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Technology for High Field Magnets with YBCO Conductors

Technology for High Field Magnets with YBCO Conductors . Presented by H.W.Weijers Collaborators U. P. Trociewitz, W. D. Markiewicz, D. C. Larbalestier and many others at NHMFL SuperPower US-Japan workshop, Dec 14, 2009. Outline. General considerations Coated conductors, Bi-2223, Bi-2212

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Technology for High Field Magnets with YBCO Conductors

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  1. Technology for High Field Magnets with YBCO Conductors Presented by H.W.Weijers Collaborators U. P. Trociewitz, W. D. Markiewicz, D. C. Larbalestier and many others at NHMFL SuperPower US-Japan workshop, Dec 14, 2009

  2. Outline • General considerations • Coated conductors, Bi-2223, Bi-2212 • Technology for 32 T • and beyond • Summary

  3. Definitions Je= I/(conductor area) Jave= N*I/(winding area) Jave=l*Je l= fill factor

  4. Applications of high-field HTS magnets • Research magnets • NMR magnets • Scattering magnets • HEP • Dipoles • Muon cooling • Very high field hybrids Multi-kA cable preferred

  5. What does it take? • Current density in windings • Manageable stress levels Key enabling parameters

  6. What does it take? • Current density in windings • Manageable stress levels • Stability against disturbance • Protection against quench and other fault conditions • AC-loss/ ramping losses • Magnetic field quality Key enabling parameters

  7. What does it take? • Current density in windings • Manageable stress levels • Stability against disturbance • Protection against quench and other fault conditions • AC-loss/ ramping losses • Magnetic field quality • Joints, terminals, insulation • Fabrication technology • Reliability • Desirable: Flexible architecture (I), wind-as-is Key enabling parameters

  8. What does it take? ~0 T 11 T20 T 25 T/30T • For 4 to 5 cm bore magnets • 25 T: Jave ~100 A/mm2, smax ~ 200 MPa • 30 T: Jave ~ 200 A/mm2, smax > 400 MPa for reasonably compact magnet • Stress goes up significantly for larger diameters 1.5 m Cross-section of an imaginary 25 T magnet based on NHMFL 21 T NMR magnet

  9. Conductor comparison All have something (most), none have everything proven for 30+T right now

  10. Ready for high field magnets?(modest bore solenoids) • 25 T magnets: Bi-2223 yes, Bi-2212 close • 30 T magnets: Bi-2223 marginal, 2212 lacking Je • YBCO: + best Je and strength suitable for 25 and 30 T + flexible architecture • Reproducibility/predictability beyond Je:TBD • Fast conductor development is double-edged (not magnet pull) • Lengths available • Lack of broad experience Hopefully coated conductor technology will be ready soon

  11. 32 T Magnet Parameters Total field 32 T Field inner YBCO coils 17 T Field outer LTS coils 15 T Cold inner bore 32 mm Uniformity 5x10-4 1cm DSV Current 186 A Inductance 436 H Stored Energy 7.54 MJ YBCO Nb3Sn NbTi Tentative: pancake winding for inner coil, layer winding for 2 larger HTS coils User magnet for NHMFL milliKelvin facilty

  12. 32 T YBCO Coil Parameters YBCO coil 1 2 3 Inner radius (mm) 20 47 77 Outer radius (mm) 42 71 101 Coil length (mm) 144 240 340 Field increment (T) 5.7 5.7 5.6 Jave (A/mm2) 225 211 211 Current density copper (A/mm2) 426 426 426 Maximum stress (MPa) 305 400 435 Conductor length (km) 0.75 2.4 5.2 The proposal design is intended to be compact and yet practical in stress and copper content for protection.

  13. YBCO Test Coils SuperPower I. Bmax = 26.8 T ΔB = 7.8 T SuperPower II. Bmax = 27 T ΔB = 7 T NHMFL I. Bmax = 33.8 T ΔB = 2.8 T NHMFL II. Bmax = 20.4 T ΔB = 0.4 T During construction

  14. YBCO Test Coils and 32 T YBCO Coils • Maximum field increment in highest background field • Homogeneous stress distribution: • Self-supporting windings • Special terminals to avoid winding reinforcement • ~1.5 mm thick, 25 mm tall windings • Standard SP4050 • 30 um Cu plating • Layer wound, epoxy impregnated • Instrumented with multiple V-taps, strain gages NHMFL I. SuperPower I. NHMFL II. 32 T YBCO Coils SuperPower II. 3 built Images are to scale

  15. Results so far • Very high Jave > 30 T (> 460 A/mm2 in test coil) • Without reaching conductor limits • Large diameter stress coils • Have not reached conductor limits at 760 MPa, 0.6% strain, Jave = 300 A/mm2 at 20 T • Terminals on thin coils that provide minimal reinforcement of windings are difficult • Compares favorably with benchmark and design Jave and s • Need to account for larger field angle (~20º) in user magnet • Repeated (protected) quenches do not affect Je • Also at self-field • Magnet technology in relatively early stage

  16. 32 T YBCO R&D topics • Winding techniques • New layer winding equip’t • Quench protection • Amount Cu needed • Heaters • Terminals • Joints (Walsh) • Insulation • Varnish, paper, UV-cure epoxy • ……

  17. Beyond 32 T YBCO R&D topics • Insulation • mm-level coatings (oxide, ..) • Support “magnet” conductor development • Reduced anisotropy at low T, high B • Round wire • Find limits, towards full potential • NMR with HTS • Focus on field quality (not high field yet) • Multi-kA cables • Test of cable at 4 K, 20 T

  18. Summary • Breakthrough coated conductor developments in last few years • Stress tolerance and Jave for 30 T+ demonstrated in conductor and coils • 32 T YBCO project pushing high-field magnet technology development • Development required in many areas • Broader supporting R&D at NHMFL • Starting research on HTS NMR and multi-kA cables

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