RESUMEN
We report the local structural and superconducting properties of undoped and Ag-doped YBa2Cu3O6+x (YBCO) films with a thickness of up to 1 µm prepared by pulsed laser deposition on SrTiO3 (STO) single crystals and on ion-beam-assisted deposition (IBAD) and rolling-assisted biaxially textured substrate (RABiTS)-based metal templates. X-ray diffraction demonstrates the high crystalline quality of the films on both single crystalline substrates and metal-based templates, respectively. Although there was only a slight decrease in Tc of up to 1.5 K for the Ag-doped YBCO films on all substrates, we found significant changes in their transport characteristics. The effect of the silver doping mainly depended on the concentration of silver, the type of substrate, and the temperature and magnetic field. In general, the greatest improvement in Jc over a wide range of magnetic fields and temperatures was observed for the 5%Ag-doped YBCO films on STO substrates, showing a significant increase compared to undoped films. Furthermore, a slight Jc improvement was observed for the 2%Ag-doped YBCO films on the RABiTS templates at temperatures below 65 K, whereas Jc decreased for the Ag-doped films on IBAD-MgO-based templates compared to undoped YBCO films. Using detailed electron microscopy studies, small changes in the local microstructure of the Ag-doped YBCO films were revealed; however, no clear correlation was found with the transport properties of the films.
RESUMEN
Superconducting windings will be necessary in future fusion reactors to generate the strong magnetic fields needed to confine the plasma, and these superconducting materials will inevitably be exposed to neutron damage. It is known that this exposure results in the creation of isolated damage cascades, but the presence of these defects alone is not sufficient to explain the degradation of macroscopic superconducting properties and a quantitative method is needed to assess the subtle lattice damage in between the clusters. We have studied REBCO-coated conductors irradiated with neutrons to a cumulative dose of 3.3 × 1022 n/m2 that show a degradation of both Tc and Jc values, and use HRTEM analysis to show that this irradiation introduces â¼10 nm amorphous collision cascades. In addition, we introduce a new method for the analysis of these images to quantify the degree of lattice disorder in the apparently perfect matrix between these cascades. This method utilises Fast Fourier and Discrete Cosine Transformations of a statistically relevant number of HRTEM images of pristine, neutron-irradiated and amorphous samples and extracts the degree of randomness in terms of entropy values. Our results show that these entropy values in both mid-frequency band FFT and DCT domains correlate with the expected level of lattice damage, with the pristine samples having the lowest and the fully amorphous regions the highest entropy values. Our methodology allows us to quantify 'invisible' lattice damage to and correlate these values to the degradation of superconducting properties, and also has relevance for a wider range of applications in the field of electron microscopy where small changes in lattice perfection need to be measured.
RESUMEN
We prepared overlap soldered joints of high-temperature superconducting tapes, using various materials and preparation conditions. In order to select the joints with optimal performance, we correlated their electrical properties (derived from current-voltage curves) with the microstructure of the respective joint cross-section by scanning electron microscopy. With the first group of joints, we focused on the effect of used materials on joint resistivity and critical current, and we found that the dominant role was played by the quality of the internal interfaces of the superconducting tape. Initial joint resistivities ranged in the first group from 41 to 341 nΩ·cm2. The second group of joints underwent a series of thermal cyclings, upon which the initial resistivity range of 35-49 nΩ·cm2 broadened to 25-128 nΩ·cm2. After the total of 135 thermal cycles, three out of four joints showed no signs of significant degradation. Within the limit of 100 thermal cycles, reliable soldered joints can be thus prepared, with normalized resistivity not exceeding 1.4 and with normalized critical current above the value of 0.85.
RESUMEN
The microstructure and texture evolution of Ni-5 at%W (Ni5W) alloy substrates were investigated by in situ tensile testing along the rolling direction (RD), transverse direction (TD), and at 45° to the RD (45°-RD), as well as by electron backscatter diffraction characterization. The tensile stress direction had a significant influence on the texture evolution. The cubic texture in the Ni-5 at%W alloy exhibited severe degradation when the tensile angle was 45°-RD. In contrast, the cubic texture was relatively stable under high deformation along the RD or TD. It was found that the slip line system in the 45°-RD specimen was the key to the contrasting behavior. The effect of the tensile testing angle on the cubic texture evolution for NiW substrates was investigated, and the corresponding effect on the superconducting properties of coated materials was studied.
RESUMEN
Lanthanum zirconate (LZO) films from water-based precursors were deposited on Ni-5%W tape by chemical solution deposition. The buffer capacity of these layers includes the prevention of Ni oxidation of the substrate and Ni penetration towards the YBCO film which is detrimental for the superconducting properties. X-ray Photoelectron Spectroscopy depth profiling was used to study the barrier efficiency before and after an additional oxygen annealing step, which simulates the thermal treatment for YBCO thin film synthesis. Measurements revealed that the thermal treatment in presence of oxygen could severely increase Ni diffusion. Nonetheless it was shown that from the water-based precursors' buffer layers with sufficient barrier capacity towards Ni penetration could be synthesized if the layers meet a certain critical thickness and density.
RESUMEN
We update here on the status of one of the main components of a 1.3 GHz NMR magnet currently being developed at the MIT Francis Bitter Magnet Laboratory (FBML): the 600 MHz HTS insert coil. Started in 2000 as a 3-phase program and currently in its final phase (Phase 3A), the HTS insert will first be installed in the bore of a 500 MHz all LTS magnet, generating a field of 25.8 T (1.1 GHz). In Phase 3B, we will place the HTS insert in the bore of a 700 MHz LTS magnet, achieving our ultimate goal of completing a high-resolution 1.3 GHz magnet. The HTS insert, built as a stack of double pancakes (DP), consists of two concentric stack of coils, the inner coil wound with YBCO tape and the outer coil with Bi2223/Ag tape. The series-connected coils, immersed in a bath of liquid helium at atmospheric pressure, will be operated in driven mode. The paper describes detailed aspects of: 1) design and fabrication of both coils, 2) testing of individual DPs at 77 K to characterize the current carrying capabilities and magnetic performance of each DP coil, 3) techniques and elements utilized in the DP-to-DP splice procedure and, 4) splice dissipation.