The HTS CrossConductor (HTS CroCo) · HTS CroCo for large magnets and DC cables Design of a Rutherford cable made of 11 HTS CroCo strands for fusion TF magnets M. J. Wolf, et al.,

KIT – The Research University in the Helmholtz Association

Institute for Technical Physics

www.kit.edu

3 mm

The HTS CrossConductor (HTS CroCo)

A versatile strand for large magnets and high-current DC conductors

Michael J. Wolf, Nadezda Bagrets, Christoph M. Bayer, Walter H. Fietz, and Alan Preuß

CCA Workshop, Aspen, CO, September 11-14, 2016

Institute for Technical Physics 2 13.09.2016

Motivation – High DC current applications

Michael J. Wolf

Fusion Magnets

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Electromechanical

Stability due to high

Lorentz forces

required

Economical

manufacturing of

the conductor and

its terminations and

joints

Institute for Technical Physics 3 13.09.2016 Michael J. Wolf

Outline

Introduction of the HTS CrossConductor:

Design

Fabrication concept

Electromechanical investigations of the HTS CroCo

Terminations and Connectors

Summary & Outlook towards high-current conductors


The HTS CrossConductor

Michael J. Wolf

64% 79% 100%

Filling factor

M. Takayasu et al. IEEE TAS

21 (3) (2011), p. 2340 ff.

D. Uglietti, et al. IEEE TAS

24 (3) (2014), Art. ID. 4800704

Ideal circular shape

Form-fit twisting

Good impossible

Use a soldered stack of REBCO tapes

of two different widths to improve the filling factor

of a Round Twisted Stacked Conductor


HTS CroCo fabrication

Michael J. Wolf

Outer diameter: ~ 9 mm

CroCo-Core

Soft filler material,

e.g. solder

Cu tube

„All-in-one“ fabrication of the HTS CroCo core:

From single REBCO tapes to a soldered & twisted stack in one step

Arrange the tapes

Pre-tin the tapes

Twist the stack

Solder all individual tapes

Form the stack

HTS CroCo core HTS CroCo


Outline


Design

Fabrication concept





The FBI test facility

Michael J. Wolf

Tensile force (100 kN)

Heater

Magnetic field (12 T)

Current (10 kA) T = 4.2-77 K

F

B

I


Parameters of the HTS CroCo sample

for FBI testing

32 REBCO tapes: 10 x 4 mm width + 22 x 6 mm width

Thickness of the tapes: ~ 165 µm, 110 µm Copper stabilizer

Outer Diameter incl. tube: 9.0 mm

Twist Pitch ~ 35 cm

Terminations by soldering the HTS CroCo to copper profiles

(details later)

Expected Ic (4.2 K, 12 T): 8.5 – 9 kA

Michael J. Wolf


V(I) measurement at T = 4.2 K, B = 12 T

Michael J. Wolf

The sample was subject to

the highest possible Lorentz forces

of the FBI test facility!


No degradation after the FBI test

Michael J. Wolf

Outlook: Temperature-dependent measurements of Ic(B)

Challenging due to the copper tube, solder, thick Cu stabilizer, 32-tape stack


Outline


Design

Fabrication concept





Three different types of terminations

Michael J. Wolf

Measurements at T = 77 K, sf


Termination resistances at T = 77 K, sf.

Michael J. Wolf


Three different types of terminations

Michael J. Wolf

+ lowest termination

resistance of all samples

(21 nW for sample 2)

- time-consuming to

prepare.

+ Reasonably low-resistive

terminations (~ 35 – 60 nW)

+ easy to prepare

+ very easy to prepare

- highest resistances

(due to geometry & more

interfaces)


Outline


Design

Fabrication concept





Angular HTS CroCo Connectors with R < 50 mm

Michael J. Wolf

The 90° connector piece consists only of a solid copper block (R = 15 mm)

reference sample

Could we do better

by adding additional

REBCO tapes?



Michael J. Wolf

Two additional staggered REBCO tape stacks of 15 tapes (6 mm width)



Michael J. Wolf

Two additional staggered REBCO tape stacks of 14 tapes in grooves

R = 50 mm, connection length = 50 mm



Michael J. Wolf

Two additional staggered REBCO tape stacks of 14 tapes in grooves

R = 50 mm, connection length = 50 mm



Michael J. Wolf

Two additional staggered REBCO tape stacks of 15 tapes in direct contact

to the HTS CroCo cores.

< 0.5 W of heating power at I = 3 kA


Outline


Design

Fabrication concept





Conclusions

Michael J. Wolf

No degradation of a fully REBCO-equipped

HTS CroCo after Lorentz forces of > 12 kN

Easy-to-fabricate „Side – Injection“

Terminations are achievable with low

resistance (35 – 60 nW)

Angular HTS Connectors with small bending

radius and low resistance possible leading to

a heating power of less than 0.5 W at 3 kA


Outlook:

HTS CroCo for large magnets and DC cables

Design of a Rutherford cable

made of 11 HTS CroCo strands

for fusion TF magnets

M. J. Wolf, et al., IEEE Trans. Appl.

Supercond. 26 (4), Art. ID. 4801504, June

2016

R. Heller, et al., IEEE Trans. Appl.

Supercond. 26 (4), Art. ID. 4201105, June

2016

Michael J. Wolf

30 – 100 kA DC Cable with

sub-cooled LN2 cooling

Poster of Alan Preuss:

Conceptual design process of

high-current HTS DC cables

Documents

The HTS CrossConductor (HTS CroCo) · HTS CroCo for large magnets and DC cables Design of a Rutherford cable made of 11 HTS CroCo strands for fusion TF magnets M. J. Wolf, et al.,