核融合マグネットへの適用をめざした
大電流高温超伝導導体の開発
核融合科学研究所

柳 長門

第16回 QUEST 研究会
2019年10月4日
九州大学 応用力学研究所
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From LHD to FFHR

Poloidal Coils
NbTi-CICC (world first)
Helical Coils
NbTi
pool-boiling

Construction : 1990-1998
Operation : 1998-

What kind of superconductor should be used?
SC Material Selection

Conductor Selection

1. LTS  Nb3Al, Nb3Sn 1. Force-cooled LTS-CIC conductor
2. Indirectly-cooled LTS conductor
2. HTS  YBCO
3. Helium gas cooled HTS conductor
A. Sagara et al., Fusion Engineering and Design 89 (2014) 2114

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High-Temperature Superconductors (HTS)
Critical Temperature (K)150 Discovery of superconductivity ofcopper-oxide materials in 1986

HgBa2Ca2Cu3Ox
Tl2Ba2Ca2Cu3Ox

 Tremendous progress of wire(tape) production technology

Bi2Sr2Ca2Cu3Ox

100

YBa2Cu3O7-y

77 K : Liquid Nitrogen
La1.2Sr0.8CuOy

50

La0.85Ba0.15CuOy

NbHg

Nb3Sn01900

1920

C60

1940

1960

MgB2
Nb3Ge

1980

2000

Year
Bismuth-based 1st generation
HTS （Bi-2212, Bi-2223)

 Applicable to semi-conductor
production, power cable, motor,transformer, MRI, medical
accelerator, MAGLEV, SMES What about for fusion magnets?
Rare Earth-based
2nd generation HTS （YBCO, GdBCO)
Copper650 A (10 mm-w) @77 K, s.f.
Fujikura
REBCO

200 A (4.2 mm-w) @77 K, s.f.
SilverSumitomo
Hastelloy

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High-Temperature Superconductor (HTS)
(1)
(2)
(3)
(4)
(5)
(6)

High critical current to high field
High cryogenic stability
Low cryogenic power
High mechanical rigidity
Industrial production of tapes
Saving helium resources

CopperRare-Earth Barium
Copper Oxide(REBCO)REBCOHastelloy

Stability Margin High field High temp.
 High heatQ  C p TC p T  2 105 (J/m3K) 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
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Pioneering Work ofapplying HTS to tokamak reactor designs

ARIES-AT (USA)VECTOR (JAEA)
copperYBCO

Hastelloy Substrate

Bi-2212YBCO
F. Dahlgren et al.
YBCO(2006)
T. Ando, S. Nishio, H. Yoshimura(2004)

Bi-2212 CIC conductor
10 kA@20 K, 12 T
T. Isono et al.
(2003)

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● controllability becomes highPioneering Work ofat high T operation,applying
to helicaldesigns(becauseHTSspecificheat ~reactor
T3)● S.SCjointS.isIto,promising
H. Hashizume,Kitajima,
K. Yagi, Y. Usui, Y. Hida, A. Sagara“Advanced Fusion
ReactorDesign using Remountable HTc SC Magnet”
andinnovative.
J. Plasma Fusion Res. SERIES 5 (2002) 532.
（Ohmic heat on cryo.
T.Horiuchi et al., Fusion Technol. 8 (19(1) Construction costof magnet< reductiona few ％of Pf）(2) Repair of magnet module if damaged(3) Maintenance ofRe-mountableblanket modules 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)

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Application of HTS to Plasma Research
RT Project at Univ. of Tokyo

Upgrade to GdBCO (2012)
Mini-RT (2003)
Bi-2223 HTS floating coils

RT-1 (2006)

HTS Magnet Concepts for Fusion in the World (2018)
FFHR-d1 (NIFS, Japan)
ARC (MIT, US)

CFETR-Phase II(ASIPP, China)

EU DEMO HTS option (EUROfusion)
FNSF-ST (PPPL, US)
Tokamak Energy (UK)8/33

Large-Current HTS Conductors
Twisted and Transposed REBCO Conductors
CORC (ACT)RSCCCT (SPC)

Roebel (KIT)
CroCo (KIT)TSTC (MIT)Slotted Core (ENEA)

Roebel (CERN)QI (NCEPU)CSRC (ASIPP)

Simply-Stacked REBCO Conductors
STARS (NIFS)

Bi-2212 CIC Conductors
Bi-2212 (ASIPP)
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100 kA-class HTS Conductor for FFHR-d1”STARS” (Stacked Tapes Assembled in Rigid Structure)
Operation current
Operation temperature
Conductor size
Current density
Number of tapes
Cabling method
Stabilizer
Outer jacket
Electrical insulation
Cooling method
Superconductor
Critical current

94 kA @12 T
20 K
62 mm ×62 mm
24.5 A/mm2
40
Simple Stacking
OFC
Stainless Steel
Organic or Inorganic
GHe or LNe
REBCO>900 A/cm @77 K, s.f.

Type-1

Type-2rotatable

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
10/33

100 kA-Class Prototype Conductor Test

GdBCO Tapes

 GdBCO tapes
Fujikura, FYSC-SC10 (IBAD + PLD)
Width: 10 mm, Thickness: 0.22 mm(Copper lamination : 0.1 mm)
Ic ~ 600 A @77 K, self-field Simple stacking of 54 GdBCO tapes
 Stainless-steel jacket for reinforcement
 FRP jacket for thermal insulation

Joint Section

1410

Copper JacketI sample MLsample

I coil11/33

100 kA-Class Prototype Conductor Test

Joint resistance~1.8 nW

 100 kA achieved @20 K, 5.3 T (quench) 118 kA achieved @4.2 K, 0.45 T (no quench) 100 kA current was successfully sustained for 1 hour @4.2 K
 Decay time constant : ~ 1000 s  Joint resistance : ~1.8 nW
 Quench occurred due to a failure in the joint manufacturing

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“Joint-Winding” of Helical Coils
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

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Evaluation of Joint ResistanceBridge-type mechanical lap joint“Invisible joint”

S. Ito (Tohoku Univ.)

Joint resistance : ~2 nW  Joint resistivity : ~10 pWm2
Required electrical power of the cryoplant at R.T. < 5 MW (for 3,900 joints)

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一体式ジョイントピースを用いた低抵抗機械的ラップ接続に成功
S. Ito, et al.
presented in SOFT 2018
to be published in FED

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LHD 後継計画 & NIFS 次期計画
LHD project

1998-2022

LHD upgrade2023-2028

Divertor tiles will be changed from graphite to tungsten
High-power steady-state plasma production (2 MW x 3 hours)

Post-LHD project2029-2038Presently, two proposals are being examined in parallel HTS heliotron by optimizing LHD magnetic configuraion
 Modular stellarator with new magnetic configurtion
LHD

W-7X

CFQS
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HTS ヘリカル装置の大きさと磁場強度
T. Goto, K. Takahata

プラズマと第一壁の間の距離を十分とるために、ヘリカルコイル巻線部の電流密度： 80 A/mm2
 R = 3.3 m, B = 4 T（現在の候補）LHD :R = 3.9 m, B ~2.7 T
40 A/mm2 （設計）(35 A/mm2 実績)

大型コイルにかかわらず、高い電流密度が要求される
 クエンチ保護が課題  短時定数遮断（耐電圧）、早期検出、クエンチヒータ、無絶縁？
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Vacuum Magnetic Surfaces of a LHD-similar configuration
with jHC = 80 A/mm2

トーラス内周部におけるエルゴディック層境界とヘリカルコイル巻線部最内層との距離： 177 mm > 150 mm

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Three Candidate Conductors (HTS 10 kA-class)
STARSFAIR(Stacked-Tapes Assembled in Rigid Structure)(FSW, Al-alloy, Indirect-cooling, REBCO)
Friction Stir Welding (FSW)

Aluminum alloy
Pure aluminum sheet
Stacked REBCO tapes

T. Mito, Y. Onodera,
N. Hirano

WISE
N. Yanagi, Y. Terazaki, S. Matsunaga,
S. Ito (Tohoku Univ.)

J. Miyazawa,
Y. Narushima,
S. Matsunaga(Wound and Impregnated Stacked Elastic tapes)

19/33Conductor for Helical Coils
LTS vs. HTS
LTS (for LHD)
NbTi/Cu + Al + Cu
13 kA @6.9 T, 57.8 A/mm2

HTS (for Post-LHD)
REBCO + Cu + SS
18 kA @ ~10 T, 80 A/mm2
Bi-2223 can also be used

Effective Young’s modulus: 100 GPa

Effective Young’s modulus: 150 Gpa
Similar bending (winding) by further
flattening

摩擦攪拌接合(FSW)、アルミニウム合金被覆(Aluminum
FAIR導体の研究開発
alloy jacket)、間接冷却(Indirect cooling)、REBCO導体の頭文字をとってFAIR導体と命名

摩擦攪拌接合（FSW)

・30枚・・・30枚・・捻り加工（1~5回転/1 m）

高純度アルミニウム
安定化材

REBCOテープ線材2次巻線
アルミニウム合金被覆

φ126 mm x 8 mm

Friction stir welding (FSW)FIRST TRIAL PRODUCTION OF
FAIR CONDUCTOR
Cross section of FAIR conductor

Twist pitch: 2 rotations / m
REBCO tapes : SuperPower Inc. SCS4050-AP

TEST RESULTS OF THE SECOND TRIAL PRODUCTIONCONDUCTOR●： No rotation Rev. 2■： 1 rotation / m Rev. 2

Thermal cycle

1000

800

c

I [A]

600

400
E = 10-4 [V/m]cDistance ofvoltage terminals
687mm
487mm
287mm

20000No rotation Ic：1056 A
1 rotation / m Ic：954 A

24681012Current-carrying No.

1416

“Wound and Impregnated” on the WISE concept
Wound and Impregnated Stacked
Elastic tapes (WISE) concept
Flexible metal tube

※TapesDrywinding※ポリィミドテープなしも可ImpregnatedLow-melting
metal

Tapes naturally deform⇒ No hard bendingWound and ImpregnatedHandmade winding

Achieved 0.16 T @ 800 A, 77 K
0.16 T

Despite𝑬𝐭𝐚𝐩𝐞
𝑬𝐜~10,

quench did notoccur.

Normalized sample
electric field [-]BC𝐸tape / 𝐸𝑐Iop( 𝐸c 0.1 mV/m )

800 A
600 s

( 15 A/mm2 )Development Plan of HTS-STARS Conductorfor the Next-Generation Helical Device

Short sample (~3 m) test
Straight @77 K, 0 T

Short sample (~3 m) test
Coiled (f0.5 m) @20 K, 9 T

Short sample (>3 m) test
Coiled (f0.6 m) @20 K, 13 T
Short sample (~3 m) test
Bent radius :1-0.2 m@77 K, 0 T
FY2019
Short length (~3 m)Conductor test
Magnetic field 0 T

FY2020

FY2021

Mechanical lap-joint(developed by Tohoku Univ.)

Longer length（> 3 m）

9T

13 T
Long conductor (~10 m)

3D helical coilwinding
technology

Helical Coil Winding
Continuous vs. Joint Continuous Winding Experience by LHD construction
 Long conductor (~ 1 km) necessary Optimized twisting angle

 Joint-Winding Challenging but rewarding ~ 4000 joints = high risk
 Industrial robot (manufacturingand inspection)

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NIFS 次期計画への適用をめざした大電流 HTS 導体の開発
 高電流密度 HTS 導体
 80 A/mm2 目標

 3種類の候補導体を並行して開発に着手
 STARS, FAIR, WISE

 クエンチ保護
 短時定数遮断、早期検出
 ２次巻線によるクエンチバック
 無絶縁巻線の可能性（励磁時定数、コイル全体温度上昇等、課題）

 ヘリカルコイル巻線
 最適な連続巻線方法の考案
 ヘリカルコイルの傾き角調整によるエッジワイズ曲げ歪の低減
 接続巻線を早期に確立 （産業用ロボットによる施工）

 今後の開発計画
 短尺試験、長尺試験  ３年以内ターゲット
 コイル試験、ヘリカル巻線  ５年以内ターゲット
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30/33

ARC & SPARC @MITSPARC
R = 1.65 m, Bt ~ 12 T
Pf ~ 50-100 MW

ARC
R = 3.3 m, Bt ~ 9 T, Bmax ~ 23 T
Pf ~ 500 MW

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32/33

F. J. Mangiarotti, Ph.D. Thesis, MIT, 2016
https://dspace.mit.edu/handle/1721.1/103659

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Improvement of in-field Ic
Effective Combination of REBCO & BMO(APC)
Ic [A/cmw] @77 K, 3T

160
140

EuBCO-BHO
141 A/cm-w

77K3T

120

100

GdBCO+BHO
85 A/cm-w

8060402000.0Commercial
Base

1.02.0BHO BSO

65K
3Tpure BZO
3.0

4.0

Thickness [μm]
Courtesy of T. Izumi (AIST)

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Extra Slides

35/33

HTS 導体を用いたヘリカル巻線に関する考察• エッジワイズ曲げ  フラットワイズ曲げ＋捻りで代用• ヘリカル巻線方向に対して捻りを調整
エッジワイズひずみを最小限に抑える• フラットな導体断面  フラットワイズに曲げやすい

K. Takahashi, N. Amemiya, et al.,IEEE TAS 22 (2012)
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Edgewise strain on the HTS tapein the FFHR-d1 helical coils Difference of path length inside a conductor is calculated
for evaluating edgewise strain

Edgewise strain on the HTS tapein the FFHR-d1 helical coils

preliminary Difference of path length (edge strain) can be minimized bytilting the whole winding package