IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, …

1 ieee TRANSACTIONS ON APPLIED superconductivity , VOL. 21, NO. 3, JUNE 20113049 Progress in Performance Improvement and NewResearch Areas for Cost Reduction of 2G HTS WiresV. Selvamanickam, Y. Chen, I. Kesgin, A. Guevara, T. Shi, Y. Yao, Y. Qiao, Y. Zhang, Y. Zhang,G. Majkic, G. Carota, A. Rar, Y. Xie, J. Dackow, B. Maiorov, L. Civale, V. Braccini, J. Jaroszynski, A. Xu,D. Larbalestier, and R. BhattacharyaAbstract Second-generation (2G) HTS wires are now beingproduced routinely in kilometer lengths using Metal OrganicChemical Vapor Deposition (MOCVD) process with critical cur-rents of 300 A/cm. While this achievement is enabling severalprototype devices, in order to reach a substantial commercialmarket, the cost-performance metrics of 2G HTS wires need to besignificantly improved in device operating conditions.

2 Zr-dopinghas been found to be an effective approach to improve in-fieldcritical current performance of MOCVD-based HTS wires. In thiswork, we have explored modifications to the Zr-doped precursorcompositions to achieve three and two-fold increase in depositionrate in research and production MOCVD systems wires made with modified Zr-doped compositionsexhibit a self-field critical current density of 50 at Kand a 55 to 65% higher performance than our previous wires withZr-doping, over magnetic field range of 0 to 30 T. We have alsodeveloped an alternate, low-cost technique, namely electrodepo-sition, to deposit silver overlayer on superconducting film.

3 Wiresmade with electrodeposited silver are able to sustain the same levelof overcurrent as sputtered silver layers. This process has beensuccessfully scaled up to 100 m Terms BZO, critical current, electrodeposition, magneticfield, MOCVD, second-generation HTS, silver, INTRODUCTIONSECOND-GENERATION (2G)(REBCO,) High Temperature Superconducting(HTS) wires have been scaled up to pilot-scale manufacturingand are produced routinely in lengths of more than a 2G HTS wire consists of biaxially-textured buffers based onion beam assisted deposition (IBAD) of MgO [1] [3] on high-strength Hastelloy substrates followed by REBCO film deposi-tion by metal organic chemical vapor deposition (MOCVD) [4],[5].

4 The use of IBAD to achieve biaxially-textured template hasManuscript received August 03, 2010; accepted December 20, 2010. Dateof publication February 22, 2011; date of current version May 27, 2011. Thiswork was supported by a Contract with the US Department of Energy. Part ofthe work at NHMFL was also supported by the National Science Selvamanickam, I. Kesgin, A. Guevara, T. Shi, Y. Yao, Y. Zhang, , and G. Majkic are with the Department of Mechanical Engineering andthe Texas Center for superconductivity , University of Houston, Houston, TX77204 Chen, Y. Qiao, G. Carota, A. Rar, Y. Xie, and J. Dackow are with Super-Power, Schenectady, NY 12304 Maiorov and L.

5 Civale are with Los Alamos National Laboratory, LosAlamos, NM 87545 Braccini, J. Jaroszynski, A. Xu, and D. Larbalestier are with the NationalHigh Magnetic Field Laboratory, Florida State University, Tallahassee, FL32306 Bhattacharya is with the National Renewable Energy Laboratory, Golden,CO 80401 USA (e-mail: Object Identifier benefits including choice of essentially any a choice allows us to employ high-strength, non magneticand high resistivity substrates. High-strength substrates providea great benefit in device fabrication, especially for high-fieldmagnets. Additionally, thin (50) substrates are possible be-cause of high strength which results in substantially higher engi-neering current density.)

6 Non magnetic and high resistivity sub-strates lead to lower ac losses. Metal Organic Chemical VaporDeposition is the only technique that has been used to demon-strate 2G HTS wires longer than a kilometer. A world-recordperformance of 300,330 A-m was demonstrated over a 1,065 mlong wire in 2009 using MOCVD [6]. While the ability to manu-facture a complex thin film using epitaxial growth over lengthsof kilometer is impressive, a major factor that needs to be ad-dressed to reach widespread commercial use of 2G HTS wire isits cost. The feedback from device manufacturers indicates that2G HTS wire price of less than $ 50/kA-m indevice operatingconditionsneeds to be achieved for a substantial commercialmarket.

7 So, our research in the last year has been focused onimproving the cost-performance metrics of 2G HTS wire in de-vice operating conditions. In addition to higher zero-field crit-ical currentat 77 K, the performance of the wire in a mag-netic field of a few Tesla is an important factor that affects thecost-performance metric. In this paper, we will present advancesmade in improving the in-field performance of MOCVD-based2G HTS wires and the successful transition to production. Ad-ditionally, we will introduce an alternate technique to depositsilver overlayer, namely electrodeposition as a low-cost alter-native to vacuum deposition processes such as sputtering thatare commonly used.

8 While the content of silver in 2G HTS wireis small, silver deposition is an important constituentof wire cost as well as production IMPROVEDCRITICALCURRENTS INMAGNETICFIELDSIn 2009, we demonstrated more than two-fold improve-ment in critical current of MOCVD-based (Gd,Y)-Ba-Cu-O(GdYBCO) films using Zr-doping [7], [8]. Zr-tetra methylheptanedionate (thd) was added to the precursor solution forZr doping [7], [8].(BZO) nanocolumns formed bya self-assembly process were found to be responsible forimproved pinning. BZO-based self-assembled nanocolumnarstructure had been previously created by several groups usingpulsed laser deposition [9] [12] to achieve improved pinning,but it was not obvious that a similar structure could be achievedby a chemical process where Zr is added to the precursorrather than BZO to the PLD target.

9 After demonstrating that it1051-8223/$ 2011 IEEE3050 ieee TRANSACTIONS ON APPLIED superconductivity , VOL. 21, NO. 3, JUNE 2011 Fig. 1. Angular dependence of critical current of thick films fabricatedin research MOCVD system using undoped and Zr-doped 2. Angular dependence of critical current of thick films fabricatedin production MOCVD system using undoped and Zr-doped indeed possible with MOCVD, optimization of Zr contentin the GdYBCO film resulted in the highest critical currentat a Zr doping level of Also, in 2009, we were ableto successfully transition the process to manufacturing [13].Figs. 1 and 2 show the angular dependence of critical currentof GdYBCO wires made in research and production MOCVD systems with and without Zr-doping.

10 A two-fold improvementin critical current is observed over a wide angular range withZr doping in both research and production systems. The highermagnitude of critical current in the production system is due tothe fact that the films were thickness compared to films fabricated in the research MOCVD superior in-field performance has been achieved withZr-doped precursor chemistry, a drawback was the need to re-duce the deposition rate in the MOCVD process. In the re-search MOCVD system, a deposition rate of in fabrication of the Zr-doped wire that is described inFig. 1, which is 1/4 of the deposition rate that is normally usedin this system.