Challenges on demountable / segmented coil concept for high-temperature superconducting magnet N. Yanagi 1, S. Ito 2, H. Hashizume 2, A. Sagara 1 1 National Institute for Fusion Science 2 Tohoku University In collaboration with Z. Hartwig MIT, Plasma Science and Fusion Center Fifth IAEA DEMO Programme Workshop (DPW-5) May 7-10, 2018, Daejeon, Republic of Korea. 1/27
2/27 Contents Quick overview of the fusion reactor design employing HTS Quick overview of the HTS conductor development for fusion magnets Demountable / segmented (joint-winding) coil concept using HTS conductors Joint-winding concept for the helical fusion reactor FFHR Demountable coil concept for the compact tokamak reactor ARC Pros and Cons for the demountable / segmented (joint-winding) coil concept
3/27 High-Temperature Superconductor (HTS) (1) High critical current to high field (2) High cryogenic stability (3) Low cryogenic power (4) High mechanical rigidity (5) Industrial production of tapes (6) Saving helium resources High field High temp. High heat Copper Rare-Earth Barium Copper Oxide (REBCO) REBCO Cp Hastelloy Stability Margin Q C T p 5 3 T 2 10 (J/m K) 10 (K) 2 (J/cc) Higher than CIC conductor Low quench risk! N. Yanagi, S. Ito, et al., Plasma and Fusion Research 9 (2014) 1405013
Pioneering Work of applying HTS to tokamak reactor designs ARIES-AT (USA) VECTOR (JAEA) YBCO copper YBCO Hastelloy Substrate F. Dahlgren et al. YBCO (2006) T. Ando, S. Nishio, H. Yoshimura (2004) Bi-2212 Bi-2212 CIC conductor 10 ka@20 K, 12 T T. Isono et al. (2003) 4/27
controllability becomes high at high T operation, (because specific heat ~ T 3 ) SC joint is promising and innovative. (Ohmic heat on cryo. < a few % of P f ) Pioneering Work of applying HTS to helical reactor designs H. Hashizume, S. Kitajima, S. Ito, K. Yagi, Y. Usui, Y. Hida, A. Sagara Advanced Fusion Reactor Design using Remountable HTc SC Magnet J. Plasma Fusion Res. SERIES 5 (2002) 532. T.Horiuchi et al., Fusion Technol. 8 (19 (1) Construction cost reduction of magnet (2) Repair of magnet module if damaged (3) Maintenance of blanket modules Re-mountable coils using HTcS.C. joints H.Hashizume et al., J.Plasma Fusion Res. SERIES 5 (2001) 532. 3~4 FFHR-2 LHD continuous helical winding (1995-1996) 5/27
6/27 HTS Magnet Concepts for Fusion in the World (2018) ARC (MIT, US) CFETR-Phase II (ASIPP, China) FFHR-d1 (NIFS, Japan) FNSF-ST (PPPL, US) EU DEMO HTS option (EUROfusion) Tokamak Energy (UK)
Large-Current HTS Conductors 7/27 Twisted and Transposed REBCO Conductors CORC (ACT) RSCCCT (SPC) Roebel (KIT) TSTC (MIT) CroCo (KIT) Roebel (CERN) Slotted Core (ENEA) CSRC (ASIPP) QI (NCEPU) Simply-Stacked REBCO Conductors Bi-2212 CIC Conductors STARS (NIFS) Bi-2212 (ASIPP)
Large-Current HTS Conductors Achievement by Prototype Conductor Samples SPC RSCCCT conductor 60 ka @5 K, 12 T NIFS-Tohoku STARS conductor 100 ka @20 K, 5.3 T 120 ka @4 K, 0.45 T CERN CORC conductor 80 ka @4 K, 12 T 8/27
100 ka-class HTS Conductor for FFHR-d1 STARS (Stacked Tapes Assembled in Rigid Structure) 9/27 Operation current 94 ka @12 T Operation temperature 20 K Conductor size 62 mm 62 mm Current density 24.5 A/mm 2 Number of tapes 40 Cabling method Simple Stacking Stabilizer OFC Outer jacket Stainless Steel Electrical insulation Organic or Inorganic Cooling method GHe or LNe Superconductor REBCO Critical current >900 A/cm @77 K, s.f. Type-1 rotatable Type-2 not rotatable Simply-stacked HTS conductor for DC helical coils Non-uniform current distribution may be allowed High mechanical strength (no void & no local deformation) Low cost and low resistance joint
Concept of Demountable / Segmented Fabrication of Helical Coils K. Uo (1985) Demountable helical coils with LTS H. Hashizume (2000) Demountable TF and helical coils with HTS A. Sagara (2001.6) Excavation of the idea for FFHR design H. Hashizume, A. Sagara (2001.12) Demountable helical coils with HTS N. Yanagi Once-through joint of HTS coils (2006) Joint-winding of HTS conductors (2010) H. Hashizume, S. Ito Remountable (demountable) HTS coils for advanced option of helical coils for advanced TF coils 10/27
Helical Coils Joint-Winding of Helical Coils Welding of neighboring windings No VPI Helium gas cooling Simple cooling system Lift up by 0.5-1 m if 1 day / joint and 4 parallel works (2 helical coils, 2 directions) 3,900 / 4 = 2.7 years 390 turns 5 segments 2 coils 3,900 joints if 0.5 day / joint and 4 parallel works (2 helical coils, 2 directions) 3,900 / 2 / 4 = 1.3 years 11/27
12/27 Fabrication of Prototype Conductor Joint S. Ito (Tohoku Univ.) Arranging GdBCO tapes (3 rows, 14 layers) in a stair-case structure Polishing joint surface (#400), Cleaning joint surface (Ethanol), Inserting indium foils Applying contact pressure to each layer Checking overlapping, contact pressure distribution, joint quality After joining all layers Placing copper jacket Placing stainless steel jacket and applying contact pressure again
Evaluation of Joint Resistance Bridge-type mechanical lap joint Invisible joint S. Ito (Tohoku Univ.) Joint resistance : ~2 nw Joint resistivity : ~10 pwm 2 Required electrical power of the cryoplant at R.T. < 5 MW (for 3,900 joints) 13/27
Reduction of Joint Resistance by Low-Temp. Heat Treatment T. Nishio, S. Ito (Tohoku Univ.) Before heating 60% Contact pressure: 100 MPa Applying large-scale conductor Joint resistance versus heating temp. (1-layer, indium inserted mechanical lap joint) Joint resistivity was reduced by 60% Variation of resistance was reduced Not needing oxygen annealing Application to other HTS devices, e.g., HTS power cables 3-row 1-layer, bridge-type lap joint before heating:25 pwm 2 after heating(90 C, 30 min):8 pwm 2! 14/27
Normal strain distribution along the winding direction of the helical coil 15/27 S. Ito (Tohoku Univ.) EM Stress Analysis of the Helical Coil and Tensile Test on a Single HTS Tape Joint H. Tamura Tensile and shear strength test for single-tape joint Distributions of in-plane shear strain in the helical coil and its xy component in the HTS tape region 50 MPa Maximum shear strength obtained by 3D-FEM analysis
16/27 Mechanical Test of HTS STARS Joint We successfully achieved - 1.8 nw (~10 pwm 2 ) at 100 ka using prototype STARS conductor joint. - Sufficient strength at 77 K using mechanical lap joint of REBCO tapes. Can we achieve sufficient strength for STARS conductor joint at lower temperature? Current achievements Sample preparation and pre-measurement at Tohoku Univ. - Design and fabricate a 10 ka class STARS conductor joint - Measure critical current and joint resistance at 77 K - Apply a tensile force of 10 kn at room temperature Measure critical current and joint resistance at 77 K again 100 kn Measurement at KIT Future tasks - Critical current and joint resistance at 4.2 K and different fields - Joint resistance at 4.2 K and 12 T for various sample elongations 12 T 10 ka FBI test facility at KIT Courtesy of C. Barth, Ph.D. Thesis 2013 (http://digbib.ubka.uni-karlsruhe.de/volltexte/1000035747)
ARC & SPARC @MIT SPARC R = 1.65 m, B t ~ 12 T P f ~ 50-100 MW ARC R = 3.3 m, B t ~ 9 T, B max ~ 23 T P f ~ 500 MW 17/27
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F. J. Mangiarotti, Ph.D. Thesis, MIT, 2016 https://dspace.mit.edu/handle/1721.1/103659 19/27
F. J. Mangiarotti, Ph.D. Thesis, MIT, 2016 https://dspace.mit.edu/handle/1721.1/103659 20/27
F. J. Mangiarotti, Ph.D. Thesis, MIT, 2016 https://dspace.mit.edu/handle/1721.1/103659 21/27
F. J. Mangiarotti, Ph.D. Thesis, MIT, 2016 https://dspace.mit.edu/handle/1721.1/103659 22/27
Pros and Cons on Demountable Coil Concept in comparison to the conventional winding method General remarks Conductor Repair of coil module Pros Fabrication of large and complex magnet becomes easy and shorter in time Short-length high-performance tapes can be used and simplestacking can be assured with joints Damaged coil segments are individually repairable Cons Too many joints and high risk (failure of SC coils happens often from joints, e.g., LHC) Repairing radio-activated coil with remote handling is difficult Joint resistance Can be sufficiently low for HTS Difficult to ensure low resistance for all the joints simultaneously Electrical insulation Mechanical strength Maintenance of invessel components Can be made with the present structure, Non-insulation can be an option Can be assured with a slight reinforcement at the joint section Accessing in-vessel components becomes easy, w/o. remote handling debating Difficult to ensure perfect insulation for all the turns simultaneously Additional support structure may be needed Applicable only to small-sized tokamaks (VV + BB altogether) 23/27
Pros and Cons on Joint-Winding Concept 24/27 in comparison to the conventional winding method General remarks Conductor Fabrication Pros Fabrication of large and complex magnet becomes easy and shorter in time Short-length high-performance tapes can be used and simple-stacking can be assured with joints Easy by using an industrial robot (with inspection also) Cons Too many joints and high risk (failure of SC coils happens often from joints, e.g., LHC) Difficult to make joints and also prefabricated segments with high accuracy Joint resistance Can be sufficiently low for HTS Difficult to ensure low resistance for all the joints Electrical insulation Can be made using an industrial robot, Non-insulation can be an option debating Difficult to ensure perfect insulation for all the joints
25/27 Non-insulation coil option? Trend for small DC HTS coils Stainless steel jacket Copper stabilizer HTS tapes Electrical insulation w./ electrical insulation w/o. electrical insulation Inductance of one double-pancake of the helical coil of FFHR-d1: ~0.5 H Resistance by partial insulation between terminals : ~ 5.6 10-8 W Charging time : ~ 100 days Might be much shorter for ARC? S. Hahn, IEEE TAS 21 (2011) 1592
Experimental Plans at 13-T, f700-mm Magnet Facility NIFS M. Takayasu (MIT) TSTC Conductors STARS Conductor First Sample 13 T, f700 mm SC Magnet Second Sample Z. Hartwig, B. Sorbom, R. Vieira (MIT) 26/27
Summary HTS option is being employed in some fusion reactor designs Demountable / segmented coil fabrication concept is supposed to be a revolutionary idea to facilitate the construction and maintenance For the LHD-type helical fusion reactor FFHR-d1, joint-winding option is being explored For the compact tokamak reactor ARC, demountable TF coils concept supports a dramatic facilitation of the maintenance work Pros and cons for demountable / segmented coil fabrication are summarized Future Work Prototype conductor sample tests at NIFS (13 T, f700 mm) Mechanical test of a STARS conductor joint at KIT Large-scale R&D coil tests employing demountable coil concept and/or joint-winding Development of industrial robot for joint-winding 27/27
Extra Slides 28/27
F. J. Mangiarotti, Ph.D. Thesis, MIT, 2016 https://dspace.mit.edu/handle/1721.1/103659 29/27