Papers by Keyword: Flux Pinning

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Authors: C. Cai, J. Zhang, Y. Lu, Hänisch, R. Hühne, B. Holzapfel
Abstract: By controlling pulse number of laser ablation, we prepared a series of quasi-multilayers of YBa2Cu3O7-δ/M (M=incomplete oxide layer) namely 70×(40/n) (n = 2, 5, 10 and 20, pulse number of M) which were characterised with nano-scale precipitates. While the texture properties of Y123 inside qusi-multilayer hardly change, its Tc appeared much different depending on the doping level of M. X-ray θ-2θ scanning and pole figures indicated that the different growth-controlled precipitates occured inside Y123 films. In the case of M=YSZ (Yttria Stabilized Zirconia), nanosized perovskite precipitates of BaZrO3 formed as a result of solid state reaction of YSZ with Y123, leading to Tc obviously decreasing with increasing of n. In the case of M=Y2O3, however, Tc did not decrease so much at the studied range of n due to no solid state reaction mentioned above. Magneto-transport and field angular dependence showed that the critical current density in films with lower doping content (such as n = 2) was improved in large ranges of field and temperature, suggesting tailorable enhancement and anisotropy of flux pinning force.
1865
Authors: Bao Rong Ni, Edmund S. Otabe, Masaru Kiuchi, Yan Wei Ma
Abstract: The superconducting Ba1-xKxFe2As2 (x = 0.4) single crystals were prepared by the so-called FeAs self-flux method. The critical temperature by ac susceptibility measurement was estimated to be about 36 K. The magnetic field and temperature dependences of critical current densities were investigated by an ac inductive measurement (Campbell’s method). Unlike the phenomenon of co-existence of the global and local critical current densities observed in many polycrystalline Fe-based superconducting pnictides, it was found that only a uniform critical current density (Jc) flows through the whole sample. The value of Jc at 20 K and 1 T was about 5×108 A/m2, which is much smaller than the local critical current density observed in polycrystalline samples. This result implies that a dissimilarity of flux pinning mechanism exists between these two kinds of materials. The force-displacement characteristic of fluxoids in sample was investigated. The Labusch parameter was found to increase monotonously with increasing magnetic field, while the interaction distance was proportional to the fluxoid spacing. These results are consistent with the prediction based on a simple flux pinning mechanism.
288
Authors: Wen Xu Sun, Bao Rong Ni, Akiyoshi Matsumoto, Hiroaki Kumakura
Abstract: It is well known that SiC doping in superconducting MgB2 improves the upper critical magnetic field (Bc2) and the critical current density (Jc) under high magnetic field. However, the relationship between SiC doping and the flux pinning mechanism has not been clarified. In this study, several MgB2 samples with and without SiC doping were prepared by the conventional in situ powder-in-tube method. The critical current densities and the force-displacement characteristics of fluxoids in samples were investigated by an ac inductive measurement (Campbell’s method). The Labusch parameter (αL) and the interaction distance (di) were estimated from the obtained force-displacement profile. It was found that SiC doping enhances the values of αL, but does not change the characteristics of the magnetic field dependence of αL apparently. Namely, αL vs. B3/2 characteristics in the pure samples and SiC doped samples are almost the same. Such a result of αL properties implies that the pinning mechanism in the SiC doped samples could be consistent with the conventional pinning theory. On the other hand, di, which is considered to be proportional to the size of pinning potential, decreases rapidly with increasing magnetic field, especially in the pure samples. For high magnetic field region, the variations of di were deduced to be caused by flux creep. The depth of pinning potential, U0, was estimated by using the values of αL and di. The values of U0 give evidence of that SiC doping can prevent the flux bundles moving to another pinning center under high magnetic field.
293
Authors: Xi Feng Pan, Guo Yan, Xiang Hong Liu, Yong Feng, Ping Xiang Zhang, Yong Zhao, Akiyoshi Mastumoto, Hiroshi Kumakura
Abstract: A series of MgB2 bulks with different porosity have been successfully prepared by in-situ solid-state reaction at ambient pressure with a toluene-treatment boron powder. The mass density reaches 1.86 g cm-3 at the most compact MgB2 bulk, which has an imporous microstructure, excellent grains coupling, clean grain boundaries and nanosized grains (100~200 nm). Our results reveal that the porosity of MgB2 can be significantly depressed by tuning the residual toluene content and heat treatment temperature in this way. Due to the degradation of porosity and thus the enhancement on grains connectivity and grains boundary pinning, the critical current density, Jc and irreversible fields Birr of MgB2 are significantly improved. For the best sample, at 20K, 4T and 10K, 6T, the Jc reach 2400 and 3700 A cm-2, which is higher than normal porous sample by a factor of 20 and 8, respectively; and the Birr at 20 K reaches 5.10 T.
208
Authors: Yong Lu, Feng Kuan Gao, Dong Gao, Ming Liang Zhang
Abstract: Magnetic flux pinning takes place between the high-temperature superconductors and magnets which can form non-contacting linkages between the individual components. This interaction is proposed for use in in-orbit assembly. This paper develops a flux pinned revolute joint which fits for the reconfiguration of modular spacecraft and details the reconfiguration mechanisms of the novel joint. Moreover, the process of reconfiguration is simulated via the rigid body dynamics. Furthermore, two flux pinned modules are constucted to confirm the feasibility of the designed flux pinned rovolute joint for reconfiguration on a testbed.
1706
Authors: Fahmi Astuti, Malik Anjelh Baqiya, Darminto
Abstract: Abstract. The powders of Bi2-xPbxSr2CaCu2O8+δ (x=0; 0.4) superconductor have been prepared by using dissolved method followed by short period of sintering and calcination process . The purpose of this research is to study about the Pb doped effect to the properties of BSCCO nanopowders especially in the electric and superconducting properties. Based on the previous result, BSCCO nanopowders have ferromagnetic properties at the room temperature. This characteristic is not appeared in bulk superconductor. The 2212 phase of Bi-based system has been formed and observed by using X-ray diffraction (XRD) measurement. The superconducting quantum interference device (SQUID) observation showed that the Bi2-xPbxSr2CaCu2O8+δ (x=0; 0.4) samples exhibited diamagnetic behaviour at the critical temperature, Tc=76 K and 78 K. The sample with partial Pb substitution exhibited stronger permanency to the external magnetic field indicating presence of flux pinning. The four point probe (FPP) measurement showed that the sample partially doped with Pb has lower resistivity (more metallic) than the Pb-free sample in the normal state.
235
Authors: Xi Feng Pan, Guo Yan, Xiang Hong Liu, Yong Feng, Ping Xiang Zhang, Yong Zhao, Akiyoshi Mastumoto, Hiroshi Kumakura
Abstract: In this paper, we have prepared a series of Fe sheathed MgB2 tapes with SiC, Malic acid and C9H11NO mono-and co-doping by in-situ powder-in-tube (PIT) method, and studied the effects of various C sources co-doping on transport critical current density and flux pinning of MgB2/Fe tapes. The results suggest by various C sources co-doping, the amount of C substitution for boron largely increase, comparing to SiC, Malic acid or C9H11NO mono-doped sample. For MgB2/Fe tapes with 5 mol% SiC+10 wt% Malic acid and 4 wt% C9H11NO+10 wt% Malic acid co-doping, the transport Jc at 4.2 K and 10 T are 14.8 and 13.5 kA/cm2, respectively, which are clearly higher than the Jc of these dopants mono-doped samples. Furthermore, it is found that at the 4 wt.% C9H11NO doped MgB2, the poor in-field Jc should be attributing to the cracks at grains boundary, which results in the bad grains-connectivity.
214
Authors: James A. Xia, Nick M. Strickland, Evgueni F. Talantsev, Nick J. Long
Abstract: We study the formation mechanism of nanoparticles in thin films of the superconductor YBa2Cu3O7-δ (YBCO). We form the films by metal-organic deposition (MOD) on buffered, textured metal substrates. Through the addition of Dy or Zr salts to the precursor solution we precipitate (Y,Dy)2O3 and BaZrO3 nanoparticles, uniformly distributed through the film thickness. By quenching samples during the film growth, we show the nanoparticles form in the precursor layer before YBCO growth. The size of the nanoparticles was quantitatively analysed by TEM. We found that Zr doping produces smaller nanoparticles than Dy doping.
15
Authors: Giovanni Giunchi, Giovanni Ripamonti, Elena Perini, Stefano Ginocchio, Enrico Bassani, Tommaso Cavallin
Abstract: The issues in the conventional sintering of the MgB2 superconductors have conducted to the discovery of a new way to densify this material. The new process is an “in situ” method that relies on the reactive liquid infiltration (RLI) of liquid Magnesium into Boron powders packed preform. The RLI process allows to obtain highly dense manufacts without the use of hot pressing apparatus and can be applied to the manufacture of large superconducting pieces. One of the peculiarities of the MgB2 superconductivity, that withstand up to 39 K, is represented by the relative insensitiveness of the supercurrent percolation to the orientation of the grain boundaries. This property allows to use polycrystalline material without loosing superconducting performance, granted that a good connectivity between the crystalline grains must be realized, as the RLI process allows to do. The microstructure of the bulk material obtained by RLI shows a variety of morphologies, according to the kind of the used Boron powders and to the process variables. A detailed analysis of the microstructure of the MgB2 obtained by RLI will be presented, as well as its analytical description and the correlation with the superconducting characteristics.
7
Authors: R. Abd-Shukor, S.Y. Yahya
Abstract: This paper reports on the effectiveness of magnetic nanoparticles as pinning center in the Bi-based superconductor tapes. Nanosize γ-Fe2O3 and ultrafine Fe3O4 have been employed to enhance the transport current density of Ag-sheathed-(Bi1.6Pb0.4)Sr2Ca2Cu3O10 superconductor tapes prepared by the powder-in-tube technique. The transport critical current density, Jc of (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(γ-Fe2O3)0.01, sintered at the optimum temperature of 845 oC is 6490 A/cm2 when measured at 77 K. A further single intermediate rolling step increases Jc to 9560 A/cm2. Samples without γ-Fe2O3 prepared under the same condition showed a lower Jc with a maximum of 1560 A/cm2. Similar results are also obtained for ultrafine Fe3O4. Magnetic impurities generally suppress superconductivity. However, our study shows great promise of magnetic nanorod γ-Fe2O3 and ultrafine Fe3O4 as novel pinning centers in enhancing the transport critical density of Ag sheathed Bi-Sr-Ca-Cu-O superconductor tapes. This is in line with previous calculations on frozen flux superconductor with magnetic nanoparticle as pinning centers.
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