1/27
Challenges on demountable / segmented coil
concept for high-temperature
superconducting magnetN. Yanagi1, S. Ito2, H. Hashizume2, A. Sagara1
1National Institute for Fusion Science2Tohoku University
1/27
Fifth IAEA DEMO Programme Workshop (DPW-5)
May 7-10, 2018, Daejeon, Republic of Korea.
In collaboration with
Z. HartwigMIT, Plasma Science and Fusion Center
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
Rare-Earth Barium
Copper Oxide
(REBCO)
Hastelloy
Copper
REBCO
pQ C T
Stability Margin
Higher than CIC conductor
Low quench risk!
5 32 10 (J/m K) 10 (K)
2 (J/cc)
pC T
N. Yanagi, S. Ito, et al.,
Plasma and Fusion Research
9 (2014) 1405013
High field
High temp.
High heat
4/27
Pioneering Work of
applying HTS to tokamak reactor designs
copper
YBCO
Hastelloy Substrate
VECTOR (JAEA)
T. Ando, S. Nishio, H. Yoshimura
(2004)
YBCO
Bi-2212
ARIES-AT (USA)
YBCO
Bi-2212 CIC conductor
10 kA@20 K, 12 T
T. Isono et al.
(2003)
F. Dahlgren et al.
(2006)
5/27
Sagara 12
Another approach using Another approach using HTcSC HTcSC for magnet coilsfor magnet coils
Even the shielding efficiency is poor,
● temperature margin is wide,
● controllability becomes high
at high T operation,
(because specific heat ~ T3)
T.Horiuchi et al., Fusion Technol. 8 (1985) 1654.
Conventional SC joint design
Re-mountable coils
using HTcS.C. joints
H.Hashizume et al.,
J.Plasma Fusion Res.
SERIES 5 (2001) 532.
● SC joint is promising
and innovative.
（Ohmic heat on cryo.
< a few ％ of Pf）
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.
FFHR-2
(1) Construction cost reduction of magnet
(2) Repair of magnet module if damaged
(3) Maintenance of blanket modules
LHDcontinuous helical winding
(1995-1996)
×3~4
6/27
ARC (MIT, US)
Tokamak Energy (UK)
CFETR-Phase II
(ASIPP, China)
HTS Magnet Concepts for Fusion in the World (2018)
FNSF-ST (PPPL, US)
EU DEMO HTS option (EUROfusion)
FFHR-d1 (NIFS, Japan)
7/27
Large-Current HTS Conductors
Twisted and Transposed REBCO Conductors
Simply-Stacked REBCO Conductors
Roebel (KIT)
CORC (ACT)
TSTC (MIT)CroCo (KIT)
RSCCCT (SPC)
Slotted Core (ENEA)Roebel (CERN)
STARS (NIFS)
Bi-2212 CIC Conductors
Bi-2212 (ASIPP)
QI (NCEPU)
CSRC (ASIPP)
8/27
Large-Current HTS Conductors
Achievement by Prototype Conductor Samples
SPC RSCCCT conductor
60 kA @5 K, 12 T
CERN CORC conductor
80 kA @4 K, 12 T
NIFS-Tohoku STARS conductor
100 kA @20 K, 5.3 T
120 kA @4 K, 0.45 T
9/27
100 kA-class HTS Conductor for FFHR-d1
”STARS” (Stacked Tapes Assembled in Rigid Structure)
Operation current 94 kA @12 T
Operation temperature 20 K
Conductor size 62 mm ×62 mm
Current density 24.5 A/mm2
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-2
not rotatable
Type-1
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
10/27
H. Hashizume (2000)
Demountable TF and helical coils with HTS
Concept of Demountable / Segmented Fabrication
of Helical Coils
N. YanagiOnce-through joint of HTS coils (2006)
“Joint-winding” of HTS conductors (2010)
K. Uo (1985)
Demountable helical coils with LTS
A. Sagara (2001.6)
Excavation of the idea for FFHR design
H. Hashizume, S. Ito“Remountable” (demountable) HTS coils
for advanced option of helical coils
for advanced TF coils
H. Hashizume, A. Sagara (2001.12)
Demountable helical coils with HTS
11/27
“Joint-Winding” of Helical Coils
390 turns×5 segments×2 coils
3,900 joints
Helical Coils
if 1 day / joint
and 4 parallel works (2 helical coils, 2 directions)
3,900 / 4 = 2.7 years
if 0.5 day / joint
and 4 parallel works (2 helical coils, 2 directions)
3,900 / 2 / 4 = 1.3 years
Lift up by 0.5-1 m
Welding of neighboring windings
No VPI
Helium gas cooling
Simple cooling system
12/27
Applying contact pressure to each layer
Checking overlapping, contact pressure distribution, joint quality After joining all layers
Placing copper jacket
Fabrication of Prototype Conductor Joint
Arranging GdBCO tapes (3 rows, 14 layers) in a stair-case structure
Polishing joint surface (#400), Cleaning joint surface (Ethanol), Inserting indium foils
S. Ito (Tohoku Univ.)
Placing stainless steel jacket and applying contact pressure again
13/27
Joint resistance : ~2 nW Joint resistivity : ~10 pWm2
Evaluation of Joint Resistance
Required electrical power of the cryoplant at R.T. < 5 MW (for 3,900 joints)
Bridge-type mechanical lap joint
“Invisible joint” S. Ito (Tohoku Univ.)
14/27
Joint resistance versus heating temp.
(1-layer, indium inserted mechanical lap joint)
Joint resistivity was reduced by 60%
Before heating
60％
Variation of resistance was reduced
Contact pressure:
100 MPa
Applying large-scale conductor
3-row 1-layer, bridge-type lap joint
before heating：25 pWm2
after heating（90C, 30 min）：8 pWm2 !
Not needing oxygen annealing
→ Application to other HTS devices,
e.g., HTS power cables
Reduction of Joint Resistance by Low-Temp. Heat Treatment
T. Nishio, S. Ito (Tohoku Univ.)
15/27
Tensile and shear strength
test for single-tape joint
Maximum shear strength
obtained by 3D-FEM analysis
50 MPa
Normal strain distribution along the
winding direction of the helical coil
Distributions of in-plane shear strain in the helical
coil and its xy component in the HTS tape region
H. Tamura
EM Stress Analysis of the Helical Coil and
Tensile Test on a Single HTS Tape Joint
S. Ito (Tohoku Univ.)
16/27
We successfully achieved…- 1.8 nW (~10 pWm2) 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?
Measurement at KIT- Critical current and joint resistance at 4.2 K
and different fields
- Joint resistance at 4.2 K and 12 T for
various sample elongationsFBI test facility at KIT
Courtesy of C. Barth, Ph.D. Thesis 2013
(http://digbib.ubka.uni-karlsruhe.de/volltexte/1000035747)
100
kN
12 T10 kA
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
Current achievements
Future tasks
Mechanical Test of HTS STARS Joint
17/27
ARCR = 3.3 m, Bt ~ 9 T, Bmax ~ 23 T
Pf ~ 500 MW
ARC & SPARC @MIT
SPARCR = 1.65 m, Bt ~ 12 T
Pf ~ 50-100 MW
18/27
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
F. J. Mangiarotti, Ph.D. Thesis, MIT, 2016
https://dspace.mit.edu/handle/1721.1/103659
23/27
“Pros and Cons” on Demountable Coil Concept
Pros Cons
General remarks Fabrication of large and complex
magnet becomes easy and shorter
in time
Too many joints and high risk
(failure of SC coils happens
often from joints, e.g., LHC)
Conductor Short-length high-performance
tapes can be used and simple-
stacking can be assured with joints
Repair of coil module Damaged coil segments are
individually repairable
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 Can be made with the present
structure,
Non-insulation can be an option
Difficult to ensure perfect
insulation for all the turns
simultaneously
Mechanical strength Can be assured with a slight
reinforcement at the joint section
Additional support structure
may be needed
Maintenance of in-
vessel components
Accessing in-vessel components
becomes easy, w/o. remote handling
Applicable only to small-sized
tokamaks (VV + BB altogether)
in comparison to the conventional winding method
debating…
24/27
“Pros and Cons” on Joint-Winding Concept
Pros Cons
General remarks Fabrication of large and complex
magnet becomes easy and shorter in
time
Too many joints and high risk
(failure of SC coils happens often
from joints, e.g., LHC)
Conductor Short-length high-performance tapes
can be used and simple-stacking can
be assured with joints
Fabrication Easy by using an industrial robot
(with inspection also)
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
Difficult to ensure perfect
insulation for all the joints
debating…
in comparison to the conventional winding method
25/27
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?
Electrical insulation
HTS tapes
Copper stabilizer
Stainless steel jacket
w./ electrical insulation w/o. electrical insulation
Non-insulation coil option ? Trend for small DC HTS coils
S. Hahn, IEEE TAS 21 (2011) 1592
26/27
13 T, f700 mm
SC Magnet
Experimental Plans at 13-T, f700-mm Magnet Facility
NIFS
STARS
Conductor
M. Takayasu (MIT)
TSTC
Conductors
First Sample
Second Sample
Z. Hartwig, B. Sorbom, R. Vieira
(MIT)
27/27
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
28/27
Extra Slides
29/27
F. J. Mangiarotti, Ph.D. Thesis, MIT, 2016
https://dspace.mit.edu/handle/1721.1/103659
