A significant increase of critical current in high magnetic field, up to 31 T, was recorded in long tapes manufactured by employing a double-disorder route. In a double-disordered high-temperature ...superconductor (HTS), a superimposing of intrinsic and extrinsic disorder takes place in a way that (i) the intrinsic disorder is caused by local stoichiometry deviations that lead to defects of crystallinity that serve as pining centers in the YBa2Cu3Ox−δ matrix and (ii) the extrinsic disorder is introduced via embedded atoms or particles of foreign material (e.g. barium zirconate), which create a set of lattice defects. We analyzed possible technological reasons for this current gain. The properties of these tapes over a wider field-temperature range as well as field anisotropy were also studied. Record values of critical current as high as 309 A at 31 T, 500 A at 18 Tm and 1200 A at 5 T were found in 4 mm wide tape at 4.2 K and B perpendicular to tape surface. HTS layers were processed in medium-scale equipment that allows a maximum batch length of 250 m while 22 m long batches were provided for investigation. Abnormally high ratios (up to 10) of critical current density measured at 4.2 K, 19 T to critical current density measured at 77 K, self-field were observed in tapes with the highest in-field critical current. Anisotropy of the critical current as well as angular dependences of n and values were investigated. The temperature dependence of critical current is presented for temperatures between 4.2 and 40 K. Prospects for the suppression of the dog-bone effect by Cu plating and upscale of processing chain to >500 m piece length are discussed.
Alternative concepts based on drum design and reel-to-reel design were studied in the course of the development of industrial technology of long (up to 600 m) YBCO coated tapes. According to our ...previous route we investigated double disordered YBCO layers deposited by using extrinsic precipitations as well as intrinsic precipitations and structural defects. These superimposing of the nano-defect and inhomogeneities resulted in very high critical currents optimized for high-field operation. The HTS layers in our experiments were deposited onto CrNi stainless steel substrates which were polished and buffered with an in-plane textured yttria-stabilized-zirconia layer, 1.2-2 μ m thick. Critical currents in 220 and 550 m long tapes were 20-30% lower compared to length of 20 m, but still representing champion current values for long tapes. Development of the process based on drum concept resulted in finding a relationship between the tape throughput and the wall thickness of the drum. A concept of light, dynamic drum with thin walls, reduced heat capacity, and radial elasticity was analyzed and employed in processing of long, up to 600 m YBCO coated tapes. Comparison between drum and reel-to-reel techniques is provided. Newest status in long tape processing is reported.
Progress in the upscaling of multibeam pulsed laser deposition (PLD) is reported. Tapes 220 m long were repeatedly processed using an extended drum in PLD installation employed for the deposition of ...ceria cap buffer and YBCO layers. A Cr-Ni stainless steel tape preliminary coated with a biaxially textured yttria-stabilized-zirconia buffer layer via alternating-beam-assisted deposition was used as a substrate. In 2014, the upscaling of the PLD technique was performed in three steps. In the first step, a 22-m-long tape with record "in-field" critical current (500 A in a 4-mm-wide tape at 4.2 K, 18 T, B//c) was achieved in February 2014. The second step enabled the deposition of 110-130-m-long tapes with moderate (20%) reduction of critical current and sufficiently small local dropouts of the current. The third step resulted in the upscaling of tape processing to 230 m in length. First tapes of such length were already obtained in December 2014. Further upscale of the tape length toward 600 m and more is in progress so far. The most important feature of the PLD process is that the critical current in the coated conductors demonstrates no reduction in the end of the tape, which was exposed to a single run of translation of the rotating drum with the tape, i.e., from one end to the other end. Moreover, in many cases, a tendency of increase of critical current was observed during deposition run. Pulses of oxygen pressure formed by the deposition system together with the influence of barium zirconate precipitations enabled rather high in-field critical currents in 230-m-long tapes.
•Preparation of mechanically alloyed powders with a wide variation of the Mg:B-ratio.•Influence of this ratio on phase composition and on grain size of in bulk samples.•Increase of irreversibility ...field for Mg deficient samples.•Transport current density of wires is increasing considerably with Mg deficiency.
In this contribution the influence of the Mg:B-stoichiometry in the precursor on the structural and electrical properties of bulks and wires prepared with mechanically alloyed powder is discussed. The Mg to B ratio in the powder was varied in the range of x=0.7 to 1.1 (MgxB2). Analysing the properties of bulks and wires prepared with such precursor powders it was found that Mg-deficiency can increase the amount of MgB2 phase, the MgB2 diffraction peak width, the irreversibility field and the critical current density considerably.
When the fault current limiter yields influential response within 0.1 milliseconds, it demonstrates ultra-fast switching behaviour that is significantly faster than the response of the best ...mechanical and superconducting devices. Such ultra-fast response was demonstrated in recently developed superconducting fault current limiters (SFCLs) of inductive type. Secondary coil of the limiter was constructed from a set of closed rings made out of 40 mm wide YBCO coated conductor that was capable of nucleating wide normal zone in the beginning of quench process. Due to reduction of heat capacity and avoiding internal and external shunts, the ultra-fast switching behaviour with characteristic times of 50-100 microseconds was achieved. The ultra-fast performance results in a suppression of energy absorbed in the device during transient/quenching process as well as in low power dissipation after quenching of the superconducting element. This allows to maintain a very low power dissipation in the limiting modus duration which may be extended therefore to hours. Drastic reduction (by a factor of 10-50 in comparison with conventional types of SFCLs) of cryoconsumption was experimentally demonstrated at both normal operating modus and limiting (quenched) modus. Different ways for implementation of ultra-fast switching performance in fault current limiters are considered and discussed.
We report experimental results from a shielded inductive type superconducting fault current limiter (SFCL) demonstrator incorporating YBCO coated conductor together with results from an analytic ...study of a large 13 MVA SFCL. Important parameters such as the superconductor temperature rise, re-cooling time and voltage characteristics following a short-circuit quench are discussed. These results are compared with the measured and predictive performance of a resistive type SFCL incorporating a similar volume of YBCO CC and providing the same level of current limiting.
The European Union contributes around 20% of the cable-in-conduit conductor lengths needed for the ITER toroidal field (TF) magnet coils. For that purpose, 97 tons of Nb 3 Sn superconducting strand ...have been fabricated over five years, the production being completed in 2014. This superconducting strand has been manufactured by two companies, namely, Bruker EAS (Germany) and OST (USA), through the bronze route and the internal tin diffusion, respectively. This paper reports the outcomes of this strand mass production and of the strand characterization as performed by the suppliers and cross-checked on a regular basis by Durham University.
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