Martin W. Rupich

Advances in second generation high temperature superconducting wire manufacturing and R&D at American Superconductor Corporation

The RABiTS?/MOD-YBCO (rolling assisted biaxially textured substrate/metal?organic deposition of YBa2Cu3O7??) route has been established as a low-cost manufacturing process for producing high performance second generation (2G) wire. American Superconductor Corporation (AMSC) has used this approach to establish a production scale manufacturing line based on a wide-web manufacturing process. This initial production line is currently capable of producing 2G wire in lengths to 500?m with critical currents exceeding 250? A?cmwidth?1 at 77?K, in the self-field. The wide-web process, combined with slitting and lamination processes, allows customization of the 2G wire width and stabilizer composition to meet application specific wire requirements. The production line is currently supplying 2G wire for multiple cable, fault current limiter and coil applications. Ongoing R&D is focused on the development of thicker YBCO layers and improved flux pinning centers. This paper reviews the history of 2G wire development at AMSC, summarizes the current capability of the 2G wire manufacturing at AMSC, and describes future R&D improvements.

Second Generation Wire Development at AMSC

AMSC has established a Second Generation (2G) High-Temperature Superconductor (HTS) wire manufacturing technology based on the Rolling Assisted Biaxially Textured Substrate and Metal Organic Deposition processes. AMSCs 2G wire (Amperium) has been used by a wide range of customers for development and testing of initial commercial HTS-based applications. Although the Amperium wire properties and quantities satisfy the requirements for these initial projects, improvements in critical current, field performance, and cost are beneficial for large-scale commercial and military applications. As Amperium wire manufacturing continues to ramp up, AMSCs R&D program has focused on increasing critical current, and the development of nonmagnetic substrates. The R&D process developed for a single-coat, 1.2 μm YBCO film has been transferred to production-scale equipment, resulting in the first Amperium wires with critical currents reaching 500 A/cm-w (77 K, self-field) in production length. A nonmagnetic substrate, which minimizes ferromagnetic substrate losses in ac cable applications, has been produced in R&D lengths and demonstrated in an Amperium cable wire.

A method for crystallographic texture investigations using standard x-ray equipment

A fast and accurate method has been developed for measuring crystalline texture in homogeneous materials. The method uses a conventional powder x-ray diffractometer capable of {theta} scans. Two scans are recorded from the sample: first, a high resolution {theta}-2{theta} scan is obtained of a Bragg peak whose diffracting planes are normal to the preferred orientation direction; second, a {theta} scan is obtained using this peak. The {theta} scan contains the required texture information, but the intensities must be corrected for defocusing and absorption to obtain the texture profile. The {theta}-2{theta} scan of the Bragg peak is used to make the defocusing correction, and first principles calculations are used to correct for absorption. The theory behind these corrections is presented here. The validity of the technique has been verified by making measurements on untextured alumina. Data obtained from Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} superconducting tape specimens with this technique are compared with texture data obtained with a four-circle diffractometer. {copyright} {ital 1998 Materials Research Society.}

Rapid doubling of the critical current of YBa2Cu3O7-δ coated conductors for viable high-speed industrial processing

We demonstrate that 3.5-MeV oxygen irradiation can markedly enhance the in-field critical current of commercial second generation superconducting tapes with an exposure time of just 1 s per 0.8 cm2. The speed demonstrated here is now at the level required for an industrial reel-to-reel post-processing. The irradiation is made on production line samples through the protective silver coating and does not require any modification of the growth process. From TEM imaging, we identify small clusters as the main source of increased vortex pinning.

Nondestructive Investigation of Position Dependent

A coated conductor wire produced by the MOD-RABiTS process was nondestructively characterized for <i>I</i> _c uniformity along its length. Regions of interest were identified by variations in the <i>I</i> _c-<i>n</i> value relationship. These regions were investigated using <i>I</i> _c(B,angle) and <i>I</i> _c(B||c) measurements. It was found that the conductor properties vary from isotropic to anisotropic over a length of a few centimeters. Additionally, the exponent of the power law fit to the field dependence is shown to vary between 0.84 and 0.67. The position dependence of <i>I</i> _c was then measured at two field orientations, <i>H</i>||c and <i>H</i>||ab, along the conductor in a new two measuring stage system. This system allows rapid characterization of a long conductor while providing easily interpreted data on the source of variations.

I_{\rm c}

Tin-based nanoparticles, proposed to be barium stannate, have been formed in YBCO films fabricated by metal-organic deposition, through modification of the precursor solution. These randomly-oriented 30-50 nm particles are dispersed throughout the film thickness, providing an enhancement in the isotropic flux pinning relative to undoped YBCO. For a low level of nanoparticle addition of 2 vol%, a flux-pinning force enhancement of up to 32% is achieved. We report field and field-angle dependence of the transport critical current, transmission electron microscopy, and X-ray diffraction of our YBCO films on RABiTS substrates, and compare with similar barium zirconate additions.

Variations in Multi-Meter Coated Conductors

We demonstrate a twofold increase in the in-field critical current of AMSCs standard 2G coil wire by irradiation with 18-MeV Au ions. The optimum pinning enhancement is achieved with a dose of 6 × 1011 Au ions/cm2. Although the 77 K, self-field critical current is reduced by about 35%, the in-field critical current (H//c) shows a significant enhancement between 4 and 50 K in fields > 1 T. The process was used for the roll-to-roll irradiation of AMSCs standard 46-mm-wide production coated conductor strips, which were further processed into standard copper laminated coil wire. The long-length wires show the same enhancement as attained with short static irradiated samples. The roll-to-roll irradiation process can be incorporated in the standard 2G wire manufacturing, with no modifications to the current process. The enhanced performance of the wire will benefit rotating machine and magnet applications.

Flux Pinning by Barium Stannate Nanoparticles in MOD YBCO Coated Conductors

Key features of the microstructure in high critical current density (<i>J_C </i>) MOD Y₁Ba₂Cu₃O_y (YBCO) films on biaxially-textured nickel substrates with intervening buffer layers are presented. 0.8 <i>mu</i>m thick MOD YBCO films on the 4cm wide RABiTS templates have 77K, self-field <i>J_C </i> and <i>I_C </i>values exceeding 3 MA/cm² and 250A/cm-width, respectively. MOD YBCO films have a laminar grain structure with a high density of YBa₂Cu₄O_y(Y124) intergrowths, which give rise to an enhanced peak in angular anisotropy measurements of <i>J_C </i> when the applied field is parallel to the ab planes of the YBCO films. Other key aspects of MOD YBCO films related to the laminar growth mode and layered microstructure are grain boundary overgrowth, grain boundary meandering, colony microstructures, incoherent precipitates of Y₂O₃ and Y₂Cu₂O₅, and phase separations.

Engineered Pinning Landscapes for Enhanced 2G Coil Wire

Key features of the nucleation and growth of metal organic deposited (MOD) Y1Ba2Cu3Oy (YBCO) films on biaxially-textured nickel substrates with intervening buffer layers are presented. Within this work, we show the formation of an oriented precursor phase, the laminar growth of the YBCO in the presence of a liquid phase, and subsequent formation of relevant defects tied to the growth process. A model is presented for nucleation and growth, second phase development, and porosity formation. Specific microstructural differences with regard to physical vapor deposited films are discussed.

Key Microstructural Features of MOD

Abstract The performance of high-temperature superconductor (HTS) composite conductors is rapidly advancing. Filament current densities of greater than 32,000 A/cm 2 (77 K, self field, 1 μV/cm) have been achieved in multifilamentary composite conductors prepared with scaleable powder in tube techniques. This has allowed the fabrication of composite conductors with overall conductor current densities of 9100 A/cm 2 . These advances are being applied to the manufacture of composite conductors with lengths in excess of 1 km and filament currents densities of 8900 A/cm 2 (77 K, self field, 1 × 10 −11 Ω-cm). Recent advances in the development of high J c composite conductors will be reviewed. The performance and characterization of long length conductors will be described and the integration of these conductors into practical applications will be reported.