Potential of Coated Conductors for Fusion Use an EU ...Pierluigi Bruzzone CC for Fusion Use CCA, Aspen, September 12th 2016. Outside the scope of EUROfusion - Tokamak Energy, UK Aim

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


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.


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.


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

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)

Un. Twente (Enschede, The Netherlands)

Comenius Un. (Bratislava, Slovakia)

Atominstitut (Vienna, Austria)

IPP (Prague, Czech Republic)

TU Cluji-Napoca (Cluji-Napoca, Romania)

IREC-ICMAB (Barcelona, Spain)

Basic tapes characterization

Neutron irradiation

Cables Current Leads

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, inter-tape resistance, modeling

Comenius University (Bratislava, Slovakia): CORT assembly and test at high temperature, modeling


8

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

HTS CrossConductor ! CroCo

optimal twistability optimal filling:

9

For economical fabrication of long lengths:

all these steps

in one continuous process

What about easy fabrication?

Arrange the tapes

Pre-tin the tapes

Twist the stack

Solder all individual tapes

Form the stack

Apply a jacket or former

Fabrication of the HTS CrossConductor (HTS CroCo)

10

Image of a HTS-CroCo partially equipped with HTS

First trials with in total 30 tapes, 150"m pure Cu + some HTS-tapes with # 100 µm electroplated Cu

m electroplated Cu

! No degradation from twisting

11

Advances in jacketing: Rotary swaging

Outer diameter: 9.1 to 9.3 mm

CroCo-Core

Soft filler material, e.g. solder

Cu tube

12

HTS CroCo types

6/4 CroCo 4/2 CroCo 3/2 CroCo

Number of REBCO tapes

22 x 6 mm 10 x 4 mm

18 x 4 mm

18 x 2 mm

17 x 3 mm 10 x 2

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

13

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$

"#$#%&'&$((#'()*+,(-((#./(0+1(2(

3"((4.5+(6+"+(

B061$C4$D(EF*$B'$)F!$G2$

)&&$ E*"$H$%&&$ *!*$H$

C4$D+7<I91$@/>@>2$$ ()$JH$C4$40-91$87.5$(($@/>@>$ (*)$JH$

11 HTS-CroCos in a Stainless-Steel-Jacket$

66.5 mm

54 mm

23 mm 35.5 mm

14

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







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.


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


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



< 15 T < 6 T> 15 T

CS

Nb3Sn NbTiHTS

The cyclic load degradation triggered parametric tests. For DEMO CS a prototype is being assembled (square stacks, 3mm tape).







REBCO cable FE modeling & experiments

21

Step 1 •!Tape material thermal-mech

properties

Step 2 •!Tape production (different T

process)

Step 3 •!Model validation

Step 4 •!Tape winding to CORC or

stacked conductor + bend

Step 5 •!Cooling to operating Top (77

K)

Step 6 •!Electromagnetic load @ Top

Ic(strain, B, T) Ic(combined

torsion + axial) Ic(transverse stress

different load profiles)

0 25 50 75

100 125 150 175 200 225 250 275 300

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Critic

al b

endi

ng ra

dius

, mm

Friction coefficient 0.6 0.7 0.8 0.9 1

50 Degree

45 Degree

40 Degree

example: critical bending radius versus friction coefficient, different winding angle

0 25 50

0 0.1 0.2 0.3

Critic

al b

endi

ng ra

dius

, mm

example: critical bending radius versus friction

T)T)T torsion + axial)

22

AC Loss & contact resistance cables Stacked tapes

CICC

CORC

Roebel cable

Supplier, number of tapes

SuperPower®/SuperOX®

15 / 16

SuNam®

90

SuperPower®

30 / 25

SuperPower®

15

Rc [n"m] @ 77.3 K @ 4.2 K

Low to very low

13 4

Moderate

357 178

Moderate to low

300 / 15 230 / --

Not measured

Hysteresis loss, Qh [mJ/cycle*cm

3]

102 to 40 51

127 to

230 440

Coupling loss time constant, n! [ms]

2,350, Cu no twist 279, Cu twisted 140, no Cu, no twist

115 30 – 80 ms (@ 77 K) 250







C<+K.,.1$>?$3914./7409$3<I7<11/7<I'$L9>=0J$H40;1&M$>?$L471<41+'$N/0K+90=0'$L9>=0J70$@><;,4.>/O><OP>,<;OB,-1$D@QPB2$40-91$0<;$+7<I91$90M1/$4>79+$$

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InsKtute of Electrical Engineering, Slovak Academy of Sciences, BraKslava, Slovakia Conductor-‐on-‐Round-‐Tube (CORT) cable and single layer coils

α

Hand-‐made CORT 5 meter long, from 4x 4 mm tapes (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

-‐1.00E+03

0.00E+00

1.00E+03

2.00E+03

3.00E+03

4.00E+03

5.00E+03

6.00E+03

7.00E+03

8.00E+03

9.00E+03

1.00E+04

200 250 300 350 400 450 500 550 600 650 700

U wire [µV]

Iwire [A]

ch1 LN2ch2 LN2ch3 LN3ch4 LN4ch1 dry coolch2 dry coolch3 dry coolch4 dry cool1 microV/cm

wire temperature: LN2+( 0.5 -‐ 1) K

21 A/mm2

Comparison of LN2 bath cooling (blue) and circula8on cooling (red): circulaKon cooling works

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.


Outside the scope of EUROfusion - Tokamak Energy, UK

Aim at operating temperature ≈ 35 K - Drastically reduce Neutron Shielding


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.


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.


Documents

Potential of Coated Conductors for Fusion Use an EU ...Pierluigi Bruzzone CC for Fusion Use CCA, Aspen, September 12th 2016. Outside the scope of EUROfusion - Tokamak Energy, UK Aim