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NED Status Report

NED Status Report. Thierry Boutboul (CERN) LPNHE 9 April 2008. 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

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NED Status Report

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

  2. CARE/NED JRA • Following the 2003 EU peer review, the scope of the NED program was revised to focus on Nb3Sn 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) WorkingGroup. • It involves 7 institutes (8 laboratories) • Total budget: ~2 M€; EU grant: 979 k€(over ~3 years).

  3. NED/TSQP Work Package • The Thermal Studies partof 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. 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. 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. 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/mm2 (1.25 mm) and ~ 2100 A/mm2 (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: • One billet with 78 sub-elements, like previous strands manufactured (~ 85 µm at nominal Φ) • One billet with 246 sub-elements corresponding to ~ 50 µm final sub-element diameter. First billet fulfilling NED specification.

  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 Nb3Sn process. The final wires were achieved in January 2008. Drawing very successful: B1/63468 strand: 246 sub-elements, 1308 m in a lone length!! 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 7

  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 - Jcnon-Cu(12 T, 4.2 K) ~ 1450 A/mm2 (Alstom, 50 h @ 660 oC) B1/20124 strand: 78 sub-elements, Φ1.26 mm, Cu/non-Cu = 1.53, Jcnon-Cu similar to B1/63468. Other HT schedules tried without big success for time being, max. Jc achieved: ~ 1600 A/mm2. SEM examinations at CERN showed Sn content at stochiometry (~ 25 at. % Sn) but big Nb3Sn grains, barrier not fully reacted (more details given in Characterization part). 8

  9. NED-CD: Status of the Alstom contract (4) • HT optimization underway to react more barrier and to try reducinggrain size. • Relatively low Jc partly due to binary Nb3Sn compound. Ti or Ta additions (limit grain growth) should enhance Jc 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. 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 oC: Jc ~ 2500 A/mm2, RRR ~ 80 Heat treatment optimization studies at CERN: general trend is to decrease reaction temperature but increase duration to try to decrease Nb3Sn grain size. 320 h @ 625 oC: - Ic = 1496 A @ 12 T and 4.2 K (gain of ~ 100 A vs 84 h @ 675 oC) - Jc = 2665 A/mm2 !!! (gain of ~ 6 % !) - RRR ~ 220 (vs 80 for 84 h @ 675 oC): much better for stability Impact of 320 h @ 625 oC HT schedule on cabling degradation (both Ic and RRR) to be checked soon. 10

  11. NED-CD: Conductor characterization (2) Alstom B1/63468 strand • Jc ~ 1440 A/mm2 for 50 h @ 660 oC (reacted and tested at Alstom) • Several other HT schedules tried at CERN: 50 h @ 645 oC, 25 h @ 660 oC, 50 h @ 620 oC and Ic measured at CERN • At Geneva University, Icmeasured as function of longitudinal strain (to check stress impact). • Jc measured at CERN or Geneva never exceeded 1590 A/mm2 (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. NED-CD: Conductor characterization (3) SEM examinations (CERN): 1. The barrier not fully reacted 2. Numerous big grains (~ 300-400 nm) Potential for more Jcevenfor low temperature reaction (50h @ 620 oC ): bad for Jc. B1/63468 micrograph (50h @ 645oC) B1/63468 micrograph (25h @ 660oC) • Currently in CERN oven: 200 h @ 660 oC. The goal: try to completely react the barrier 12

  13. NED-IDI Work Package (1) TheInsulation Development and ImplementationWork 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) 13

  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 Nb3Sn strand from NED. First magnet foreseen to be tested in Sept-Oct at CERN (Courtesy P. Ferracin, LBNL)

  15. Deliverables

  16. Publications in 2007 • S. Farinon, T. Boutboul, A. Devred, D. Leroy, L. Oberli,NB3SN wire layout optimization to reduce cabling degradationMT20 • 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 • M. Di Michiel, C. Scheuerlein,Phase transformations during the reaction heat treatment of powder-in-tube Nb3Sn superconductorsSupercond. Sci. Technol. 20, (2007) L55-L58 • C. Scheuerlein, M. Di Michiel, A. Haibel,On the formation of voids in Nb3Sn superconductors", Appl. Phys. Lett., 90, 132510, (2007) • 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

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