HTS Roebel and Rutherford Cables for High-Current Applications

Transcription

1 HTS Roebel and Rutherford Cables for High-Current Applications S.I. Schlachter, W. Goldacker, F. Grilli, R. Heller, A. Kudymow, R. Nast, S.Terzieva KARLSRUHE INSTITUTE OF TECHNOLOGY, INSTITUTE FOR TECHNICAL PHYSICS KIT University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association

2 Outline Introduction Why do we need cables? Examples of existing cables: Low-temperature superconductors High-temperature superconductors Application case: magnets for fusion reactors ITER DEMO? HTS Roebel cables Rutherford cables with Roebel strands Concept Tape properties Bending experiments Striations to reduce hysteresis losses Conclusions and Outlook 2

3 Outline Introduction Why do we need cables? Examples of existing cables: Low-temperature superconductors High-temperature superconductors Application case: magnets for fusion reactors ITER DEMO? HTS Roebel cables Rutherford cables with Roebel strands Concept Tape properties Bending experiments Striations to reduce hysteresis losses Conclusions and Outlook 3

4 High-Current Conductors: Why superconducting cables? High current-carrying capability ( large cross section and high flexibility) Reduction of ac losses small filament size Possible applications: High-field magnets with low induction (e.g. fusion reactors) Accelerator magnets Busbars Transformers Motors, Generators 4 MVA HTSL Generator (SIEMENS) ITER TF Cable Bi2223-Roebel-cable 4 IOP Superconductivity Group Seminar Development and Applications of HTS Conductors, London

5 Types of Superconducting Cables for Magnets Rope Type: Mainly applied in Cable-in- Conduit Conductors, e.g. in ITER coils Braid Type: Similar to Rutherford cables, but more vulnerable to forces applied to broad surface Rutherford Type: High packing factor, good stacking possibilities Roebel Type: Similar to Rutherford cables but tape remaining in one plane. Suitable for HTS Nuclotron Type: Inner tube or helix for forced flow of coolant Gerard Willering, Thesis (2009), ISBN

6 Examples for superconducting cables NbTi, LCT + NET Nb 3 Sn ITER TF Cable MgB 2 Cables, KIT BSCCO Roebel Cable, Siemens REBCO Rutherford Cable, Oak Ridge - Ultera 6

7 Outline Introduction Why do we need cables? Examples of existing cables: Low-temperature superconductors High-temperature superconductors Application case: magnets for fusion reactors ITER DEMO? HTS Roebel cables Rutherford cables with Roebel strands Concept Tape properties Bending experiments Striations to reduce hysteresis losses Conclusions and Outlook 7

8 Magnetic Plasma Confinement in Fusions reactors Tokamak: Transformer induces plasma current E.g. ITER (Cadarache), JT-60SA Stellarator Helical magnetic field without plasma current E.g. W7-X, Greifswald 8

9 The ITER LTS Magnet System Purpose Toroidal Field Coil Plasma Confinement Central Solenoid Coils Transformer Plasma current Poloidal Field Coils Pinch Plasma away from walls Plasma shape and stability Correction Coils Correction of error field harmonics Number of Coils (9 pairs) Material Nb 3 Sn Nb 3 Sn NbTi NbTi Temperature 4.5 K 4.5 K 4.5 K 4.5 K Peak Field 11.8 T 13 T 6 T 4T Current 68 ka ~ 45 ka 45 ka (52 ka backup mode) Energy 41 GJ 6.4 GJ 4 GJ 7.5 ka Weight 6540 t 974 t 2163 t 85 t Conductor Length 82.2 km (strand length km) 35.6 km 61.4 km 8.2 km N. Mitchell, Matefu Spring Training school superconducting magnets April 05-09, 2009, Le Château CEA Cadarache St Paul Lez Durance France M. Huguet et al., Nuclear Fusion, Vol. 41, No. 10 (2001) 9

10 Why HTS for fusion magnets beyond ITER? The higher TOP the higher the efficiency! Estimation of electrical power consumption for cooling of superconducting magnets that can be operated at 65 K: LTS solution 4.5 K Circulation, torus & NBI cryo pumps 80 K HTS solution 4.5 K 65 K 80 K f 12 MW - 12 MW - - d h a e c Magnet system 7 MW MW 5 MW b g Thermal shield - 14 MW - Electrical power saving: 13 MW ( 40%) Complex radiation shield can be avoided Reduction of complexity Decrease of reactor size J.L Duchateau et al., R. Heller et al., EFDA Contract TW4-TMS-HTSMAG

11 Outline Introduction Why do we need cables? Examples of existing cables: Low-temperature superconductors High-temperature superconductors Application case: magnets for fusion reactors ITER DEMO? HTS Roebel cables Rutherford cables with Roebel strands Concept Tape properties Bending experiments Striations to reduce hysteresis losses Conclusions and Outlook 11

12 The ROEBEL bar concept for cabling Invented for generator Cu-cables, already applied for NbTi-LCT coils, NET, BSCCO-cable (SIEMENS) Ludwig Roebel, born at Kusel May 6th, The ROEBEL bar, an assembling method for low AC loss cables Patent (1912) of Ludwig Roebel BBC (STOTZ) Mannheim for low loss generator Cu-Cables in power generators 12

13 ROEBEL Assembled Coated Conductors Sequential assembling to RACC structure Cable No.1 from THEVA DyBCO-CC W. Goldacker et al. EUCAS-2005 Journal of Physics, Conf Series, Vol 43, 2006 p

14 2 ka class Coated Conductor ROEBEL cable Width: 12 mm Length: 1.1 m 45 tapes (15 stacks à 3 tapes) Transposition length: 188 mm Ic (77K, s.f.) = 2628 A (criterion 5µV/cm) 14

15 Outline Introduction Why do we need cables? Examples of existing cables: Low-temperature superconductors High-temperature superconductors Application case: magnets for fusion reactors ITER DEMO? HTS Roebel cables Rutherford cables with Roebel strands Concept Tape properties Bending experiments Striations to reduce hysteresis losses Conclusions and Outlook 15

16 Rutherford cable from CC ROEBEL strands Current carrying capability > 20 ka (B 0, T< 77 K )? Large magnets: nuclear fusion (DEMO), accelerators Roebel strands ~50 mm 16

17 Multi stacking of tapes to enhance Ic: 3 Roebel cables with different numbers of punched tapes Width 4 mm transposition length: 109 mm Samples No. of punched tapes Thick-ness (mm) Ic(A) DC,s.f. 77 K Roebel (14x1) Roebel (13x3) Roebel (10x5) strands 39 strands 50 strands 50strands Transport ac-loss measurements performed at IEE Bratislava: Transport losses of Roebel cables are significantly smaller than of bar with same cross section ( transposition!) S. Terzieva et al. Superc.Sci. and Technology 23 (2010)

18 Strand test in full-size Rutherford cable model Roebel Strand: Width: 4 mm Transposition length 120 mm 16 punched tapes (old SuperPower CC with Ic ~ 85 A) Cooling gas channel? 15 mm 50 mm Rutherford Cable: Al former: Width: 50 mm, height: 15 mm Transposition length 340 mm Transposition angle 20 Width of grooves: 4.5 mm 1 superconducting strand in model / 20 strands possible 18

19 Transport current test before and after assembling Roebel strand straigth: Utotal with current feeds 150 Voltage [ µv ] Usc, calc. without resistive part Roebel strand on Rutherford support structure: Utotal with current feeds 100 Usc, calc. without resistive part Result: No degradation observed! Rutherford 50 straight Current [ A ] 19 Feasibility of approach obvious and promising!!!

20 Rough estimation of current carrying potential of a CC-Rutherford cable with ROEBEL strands Specifications Size (strand / cable): 4 x 3 mm / 15 x 50 mm Twist (strand / cable): 120 mm / 340 mm 50 tapes Number of Roebel strands : 20 strands à 50 punched tapes Y.-Y. Xie et al. ; 2009 KEPRI-EPRI Joint Superconductivity Conference, Nov 16-19, 2009 Daejeon, South Korea x 20 Extrapolation: Ic of single punched tapes (@77K, self field: ~ 55 A) Ic(50 K, 10 T) ~ 0.3 Ic(77K, self field) Expected current for cable: ~ 16.5 ka (T = 50 K and B = 10 T) 20

21 Subsize Coated Conductor Rutherford Cable Properties of Rutherford cable: 10 Roebel cables, each with 10 punched tapes Width of former: 25 mm Height of former: 10 mm Twist pitch: ~184 mm 21 Properties of Roebel Strands: CC from SuperPower original tape width: 4 mm Ic of original tapes (77 K, s.f.): Width of punched tapes: Twist pitch Roebel cable: Strand-length (excl. joints): > 135 A 2 mm 113 mm ~ 476 mm

22 Field dependence of Ic in original tapes SP-KIT : REBCO: 4 mm wide 200 B_ _ B tape surface B _ _ tape surface 180 B B 160 Ic (A) K 70 K K B (mt) 22

23 Angular dependence of Ic in original tapes 160 SP-KIT : REBCO: 4 mm wide 140 B_ _ T = 68 K: 500 mt B B 120 Ic (A) 100 T = 77 K: 50 mt 100 mt 200 mt 500 mt Ic,min and Ic,max not in perpendicular and parallel orientation: doping! 23

24 Ic-measurement of Roebel Cable 3000 Roebel Cable with 10 Strands, 4 mm width Distance of Voltage Taps on Strands: 2x ltwist-pitch E=1 µv/cm 20 Voltage (µv) Voltage (µv) Current (A) Current (A) 24

25 Torsion + Bending in Rutherford Winding: Rutherford winding of strands causes simultaneous torsion + bending Test of torsion + bending properties of tapes and Roebel cables Ø angle 25

26 Torsion + Bending in Rutherford Winding: Ic( ) / Ic( =0) Ic( ) / Ic( =0) reversible irreversible REBCO tape, 4 mm width: d = 10 mm Rutherford winding angle ( ) 0.2 REBCO tape, 4 mm width: d = 5 mm d = 10 mm Rutherford winding angle ( ) 26

27 Stresses due to Torsion and Bending Torsion Bending Longitudinal strain (tensile, compressive, Longitudinal strain (tensile, compressive) depending on boundary conditions / neutral axis) + Shear stresses 27

28 Torsion-Bending of Roebel Cable Measurement results 1.2 REBCO Roebel Cable, 4 mm width: d = 10 mm 1.0 Ic( ) / Ic( =0) Cable after torsion + bending solder Rutherford winding angle ( ) Cable destroyed due to soldering close to bending area. Measurement of cable-ic difficult! 28

29 Rutherford Cables with Roebel Strands Joint resistance leads to inhomogeneous current distribution in Roebel cables Ic measurements difficult, especially for short cables Jointing on long length necessary Roebel Cable with 10 Strands, 4 mm width Distance of Voltage Taps on Strands: 2x ltwist-pitch E=1 µv/cm 20 Voltage (µv) Voltage (µv) Good bending properties as long as strands are free to move in cable direction: Current (A) 0 Large distance between step-overs Soldering or glueing after winding Edge-to-edge distance of Rutherfordcable twist pitch of Roebel cable Current (A)

30 Outline Introduction Why do we need cables? Examples of existing cables: Low-temperature superconductors High-temperature superconductors Application case: magnets for fusion reactors ITER DEMO? HTS Roebel cables Rutherford cables with Roebel strands Concept Tape properties Bending experiments Striations to reduce hysteresis losses Conclusions and Outlook 30

31 Reduction of hysteresis losses: striation of strands Reduction of hysteresis losses: Reduction of tape width Filamentarization striation of strands Strands with Ag cap layer (no Cu stabilizer) Striations with IR picosecond laser 31

32 Accuracy of IR picosec. laser grooving Actually 25 micron width Cutting down to substrate No melting effects Option for width: < 10 microns 32 Ag cap layer grains YBCO pieces Buffer layer AFM SEM

33 Preliminary results on AC losses (inductively measured) B (90 deg) 72Hz 36Hz 18Hz 72Hz 36Hz 18Hz single nonstriated strand 1 10 ROEBEL cable ROEBEL cable with striated strands Q\B2 Q\B2 B (90 deg) single striated strand 72Hz 36Hz 18Hz 72Hz 36Hz 18Hz Magnetic field, 0H [T] Magnetic field, 0H [T] Inductive measurements: Loss reduction is more effective in the case of the single strand Coupling currents between different striated strands in the cable occur! Resistive measurements: Coupling of ends (joints) prevents loss reduction transposition necessary 33

34 Outline Introduction Why do we need cables? Examples of existing cables: Low-temperature superconductors High-temperature superconductors Application case: magnets for fusion reactors ITER DEMO? HTS Roebel cables Rutherford cables with Roebel strands Concept Tape properties Bending experiments Striations to reduce hysteresis losses Conclusions and Outlook 34

35 Conclusions and Outlook f d h a e c b Cables with high current carrying capability needed for several applications g Future fusion reactors could be more effective and less complex with HTS magnets Cabling method for 2G REBCO HTS tapes: Roebel technique Enhancement of current carrying capability: Rutherford cables with Roebel strands Open questions: Strand Coupling Bending / mechanical properties Electrical stabilization AC loss reduction 35