Superconducting Magnets for Fusion Part II

Walter H. Fietz

Institue for Technical

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association www.kit.edu Superconducting Magnets for Fusion II

Tokamak • JT-60SA

Stellarators • LHD • W7-X

HTS concepts and applications • Current Leads • Future Fusion Magnets with HTS

2 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Broader Approach and JT60

Within the Broader Approach the existing Japanese JT60 shall be upgraded to JT60-SA with superconducting magnets to support ITER and the way to DEMO.

3 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 JT60: Replacing Cu magnets by SC magnets: JT60-SA

JT60-SA parameter

4 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 with courtesy of Yutaka KAMADA, TCM-25 meeting, Aviles, Spain, 2016

5 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 2017 07 05 TCM in Naka

Technical Coordination Meeting

6 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Detail view of JT60-SA Assembly

7 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Mechanical Connection of TF Coils

8 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Status summer 2018: All TF coils are assembled!

9 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 JT-60SA - All CS-Modules finalized

• The manufacturing of the last central solenoid (CS) module (CS3) has been completed. • All four modules have been manufactured. At present, they are being prepared for integration. • The four CS modules will be integrated and transported to the QST Naka site. • The integrated CS weighs 100 t and is 11 m high.

http://www.jt60sa.org/b/index_news101.htm?news101/news101.php http://www.jt60sa.org/b/index_news102.htm?news102/news102.php

10 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 EU-share of JT-60SA close to completion

On 31 March 2018, F4E (and Europe!) has, for the first time reached 98.9% of the planned commitments: we are on schedule, perfectly aligned for the final approach to the first in September 2020.

But looking back our path is marked by milestones ... • the great achievement of the Cryostat, fully supplied by CIEMAT with excellent quality and ahead of schedule, • the successful and timely completion of the supply of the High Temperature Superconductor Current Leads (HTS-CLs) by KIT, • the successful tests of the first part of the Superconducting Magnets Power Supplies (SCMPS) by CEA, • the Switching Network Units (SNU) (by ENEA) • The Cryoplant (by CEA) fully installed and operational since December 2016, • of the Quench Protection Circuits (QPC) by CNR-RFX ready since 2015 and opening the way to European on-site installation at the QST Naka site.

http://www.jt60sa.org/b/index_news100.htm?news100/news100.php

11 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 JT60-SA is on a good path!

12 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 : (LHD) Nat. Inst. of Fusion Science (NIFS), Japan

Outer diameter of the machine 13.5m Toroidal plasma diameter Approx. 8m Poloidal plasma diameter 1.0 to 1.2m

13 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Stellarator: Large Helical Device

Superconducting Helical coils manufactured on site 11 km superconductor NbTi

Iop: 13 kA (average 11 kA)

Helical coils http://tell.la/view/1268

1998 first plasma

First plasma Large Helical Device http://www.ipp.mpg.de/ippcms/de/presse/a http://tell.la/view/1268 rchiv/03_98_pi.html

14 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Poloidal conductor 2018 ... A lot of years later

15 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 LHD Superconducting Magnet System N. Yanagi, NIFS

Helical Coils Poloidal Coils 27.5 mm 18 mm Conductor current : 13 kA : 6.9 T NbTi/Cu Rutherford, Al-stabilized Pool-cooled by liquid helium Temp. 4.4 K è 3.8 K (subcooled)

Conductor current : 31.3 kA Magnetic field : 5 T NbTi/Cu Cable-in-Conduit Force-cooled by supercritical helium Temp. 4.5 K

16 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 LHD

17 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 LHD was the outstanding Stellarator for a decade

Next step with HTS?

18 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS for the next generation of LHD

https://nucleus.iaea.org/sites/fusi onportal/Shared%20Documents/ DEMO/2018/3/Yanagi.pdf

19 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Applying HTS to Helical Reactors

https://nucleus.iaea.org/sites/fusi onportal/Shared%20Documents/ DEMO/2018/3/Yanagi.pdf

20 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 LHD with HTS may be the milestone towards a continuous operating plant

21 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Modular Stellarator W7-X Main field coils and helical coils grow together to non-planar modular coils.

Toroidal Helical Modular coils field coils field coils

H.S. Bosch, 9.5.2006, HGF – Siemens Fusions-Workshop, Karlsruhe

22 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Wendelstein 7-X

Stellarator, operated by IPP in Greifswald

Technical Data: Plasma major radius 5,5 m Plasma minor radius 0,53 m Magnetic field 3 T Plasma heating 14 MW Plasma volume 30 m³ Plasma inventory 5 - 30 mg Plasma temperature 10 to 60 106 K

23 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Test of W 7-X DEMO-coil in TOSKA

24 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 W7-X Conductor

243 NbTi-Strands each composed from NbTi- filaments in a Cu-matrix

3 of them twisted... 3 triplets twisted again...... over 5 twist stages ... -> 35 -> 243 Strands in the cable

This cable was inserted in a Strand fromP. Komarek, Hochstromanwendungen square aluminum jacket der Supraleitung, Teubner Stuttgart, 1995 Cable + jacket = Conductor. This conductor was wound to form the winding pack.

25 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Testing of W7-X Coils All W7-X coils have been tested in a dedicated test facility in Saclay (CEA).

26 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Wendelstein 7-X - complex installation!

27 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Two Installation sites for half modules (2009)

28 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 29 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 To optimize case cooling, copper strips were applied

30 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Pipe Routing – a Challenge!

31 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Feeder Preparation

32 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 W7-X installation and module mounting

T. Rummel, TOFE 2012, Nashville, August 2012

33 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 W7-X Current Leads are installed

34 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 W7-X finalized, commissioned and operational

W7-X machine close to finalization The system with all magnets & feeders incl. KIT current leads and gyrotrons are operational

35 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 First Hydrogen Plasma in W7-X in Feb 2016

https://www.mpg.de/9926419/ wendelstein7x-start

36 Sept. 7th, 2018 W.H. Fietz - Superconducting magnets for fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 W7-X 2018 upgrade with subsequent Record Results

Over 8,000 graphite wall tiles Stellarator record for fusion product and ten divertor modules have Plasmas lasting up to 26 seconds were produced been installed in the plasma with a heating energy of up to 75 megajoules vessel plus new heating and fed into the plasma. measuring facilities In 15 months upgrade work At an ion temperature of about 40 million degrees https://www.ipp.mpg.de/4254576/08_17 and a density of 0.8 x 1020 particles per cubic meter, W7-X has attained a fusion product affording a good 6 x 1026 degrees x second per cubic meter, the world’s stellarator record.

https://www.ipp.mpg.de/4413312/04_18

37 Sept. 7th, 2018 W.H. Fietz - Superconducting magnets for fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 2018: W7-X is performing plasma operation with much more power

38 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Long Term Fusion Magnet R&D towards DEMO

Need for Efficiency

ITER DEMO Fusion Power Plant ≈ 2025 ≈ 2050

Current leads will use HTS for efficiency - already for ITER

39 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 BSCCO application for Current Leads (CL) Current leads transfer current No losses with a BiSCCO-modul from 60 K to 4 K ! from room temperature to the 4 K Lower heat conduction from 60 K to 4 K, too. level in the cryostat vacuum. HTS CL are much more efficient compared to Cu CL An enormous amount of cooling èfor ITER approx. 1 M€ saving power cost / year power is necessary to cool the CL Current, e.g 68.000 A Conventional HTS Cu current lead current lead current 20 ∘ C 300 K

Cu heat exchanger

4 K He 4 K 60 K coolin g no BSCCO losses! -270∘C = 4 K 4 K coil current Isolation vacuum to coil

40 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS Current Lead Demonstrator for ITER (KIT & SPC)

Connection to busbar HTS module (Bi - 2223/AgAu) Copper heat exchanger (HEX) 4.5 K 4.5 K - 65 K 65 K - 300 K

Cooled [email protected] K HTS module only conduction cooled Cooling of HEX with 50 K He (design value) Module Stack BSCCO Tape

HTS Current Lead Demonstrator successfully operated in 2004 - even at 80 kA! * *W.H. Fietz et al, Fusion Engineering and Design Subsequent decision of ITER to use HTS current leads. 75–79 (2005) 105–109 ITER feeder system was negotiated earlier to be in the hands of China. Therefore China is building HTS current leads for ITER.

41 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS Current Leads for W7-X by KIT 16 HTS CL (17.6 kA) for W7-X Construction started in 2007 Two prototypes tested in Paschen tight layout All 14 series current leads successfully tested, delivered and installed All series current leads are operational

42 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS Current Leads for JT-60SA by KIT 26 HTS Current Leads (20 & 26 kA) for JT-60SA Construction started in 2013 Current Lead Testing facility Karlsruhe (CuLTKA) was constructed to speed up testing All 26 current leads successfully tested & delivered Project finished 20217 within budget and schedule

Test of JT-60SA CL in Test facility CuLTKa

43 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS Current Lead technology transferred to REBCO

The ITER HTS CL demonstrator and the W7-X and JT-60SA HTS current leads use 1. Generation HTS material BiSrCaCuO. But industry has shifted to superior REBaCuO. Is it possible to use REBCO material? Main problem: Current feeding to the superconductor stack

For BSCCO stacks this is trivial For REBCO a staircase connection is necessary The current can pass from tape to tape

1st 20 kA current lead with HTS material REBCO built and tested successfully! REBCO HTS module with staircase connections at each end, waiting for REBCO tapes

R. Heller et al. 2018 Supercond. Sci. Technol. 31 015021

R. Heller et al 2018 Supercond. Sci. Technol. 31 055014

44 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Outline

Intro – from LTS to HTS

Technical HTS Materials: Properties, challenges and perspectives BSCCO (Bi-2223) REBCO

Applications of HTS in Fusion HTS Current Leads HTS for Fusion Magnets

Conclusion

45 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Long Term Fusion Magnet R&D towards DEMO

Need for Efficiency

ITER DEMO Fusion Power Plant ≈ 2025 ≈ 2050

HTS for FPP

Can a TF coil for a future Fusion Power Plant be built with HTS?

46 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS Cables with coated conductors

Problem: REBCO Coated Conductors are available as flat tapes only Ø cabling difficult due to bad bending properties in tape plane

But: There are different concepts to make cables out of REBCO coated conductors:

47 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 REBCO High Current Cable Concepts

CORC: TSTC: Roebel - Cable: Conductor on Round Core Twisted Stacked Tape Cable

D. van der Laan, M. Takayasu et al., W. Goldacker et al., SUST 22 (2009) 065013 IEEE TAS 21 (3) (2011), 2340 IEEE TAS 17 (2) (2007) 3398ff.

D. van der Laan M. Takayasu W. Goldacker snf.ieeecsc.org/file/5531/download?token=yI9Mw https://indico.cern.ch/event/308828/contr Supercond. Sci. Technol. 27. (2014) 093001 ga0 ibutions/1680713/attachments/589814/81 1821/WAMHTS-1_Takayasu.pdf

48 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Stacked-Tape HTS High Current Cable Concepts

TSTC Twisted Stacked Tape Cable TSTC - CICC M. Takayasu et al., STARS G. Celentano, et al., IEEE TAS 21 (3) (2011), 2340 N. Yanagi, IEEE TAS 24 (3) (2014), 4601805 FUS. SC. & TECH. 60 (2) (2011), 648

Round - TSTC HTS CrossConductor D. Uglietti, et al., M. J. Wolf, et al., IEEE TAS 24 (3) (2014), 4800704 IEEE TAS 26 (2) (2016), 6400106

49 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Forming Round strands by enclosing conductor stacks in Cu half shells (Swiss Plasma Center)

Fabrication Trials of Round Strands Composed of Coated Conductor Tapes. D. Uglietti et al., IEEE TAS 23(3),(2013) 4802104

Test of 60kA coated conductor cable prototypes for fusion magnets D Uglietti et al., 60 kA cable for large magnets Supercond. Sci. Technol. 28 (2015) 124005 demonstrated @ 4.2 K and 12 T

50 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS CroCo – one step from single tapes to the CrossConductor

Producing HTS CroCo from up to 60 HTS tapes in a single step! Optimized superconductor content in cross form Fabrication demonstrated up to 8 m length

51 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS CroCo – twisted during fabrication without stress

52 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Conceptional design of a TF coil for a future Fusion Power Plant Using EUROfusion DEMO baseline 2015 parameters as orientation

53 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Design aspects of a TFC winding pack (WP) Machine Material / SC

Field at plasma & conductor Ic(B,T) Number of TF coils Strain dependence Dimensions of coils irradiation Space for WP

Winding pack Conductor Number of windings: Copper cross-section Operational current, Void fraction Inductance of coil He pressure drop Voltage at discharge Conductor Ic & temperature margin Geometry of WP, jacket + cable space Mechanical limits of the cable Mechanical strength of jacket and Hot spot temperature at quench Insulation AC losses

54 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Conceptual Designof an HTSTF Coil for a Fusion Power Plant (FPP) by KIT CroCo monolithic strand ∅10.4mm as basis for conductor design

6 around 1 cable with Iop=50 kA embedded in SS jacket Winding pack 12 x 24 turns (radial x toroidal, layer wound) Cable dimension is unchanged for different layers Jacket wall thickness constant in toroidal direction and increased in radial direction 9.5 3.5

4/3 CroCo with thicker Cu tube for 6 around 1 cable, Iop=50 kA

55 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Conceptual Design of an HTS TF coil for a FPP 2-dim structural assessment turn insulation

Turn insulation 1.5 mm Layer insulation 2 mm Ground insulation 10 mm

56 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Conceptual Design of an HTS TF coil for a FPP

Temperature margin Parameter VALUE Operation current Iop 50 kA Peak field on conductor 12.124 T Total number of turns 288 Inductance 5.61 H Iop/Ic 0.68 Discharge time constant 30 s Discharge voltage 9.275 kV Operating temperature 4.5 K Current sharing temperature 14.2 K Temperature margin 9.7 K Nuclear heat deposition / coil 200 W He mass flow rate / layer (2-in-hand) 3.3 g/s Pressure drop 0.43 bar Tmax in jacket during quench 172 K Tmax in cable/core during quench 223 / 236 K Linearized Tresca stress in case (f=0.3) 581 / 678 MPa Linearized Tresca stress in jacket (f=0.3) 609 / 788 MPa Quench analysis Shear vs compression in turn insulation Within allowable tDEL = 12.45 s + 1.1 s = 13.55 s

A HTS TF coil for a future Fusion Power Plant is feasible

57 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS CroCo - a Superconductor Strand for Fusion Magnets, Power Transmission and more ... Current Density up to 500 A/mm² at 4.2 K,12 T Designed for industrial, long length fabrication Invented for fusion magnets, but applicable for power transmission, Aluminum electrolysis, First Prize of EU Commission for and many more High Power Applications Innovation in Fusion Research Large Magnets (e.g. for Fusion) Power Transmission 6 HTS CroCo's around a Cu rod can 12 HTS CroCo's form a 35 kA cable, form a 50 kA cable for fusion coils cooled with liquid N2 at 77 K

TF-coil Conductor 50 kA cross-section at 12 T, 4.5 K

58 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 35 kA cable demonstrator with HTS CroCo

12 HTS CroCos

Cu – busbars

59 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 HTS CroCo 35 kA DC Cable Demonstrator at 77 K 12 HTS CroCo with 22*6 mm tapes and 10*4 mm tapes carried 35 kA

at LN2 temperature

60 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Conclusions Several HTS materials are available for use in fusion

f BSCCO HTS material is used for current leads h d a REBCO HTS material with good electromechanical properties e c is now available in long length from industry b g

Several cabling concepts for high current HTS cables are existing a: Blanket modules e: equatorial ports b: Divertor plates f: upper ports c: cold shield (permanent) g: divertor ports d : vacuum vessel h: TF coils HTS current leads: are (will be) used for W7-X JT-60SA and ITER

HTS magnets First full-size HTS conductor tests were performed successfully HTS CroCo could be used as a strand for fusion magnets Operation at T = 4.5 K with large temperature margin possible A HTS TF fusion coil is feasible!

HTS conductors can be used for power transmission, too

61 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Thanks' for your attention

An actual review " High Temperature Superconductors for fusion magnets" can be found here: Bruzzone et al 2018 Nucl. Fusion https://doi.org/10.1088/1741-4326/aad835

62 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Compact Tokamak Concepts The ARC concept by MIT (ARC = Affordable, Robust, Compact)

Compact design: 3.3 m plasma major radius • Magnetic fields up to 23 T

• Top = 20 K • Superconductor grading in the conductor • Stresses of 675 MPa (inner leg of TF coil) • Only possible with HTS magnets • Idea of demountable joints

In 2018 this idea was modified to SPARC (Smallest Possible ARC) https://www.psfc.mit.edu/research/topics/sparc

B.N. Sorbom et al., Fus. Eng. & Des. 100, (2015), 378–405

63 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018 Comments to compact Tokamak concepts like (SP)ARC To go to higher fields with REBCO is feasible. 13 T or 15 T at 4.5 K is ok. 23 T at 20 K – to be demonstrated!

ITER structure material (12 T, 5 K, 68 kA) is already at the limit ARC is planned to go to >23 T (20 K, 70 kA) -> Elastic limit of 316LN will be critical (higher temperature is detrimental)

Demountable joints to “open” the magnets is a fascinating idea – but to open and reclose thousands of REBCO joints is challenging!

0.1 mm

Divertor and breeding blankets for ITER are challenging. How to handle higher divertor loads & Tritium self-sufficiency in such an ARC?

64 Sept. 7th, 2018 W.H. Fietz - Superconducting Magnets for Fusion - Part II ESAS Summer School on Applied Superconductivity, Vienna, Sept. 3-7, 2018