Second-generation HTS Wire for Wind Energy Applications

Second-generation HTS Wire for Wind Energy Applications Venkat Selvamanickam, Ph.D. Department of Mechanical Engineering Texas Center for Superconductivity University of Houston, Houston, TX SuperPower Inc. Symposium on Superconducting Devices for Wind Energy February 25, 2011 Barcelona, Spain 1

Superconductivity can have a wide range of impact on wind energy Light-weight, higher-power, direct drive turbines Preferred for off-shore wind energy for economy & less maintenance Less than 500 tons for 10 MW compared to ~ 900 tons for conventional direct drive More efficient, especially at part load High air-gap flux density Superconducting Magnetic Energy Storage to address intermittency Very efficient, short-term storage, complementing other storage methods Low-loss, long-distance power transmission from remote areas Much reduced right of way (25 ft for 5 GW, 200 kv compared to 400 feet for 5 GW, 765 kv for conventional overhead lines) Fault Current Limiters and Fault Current Limiting Transformers Built-in fault current limiting capability while benefiting from high efficiency Liquid nitrogen coolant is also dielectric medium (no oil) eliminates the possibility of oil fires and related environmental hazards 2

2G HTS wire: Great potential for applications Second-generation (2G) HTS- HTS is produced by thin film vacuum deposition on a flexible nickel alloy substrate in a continuous reel-to-reel process very different from mechanical deformation & heat treatment techniques used for Nb-Ti, Nb 3 Sn and 1G HTS wires Only 1% of wire is the superconductor ~ 97% is inexpensive Ni alloy and Cu Automated, reel-to-reel continuous manufacturing process Quality of every single thin film coating can be monitored on-line in real time! 40 μm Cu total 2 μm Ag 20μm Cu 1 μm YBCO - HTS (epitaxial) 100 200 nm Buffer 50μm Ni alloy substrate 20μm Cu

2G HTS wires provide unique advantages 2G HTS wires provide the advantages of high temperature operation at higher magnetic fields. Mechanical properties of 2G HTS wires are also 20μm Cu superior 50μm Hastelloy YBCO (H//c) YBCO (H//ab) NbTi Nb3Sn (Internal Sn) 100000 Nb3Sn (Bronze) < 0.1 mm 20μm Cu non-cu Jc ( A/mm 2 ) 10000 1000 100 0 5 10 15 20 25 30 35 Stress (MPa) 800 600 400 High Strength 1G HTS Low Je SP 2G HTS High Je Applied Field ( Tesla ) 200 0 Low Strength 1G HTSModerate Je Nb3Sn Moderate Je 0 0.1 0.2 0.3 0.4 0.5 4 Strain (%)

Advantages of IBAD MgO-MOCVD based 2G HTS wires Use of IBAD MgO as buffer template provides the choice of any substrate High strength (yield strength > 700 MPa) Non-magnetic, high resistive (both important for low ac losses) Ultra-thin (enables high engineering current density) Low cost, off-the-shelf High deposition rate and large deposition area by MOCVD enable high throughput Precursors are maintained outside deposition chamber Long process runs (already shown 50+ hours) < 0.1 mm 20μm Cu 2 μm Ag 1 μm YBCO - HTS (epitaxial) ~ 30 nm LMO (epitaxial) ~ 30 nm Homo-epi MgO (epitaxial) ~ 10 nm IBAD MgO YBCO 100 nm LaMnO 3 50μm Hastelloy substrate 20μm Cu MgO (IBAD + Epi layer) Y 2 O 3 Al 2 O 3 Hastelloy C-276 5

Successful scale-up of IBAD-MOCVD based 2G HTS wires 500 m 2G HTS wire first demonstrated in January 2007 (crossed 100,000 A-m) 1,000 m 2G HTS wire first demonstrated in July 2008 (crossed 200,000 A-m) Crossed 300,000 A-m in July 2009 with 1,000 m wire. 1,400 m lengths are now routinely produced. High throughput processing (>> 100 m/h* in IBAD & buffer processes, > 100 m/h* in other processes) Manufacturing capacity of few hundred km/year *4 mm wide equivalent 320,000 280,000 240,000 200,000 160,000 120,000 80,000 40,000 0 1 2 3 3 4 5 5-0 v l-0 r-0-0 -0 o u J a v g r-0-0 o u p c e N M N A A D ) -m (A t h g n e L * t n e r u C l a ic r it C 90 A-m to 300,330 A-m in seven years 595 m 322 m 427 m 1 m 18 m 97 m 206 m 158 m 62 m 6-0 g u A 7 r-0 p A 1,065 m 1,030 m 935 m 790 m 8-0 n a J 8-0 p e S 9-0 y a M 6

Meeting application requirements for HTS wire: Superior performance in operating conditions Application Operating Field (Tesla) Operating Temp. (K) Key requirements Wire needed per device (ka-m) Cables 0.01 to 0.1 (ac) 0.1 to 1 (DC) 70 to 77 Low ac losses (ac) High currents (dc) 40,000 to 2,500,000 Generators 1 to 3 30 to 65 In-field I c 2,000 to 10,000 Transformers 0.1 65 to 77 Low ac losses 2,000 to 3,000 Fault current limiters 0.1 65 to 77 Thermal recovery High volts/cm 500 to 10,000 SMES 2 to 30 T 4 to 50 In-field I c 2,000 to 3,000 7

Wire price-performance is the key factor for commercialization Today s 2G wire (4 mm wide, copper stabilized) : 100 A performance at 77 K, zero applied magnetic field, Price $ 30-40/m = $ 300-400/kA-m. At this price, cost of wire for typical device project (other than cable) > $ 1 M (more expensive than the typical cost of the device itself!) Cost of wire for a 500 km cable project = $ 20 M (~ cost of cable project itself!) Metric Today Customer requirement Price $ 300-400/kA-m < $ 100/kA-m* For commercial market entry (small market) < $ 50/kA-m* For medium commercial market < $ 25/kA-m* For large commercial market Four to 10-fold improvement in wire price-performance needed! *at operating field and temperature

Need for wire performance improvements Ten-fold reduction in price essentially impossible with $/m cost reduction. Increasing amperage is key to reaching price ($/ka-m) targets Opportunity to substantially increase self-field critical current in 2G wire by increasing film thickness HTS is still only 1 to 3% of 2G wire compared with 40% in 1G wire and is the only process that needs to be changed in 2G wire for high critical current Opportunity to significantly modify in-field critical current performance of 2G wire Numerous possibilities of rare-earth, dopant, nanostructure modifications to tailor in-field critical current 9

SuperPower-UH 2G wire development strategy SuperPower s technology operations consolidated in Houston which enabled total focus on manufacturing in Schenectady. Manufacturing objectives High yield, high volume operation On-time delivery of highquality wire Incorporate new technology advancements Technology objectives High performance wires Highly efficient, lower cost processes Advanced wire architectures Successful transition to manufacturing Manufacturing Operations in NY SuperPower Manufacturing at Schenectady, NY Customers SP staff @ Houston National Labs Best of both worlds : strong and concentrated emphasis on technology development & manufacturing Technology in Houston UH research staff CRADAs

Outline Higher performance in operating conditions of interest Low ac loss wires Improving yield and reducing cost 11

Jc (MA/cm 2 ) Need for higher amperage production wires 8 7 6 5 4 3 2 1 Research MOCVD Pilot MOCVD Critical current (A/cmwidth) 1000 800 600 400 200 0 0 1 2 3 Thickness (µm) 0 Address problems with decreasing 0 0.5 1 1.5 2 2.5 3 3.5 HTS film thickness current density with thickness High currents without significantly Now I c up to 375 A/cm (150 A/4 mm) in long lengths increasing film thickness by increasing current density (Jc) SP M3-714 Increasing Ic 2016 1000 A 2014 750 A/cm 2012 500 A/cm Goal Microstructural improvement (texture, secondary phases, a-axis, porosity) Pinning improvement (interfacial & bulk defects) Opportunity to reduce factor of two difference between pilot and research MOCVD systems 12

Improvement in critical currents of thick film coated conductors with higher rare earth content 6 5 77K Jc (MA/cm 2 ) 4 3 2 1 0T 1T, //ab 1T, //c 1T, min 0 0.9 1.1 1.3 1.5 1.7 1.9 Gd+Y 13

Improved pinning by Zr doping of MOCVD HTS wires Systematic study of improved pinning by Zr addition in MOCVD films at UH. Two-fold improvement in in-field performance achieved! Process for improved in-field performance successfully transferred to manufacturing at SuperPower

Large improvements in in-field I c of Zr-doped wires 100 A/4 mm 100 A/4 mm achieved at 65 K, 3 T in Zr-doped wire compared to 40 K, 3 T in undoped wire 165 A/4 mm achieved at 40 K, 5 T in Zr-doped wire compared to 18 K, 5 T in undoped wire

Large improvements in in-field I c of Zr-doped wires 65 K Retention of 3 T 77 K, zero field I c 40 K 3 T 18 K 3 T Undoped wire 0.27 1.02 2.13 Doped wire 0.73 1.99 3.50 Retention factor of doped wire is higher by 2.7 1.9 1.6 77 K zero-field I c of 2009 undoped wire = 250 A/cm 77 K zero-field I c of new doped wire = 340 A/cm Retention factor of doped wire including higher zero field Ic is higher by 3.71 2.64 2.23

Superior performance at 4.2 K in recent Zr-doped MOCVD production wires 60 50 40 Production wire 1.1 µm thick HTS film I c (77 K, 0 T) = 310 A/cm 1000 T=4.2K Jc, MA/cm 2 30 20 10 0 0 20 40 60 80 T, K J c @ 4.2 K (A/4 mm) 2009 2010 10 T, B wire 201 310 20 T, B wire 118 183 5 T, B wire 1,219 1,893 10 T, B wire 1,073 1,769 I c - 4mm width (A) 100 undoped, B perp. wire undoped, B wire FY'09 Zr-doped, B perp. wire FY'09 Zr-doped, B wire FY'10 Zr-doped, B perp. wire FY'10 Zr-doped, B wire 1 10 B (T) Measurements by V. Braccini, J. Jaroszynski, A. Xu,& D. Larbalestier, NHMFL, FSU In-field performance of Zr-doped production wires improved by more than 50% in high fields at 4.2 K

Benefit of Zr-doped wires realized in coil performance Coil properties With Zr-doped wire With undoped wire Coil ID 21 mm (clear) 12.7 mm (clear) Winding ID 28.6 mm 19. 1 mm # turns 2688 3696 2G wire used ~ 480 m ~ 600 m Wire I c 90 to 101 A 120 to 180 A Field generated at 65 K 2.5 T 2.49 T Same level of high-field coil performance can be achieved with Zr-doped wire with less zero-field 77 K I c, less wire and larger bore

Goals for further performance improvements Two-fold improvement in in-field performance achieved with Zr-doped wires Further improvement in I c at B c : Now 30% retention of 77 K, zero field value at 77 K, 1 T ; Goal is 50%. Improvement in minimum I c controlling factor for most coil performance : Now 15 to 20% retention of 77 K, zero field value at 77 K, 1 T ; Goal is first 30% and then 50% Together with a zero-field I c of 400 A/4 mm at 77 K, self field 200 A/4 mm at 77 K, 1 T in all field orientations. Achieve improved performance levels at lower temperatures too (< 65 K) Critical current (A/4 mm) 200 100 10 10x Standard MOCVD based HTS tape MOCVD HTS w/ self assembled nanostructures Goal 77 K, 1 T c axis 0 30 60 90 120 150 180 210 240 Angle between field and c axis ( )

Ongoing research in pinning improvements Raise minimum I c in angular dependence Most defects in Zr-doped MOCVD wires are directional, BZO nanocolumns along the c-axis (with splay) and RE 2 O 3 precipitate arrays along the a-b plane. Create new defect structure that is not directional or modify existing defect structure to be isotropic Create a splay in defects along a-b plane to broaden the peak in Ic at B a-b just like the peak at B c Determine contribution of different defect structures at lower temperatures and higher fields Critical current (A/4 mm) 200 100 10 10x Standard MOCVD based HTS tape MOCVD HTS w/ self assembled nanostructures Goal 0 30 60 90 120 150 180 210 240 Angle between field and c axis ( ) c axis

Multiple strategies to enhance in-field performance : higher I c, more isotropic Superconductor process modification Chemical modifications in MOCVD to modify defect density, orientation and size. Influence of film thickness on in-field I c of Zr-doped films Influence of rare earth type and content Influence of Zr content at fixed rare-earth type and content Influence of other dopants Influence of deposition rate Buffer surface modification buffer prior to superconductor growth Post superconductor processing modification such as post annealing etc. 2

Improvement with Zr in thicker films All samples were of composition Y 0.6 Gd 0.6 BCO Improvement in in-field critical current of Zr-doped wires increases with film thickness

In-field performance of Zr-doped films is drastically modified by rare earth content Zr content maintained at 7.5% in all three samples Y 1.2 c axis (Y,Gd) 1.5 20 nm Fewer defects along a b plane in Y 1.2 ; defects prominent along a b plane in (Y,Gd) 1.5

Thick film multilayers of Zr doped (Y,Gd) 1.5 and (Y,Gd) 1.2 compositions 7.5% Zr doping. 0.7 µm HTS film deposited in each pass. Zero-field and in-field performance measured after each pass.

Multfilamentary 2G HTS tapes for low ac loss applications Filamentization of 2G HTS tapes is desired for low ac loss applications. So far, there is no proven technique to repeatedly create high quality mulfilamentary 2G tapes. Also, adds substantial cost. ac loss (W/m) 2 1 100 Hz 0 0.00 0.01 0.02 0.03 0.04 0.05 0.06 B ac rms (T) unstriated 5.1 x multifilamentary 4 mm 5-filament tape, 4 mm wide (produced up to 15 m) 32-filament tape, 4 mm wide (difficult to make even 1 m lengths)

Goals in multifilamentary 2G HTS wire fabrication Maintaining filament integrity uniform over long lengths (no Ic reduction) Striated silver and copper stabilizer (minimize coupling losses) Minimum reduction in non superconducting volume (narrow gap) and fine filaments Ag HTS Substrate Cu A fully filamentized 2G HTS wire would need to have 20 50 µm of copper stabilizer striated!

Approach to make fully-filamentized 2G HTS wire 1. Coat photoresist on silver Photoresist 2. Transfer pattern from mask to photoresist 3. Electroplate copper Ag YBCO Substrate 4. Remove remaining photoresist Cu 5. Wet etch silver and HTS X. Zhang and V. Selvamanickam, US 7,627,356

Approach to make fully-filamentized 2G HTS wire Cu Ag HTS substrate 100 μm Cu 1 mm Fully-filamentized 2G HTS wire demonstrated, but still involves etching 2

Alternate bottom-up approach being developed Striate buffer layer, then deposit REBCO. REBCO Buffer Stack Substrate Substrate Substrate Prerequisites: 1.) striation phase needs favorable properties for minimal coupling 2.) no widening of striation phase into REBCO 3.) No poisoning of REBCO (no diffusion barrier) 4.) No porosity or features that may initiate cracks 5.) Fully-filamentized silver and copper stabilizer

Striation of buffer layers 500 µm Mechanical striation with a diamond tip: 1 mm separation Milling reveals ~1.8 micron depth Width ~ 25 µm. Repeated experiments with load control : width decreased to 12 µm

Striated buffer after MOCVD REBCO texture typical of nonstriated tape Striated texture polycrystalline, rough No apparent widening of striation!

Cross section of striated region after MOCVD

Factor of five lower ac loss in multifilamentary wire made by bottom-up approach SCR 5,6 multifilamentary ; SCR 7ref reference, no filaments

Improving yield through on-line vision QC in MOCVD Vision inspection algorithms assign quality values to images taken every ~15 mm of the wire as it emerges from the MOCVD deposition chamber Comparisons of quality map with reference tape to discern process drift in real time 0 Training from Reference Images No Partial Training COVG Ic1T 500 20 400 Defect Code Value (%) 40 60 80 300 200 100 Ic-1T (Amps) 100 0 850 900 950 1,000 1,050 1,100 1,150 1,200 1,250 1,300 Absolute Position (m) Real-time prediction of Ic during MOCVD process enabled by improved on-line Vision system

Critical Current (A/cm) Early detection of a-axis growth during MOCVD is valuable for high current wires 300 250 200 150 100 50 0 0 0.5 1 1.5 YBCO (200)/(006) ratio Predicted critical current (A) Critical current predicted based on (006) XRD peak intensity 400 300 200 100 0 Ic=4.95*counts (006)-125 y = 1.0007x - 0.0235 R² = 0.8411 0 100 200 300 400 Measured critical current (A) Good correlation between measured I c and (006) XRD peak intensity

On-line XRD in new pilot-mocvd system for real-time quality control 36

Significant improvement in quality of production wires in 2010 % wires > 2009 2010 250 A/cm 25% 60% 300 A/cm 8% 22%

Rapidly decreasing price of 2G HTS wire through technology advancements 10 m demo 100 m demo First year of pilot production 500 m demo 2 to 4x higher throughput 1,000 m demo Creation of separate Manufacturing and R&D facilities AP wire (Zr-doped) product introduction

Projected improvements in in-field performance of production wires through technology 10-fold improvement by combination of higher self-field critical current and improved retention of in-field performance through technical innovations. Even at 4.2 K, 15 T, 2G HTS wire is comparable now with Nb 3 Sn wire. Opportunity to improve to be 10X better than Nb 3 Sn!

Significant price improvements projected through technological advancements Prototype device market c Small commercial market Medium commercial market Large commercial market Price reduction due to improvements in zero-field critical current, retention of in-field critical current and cost reduction ($/m) Applications that involve magnetic field benefit from the additional improvement factor in in-field Ic retention Increasing market opportunities with decreasing price at operating condition.

Magnetic Field (T) Magnetic Field (T) 35 30 25 20 15 10 35 30 25 20 15 10 5 0 Roadmap to realize large market potential 5 0 Now to 2 years D 0 10 20 30 40 50 60 70 80 90 Temperature (K) D C C B 2G HTS Large market 2G HTS Medium market 2G HTS Small market Niobium Tin LTS Niobium Titanium LTS B 2G HTS demo market Niobium Tin LTS Niobium Titanium LTS A. Cables, Transformers, Fault Current Limiters B. Motors, Generators, Transportation, Aerospace C. High field Magnets D. High field Inserts A 5+ years A. Cables, Transformers, Fault Current Limiters B. Motors, Generators, Transportation, Aerospace C. High field Magnets, MR, High Energy Physics, Fusion Reactors D. High field Inserts, MR, High Energy Physics, Fusion Reactors A Large market potential outside the capability of LTS wire. Wide range of applications with broad operating conditions & unique requirements need highly sophisticated & engineered wire. Abundant opportunity to lead market capture through technology to improve wire performance and cost-profile 0 10 20 30 40 50 60 70 80 90 Temperature (K) Magnetic Field (T) 35 30 25 20 15 10 5 0 D 2G HTS Large market 2G HTS Medium market 2G HTS Small market Niobium Tin LTS Niobium Titanium LTS C 0 10 20 30 40 50 60 70 80 90 Temperature (K) B 2 to 5 years A. Cables, Transformers, Fault Current Limiters B. Motors, Generators, Transportation, Aerospace C. High field Magnets, D. High field Inserts A

Applied Research Hub to accelerate technology transfer and commercialization Formed in 2010 with $3.5 M funding from the state of Texas through the Emerging Technology Fund. Additional $3.8 M provided by UH. The initial focus of the Applied Research Hub is on power applications of high temperature superconducting wire. SuperPower is the first industry partner Labs now in UH campus expanding to 70-acre UH Energy Research Park New pilot-scale MOCVD system procured and will be set up this summer. SuperPower to establish Specialty Products Facility in UH Energy Research Park this summer Rapid transfer of technology advances to manufacturing to accelerate commercialization of HTS for wind energy and other applications

Abundant potential for 2G HTS wires for several applications 2G HTS wires have come a long way by combining complex materials with novel processes and equipment innovations. Among all superconducting materials, 2G HTS wires are the most tunable plenty of opportunities to meet goals through R&D. Potential for large improvements in performance (critical current in operating condition) with modest price reduction ($/m) Opportunities to tailor wire to meet complete specifications (ac losses, stabilization, mechanical properties) Focused R&D effort underway along with maturing manufacturing operation for broad insertion of 2G HTS wire in several applications