F ll fil ti d HTS t dFully-filamentized HTS coated conductors by striation and y

selective electroplating

V. Selvamanickam, I. Kesgin, X. Cai and G. Majkic

Department of Mechanical EngineeringTexas Center for Superconductivity

University of Houston, Houston, TX, USA

1Coated Conductors for Applications, Heildelberg, Germany, November 13 - 16, 2012

Project funded by SuperPower Inc.

Multfilamentary coated conductors for low ac loss applicationsac loss applications

• Filamentization of coated conductors is desired for low

2

100 Hz unstriated

conductors is desired for low ac loss applications.

• Maintaining filament integrity if l l th

1

ac lo

ss (

W/m

)

5.1 x

uniform over long lengths (no Ic reduction)

• Minimum reduction in non 4 mm

0.00 0.01 0.02 0.03 0.04 0.05 0.060

Bac rms (T)

multifilamentary

superconducting volume (narrow gap) and fine filaments

4 mmAg HTS

• Striated silver and copper stabilizer (minimize coupling losses)

Substrate

CuCu

A fully filamentized coated conductor would need to have 20 – 50 µm of copper stabilizer striated !

One approach to make fully-filamentizedd d Ag

REBCO1. Coat photoresist

on silver

coated conductor

2. Transfer pattern from mask to photoresist

3. Electroplate copper

PhotoresistSubstrate

REBCOon silver

photoresist

4. Remove remaining photoresist5 Wet etch silver and HTS

Cu

5. Wet etch silver and HTS

X. Zhang and V. Selvamanickam, US 7,627,356

One approach to make fully-filamentized coated pp yconductor

Cu Ag HTS

substrate

100 μm

Cu

1 mm

Fully-filamentized coated conductor demonstrated, but still involves etching

X. Zhang and V. Selvamanickam, US 7,627,356

A bottom-up approach make fully-fil i d d dMechanical scribing of buffer layer, h d i REBCO d A d C l i l REBCO

filamentized coated conductor

then deposit REBCO and Ag and Cu selectively

Substrate

Buffer Stack

Substrate Substrate

REBCO

Substrate Substrate Subs a e

500 µm

G. Majkic, I. Kesgin, Y. Zhang, Y. Qiao, R. Schmidt, and V. Selvamanickam, “AC Loss Filamentization of 2G HTS Tapes by Buffer Stack Removal”, IEEE Trans. Appl. Supercond. 21, 3297 (2011)

5X ac loss reduction without Ag or Cu

Another bottom-up approach make fully-p pp yfilamentized coated conductor with no material removal

Substrate with buffer

Inkjet deposited insulator stripes

6

X. Cai, I. Kesgin, R. Schmidt, Y. Chen and V. Selvamanickam, “Completely Etch-free Fabrication of Multifilamentary Coated Conductor Using Inkjet Printing and Electrodeposition”, IEEE Trans. Appl. Supercond. (submitted)

Reel-to-reel inkjet printing of insulator j p gstripes on buffered substrate

7

Selective epitaxial REBCO in between inkjet printed insulator stripes

8

Selective Ag electroplating on epitaxial REBCO g p g pin between inkjet printed insulator stripes

9

Lowered ac losses in filamentized conductor made with no material removal

10-fold reduction in ac loss in 12-filament conductor made with no material removal

10

Fully-filamentized conductor by mechanical y yscribing and selective electroplating

ElectroplatedREBCO

Buffer Stack

Ag Electroplated Cu

HastelloyStack

Oxide Layer Hastelloy

Mechanical Scribing + oxygenation

Non-striated 12-filament ,12 id

12-filament tape ith l t l t d

Selective Cu Electroplating

Mechanical Oxygenation

12 mm wide Ag sputtered tape

12 mm widetape

with electroplated Cu

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Mechanical Scribing

Oxygenation + ED Cu

Significant ac loss reduction in full-filamentizedconductor with copper stabilizer• Critical current of standard 16

0 02 Tconductor = 207 A• Critical current of 12-filament

conductor = 197 A 101214

W/m

)

Multfilamentary

0.02 T

• Critical current of 12-filament conductor after 10 µm copper stabilizer = 200 A 4

68

ac lo

ss ( Multfilamentary

StandardMultfilamentary + CuStandard + Cu

AC loss of 12-fiament conductorat 60 Hz is 11 times lower than

02

0 100 200 300 400ac field frequency (Hz)

that of unstriated conductorwithout copper stabilizer and 13 times lower with copper

ac field frequency (Hz)

times lower with copper stabilizer, at higher fields

Investigated selectively electroplated copper g ythickness & coupling effects

S1 S2 S3 S4 S5 S6

~20 µm ~30 µm ~44 µm ~36 µm ~33 µm~10 µm µ µ µ

Fully coupled NoFully coupledMechanicallyscribed, no oxidation and C l t d

No filamentization

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Cu plated

Sideways growth of electroplated copper y g p ppreduces groove width between filaments

S1 S3Filament GrooveGrooveOxide

CopperGrooveOxide

FilamentCopper

FilamentCopper

40 µm 15 µm

Copper

No couplingMechanically scribed, oxidized and

No couplingMechanically scribed, oxidized and

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Mechanically scribed, oxidized and Cu plated (~ 10 µm)

Mechanically scribed, oxidized and Cu plated (~ 30 µm)

Partially and fully-coupled filamentized tape y y p pwith copper stabilizer

S4 S5Groove FilamentGroove

partial Cu

FilamentGrooveCopper

FilamentCopper

Filament Copper

Copper

Fully coupledMechanically scribed, no oxidation

Partially coupledMechanically scribed, oxidized and

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Mechanically scribed, no oxidation and Cu plated (~ 33 µm)

Mechanically scribed, oxidized and Cu plated (~ 44 µm)

No significant loss contribution up to 30 µm g p µstabilizer in fully-filamentized conductor at 40 Hz

Non-striated B-I with Ic=195 A

40 Hz

with Ic=195 A

Striated B-I with Ic=195 A

• 15-fold ac loss reduction even with 30 µm Cu stabilizer• Lower ac loss reduction with 40 µm Cu stabilizer 16

No significant loss contribution up to 30 µm g p µstabilizer in fully-filamentized conductor even at 400 Hz

400 Hz

17

15-fold ac loss reduction in fully-filamentizedyconductor with up to 30 µm stabilizer

M ti

~15 times reduction @ 40 Hz

Electrical Coupling + eddy

current

Magnetic

current

Reduction is still more than 12-fold but decreases in field @ 400 Hz (heating

effects)

18Loss ratio: ac loss of filamentized conductor S3/ac loss of non-striated conductor S6

5-fold ac loss reduction at 40 Hz even in partially-coupled filamentized conductor with 44 µm stabilizer

Magnetic Almost 5 times reduction @ 40 Hz

Electrical Coupling + eddy

@

Coupling + eddy current

Striation becomes ineffective at 400 Hz

19Loss ratio: ac loss of filamentized conductor S4/ac loss of non-striated conductor S6

Fully-coupled filamentized conductor with 36 µm stabilizer shows comparable ac loss at 40 Hz and higher loss at 400 Hz

Weak effect of striation @ 40 Hz

Electrical Coupling

Striation ineffective @ 400 Hz

Losses increases beyond S6 due to Magnetic + Electrical coupling

20Loss ratio: ac loss of filamentized conductor S5/ac loss of non-striated conductor S6

Summaryy• Selective electroplating has been proven to achieve fully-filamentized coated

conductor even with thick copper stabilizer.

• Coated conductor with up to 30 µm copper stabilizer can be fully-filamentizedwithout any coupling.

– 15-fold ac loss reduction achieved compared to reference non-striated– 15-fold ac loss reduction achieved compared to reference non-striated coated conductor with ~ 30 µm copper stabilizer

• Coated conductor with 40 µm copper stabilizer can be fully-filamentized with partial coupling (due to sideways growth of copper across groove)partial coupling (due to sideways growth of copper across groove)

• 5-fold ac loss reduction achieved at 40 Hz even with partial coupling compared to reference non-striated coated conductor

• Fully-filamentized coated conductor with no coupling can be achieved even with thicker copper stabilizer using wider grooves

• Fully-coupled filamentized conductor (conductive material in groove) shows y p ( g )higher ac loss than non-striated conductor: in this case striation makes the situation worse!

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