Are HTS conductors up to the Magnet Builders’ vision yet? David Larbalestier On behalf of the YBCO Conductor Group (Dmytro Abraimov, Tolya Polyanskii, Aixia Xu, Pei Li, Yan Xin, Valeria Braccini, Chiara Tarantini, Jan Jaroszynski), the 2212 Group (Tengming Shen, Eric Hellstrom, Ulf Trociewitz, David Myers, Andrea Malagoli, Jianyi Jiang, Fumitake Kametani) and the HTS Coil R&D group (Huub Weijers, Ulf Trociewitz, Jun Lu, Jan Jaroszynski, Patrick Noyes, Matthieu Dalban, David Hilton, Valeria Braccini and Aixia Xu) and 32 T (Denis Markiewicz).

David Larbalestier NHMFL David Larbalestier NHMFL Slide 2 What does HTS offer us? A decisive break from Nb-Ti and Nb 3 Sn Jc is always limited by proximity to H c2 Bruker has just achieved the 1 GHz (23.5T at ~1.5K) in a Nb-Ti/Nb 3 Sn NMR magnet A magnificent but asymptotic advance! HTS removes the Hc2 or Hirr restriction but imposes new ones Stress Quench A young and still primitive conductor technology because the materials are so much more complex than Nb-Ti or Nb 3 Sn Nb 3 Sn is limited to ~18 T in saddle magnets and ~ 24 T in solenoid magnets

David Larbalestier NHMFL David Larbalestier NHMFL Slide 3 Plot maintained by Peter Lee at: Short sample J e of 2212 and YBCO soon exceed Nb 3 Sn

David Larbalestier NHMFL David Larbalestier NHMFL Slide 4 2 (or3?) viable HTS magnet conductors YBCO with phenomenal Jc - ~20 x 10 6 A/cm 2 at 25T But YBCO is ~1% of cross-section 50% is high strength superalloy Round wire Bi-2212 – the preferred shape for cabling 2  m Ag 20  m Cu 50  m Hastelloy substrate 1  m HTS ~ 30 nm LMO ~ 30 nm Homo-epi MgO ~ 10 nm IBAD MgO < 0.1 mm YBCO coated conductor 4 x 0.1 mm Bi-2212 round wire ~ 1mm dia. Bi-2223 tapes represents a third possibility exhaustively studied for power applications 30-77K Now mature – lower Je than 2212 and YBCO

David Larbalestier NHMFL David Larbalestier NHMFL Slide 5 Manufacturing processes are quite different Powder in tube: 2212 and 2223 IBAD-YBCO

David Larbalestier NHMFL David Larbalestier NHMFL Slide 6 Longitudinal defects in YBCO limit transverse current transport YBCO is a pilot plant product Pilot manufacture at SuperPower and AMSC Pre-pilot at Fujikura, Bruker, Sunam….. Pilot means many defects – manufacturing lengths of m lead to m deliveries Transport I c over 5 m lengths 1 km spool MO by Polyanskii, I c (length) by SuperPower 4 mm

David Larbalestier NHMFL David Larbalestier NHMFL Slide 7 Debugging a recent test coil Expected > 5T in 31T from 120m of tape Coil quenched at about 20% expected Ic The Tapestar Hall array shows more local and bigger Ic drops n value Transport I c TapeStar Xu conductor, Trociewitz and Dalban coil YBCO Hastelloy

David Larbalestier NHMFL David Larbalestier NHMFL Slide 8 Deconstructed YBCO coil shows some present challenges ~  m layer spacing due to “dog-boning” of conductor Packing density ~69 % No visible cracking of the epoxy Glass fiber thread spacer between filaments Interlayer (wrapping paper) Trociewitz, Dalban

David Larbalestier NHMFL David Larbalestier NHMFL Slide 9 Bi-2212 is normally reacted in place NHMFL has made small coils generating 32T in 31T Oxford has made coils giving 2.5T in 20T Round wire conductor (OST) allows easy winding and cabling for high current May be good for NMR Time Temperature ~880ºC 2212 formed 2212 melted Slow cooling t melt, time in the melt Complex heat treatment We lead a DOE-HEP effort to understand the limits of Bi-2212 for making strand, Rutherford cables and test coils VERY HIGH FIELD SUPERCONDUCTING MAGNET COLLABORATION (VHFSMC) Reasons for the complexity are being addressed Shen, Jiang

David Larbalestier NHMFL David Larbalestier NHMFL Slide 10 OST wires with reduced porosity have high J c (4.2K,5T) = 2900A/mm 2 (I c (4.2K,5T) = 862A) Before reaction After reaction Shen, Jiang et al in VHFSMC collaboration with OST

David Larbalestier NHMFL David Larbalestier NHMFL Slide 11 Challenges remain with 2212 coils too Layer 1…Layer 3…Layer 11…Layer 20 Myers, Trociewitz Liquid BSCCO can leak through the Ag sheath Coil performance is ~2/3 short sample performance We are beginning to understand why

David Larbalestier NHMFL David Larbalestier NHMFL Slide 12 Conductor and Coil technologies are intimately linked Coils, R&D Test Beds 27T with SuperPower 31T 2212 NHMFL 34 T YBCO NHMFL HTS Magnet Systems 32 T Zeemans Conductors YBCO

David Larbalestier NHMFL David Larbalestier NHMFL Slide 13 Major macro issue: the DOE budget request to Congress January 2010 YBCO is commercial and DOE is going to end support and search for RT superconductors!

David Larbalestier NHMFL David Larbalestier NHMFL Slide 14 A 2017 vision YBCO and Bi-2212 will both be available in affordable, uniform, multi- km lengths We will be transitioning to round wire, multi- filament YBCO 32T will have satisfied many, many users Small coils will have achieved T HTS magnets will be widespread

David Larbalestier NHMFL David Larbalestier NHMFL Slide 15

David Larbalestier NHMFL David Larbalestier NHMFL Slide 16 Summary Strengths The lab has a long tradition in HTS magnets – and now conductors Weaknesses Very complex materials in pilot plant stage Weakening DOE support Opportunities Make magnets impossible with Nb Fulfill COHMAG Make wise collaborations Threats Underestimate the challenges Overpromise and under-deliver