Conduct. Nb3Sn (sealed insulation) No He II reaches the strands Heat goes through solid conduction first, then to He II Tb R insulationEp.+G.Fiber R Kapitza Epoxy.-He II. Q He II bath, Tb=1.9 Cable, Tc=Tb+DT TC Q: Solid Conduction

6. Bulk resistance of 0.1 mm thick Kapton [7] ~2 times larger than 0.2 mm thick epoxy+fiberglass [2] Boundary resistance(Kapitza):Kapton [8] (& Ep.+F.) ~6times larger than Cu [9] HE II channel resistance: -depends on insulationporosity (channel lengthsand cross-areas) Equivalent Thermal Resistances -is always smaller than Kapton and epoxy+fiberglass but is limited by saturation

7. Experimental (B. Baudouy et al Cryogenics 39, 921 (1999) SSC dipole LHC dipole Solid Conduction Predominance: Superfluid Conduction

8. We consider two coils in a He II bath (Tb=1.9) : Nb3Sn with sealed insulation Nb-Ti with porous insulation We impose the sameeng-ineering current density Jengand operative peak field B We get the temperature margin DT=Tc-Tb we combine it with the heat transfer correlations and we obtain the corresponding heat flux Comparison for Operating Conditions:Same or Specific We impose J and Bultspecific of their practical use

9. Temperature Margin Comparison for Same B (9T) and Jeng Cu/Sc Nb-Ti 1.5 Nb3Sn 1 Tb=1.9

10. Maximum Heat Flux for Same B (9T) and Jeng SSC dipole LHC dipole Enhanced Bare cable Nb3Sn Bare cable asymptotic limit Cu/Sc Nb-Ti 1.5 Nb3Sn 1 Nb3Sn Enhanced LHC dipole SSC dipole

11. B= 9 T for NbTi B= 13.5 T for Nb3Sn Maximum Heat Flux for SpecificConditions Bare cable asymptotic limit Enhanced Nb3Sn LHC Main SSC J/Jc (Tb,Bult)

12. it corresponds to ~ 220 mW/m per cable it corresponds to ~830 mW/m per cable

13. Enhanced porosity

14. Porosity checker/1 Air enters the stack of cable longitudinally (A) and can exit longitudinally (C), without crossing the insulation or radially (B) crossing the insulation. Insulation porosity is evaluated from the comparison between radial and longitudinalflow Flow out (C) C A Flow out (B) B Flow in (A)

15. Porosity checker/2

16. Tests Results/1 Vertical compression 10 MPa

17. Tests Results/2

18. Heat transfer tests

19. For same B and Jeng, Nb3Sn coils made by Rutherford cables can draw one order of magnitude more heat than typical Nb-Ti coils For the same margin to critical surface (specific operating conditions), Nb3Sn coils made by Rutherford cables can draw three times more heat than typical LHC Nb-Ti coils …however… there is a large potential to increase the dimension of the cooling channels thus moving their saturation at higher heat fluxes The use of this potential in HeII provides a spectacular increase of heat evacuation capabilities of NbTi coils competing/exceeding Nb3Sn @ fields below 9 T Conclusions

20. C. Meuris, B. Baudouy, D. Leroy, B. Slezess, Heat transfer in electrical insulation of LHC cables cooled with superfluid Helium, Cryogenics 39, 921 (1999) L. Imbasciati et al.,Thermo-mechanical Characterization of Insulated and Epoxy-Impregnated Nb3Sn composites, IEEE Trans. on Appl. Supercond., Vol. 13, Issue 2, 1788 (2003) D.S. Matsumoto, C.L. Reynolds Jr., A.C. Anderson, Thermal Boundary Resistance at Metal Epoxy Interfaces, Phys. Rev. B, Vol. 16 n.8, 15 Oct. 1977. F. Rondeaux, P. Bredy, J.M. Rey, Thermal Conductivity Measurements of Epoxy Systems at Low Temperatures, Adv. Cryo. Eng. 48A (Materials), 197 (2002) J. Gorter, J. H. Mellink, On the Irreversible Processes in Liquid Helium II, Physica 15, 285 (1949) V. Arp, Heat transport through Helium II, Cryogenics 10, 96 (1970) J. Lawrence, A.B. Paterl, J.G. Brisson, The Thermal Conductivity of Kapton HN between 0.5 and 5 K, Cryogenics 40, 203 (2000) B. Baudouy, Kapitza Resistance and Thermal Conductivity of Kapton in Superfluid Helium, Cryogenics 43, 667 (2003) A. Kashani, S.W. Van Sciver, Kapitza Conductance of Technical Copper with Several Different Surface Preparations, Cryogenics 25, 238 (1985) E. Todesco, J.P. Koutchouk, Scaling Laws for b* in the LHC Interaction Regions, CARE Workshop LUMI-06, 17th October 2006, Valencia, Spain. N. Kimura et al., Heat Transfer from Insulated Rutherford Type Cables Immersed in Pressurized He II, Adv. Cryo. Eng. 43 References