1. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 123rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 High Temperature Superconductors for the ITER Magnet System and Beyond W.H. Fietz, S. Fink, R. Heller, P. Komarek, V.L. Tanna, G. Zahn Forschungszentrum Karlsruhe, Institut für Technische Physik, Karlsruhe, Germany G. Pasztor, R. Wesche Centre de Recherches en Physique des Plasmas, Villigen, Switzerland E. Salpietro, A. Vostner European Fusion Development Agreement, Close Support Unit, Garching, Germany Motivation HTS Basics Fusion relevant application of HTS superconductor BiSCCO Prospects and Challenge for YBCO superconductor

2. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 223rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Use of High - T c Superconductors allows higher operating temperatures of 20 K to 77 K  save investment  higher efficiency much lower effort for thermal shielding  save investment ITER Demo / Proto Commercial Fusion Power Plant ≈ 2012 ≈ 2030≈ 2045 Long Term Fusion Magnet R&D Need for Efficiency

3. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 323rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Efficiency optimization For commercial power plants it is essential to reduce power consumption ITP - refrigerator: 2 kW@ 4.4 K = 0.7 MW electric power ITER: 64 kW@ 4.4 K = 22 MW electric power DEMO or Proto: ??? With a magnet system at 20 K a fusion machine would be much more efficient by a factor of 5 - 10 on electric power consumption for cryogenics. Great would be a machine with a superconducting magnet system at 65 K to 77 K! Cooling with liquid nitrogen would be possible!

4. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 423rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 T c of Superconductors BiSCCO YBCO in 2001: MgB 2 (39K) Pressure HgBaCaCuO TlBaCaCuO BiSrCaCuO YBaCuO LaSrCuO LaBaCuO

5. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 523rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Use of High - T c Superconductors (HTS) allows higher operating temperatures YBCO @ 20 K BISCCO @ 20 K YBCO @ 65 K but Carnot makes sure: even 20 K would ensure much higher efficiency YBCO is most promising

6. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 623rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Problems of High - T c Materials For example: 90 K Superconductor YBa 2 Cu 3 O 7 CuO 2 - Layers (s.c.) Spacing Layer CuO 2 - Layers (s.c.) Charge Reservoir / Doping Layered structures Correct orientation necessary! S.C. properties depend on doping Grain boundaries are detrimental Brittle materials (ceramics)  Long time R&D was necessary on the road to High - T c cables

7. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 723rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 c - axis orientation necessary for BiSCCO - > rolled tapes Long length of BiSCCO superconductor are available on the market from several companies. For example: 1200m BiSCCO tape from European Advanced Superconductor, Hanau, Germany BiSCCO is available for technical use c - axis

8. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 823rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 HTS current lead for ITER (BiSCCO) In the frame of the EU Fusion Development Program, a 70 kA HTS current lead with Bi - 2223/AgAu superconductor was developed and tested in FZK. The ITER requirements: Safety: Withstand a loss of He mass flow for 3 min at nominal current (ITER TF - coil @ 68 kA). Space: Horizontal installation in coil - terminal - boxes. Solution: Current lead consisting of three parts: Connection to low T c S.C. HTS module (Bi - 2223/AgAu) Copper heat exchanger 4.5 K 4.5 K - 65 K 65 K - 300 K

9. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 923rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 HTS module was fabricated by American Superconductor (AMSC) HTS tapes are sintered to stacks Stacks are soldered on SS panels 12 panels are arranged to form the HTS module Stainless Steel Stacks

10. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1023rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 70 kA HTS current lead Bus bar III (for connection and in addition for current distribution measurements) B300 Vacuum vessel 70 kA HTS Current Lead Test Arrangement in TOSKA 80 kA conventional current lead

11. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1123rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Results from BiSCCO HTS current lead Stable operation up to 80 kA World record for HTS !! Temperature profiles agree with calculations Contact resistances in HTS module okay but for Cu - Cu screw contact too high Current sharing temperature 77 K at 68 kA (10  V criterion) Refrigerator power consumption reduced by a factor of 5 compared to conventional lead He mass flow stopped at a current of 68 kA ! The current lead carried the 68 kA without cooling for more than 6 (!) minutes until a quench occurred HTS current lead is very robust. HTS material can be fabricated in industry with high and reproducible quality. Quench performance of HTS module excellent. HTS current leads can be used in ITER Details: Poster P2T - E - 284

12. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1223rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Steady state operation (1) @ 65K T - profiles for 0 kA and 68 kA Heat load at 4.5 K without current

13. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1323rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Steady state operation (2)

14. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1423rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Operation limits Quench temperature higher than estimated but influenced by current redistribution No changes after current cycling Critical current (1  V/cm criterion) vs. temperature estimated using the data of the manufacturer and measured quench data

15. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1523rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Summary of Results Contact resistance Soldered contact HTS module bus bar copper terminal1.9 nOhm Cold end cap of HTS (12 panels in parallel)(0.86± 0.1) nOhm Warm end cap of HTS(12 panels in parallel)(2.95 ± 0.4) nOhm Screw contact HTS module heat exchanger40 - 80 nOhm Current distribution at 68 kA(5530 ± 1800) A Heat load and cooling power Heat load at 4.5 K for 0 kA, THTS = 65 K13.5 W (45% from HTS) (HTS module + current lead structure) Resistive losses at 68 kA12.9 W 50 K He mass flow rate at 68 kA4.65 g/s (Screw contact contribution subtracted) Refrigerator power consumption0 kA / 13.5 kW 68 kA / 29.6 kW Reduction factor for ITER duty cycle of 25%5 Operation limits Quench temperature at 68 kA (10  V/m criterion)(77 ± 3) K Maximum temperature and voltage during quench160 K and 90 mV Safety margin at 68 kA in case of loss of He mass flow6 min 20 s

16. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1623rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Option YBCO? YBCO @ 20 K BISCCO @ 20 K YBCO @ 65 K what's about YBCO? BISCCO @ 20K is ok but  Same problems as BiSCCO plus 3D orientation necessary! But 65 K would be possible! c - axis

17. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1723rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Methods to grow oriented layers of YBCO Ion Beam Assisted Deposition + Pulsed Laser Deposition These vacuum methods work well but growth rate is too low for large scale application RABiTS (Rolling Assisted Biaxially Textured Substrates) Textured substrates are used for the growth of ideal oriented YBCO films. Under ideal rolling and tempering conditions the {001} - plane is parallel to the rolling plane and the - direction points to the rolling direction. Thus we have a textured substrate A buffer layer avoids chemical YBCO / tape reaction The YBCO layer adopts the orientation of the tape On top a protection layer is placed This is the "Coated Conductor"

18. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1823rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Current Status: 10 - 50 m high current coated conductor ( 1 - 2 · 10 6 A/cm 2 @ 77 K, self field) Demonstration of 500 m coated conductor (vacuum methods) aimed for 2006 (Nexans) / 2007 (Japan) / 2008 (USA) Status of the Coated Conductor Basic idea realized in 1996 for short length samples - anyhow major difficulties exist: Homogeneity of long substrates Buffer layer problem (complicated and time consuming) Slow growth of YBCO film by sputtering or evaporation

19. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 1923rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Open challenges (1): Focus at present on cube textured Ni - alloy substrate tape Challenge: Alternative tapes for fusion application Focus at present on buffer layers / CeO 2 on Ni Challenge: New conductive buffer - or no buffer at all ? (increasing stabilization) Best results with slow deposition techniques Challenge: Speed up! - > chemical deposition Industries active in chemical route: - Nexans - Trithor (starting) - American Superconductor G. Kotzyba R. Nast B. Obst S. Schlachter W. Goldacker FZK/ITP Chemically deposited buffer on Ni RABiTs tape and YBCO on SrTiO 3 Already achieved in FZK: New Virtual HGF Institute for chemical deposition of YBCO (FZK and Universities of Braunschweig, Tübingen, Dresden & Wuppertal

20. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 2023rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Open challenges (2): 1) From basic physics to technical solutions - Adopt HTS R&D to fusion needs (e.g. Ni substrates are not ideal for fusion) - Development of bundling and cabling techniques (ac loss optimization)

21. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 2123rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Development of bundling and cabling techniques ac - loss optimization is one of the most crucial points! ac - loss optimized TFMC conductor : Multi stage twisted cable in conduit with central cooling channel, Rated current: 70 kA @ 11.8 T and 4.6 K Nb 3 Sn strand (  =0.81mm) (Europa Metalli - LMI) Classic concepts

22. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 2223rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Open challenges (2): 1) From basic physics to technical solutions - Adopt HTS R&D to fusion needs (e.g. Ni substrates are not ideal for fusion) - Development of bundling and cabling techniques - Strand and subcable tests - Fusion conductor development in collaboration with industry 2) Design, Manufacturing and Test of a HTS - Model - Solenoid 3) Design Manufacturing and Test of a TF HTS - Demonstration Coil in Collaboration with Industry

23. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 2323rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 Conclusion: The development, construction and demonstration of a High Temperature Superconductor coil system for Fusion is a scientific and technologic long term challenge which has to be tackled already now for becoming ready in time. This work should be done in close collaboration of European associations and industry. The benefit from a HTS coil system will help Fusion - to be a commercial success - to secure worlds power generation during the next decades - to generate spin - offs (e.g. power engineering).

24. Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft FZK – EURATOM FUSION ASSOCIATION # 2423rd SOFT, 20 - 24 Sept. 2004, Venice, ItalyW.H. Fietz, 21.9.2004 END