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Low-frequency flux noise in current-carrying high critical temperature superconducting films

Second generation (2G) high temperature superconductor (HTS) wires are based on a coated conductor technology. They follow on from a first generation (1G) HTS wire consisting of a composite multifilamentary wire architecture. During the last couple of years, rapid progress has been made in the development of 2G HTS wire, which is now displacing 1G HTS wire for most if not all applications. The engineering critical current density of these wires matches or exceeds that of 1G wire, and the mechanical properties are also superior. Scale-up of manufacturing is proceeding rapidly, with several companies already supplying the order of 10 km annually for test and demonstration. Coils of increasing sophistication are being demonstrated. One especially attractive application, that relies on the specific properties of 2G HTS wire, is fault current limitation. By incorporating a high resistivity stabilizer in the coated conductor, one can achieve high resistance in a quenched state during a fault event and at the same time provide significant heat capacity to limit the temperature rise. A test of a 2.25 MVA single phase system at 7.5 kV employing such wire by the Siemens/AMSC team has demonstrated all the key features required for a cost-effective commercial system. A novel approach to providing fault current limiting functionality in HTS cables has also been introduced.

We demonstrate that 3.5-MeV oxygen irradiation can markedly enhance the in-field critical current of commercial 2 nd generation superconducting tapes with an exposure time of just one second per 0.8 cm 2 . 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. 2Increasing the current carrying capacity of 2 nd generation (2G) YBCO high temperature superconducting (HTS) wires in the presence of high magnetic fields is critical for the commercialization of HTS based rotating machine applications such as lightweight and compact off-shore wind turbines and motors as well as various HTS magnet applications [1][2][3][4]. For these, operation in magnetic fields of several Tesla and at temperatures around 30K is envisioned. Although conductors of hundreds of meters in length with self-field critical current densities J c of more than 3 -4 MA/cm 2 (more than 300 -400 A/cm-width) at 77 K can now reliably be manufactured, the rapid suppression of J c in even modest applied magnetic fields continues to be a major challenge for HTS conductor development.In recent years, impressive advances in the in-field performance of short-length samples have been achieved [5][6][7][8][9][10], largely due to the strict control over the micro-and nanostructures. The formation of the desired pinning centers depends sensitively on the film deposition technique and substrate architecture. For instance, self-assembled nanorods can be engineered in films grown by pulsed laser deposition (PLD) or MOCVD from material containing excess metal oxides such as BaZrO 3 [11][12][13][14], BaSnO 3 [15] or BaHfO 3 [16], whereas the deposition of films with excess Zr using metal organic deposition (MOD) on single-crystal substrates [17] and on IBAD substrates [18] does not yield nanorods but nanoparticles. In general, the enhanced vortex pinning arises from the complex combined effects of the introduced second phases (nanorods or nanoparticles), additional structural disorder such as twin boundaries, stacking faults and point defects, as well as from isotropic pinning due to strain fields [5,17]. In short-length samples, critical current densities as high as ~ 7 MA/cm 2 at 30 K and 9 T applied parallel to caxis have been reported [9]. The translation of these advances into a reliable large-scale production process is a time consuming process currently under development.An alternative to increase the critical current density by modifying the chemical synthesis is afforded by particle irradiation, which may be applicable to all superconducting materials. Depending on the mass and energy of the ions and the properties of the superconducting material, irradiation enables the creation of defects with well-controlled density and topology, such as points, clusters or tracks. The...

The RABiTS™/MOD-YBCO (rolling assisted biaxially textured substrate/metal-organic deposition of YBa 2 Cu 3 O 7−δ ) 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 cm −1 width 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.