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Superconductivity - An overview of science and technology

Superconductivity - An overview of science and technology. Prof Damian P. Hampshire Durham University, UK . Structure of the Talk. I) The fundamental building blocks (G-L) Ginzburg-Landau and (B-C-S) Bardeen-Cooper-Schrieffer theories The Josephson effect

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Superconductivity - An overview of science and technology

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  1. Superconductivity- An overview of science and technology Prof Damian P. Hampshire Durham University, UK

  2. Structure of the Talk I) The fundamental building blocks • (G-L) Ginzburg-Landau and (B-C-S) Bardeen-Cooper-Schrieffer theories The Josephson effect Critical current and pinning (zero resistance) II) The important materials Classic LTS high field materials – NbTi and Nb3Sn The high temperature superconductors • The pnictides (Superconductivity and magnetism) III) Technology – MRI, LHC, ITER and beyond..

  3. ii) Microscopic BCS theory – describes why materials are superconducting There are two main theories in superconductivity: i) Ginzburg-Landau Theory – describes the properties of superconductors in magnetic fields

  4. Ginzburg-Landau Theory Ginzburg and Landau (G-L) postulated a Helmholtz energy density for superconductors of the form: where α and β are constants and ψ is the wavefunction. α is of the form α’(T-TC) which changes sign at TC High magnetic fields penetrate superconductors in units of quantised flux (fluxons)!

  5. A fluxon has quantised magnetic flux - its structure is like a tornado

  6. The Mixed State in Nb Vortex lattice in niobium – the triangular layout can clearly be seen. (The normal regions are preferentially decorated by ferromagnetic powder).

  7. Reversible Magnetic Properties of ‘Perfect’ Superconductors • Below Hc, Type I superconductors are in the Meissner state: current flows in a thin layer around the edge of the superconductor, and there is no magnetic flux in the bulk of the superconductor. (Hc : Thermodynamic Critical Field.) • In Type II superconductors, between the lower critical field (Hc1), and the upper critical field (Hc2), magnetic flux – fluxons - penetrates into the sample, giving a “mixed” state.

  8. Josephson dc. SQUID

  9. Josephson diffraction The voltage across a biased SQUID as a function of field

  10. BCS Theory - the origin of superconductivity Bardeen Cooper and Schrieffer derived two expressions that describe the mechanism that causes superconductivity, where Tc is the critical temperature, Δis a constant energy gap around the Fermi surface, N(0) is the density of states and V is the strength of the coupling.

  11. Model for a polycrystalline superconductor – with strong pinning • A collection of truncated octahedra G. J. Carty and Damian P. Hampshire - Phys. Rev. B. 77 (2008) 172501 also published in Virtual journal of applications of Superconductivity 15th May 2008

  12. Critical current (Jc) measurements 77 K, zero field YBCO 4.2 K, variable B-field, Nb3Sn

  13. Fluxons do not move smoothly through a polycrystalline superconductor • The motion of flux through the system takes place predominantly along the grain boundaries. • TDGL movie 0.430Hc2 Psi2

  14. Structure of the Talk I) The fundamental building blocks • (G-L) Ginzburg-Landau and (B-C-S) Bardeen-Cooper-Schrieffer theories The Josephson effect Critical current and pinning (zero resistance) II) The important materials Classic LTS high field materials – NbTi and Nb3Sn The high temperature superconductors • The pnictides (Superconductivity and magnetism) III) Technology – MRI, LHC, ITER and beyond..

  15. NbTi multifilamentary wire – the workhorse for fields up to ~ 10 Tesla Alloy - NbTi Tc ~ 9 K BC2 ~ 14 TDuctile

  16. Nb3Sn superconducting wires- the workhorse for ITER OST MJR Nb3Sn Furukawa ITER Bronze-route Nb3Sn Outokumpu Italy (OCSI) ITER Internal tin Nb3Sn EM-LMI ITER Internal-tin Nb3Sn Intermetallic compound Nb3Sn Tc ~ 18 K BC2 ~ 30 TBrittle

  17. The critical current density (JC) depends on the magnetic field, the temperature and the strain-state of the superconductor. Superconducting magnets: large strains due to the differential thermal contraction during cool-down and the Lorentz-forces during high-field operation. Why is the effect of strain on JC important ? 1000 9 Temperature: 4.2 K 10 Magnetic Field: 8 T 100 8 10 10 Engineering Critical Current Density (Am-2) Critical Current (A) 7 10 1 23 T 6 10 0.1 5 10 -1.5 -1.0 -0.5 0.0 0.5 Nb3Sn Wire Applied Strain (%)

  18. HTS – BiSrCaCuO (BiSCCO) - Powder-in-tube fabrication - Granularity is an issue - d-wave

  19. HTS coated conductors - Kilometre long single crystals Configuration of SuperPower 2G HTS Wire™

  20. MgB2 - Brittle compound Tc ~ 40 K, BC2 (//c) ~ 20 T A nodeless BCS-type gap !

  21. Conductors in the USA

  22. Conductors in the USA 10000 YBCO B Tape Plane YBCO B|| Tape Plane SuperPower tape used in record breaking NHMFL insert coil 2007 RRP Nb3Sn Nb-Ti Complied from ASC'02 and ICMC'03 papers (J. Parrell OI-ST) 1000 427 filament strand with Ag alloy outer sheath tested at NHMFL 2212 JE (A/mm²) YBCO Insert Tape (B|| Tape Plane) Maximal JE for entire LHC Nb­Ti strand production (CERN-T. Boutboul '07) YBCO Insert Tape (B Tape Plane) 100 Bronze Nb3Sn MgB2 19Fil 24% Fill (HyperTech) MgB2 2212 OI-ST 28% Ceramic Filaments NbTi LHC Production 38%SC (4.2 K) 4543 filament High Sn Bronze-16wt.%Sn-0.3wt%Ti (Miyazaki-MT18-IEEE’04) Nb3Sn RRP Internal Sn (OI-ST) 18+1 MgB2/Nb/Cu/Monel Courtesy M. Tomsic, 2007 Nb3Sn High Sn Bronze Cu:Non-Cu 0.3 10 0 5 10 15 20 25 30 35 40 45 Applied Field (T)

  23. HTS materials and exotic materials A schematic of a high-Tc phase diagram Phase diagram for the ferromagnet UGe2

  24. The Pnictide Superconductors – the iron age revisited Iron Man : In cinemas now from Paramount Pictures and Marvel Entertainment

  25. The Pnictides - the original discovery • Layered structure • Original material: Tc 3-5 K 2006 LaOFeP

  26. A big class of new materials (> 2000 compounds) • Re-O-TM-Pn. • Pn • TM = • Re = La+

  27. Comparing HTS and pnictide structure In both cases, the superconductivity is in metallic layers, there is a charge reservoir and they are antiferromagnetic in their undoped state.

  28. Tc of the iron-based system is quite high • Tc 3-5 K 2006 LaOFeP • Tc 26 K, LaOFFeAs. Jun. 2008 • Tc 43 K with high pressure (4 GPa) LaOFeAs. Feb. 2008 Possibly the 1st 40K-class LTS superconductor • Tc 55 KNdFeAsO1-d. April/May 2008. (Also 111 phase and 122 phase)

  29. Oxygen concentration is critical for superconductivity • For the NdFeAsO1-d with different O concentration • A dome-shaped superconducting bubble has been found

  30. Page 1224 Point-contact spectroscopy Tc ~ 42K Sweep the V I - V dI/dV - V

  31. A nodeless BCS-type gap !

  32. Does Superconductivity coexist or compete with magnetism ? • This sharp drop about 150 K is due to a SDW – confirmed using neutron diffraction - P. C. Dai Nature (2008)

  33. BC2 is high • Larbalestier et al measured the resistance of F doped LaOFeAs at high fields up to 45 T. Nature 453 903 Two-gap model is qualitatively consistent with their data. H.H. Wen et al measured F doped NdOFeAs. Hc2 ~ 300 T in the ab plane and ~60-70T in c axis. Arxive:cond-mat/0806.0532

  34. High critical current in polycrystalline pnictides !

  35. Structure of the Talk I) The fundamental building blocks • (G-L) Ginzburg-Landau and (B-C-S) Bardeen-Cooper-Schrieffer theories The Josephson effect Critical current and pinning (zero resistance) II) The important materials Classic LTS high field materials – NbTi and Nb3Sn The high temperature superconductors • The pnictides (Superconductivity and magnetism) III) Technology – MRI, LHC, ITER and beyond..

  36. MRI Body scanners LHC ITER Transport Power transmission Public outreach Applications using Superconductors

  37. MRI - $1B annual market

  38. Large hadron collider – LHC ~ $ 6B 6000 superconducting magnets will accelerate proton beams in opposite directions around a 27 km-long ring and smash them together at energies bordering on 14 TeV.

  39. Some facts about the LHC • Protons are accelerated to 99.999999991% of the speed of light • The LHC lets us glimpse the conditions 1/100th of a billionth of a second after the Big Bang: a travel back in time by 13.7 billion years • High energy collisions create particles that haven’t existed in nature since the Big Bang Find out what makes the Universe tick at the most fundamental level

  40. ITER – Building a star on planet earth

  41. We need extreme conditions … At 200 million ºC, Matter becomes a plasma Picture courtesy of the SOHO/EIT collaboration

  42. ITER – A large transformer

  43. The fuel for ITER is from seawater

  44. 16 Nb3Sn toroidal field coils - each coil is ~ 290 tonnes, has 1100 strands, ~ 0.8 mm diameter to form a conductor 820 m long.

  45. A burning plasma

  46. Fusion powers the Sun and stars and has many potential attractions • Essentially limitless fuel • No green house gases • Major accidents impossible • No long-lived radioactive waste • Could be a reality in 30 years

  47. Transport Applications using Superconductors In Jan 08, the Central Japan Railway Company (JR Central) announced that it plans to construct the world's fastest train, a second-generation maglev train that will run from Tokyo to central Japan. Cost ~ 44.7 billion dollars Completion in 2025 Speed ~ 500 kilometers per hour Length ~ 290 kilometers

  48. Superconducting power transmission - currently we waste ~ 20 % of our energy just transporting it around - potentially the next industrial revolution Applications using Superconductors

  49. Conclusions The many uses for superconductivity means that many of the technological tools required to exploit new materials are in place. The new materials discovered in the last 20 years were found by relatively small determined groups. Superconductivity offers excellent science, excellent technology, excellent training and the possibility of saving the planet !! Using world-class science to produce technology is tough. It requires first class scientists, time, perserverance, creativity, luck and funding.

  50. References + Acknowledgements Acknowledgements: Xifeng Lu + colleagues in Beijing, Mark Raine, Georg Weiglein (IPPP, Durham), Eric Hellstrom (ASC Florida), Chris Carpenter (Culham) + many others ……. Bibliography/electronic version of all talks and publications are available at: http://www.dur.ac.uk/superconductivity.durham/

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