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Fabrication and Performance of Nb3Sn Rutherford-type Cable with Cu Added as a Separate Component 18 th Conference on Magnet Technology October 20 - 24, 2003 Mirco Coccoli. Outline. Introduction Mixed-strand Cable Manufacturing and Testing MC Power Losses Measurement

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Outline

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  1. Fabrication and Performance of Nb3Sn Rutherford-type Cable with Cu Added as a Separate Component18th Conference on Magnet TechnologyOctober 20 - 24, 2003Mirco Coccoli Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  2. Outline • Introduction • Mixed-strand Cable Manufacturing and Testing • MC Power Losses Measurement • A more general approach: Copper Added as a Separate Component • Quench Propagation Performance Simulated • Conclusions Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  3. Introduction • Foreseeing future Hadron Colliders, such as a 35km radius VLHC, it is desirable to investigate low cost (conductor) solutions • From the stand point of overall conductor cost, it is desirable to minimize the amount of copper that is co-processed with the superconductor during strand fabrication. • A possible solution is to add a copper fraction at final, ie cabling stage Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  4. MC Manufacturing • Two Mixed-strand Cables (MC) have been fabricated, winded in coils and tested • The first difficulty has been the matching of the elongation between the two types of strand, resulting in a mechanically instable cable (popped strands) Superconducting Strands Pure Copper Strands Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  5. MC Electrodynamic Study Field Sweep • P~Pc(FO) NsNs,sc - Less eddy current loops  Smaller power loss - This feature has been measured (M. D. Sumption et al, “AC Loss of Nb3Sn-based Rutherford Cables with Internally and Externally Added Cu” ASC02) on the tested cable and in agreement with the formula Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  6. Mixed Strand Test in SMTF (1) • The mechanical problem noticed during the cable fabrication have been shown by the tests performed in the Subscale Magnet Test Facility (SMTF) at Berkeley Lab • Two coils have been wounded out of Mixed Strand cables • Simple mixed strand • Mixed strand cable with SS core for mechanical stability • Results of the Power tests have not been satisfactory (40% and 70% of ss limit) leading to the conclusion that a good compaction in these coils is too difficult to achieve Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  7. Mixed Strand Test in SMTF (2) . B (T/s) • Short Sample limit reached in Nb3Sn coil • MC 1 reached ~40% ss • MC 2 reached ~70% ss Iquench/Iss • New Solution Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  8. Copper Added as a Separate Component • Add the copper as a core • Pure copper cored  poor quality • SS-Cu strip assembled in a “sandwich stile” ss-cu-ss • Most likely alternative: cu-ss-cu  good mechanical stability Ready a coil to be tested in SMTF Ready a coil to be tested in SMTF Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  9. Quench Speed Simulations: MC vs Trad • Copper Added separately as a core means no advantage for the power losses (~) • Protection  10 times faster quench • Subject to verification in magnet tests (LBNL) • No quench heaters in Future Accel Magnets? Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  10. Quench Speed Simulations: Gel • Two “wires” model • Simulated the dependence from the electrical conductance between the sc strand and the cu strip • Quench speeds in the 1km range • To be measured in a test… Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  11. Quench Speed Simulations: added copper RRR • Added copper RRR effect on quench speed • Small effect  one degree of freedom added to the cable design • High Copper RRR  better heat conduction property  lower peak temperatures • Simulations and practical test are foreseen Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  12. Quench Speed Simulations:SC strand RRR • Effects of Sc strand RRR • Good for low RRR • Of course there is a lower limit • Typical choice ~ 40  good enough for quench speed • Stability must be addressed as a next step of this study Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  13. Quench Velocity Model Normal Zone Superconducting Zone R (z) I1(z) I1(z0) Gel Gel Gel Gel Gel Gel R (z) I2(z0) I2(z) z • The current redistributes in the nearby copper passing trough the Gel  initial hot spot • The current flows in the pure copper and redistributes back to the sc strand Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  14. Conclusions • Several alternative methods for adding Cu to a Rutherford-type superconducting cable have been investigated • This cabling technique begun as a cost effective approach to conductor/cabling in view of future HEP accelerator magnets (VLHC) • The hypothesis of protection advantages related to quench propagation velocity is being investigated • The thermal conduction channel represented by the separately added fraction of copper has been measured to be a mean of stability against “external” heat/energy sources  more test needed • Good performance in actual magnet coils has not yet been demonstrated (<first half of 2004 at LBNL?) • Testing in the Subscale Magnet Test Facility is neither a trivial nor an expensive task Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  15. End Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

  16. Auxiliary Page Mirco.Coccoli@cern.ch RMScanlan@lbl.gov

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