1. CARE steering April 9th 2008 1 NED Status Report Thierry Boutboul (CERN) LPNHE 9 April 2008

2. CARE steering April 9th 2008 2 CARE/NED JRA Following the 2003 EU peer review, the scope of the NED program was revised to focus on Nb 3 Sn conductor and insulation development. The NED JRA has been articulated around four Work Packages and one Working Group 1 Management & Communication (M&C), 2 Thermal Studies and Quench Protection (TSQP), 3 Conductor Development (CD), 4 Insulation Development and Implementation (IDI), 5 Magnet Design and Optimization (MDO) Working Group. It involves 7 institutes (8 laboratories) Total budget: ~2 M€; EU grant: 979 k€ (over ~3 years).

3. CARE steering April 9th 2008 3 NED/TSQP Work Package The Thermal Studies part of the TSQP Work Package was completed with the publication of the final report in December 2007 (CARE-Report-2007-033-NED) (CEA and WUT; Task Leader: B. Baudouy, CEA) The quench computation task was already completed before (INFN-Mi; Task Leader: G. Volpini).

4. CARE steering April 9th 2008 4 NED- CD Work Package The CD Work Package includes two main Tasks –conductor development two industrial contracts under CERN supervision: Alstom/MSA (F) and EAS/SMI (NL/D); Task Leader: L. Oberli –conductor characterization (CEA, INFN-Ge, INFN-Mi, and TEU; Task Leader: A. den Ouden, TEU) It is the core of the Program and absorbs ~70% of the EU funding. It is complemented by two extensions of scope –FE wire model development to simulate cabling effects (INFN-Ge & CERN; Task Leader: S. Farinon, INFN-Ge), –heat treatment study (CERN; Task Leader: C. Scheuerlein).

5. CARE steering April 9th 2008 5 NED- CD: Status of the SMI contract EAS/SMI completed the step 2 with the successful cabling trial of a 40- strand Rutherford cable performed at LBNL in summer 2007, for which a critical current degradation of 4-8 % was measured at both CERN and Twente University for extracted strands. EAS/SMI was then awarded the green light to launch the final strand production. Final strand manufacturing (12.7 km of strand) is currently underway under the responsibility of EAS with part of process done at Hanau (EAS) and part at Enschede (SMI). The total strand is fabricated from 4 billets. The first length (~ 3 Km) expected to be completed by end of May 2008 (3 months of delay) The 3 remaining strand amounts expected by summer 2008. Part of the final strand (~ 1 length) will be used to produce at CERN a 14-strand cable for Short Model Coil (SMC) program.

6. CARE steering April 9th 2008 6 NED- CD: Status of the Alstom contract (1) During Step 2, Alstom produced a wire, B1/14508. This strand included 78 sub-elements and was processed by means of cold drawing only. B1/14508 strand was characterized by workability problems (numerous breakages), like B1/21204 wire (cold drawing as well). The best critical current densities obtained for B1/14508 are ~ 1900 A/mm 2 (1.25 mm) and ~ 2100 A/mm 2 (0.83 mm). Then, to ensure better workability, emphasis put on another process, based on hot extrusion to guarantee a fair cohesion between Nb barrier and copper can. Two final billets assembled with this sub-element material: 1.One billet with 78 sub-elements, like previous strands manufactured (~ 85 µm at nominal Φ) 2.One billet with 246 sub-elements corresponding to ~ 50 µm final sub-element diameter. First billet fulfilling NED specification.

7. CARE steering April 9th 2008 7 NED- CD: Status of the Alstom contract (2) Drawing of sub-elements and final billets were done by means of a new set of drawing dies, more suitable to Nb 3 Sn process. The final wires were achieved in January 2008. Drawing very successful: 1.B1/63468 strand: 246 sub-elements, 1308 m in a lone length!! 2.B1/20124 strand: 78 sub-elements, 826 m + 402 m In addition, sub-elements nicely shaped, as shown by the micrograph: B1/63468 cross-section

8. CARE steering April 9th 2008 8 NED- CD: Status of the Alstom contract (3) Drawing successfully 246 sub-elements very challenging!! As a comparison, the American company OST, after many years of development, is currently drawing kilometric strand lengths of up to 108 sub-elements, corresponding to ~ 80 µm final element diameter at NED strand nominal diameter (1.25 mm). B1/63468 strand: - 246 sub-elements - Strand diameter = 1.26 mm - Cu/non-Cu = 1.08 - J c non-Cu (12 T, 4.2 K) ~ 1450 A/mm 2 (Alstom, 50 h @ 660 o C) B1/20124 strand: 78 sub-elements, Φ1.26 mm, Cu/non-Cu = 1.53, J c non-Cu similar to B1/63468. Other HT schedules tried without big success for time being, max. J c achieved: ~ 1600 A/mm 2. SEM examinations at CERN showed Sn content at stochiometry (~ 25 at. % Sn) but big Nb 3 Sn grains, barrier not fully reacted (more details given in Characterization part).

9. CARE steering April 9th 2008 9 NED- CD: Status of the Alstom contract (4) HT optimization underway to react more barrier and to try reducing grain size. Relatively low J c partly due to binary Nb 3 Sn compound. Ti or Ta additions (limit grain growth) should enhance J c by ~ 50 %. Indeed solutions using Ta are currently implemented to achieve the Step 2. Alstom seems to be close to success although ~ 6 months are needed to produce strands. The final strand production would be launched in parallel to Step 2 completion and could not be completed by end of 2008. It would require a delay of several months. Meeting with Alstom people yesterday afternoon at CERN to discuss NED program completion. They will send to CERN very shortly a letter to express their commitment to finish the final strand production.

10. CARE steering April 9th 2008 10 NED- CD: Conductor characterization (1) EAS/SMI B215 wire B215 is the successful prototype wire developed by SMI during Step 2. According to its design, the final strand is currently produced. 288 filaments (~ 50 µm), 84 h @ 675 o C: J c ~ 2500 A/mm 2, RRR ~ 80 Heat treatment optimization studies at CERN: general trend is to decrease reaction temperature but increase duration to try to decrease Nb 3 Sn grain size. 320 h @ 625 o C: - I c = 1496 A @ 12 T and 4.2 K (gain of ~ 100 A vs 84 h @ 675 o C) - J c = 2665 A/mm 2 !!! (gain of ~ 6 % !) - RRR ~ 220 (vs 80 for 84 h @ 675 o C): much better for stability Impact of 320 h @ 625 o C HT schedule on cabling degradation (both I c and RRR) to be checked soon.

11. CARE steering April 9th 2008 11 NED- CD: Conductor characterization (2) Alstom B1/63468 strand Jc ~ 1440 A/mm 2 for 50 h @ 660 o C (reacted and tested at Alstom) Several other HT schedules tried at CERN: 50 h @ 645 o C, 25 h @ 660 o C, 50 h @ 620 o C and I c measured at CERN At Geneva University, I c measured as function of longitudinal strain (to check stress impact). J c measured at CERN or Geneva never exceeded 1590 A/mm 2 (12 T). SEM/EDS examinations (CERN) showed that the Sn content is nearly stochiometric (~ 25 at. % Sn) and there is no Sn leak into copper (expected from high RRR values).

12. CARE steering April 9th 2008 12 NED- CD: Conductor characterization (3) SEM examinations (CERN): 1. The barrier not fully reacted 2. Numerous big grains (~ 300-400 nm) Potential for more J c even for low temperature reaction (50h @ 620 o C ): bad for J c. B1/63468 micrograph (25h @ 660 o C)B1/63468 micrograph (50h @ 645 o C) Currently in CERN oven: 200 h @ 660 o C. The goal: try to completely react the barrier

13. CARE steering April 9th 2008 13 NED-IDI Work Package (1) The Insulation Development and Implementation Work Package includes two main Tasks –studies on “conventional” insulation systems relying on ceramic or glass fiber tape and vacuum-impregnation by epoxy resin (CCLRC/RAL; Task Leader: S. Canfer) Completed with a final report in March 2007 –studies on “innovative” insulation systems relying on pre- impregnated fiber tapes and eliminating the need for a vacuum impregnation (CEA; Task Leader: F. Rondeaux). Completed with a final report in December 2007 (CARE-Report-2007-037-NED)

14. CARE steering April 9th 2008 14 Next Step: Short Model Coil SMC Participant funding only (formally outside FP6-CARE-NED ) CCLRC/RAL, CEA and CERN have agreed to manufacture and test a series of LBNL-type Short Model Coils wound from NED-sub-cables so as to investigate –cable and insulation performances in real coil environment, –design limits for transverse and longitudinal loads. Coil design finished, cold mass design being finalized, winding tests with dummy in progress by RAL-CERN team (interactions with LBNL). Waiting for Nb 3 Sn strand from NED. First magnet foreseen to be tested in Sept-Oct at CERN (Courtesy P. Ferracin, LBNL)

15. CARE steering April 9th 2008 15 Deliverables NED24Final report on Heat Transfer Measurements ReportWP2CEA- WUT doneDec 07 NED30Report on innovative insulationreportWP4CEAdoneDec 07 NED25Final wire productionPrototypeWP3CERNLate 08 NED26Final report on wire characterizationreportWP3CERNLate 08 NED27Final cable productionPrototypeWP3CERNLate 08 NED28Final report on cable performancesreportWP3CERNLate 08

16. CARE steering April 9th 2008 16 Publications in 2007 1.S. Farinon, T. Boutboul, A. Devred, D. Leroy, L. Oberli,NB3SN wire layout optimization to reduce cabling degradationMT20 2.T. Boutboul, A. den Ouden, A. Devred, P. Fabbricatore4, M. Greco, D. Leroy, L. Oberli, D. Pedrini and G. Volpini,Nb3Sn conductor development and characterization for NEDEUCAS 2007 3.M. Di Michiel, C. Scheuerlein,Phase transformations during the reaction heat treatment of powder-in-tube Nb3Sn superconductorsSupercond. Sci. Technol. 20, (2007) L55- L58 4.C. Scheuerlein, M. Di Michiel, A. Haibel,On the formation of voids in Nb3Sn superconductors", Appl. Phys. Lett., 90, 132510, (2007) 5.Polinski J., Canfer S., Ellwood G., Baudouy B.,Low Temperature Heat Transfer Properties of Conventional Electrical Insulation For The Next European Dipole.CEC- ICMC 2007