J. Reeves

Recent Progress in Second-Generation HTS Conductor Scale-Up at SuperPower

YBa2Cu3Ox (YBCO) second-generation (2G) HTS conductors have been produced in lengths over 300 m in pilot scale facilities established at SuperPower. High throughput pilot-scale manufacturing has been demonstrated with tape speeds at or above 30 m/h of 12 mm wide tape (corresponding to 90 m/h of 4 mm wide conductor) in all steps. A 322 m long conductor with a minimum critical current value of 219 A/cm has been produced, which corresponds to a critical current x length value of 70,520 A-m. A 270 m long, 4 mm wide conductor with an end-to-end critical value of 100 A has also been demonstrated. In a campaign to manufacture 2G conductor for the Albany cable project, SuperPower has produced 12,470 m of conductor that meets or exceeds the specification for piece length (42.4 m) and critical current (100 A/cm). In fact, more than 55% of the conductor produced is at least 100 m in piece length and more than 27% greater than 200 m in piece length. In addition to scaling up 2G conductors to high-throughput pilot-scale manufacturing, we have demonstrated high critical currents in short samples produced by Metal Organic Chemical Vapor Deposition (MOCVD). Critical current values of 557 A/cm have been achieved in 2.1 micrometer thick films in 12 mm wide, 10 cm long tapes. These samples exhibit a critical current value of 116 A/cm at 1 T and 76 K, in the orientation of field parallel to the c-axis. We have also constructed a 4-pancake coil that generated a magnetic field of 1.1 T at 77 K and 2.4 T at 64 K. A Fault Current Limiter (FCL) assembly has been successfully constructed and tested at high power levels. A prospective current of 90 kA was successfully limited to 32 kA within 1 ms without any HTS element failure.

Stability and quench protection of coated YBCO "Composite" tape

The paper presents results, experiment and simulation, of quench/recovery study of coated YBCO composite test samples, cooled by boiling liquid nitrogen and subjected to an over-current pulse. To operate stably and be protected from damage under adverse operating conditions of a real device, the YBCO tape must be a composite, loaded with normal metal of a sufficient thickness that significantly increases the thickness of the original YBCO tape.

Fabrication of 100 A class, 1 m long coated conductor tapes by metal organic chemical vapor deposition and pulsed laser deposition

Abstract SuperPower has been scaling up YBa 2 Cu 3 O x -based second-generation superconducting tapes by techniques such as pulsed laser deposition (PLD) using industrial laser and metal organic chemical vapor deposition (MOCVD). Both techniques offer advantage of high deposition rates, which is important for high throughput. Using highly-polished substrates produced in a reel-to-reel polishing facility and buffer layers deposited in a pilot ion beam assisted deposition facility, meter-long second-generation high temperature superconductor tapes have been produced. 100 A class, meter-long coated conductor tapes have been reproducibly demonstrated in this work by both MOCVD and PLD. The best results to date are 148 A over 1.06 m by MOCVD and 135 A over 1.1 m by PLD using industrial laser.

An overview of the coated conductor progress at IGC-SuperPower

Abstract The application and commercialization of high TC superconductors require consistent high JC (critical current density) over the length of the conductor. High JC is not difficult to achieve using a Y–Ba–Cu–O (YBCO) superconductor on well-polished ceramic single crystal substrates. However, the application of the coated superconductor to longer lengths needs to have smooth and uniform metal substrates. Smooth and uniform metal substrates are critical for the uniformity of texture for the buffer layers and the subsequent epitaxial growth of the YBCO conductor. In comparison with ceramics, a highly polished metal substrate is hard to achieve without scratching and deformation since it is ductile. It is even more challenging to attain these properties over long lengths of metal substrates. Aimed at solving this problem and making it possible to produce coated superconductors, we have developed a reel-to-reel polishing process which can produce long length, highly polished metal substrates. The typical average surface roughness (Ra) of these long lengths of tape is about 3 nm in a scan area of 160×120 μm2 using optical profilometer. A uniform buffer layer with good texture has been deposited on this metal substrate in continuous mode. YBCO deposited on to the buffered metal tape in a moving mode shows excellent epitaxial growth and superconducting properties. The critical current density (JC) over several centimeters of tape exceeds 106 A/cm2 at 77 K.

Microstructural and electrical characterization of gas cluster ion beam-smoothed YBCO films

The decrease in the critical current density (J/sub c/) of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films with increasing film thickness was investigated for 0.2 - 2.4-/spl mu/m-thick films grown on single crystal substrates. Microstructural and electrical properties were characterized by focused ion beam (FIB) microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy in a field emission scanning electron microscope, atomic force microscopy, and current-voltage measurements at 77 K in self-field. FIB cross sections directly showed that the top 30% -40% thickness of YBCO films contained pores, misoriented YBCO grains, and Ba-rich second phase particles that collectively produced a dead top layer which is believed to limit the J/sub c/ of YBCO films thicker than 1 /spl mu/m. A gas cluster ion beam etching and smoothing process partially removed the dead top layer and smoothed the film surface. In a 0.9-/spl mu/m-thick YBCO film, removal of a 0.22-/spl mu/m-thick dead layer yielded a 35% increase in J/sub c/ (up to 2.8 MA/cm/sup 2/) and a 25% decrease in film roughness. In a 1.3-/spl mu/m-thick YBCO film, removal of a 0.45-/spl mu/m-thick dead layer yielded an 85% increase in J/sub c/ (up to 1.1 MA/cm/sup 2/) and a 49% decrease in surface roughness. This study suggests that eliminating the dead top layer and smoothing the film surface might be key processing steps in the production of thick YBCO films with high J/sub c/.

Coated conductor scale-up program at IGC-SuperPower

The objective of the coated conductor program at IGC-SuperPower is to scale up substrate, buffer, and YBCO deposition process to manufacturing. Recently, pilot-scale manufacturing facilities were established for substrate, buffer, and YBCO preparation at IGC-SuperPower. High-quality substrate, buffer, and Y-Ba-Cu-O (YBCO) tapes are being produced in the pilot-scale facilities.