Ibrahim Kesgin

Progress in Performance Improvement and New Research Areas for Cost Reduction of 2G HTS Wires

Second-generation (2G) HTS wires are now being produced routinely in kilometer lengths using Metal Organic Chemical Vapor Deposition (MOCVD) process with critical currents of 300 A/cm. While this achievement is enabling several prototype devices, in order to reach a substantial commercial market, the cost-performance metrics of 2G HTS wires need to be significantly improved in device operating conditions. Zr-doping has been found to be an effective approach to improve in-field critical current performance of MOCVD-based HTS wires. In this work, we have explored modifications to the Zr-doped precursor compositions to achieve three and two-fold increase in deposition rate in research and production MOCVD systems respectively. Production wires made with modified Zr-doped compositions exhibit a self-field critical current density of 50 MA/cm2 at 4.2 K and a 55 to 65% higher performance than our previous wires with Zr-doping, over magnetic field range of 0 to 30 T. We have also developed an alternate, low-cost technique, namely electrodeposition, to deposit silver overlayer on superconducting film. Wires made with electrodeposited silver are able to sustain the same level of overcurrent as sputtered silver layers. This process has been successfully scaled up to 100 m lengths.

Multifilament, copper-stabilized superconductor tapes with low alternating current loss

Multifilament fully stabilized second generation superconductor tapes have been fabricated with filaments widths as small as 180 μm. Each superconducting filament is copper stabilized, with copper thickness up to 30 μm, without compromising the beneficial effect of striations on magnetization AC losses. This has been accomplished by a combination of laser scribing (ablation), post-ablation oxidation, and subsequent selective electroplating of copper. Twelve millimeters wide superconductor tapes divided into 48 filaments with 10 μm thick copper stabilizer is found to meet an AC loss target of 1 W/kA/m in applied alternating magnetic field of 0.075 T at 100 Hz. This technique has a potential to be transferred to a large scale manufacturing of stabilized, low loss multifilament coated conductors.

Composition Effects on the Critical Current of MOCVD-Processed Zr:GdYBCO Coated Conductors in an Applied Magnetic Field

Zr:GdYBCO films were grown by reel-to-reel metal organic chemical vapor deposition (MOCVD) on hastelloy tapes with IBAD-MgO-based buffer. The composition was varied systematically to investigate the effects of changes in (Gd+Y)/Ba, (Gd+Y)/Cu and Gd/Y ratios and Zr-doping concentration on the critical current density (Jc) of the films in an applied magnetic field (B). The magnetic-field-angle dependence of Jc measured at 77 K and 1 T showed that (1) for Gd+Y content ranging from 1.2 to 1.5, the minimum Jc for any angle did not vary significantly with the Gd+Y content; while the Jc at B//c varied significantly and took its maximum value at Gd+Y content of 1.2; (2) increasing Gd+Y could suppress or level off the Jc peak at B//c which was associated with the pinning from BaZrO3 nano-columns; (3) the optimum Zr-concentration for the highest Jc(77 K, 1 T) is in the range of 0.04-0.07 in the film; in this range under certain growth condition, the c-peak in the angular dependence of Jc could be higher than the ab-peak; (4) increasing Gd/Y ratio increased Jc_min(77 K, 1 T); (5) in self-field or low field, however, the optimized Gd/Y ratio was about 1.

Completely Etch-Free Fabrication of Multifilamentary Coated Conductor Using Inkjet Printing and Electrodeposition

Filamentization has been proven to be an effective way to reduce the ac loss of coated conductor superconducting tapes. However, all filamentization techniques to date involve material removal at some stage of processing. Utilizing inkjet printing and electrodeposition, a novel, completely etch-free method of fabricating multifilamentary RE-Ba-Cu-O (REBCO,

Influence of Oxygenation in Copper Stabilized Multifilamentary 2G HTS Tapes Made by Selective Electroplating and Laser Ablation

\hbox{RE} = \hbox{rare-earth}

Effect of Selectively Electrodeposited Stabilizer Thickness on AC Loss Behavior of Fully-Filamentized HTS Wire

) superconducting tapes has been developed. Multiple insulating lines were fabricated on biaxially-textured MgO-buffered substrates by inkjet printing. Multifilamentary REBCO was obtained by preferential deposition of the superconductor between the insulating lines. Selective deposition of silver by electrodeposition on REBCO filaments was also achieved to create a multifilamentary conductor with a complete etch-free process. Due to the highly resistive barrier lines, reduced ac loss with minimized coupling was achieved in the multifilamentary REBCO tapes. Optimization of the inkjet and REBCO deposition process is underway to achieve a combination of high critical current and low ac losses by this completely etch-free technique.

Reel-to-Reel Selective Electroplating of Cu Stabilizer for Multifilamentary Coated Conductors

Striation and selective electroplating of copper stabilizer layer has been proven to be an effective way of reducing the hysteretic AC loss of second generation high temperature superconducting (2G-HTS) tapes. This method consists of a top down laser material removal (ablation) followed by post-oxygenation to create resistive oxide layer on the grooves and selective electroplating of a thick Cu stabilizer layer on the filaments. In such a filamentization technique, scalability, the degree of coupling loss contribution and critical current (Ic) degradations are the main concerns. In this study, we have investigated the post-oxygenation temperature effect on the Ic degradation and coupling loss contribution. The results showed that post-oxygenation temperature has immense effect on the Ic degradation and also alters the coupling loss contribution to the total magnetization AC losses. The coupling loss contribution was found to be less in samples oxygenated at higher temperatures; however, the degradation of Ic was found to be higher. In addition, preliminary experiments were conducted to scale-up this newly-developed technique. Initially, 10 m long fully-filamentized tape with thick Cu stabilizer layer was fabricated and at least 5 times reduction in AC loss was observed.

Properties of recent IBAD–MOCVD coated conductors relevant to their high field, low temperature magnet use

The influence of thickness of stabilizer layer on fully-filamentized RE-Ba-Cu-O (REBCO, RE = rare earth) coated conductors fabricated by using our recently developed selective electroplating technique on magnetization ac losses is investigated over a frequency range of 40 to 500 Hz at ~ 77 K. The results showed no significant loss contribution by the increasing thickness of the stabilizer in fully-filamentized or decoupled 12-filament tape. The losses for 12-filament decoupled tapes were found to be almost 15 times lower than that for nonstriated reference at relatively high field amplitudes and low frequencies while this number is slightly reduced at high frequencies. Furthermore, magnetization ac losses of partially- and fully-coupled tape structure were investigated since excessive deposition of electroplated copper results in merging of the metal in the middle of the groove, which eventually bridges the superconducting filaments. Such structures resulted in a drastic increase in the losses, and the filamentization became ineffective above the penetration field to an extent that the losses exceeded that of a nonstriated reference tape at relatively low field amplitudes. The thickness for the selectively-coated copper stabilizer on filaments without bridges that leads coupling was achieved to be 30 μm and estimated up to 35 to 40 μm for a groove width of 40 to 55 μm.

Influence of Zr and Ce doping on electromagnetic properties of (Gd,Y)―Ba―Cu―O superconducting tapes fabricated by metal organic chemical vapor deposition

A continuous, reel-to-reel DC electroplating process has been developed to produce high-quality Cu stabilizer for multifilamentary coated conductors. Due to the large resistivity difference between the silver-coated superconducting filaments and the insulating oxidized grooves between the filaments, selective electroplating was achieved on laser-striated multifilamentary tapes. Every superconducting filament in the tape was homogeneously copper-coated without continuous deposition of copper on the insulating grooves. The multifilamentary tapes are then fully stabilized without significant reduction in critical current and the benefit from filamentization on AC loss is maintained. The high flexibility of electroplating enabled us to produce multifilamentary coated conductors with copper stabilizer thickness from 5 to 30 μm. A 10-m tape was fabricated to demonstrate the scalability of fully-stabilized, low-loss multifilamentary coated conductors. The stabilized 12-filamentary CC tape is able to achieve four-fold AC loss reduction with minimal reduction in its critical current.