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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)
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
11
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
13
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
14
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
15
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!
21