Potential of Coated Conductors for Fusion Use
an EU perspective
Pierluigi Bruzzone
EPFL- Swiss Plasma Center, Villigen-PSI, Switzerland
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
Outline
CC and Fusion
The EUROfusion Workprogram
Outside EUROfusion
The future
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
Fusion and Coated Conductors
Does Fusion must use CC?
Depends on the machine layout! From the
point of view of operating field, only the ARC
design (MIT, 20 T peak field) must use CC.
Does Fusion may use CC?
At operating field < 16 T, CC may always be used. However, the
potential advantages of CC (higher operating temperature/margin,
higher non-Cu Jc with very thin substrate) are balanced by prohibitive
cost and (today) by production length limitations.
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
Fusion Projects and Coated Conductors
Disregarding the must/may question, few fusion projects
world-wide consider the use of CC at conceptual design level
for magnets.
BTW, ALL projects have HTS current leads. Here a trend
started to move from the BSCCO to the CC technology.
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
EUROfusion
On behalf of the European Commission, a consortium of European
Laboratories (EUROfusion) coordinates the conceptual design
activities toward a Fusion Demonstration Power Plant – DEMO.
The PROCESS system code gives
the DEMO baseline reference:
Pe = 500 MW
Major Radius = 9 m
Field on Torus = 7 T
Peak Field on TF coils = 12.3 T
Magnet Technology = LTS
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
EUROfusion and CC
A small fraction of the R&D effort is devoted to Advanced Magnet
Technology (AMT), exploring the potential use of HTS for DEMO and
beyond. The participating labs are:
KIT (Karlsruhe, Germany)
SPC (Villigen, Switzerland)
Current Leads
Cables
Un. Twente (Enschede, The Netherlands)
Comenius Un. (Bratislava, Slovakia)
Atominstitut (Vienna, Austria)
IPP (Prague, Czech Republic)
Neutron irradiation
TU Cluji-Napoca (Cluji-Napoca, Romania)
Basic tapes characterization
IREC-ICMAB (Barcelona, Spain)
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
EUROfusion and CC cables
KIT (Karlsruhe, Germany): Twisted Stack (CroCo) assembly, all CC TF
WP design, Sub-size test in FBI.
SPC (Villigen, Switzerland): Twisted Stack, mechanical investigations,
inter-tape resistance, 60 kA 12 T prototype, cyclic loading, magnetization,
test in EDIPO/SULTAN, CS high grade design.
Univeristy of Twente (Enschede, The Netherlands): AC loss, intertape resistance, modeling
Comenius University (Bratislava, Slovakia): CORT assembly and test
at high temperature, modeling
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
Could we come to a round strand with optimized jc, eng?
We could try to fill the round strand almost completely with superconductor tapes.
However, this is in contrast to the requests: Good twistability & easy manufacturing.
Therefore we propose a compromise between
optimal twistability
8
HTS CrossConductor
CroCo
!
optimal filling:
What about easy fabrication?
Fabrication of the HTS CrossConductor (HTS CroCo)
Arrange the tapes
Pre-tin the tapes
Solder all individual tapes
Form the stack
Twist the stack
Apply a jacket or former
9
For economical fabrication
of long lengths:
all these steps
in one continuous process
Image of a HTS-CroCo partially equipped with
HTS
First trials with in total 30 tapes,
m electroplated Cu
150"m pure Cu + some HTS-tapes with # 100 µm
! No degradation
from twisting
10
Advances in jacketing: Rotary swaging
Outer diameter: 9.1 to 9.3 mm
CroCo-Core
Soft filler material,
e.g. solder
Cu tube
11
HTS CroCo types
6/4 CroCo
Number of
REBCO tapes
12
22 x 6 mm
10 x 4 mm
4/2 CroCo
3/2 CroCo
18 x 4
17 x 3 mm
mm
10 x 2
18 x 2
mm
mm
Ø incl. tube
9.1 mm
6.8 mm
5.7 mm
Ic(77 K, s.f.)
3160 A
2010 A
1460 A
Ic(65 K, s.f.)
7900 A
5000 A
3480 A
Ic(4.2 K, 12 T)
8600 A
5400 A
3550 A
Min. bending
radius Rmin
60 cm
40 cm
30 cm
CroCo Performance at 13.5 T and 4.2 K
Single CroCo !!"#$%&&'$("#$)&&'$*"$µ&$+,-+./0.12$
3045$.061$7+$8199$+.0-797:1;$87.5$0<$1<=19>61$>?$*"$µ&$@,$A$
"#$#%&'&$((
3"((
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4.5+(6+"+(
B061$C4$D(EF*$B'$)F!$ )&&$ E*"$H$
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%&&$ *!*$H$
C4$D+7<I91$@/>@>2$$
()$JH$
C4$40-91$87.5$(($
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@/>@>$
11 HTS-CroCos
in a Stainless-Steel-Jacket$
23 mm
54 mm
66.5 mm
13
35.5 mm
HTS CroCo for large magnets
Large high-field magnets
e.g. fusion magnets
Design concept of a
compact Rutherford cable
for a DEMO TF coil with
Ic(4.2 K, 12 T) = 80 kA
Cross section of a magnet winding pack
14
EUROfusion and CC cables
KIT (Karlsruhe, Germany): Twisted Stack (CroCo) assembly, all CC TF
WP design, Sub-size test in FBI.
SPC (Villigen, Switzerland): Twisted Stack, mechanical investigations,
inter-tape resistance, 60 kA 12 T prototype, cyclic loading, magnetization,
test in EDIPO/SULTAN, CS high grade design.
Univeristy of Twente (Enschede, The Netherlands): AC loss, intertape resistance, modeling
Comenius University (Bratislava, Slovakia): CORT assembly and test
at high temperature, modeling
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
The soldered twisted stacks at SPC
A rectangular/square stack of tapes is packed between two half shells of soft
copper, twisted and soldered to build a solid, round “strand” to be used in a
multi-strand, cored flat cable.
Strand geometry optimization
Bending, twist and transverse compression tests, for CC and BSCCO tapes.
From the bending test results, a 20 strands cable prototype is designed and
modeled with optimization of the core size and twist pitch, to keep the strain
within the reversible limits.
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
The 60 kA prototype conductor at SPC
A 20 strand cable prototype is built at SPC (two short lengths with
Superpower and SuperOx tapes).
A short length EDIPO sample was assembled and tested in 2015
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
Magnetization on stacks of tapes
Demagnetization effect - When the magnetization is large (low T), the
loss per tape decreases with the number of tapes in the stack
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
> 15 T
< 15 T
<6T
CS
HTS
Nb3 Sn
The cyclic load degradation triggered parametric tests. For DEMO
CS a prototype is being assembled (square stacks, 3mm tape).
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
NbTi
EUROfusion and CC cables
KIT (Karlsruhe, Germany): Twisted Stack (CroCo) assembly, all CC TF
WP design, Sub-size test in FBI.
SPC (Villigen, Switzerland): Twisted Stack, mechanical investigations,
inter-tape resistance, 60 kA 12 T prototype, cyclic loading, magnetization,
test in EDIPO/SULTAN, CS high grade design.
Univeristy of Twente (Enschede, The Netherlands): AC loss, intertape resistance, modeling
Comenius University (Bratislava, Slovakia): CORT assembly and test
at high temperature, modeling
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
REBCO cable FE modeling & experiments
•! Tape material thermal-mech
Step 1 properties
•! Tape production (different T
Step 2 process)
•! Model validation
•! Tape winding to CORC or
Step 4 stacked conductor + bend
•! Cooling to operating Top (77
Step 5 K)
Step 6
•! Electromagnetic load @ Top
Ic(strain, B, T)
T
Ic(combined
torsion + axial)
Ic(transverse stress
different load profiles)
300
275
250
225
200
175
150
125
100
75
50
25
0
Critical bending radius, mm
Step 3
50 Degree
45 Degree
40 Degree
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Friction coefficient
example: critical bending radius versus friction
coefficient, different winding angle
21
AC Loss & contact resistance cables
Stacked tapes
CICC
CORC
Roebel cable
SuperPower®/SuperOX®
SuNam®
SuperPower®
SuperPower®
15 / 16
90
30 / 25
15
Rc [n"m]
Low to very low
Moderate
Moderate to low
@ 77.3 K
@ 4.2 K
13
4
357
178
300 / 15
230 / --
Not measured
Hysteresis loss, 3
Qh [mJ/cycle*cm ]
102
to
40
51
127
to
230
440
115
30 – 80 ms
(@ 77 K)
250
Supplier,
number of tapes
Coupling loss time constant, n!
[ms]
2,350, Cu no twist
279, Cu twisted
140, no Cu, no twist
22
EUROfusion and CC cables
KIT (Karlsruhe, Germany): Twisted Stack (CroCo) assembly, all CC TF
WP design, Sub-size test in FBI.
SPC (Villigen, Switzerland): Twisted Stack, mechanical investigations,
inter-tape resistance, 60 kA 12 T prototype, cyclic loading, magnetization,
test in EDIPO/SULTAN, CS high grade design.
Univeristy of Twente (Enschede, The Netherlands): AC loss, intertape resistance, modeling
Comenius University (Bratislava, Slovakia): CORT assembly and test
at high temperature, modeling
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
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InsKtute of Electrical Engineering, Slovak Academy of Sciences, BraKslava, Slovakia Conductor-­‐on-­‐Round-­‐Tube (CORT) cable and single layer coils Hand-­‐made CORT 5 meter long, from 4x 4 mm tapes α
(SuNam) on Cu tube 6 mm used to manufacture single-­‐layer coil (5 turns, diameter 323 mm) cooled by LN2 circulaKng through the central tube, polyurethane foam as thermal insulaKon Comparison of LN2 bath cooling (blue) and circula8on cooling (red): circulaKon cooling works 1.00E+04
9.00E+03
ch1 LN2
ch2 LN2
ch3 LN3
ch4 LN4
ch1 dry cool
ch2 dry cool
ch3 dry cool
ch4 dry cool
1 microV/cm
8.00E+03
7.00E+03
U wire [µV]
6.00E+03
5.00E+03
4.00E+03
3.00E+03
wire temperature: LN2+( 0.5 -­‐ 1) K 2
21 A/mm
2.00E+03
1.00E+03
0.00E+00
-­‐1.00E+03
200
250
300
350
400
450
Iwire [A]
500
550
600
650
700
Outside the scope of EUROfusion – ENEA, Italy
The stacks of tapes are placed into the slots of an extruded and twisted
Aluminum profile. The number of slots and the number of tapes in each slot
may vary.
So far, the manufacturing process has
been demonstrated on short dummy
and partially dummy conductors.
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
Outside the scope of EUROfusion - Tokamak Energy, UK
Aim at operating temperature ≈ 35 K - Drastically reduce Neutron Shielding
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
Who are we
•  Established in ~ 2010
•  Venture capital funded, mainly by individuals
•  ~30 full time, permanent employees (from around ten 18 months ago)
•  >50 part time consultants
•  Produce a small, modular fusion reactor based on the combination of
spherical tokamaks and high temperature superconductors
Strategy
1.  Demonstrate scientific viability of STs
2.  Develop HTS technology towards commercial viability
3.  Combine STs and HTS in a series of engineering prototypes
Compara1ve Strategy
Summary - The Present
For the time being, the use of CC in the EUROfusion roadmap to fusion is
not in the baseline, just a (remote?) conceptual option. Nonetheless, many
labs are hard working in the R&D, well beyond the allocate resources.
The DEMO of stellarator, HELIAS, does not consider HTS at all.
An innovative proposal has been launched for a divertor coil to be installed
in the TCV Tokamak in Lausanne, made of CC, up to 2.5 T, sub-cooled LN2
TE, a dynamic, highly motivated group of fusion experts, brings a fresh
breeze in the field, with a realistic, unconventional strategy based on CC.
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016
The Future
In the medium term, there is room for small size “technology demonstrators”
and “proof-of-principle” devices made by CC.
The R&D for high current cables, quench management, joints and radiation
resistance is surely a mandatory condition for future projects.
The commercial availability of long (>1 km), high performance CC tapes and
the prohibitive price compared to LTS are obstacles toward the use of CC
for reactor relevant projects, skyrocketing the overnight cost and the cost of
electricity for a fusion power plant.
Pierluigi Bruzzone
CC for Fusion Use
CCA, Aspen, September 12th 2016