共查询到20条相似文献,搜索用时 15 毫秒
1.
Bi2Sr2CaCu2Ox/AgMg conductors are potentially important for many applications up to 20 K, including magnets for cryogen-free magnetic resonance imaging and high field nuclear magnetic resonance research. One promising approach to increased critical current density is partial-melt processing in the presence of a magnetic field which has been shown to enhance c-axis texturing of wide, thin tape conductors. Here, we report on low aspect ratio rectangular conductors processed in an 8 T magnetic field. The magnetic field is applied during different stages of the heat treatment process. The conductors are electrically characterized using four-point critical current measurements as a function of magnetic field and magnetic field orientation relative to the conductor. The superconductive transition and magnetization hysteresis are measured using a SQUID magnetometer. The microstructures are characterized using scanning electron microscopy and energy dispersive spectroscopy and analyzed using digital image processing. It is found that the presence of a magnetic field during split melt processing enhances the electrical transport and magnetic behavior, but that the anisotropy is not consistently affected. The magnetic field also affects development of interfilamentary Bi2212 bridges, and that this depends on the initial shape of the Bi2212 filament. At least two behaviors are identified; one impacts the oxide phase assemblage and the other impacts textured growth. 相似文献
2.
J. Sosnowski 《低温学》1984,24(5):271-275
The coupling current losses in a superconducting multifilamentary composite exposed to trapezoidally varying external magnetic field and carrying a small transport current are investigated for the volume pinning force density described with the dependence: Fv = α B1?γ. Such a model allows estimation of the deviations from the solution based on Bean's (γ = 0) critical state model. Results indicate that there exists a region of small magnetic field amplitudes for which discrepancies are largest. They are also very sensitive to the rate of magnetic field change. 相似文献
3.
In the frame work of the critical state model (CSM), the magnetic response of a thin type-II superconducting disk that carries a radial transport current and is subjected to an applied magnetic field have been studied. To this end, we have studied the process of the magnetic flux-penetration. For a disk initially containing no magnetic flux but carrying a radial current, when a perpendicular magnetic field is applied, magnetic flux-penetration occurs in three stages: (1) the magnetic flux gradually penetrates from the edges of the disk until an instability occurs, (2) there is a rapid inflow of magnetic flux into the disk’s central region, which becomes resistive, and (3) magnetic flux continues to enter the disk, while persistent azimuthal currents flow in an outer annular region where the net current density is equal to J c . Also the behavior of a current-carrying disk subjected to an AC magnetic field is calculated. The magnetic flux, the current profiles and the magnetization hysteresis loops are calculated for several commonly used J c (B) dependences. Finally, the results of the applications of the local field-dependent of the critical current density J c (B) are compared with those obtained from the Bean model. 相似文献
4.
W. M. Woch M. Kowalik M. Giebułtowski R. Zalecki A. Szeliga J. Przewoźnik Cz. Kapusta 《Journal of Superconductivity and Novel Magnetism》2017,30(3):569-574
The magnetoresistance, irreversibility fields, and critical current density were studied for a commercial 2G tape at the two relative orientations of magnetic field and superconductor plane. The critical temperatures of this tape of T c50 % = 91.5 K and T c0 = 90 K and the width of superconducting transition of ΔT = 1.5 K were obtained. The widths of the transition from the normal to the superconducting state do not increase at the applied magnetic field up to 90 kOe and do not depend on the orientation of the magnetic field with respect to the tape plane. The irreversibility field values were obtained and successfully fitted as a function of temperature using the formula: \(H_{\text {irr}} =H_{\text {irr0}} \left ({1-\frac {T}{T_{\text {c0}} }} \right )^{n}\). The irreversibility fields show an anisotropy, and at the liquid nitrogen temperature, they reach H irr = 430 kOe and H irr = 106 kOe for the parallel and perpendicular directions, respectively. The anisotropy ratio amounts to γ = 4 at 77 K and is small in comparison with other high-temperature superconducting materials. The critical current density of this tape was found to be of the order of 106 A cm?2 at 77 K in the self-magnetic field. 相似文献
5.
G.W. Schulz H.W. Weber R.E. Gladyshevskii R. Flükiger 《Journal of Superconductivity》1998,11(1):115-116
Experimental results on the angular dependence of the critical current densities in silver-sheathed Tl-1223 tapes are presented.We show, that the improved texture of the Tl-based tapes leads to a better fit of the angular dependence of the critical current density Jc to the 2D-model. Deviations are found at very low magnetic fields, where the crystallographic misalignment of the tape structure becomes dominant. We observe a rapid decay of Jc with magnetic field, which implies weak-link dominated current transport. Both the angular and the magnetic field dependence of Jc are measured on fluorine-free and fluorine-containing samples. 相似文献
6.
Donghui Liu Huadong Yong Youhe Zhou 《Journal of Superconductivity and Novel Magnetism》2016,29(9):2299-2309
Bi2Sr2CaCu2O8+x (Bi-2212) round wires have outstanding electromagnetic behaviors in a high magnetic field. However, the filaments’ fracture or gas bubble is difficult to avoid during the fabrication and application of Bi-2212 round wire, which would affect the critical current density seriously. In this paper, the engineering current density is studied based on Kim model for 7-bundle and 18-bundle wires with filament fracture by considering the effect of bridges between filaments. The distributions of critical current density of filaments are also investigated for different external fields. Finally, we present the relation between the number of cracked filaments and the applied strain. 相似文献
7.
《低温学》2018
High-temperature superconductor (HTS) rare-earth-barium-copper-oxide (REBCO) tapes are very promising for use in high-current cables. The cable geometry and the layout of the superconducting tapes are directly related to the performance of the HTS cable. In this paper, we use numerical methods to perform a comparison study of multiple-stage twisted stacked-tape cable (TSTC) conductors to find better cable structures that can both improve the critical current and minimize the alternating current (AC) losses of the cable. The sub-cable geometry is designed to have a stair-step shape. Three superconducting tape layouts are chosen and their transport performance and AC losses are evaluated. The magnetic field and current density profiles of the cables are obtained. The results show that arrangement of the superconducting tapes from the interior towards the exterior of the cable based on their critical current values in descending order can enhance the cable’s transport capacity while significantly reducing the AC losses. These results imply that cable transport capacity improvements can be achieved by arranging the superconducting tapes in a manner consistent with the electromagnetic field distribution. Through comparison of the critical currents and AC losses of four types of HTS cables, we determine the best structural choice among these cables. 相似文献
8.
E. Taylan Koparan A. Öztürk T. Bayazıt A. Surdu A. Sidorenko E. Yanmaz 《Journal of Superconductivity and Novel Magnetism》2013,26(2):267-271
MgB2 thin films were deposited on MgO (100) substrate and r-plane Al2O3 $(1\bar{1}02)$ substrate by ex-situ annealing of boron film in magnesium vapor. The thickness of ex-situ annealed MgB2 films is approximately 600 nm according to data observation by ellipsometer. The magnetic properties of samples were determined using a vibrating sample magnetometer. The magnetic field dependence of the critical current density J c was calculated from M–H loops and also the magnetic field dependence of F p was compared for the different temperature ranges from 5 to 25 K. The critical current density J c was found to be around 1.0×106 A/cm2 and 1.7×106 A/cm2 in zero field at 5 K for MgB2 films deposited on MgO and r-plane Al2O3 substrates, respectively. It was found that the critical current density of the film deposited on MgO became stronger than that of r-plane Al2O3 in the magnetic field. The superconducting transition temperature was determined by ac susceptibility measurement using physical properties measurement system. ac susceptibility measurements for MgB2 films deposited on MgO and r-plane Al2O3 substrates were performed as a function of temperatures at constant frequency and ac field amplitude in the absence of dc bias field. The critical current densities as a function of temperature were estimated from the ac susceptibility data. 相似文献
9.
M. Polák M. Majoro F. Hanic J. Pitel M. Kedrová P. Kottman J. Talapa L. Vencel 《Journal of Superconductivity》1989,2(2):219-233
A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current densityJ
cs
and the intergranular transport current densityJ
cr
are identical if the measurement conditions are similar. A degradation ofJ
cs
measured in the external field with AC ripple has been observed. 相似文献
10.
Xiaobo Ma Shengnan Zhang Zeming Yu Guoqing Liu Huiling Zheng Chengshan Li Jinshan Li Pingxiang Zhang 《Journal of Superconductivity and Novel Magnetism》2018,31(10):3105-3110
Thirty-seven-filamentary AgAu-sheathed Bi-2223 tapes were fabricated by a powder-in-tube (PIT) process. And, the round wires (? 1.86 mm) were rolled to 0.35-mm tapes with 12, 7, 5, and 4 rolling passes through flat rolling, respectively. The influences of different rolling passes on the core density, deformation, and transport properties of Bi-2223/AgAu tapes were systematically investigated. It was noticed that after rolling, the Vickers microhardness of the superconducting core and deform homogeneity along both the horizontal and vertical directions on the cross section of seven-pass rolled tape were better than those on the tapes with other passes, which proved the larger core density and uniform deformation with the seven-pass rolling process. Meanwhile for the wires with 12 and 7 passes, the AgAu/superconducting core interfaces were much flatter. With the rolling passes decreasing from 12 to 4, the critical current density (Jc) first increased and then decreased. Due to the better homogeneity and flatter interfaces, Jc reached the maximum value of 17.3 kA/cm2 on the seven-pass sample. Meanwhile, the enhancement of current capacities in magnetic field applied parallel to the Bi-2223/AgAu tape surface could also be recognized as the evidence of improving intergrain connections due to the higher density in seven-pass rolled tapes. 相似文献
11.
Abstract Bi2 Sr2 CaCu2 Ox/AgMg conductors are potentially important for many applications up to 20 K, including magnets for cryogen-free magnetic resonance imaging and high field nuclear magnetic resonance research. One promising approach to increased critical current density is partial-melt processing in the presence of a magnetic field which has been shown to enhance c-axis texturing of wide, thin tape conductors. Here, we report on low aspect ratio rectangular conductors processed in an 8 T magnetic field. The magnetic field is applied during different stages of the heat treatment process. The conductors are electrically characterized using four-point critical current measurements as a function of magnetic field and magnetic field orientation relative to the conductor. The superconductive transition and magnetization hysteresis are measured using a SQUID magnetometer. The microstructures are characterized using scanning electron microscopy and energy dispersive spectroscopy and analyzed using digital image processing. It is found that the presence of a magnetic field during split melt processing enhances the electrical transport and magnetic behavior, but that the anisotropy is not consistently affected. The magnetic field also affects development of interfilamentary Bi2212 bridges, and that this depends on the initial shape of the Bi2212 filament. At least two behaviors are identified; one impacts the oxide phase assemblage and the other impacts textured growth. 相似文献
12.
Z. D. Yakinci E. Altin 《Journal of Materials Science: Materials in Electronics》2013,24(10):3660-3667
Approximately 1 μm thick high quality epitaxial c-axis oriented (Hg0.8Re0.2)Ba2Ca2Cu3Ox superconducting films have been prepared on MgO (100) substrates using spraying technique and post-Hg-Vapor annealing. The effect of the heating temperature–time combinations and the filling factor of Hg (ffHg) on the physical, electrical and magnetic properties of the thick films have been investigated. The XRD investigations showed that the a–b plane of HgRe-1223 phase align parallel to the substrate surface. The best T c and T zero were found to be 130.6 and 127.2 K, respectively. The superconducting transition of the films has been measured under applied magnetic field up to 6 T. The results obtained suggested that dissipative resistivity can be explained by thermally activated flux motion below critical temperature under applied magnetic field. The temperature and field dependences of the activation energy in the thermally activated flux flow region have also been investigated. The calculated values of m and α values were found to be 1.42–1.49 and 0.498–0.518 respectively and suggesting a 3D like behavior and the thermally activated flux flow mechanism for all films fabricated. Magnetic properties of the films up to 6 T have also been investigated. The calculated value of critical current density, J c, was found to be 4.7 × 106 A/cm2 at 10 K for the optimally treated films. 相似文献
13.
(Bi1.6Pb0.4)Sr2Ca2Cu3O10–(NiO) x superconductor with x=0, 0.01, 0.02, 0.03, 0.04, and 0.05 wt.% was prepared using the coprecipitation technique. The average size of NiO used was 8 nm and 16 nm. The highest value of the transport critical current density, J c in the bulk form was observed in the x=0.01 wt.% samples for both sizes. Based on this result, Ag sheathed superconductor tapes with starting composition (Bi1.6Pb0.4)Sr2Ca2Cu3O10–(NiO)0.01 (with NiO particle size 8 and 16 nm) were fabricated using the powder-in-tube method. The effect of these nanoparticles addition on the microstructure, phase formation, and transport critical current density were studied. The J c of the tape at 77 K in zero fields with NiO (8 nm) addition (4500 A/cm2) was slightly higher than that of NiO (16 nm) added tape (4120 A/cm2). The nonadded tape showed a lower J c (1080 A/cm2 at 77 K). These results indicated that magnetic nanoparticles such as NiO could act as an effective flux pinning centers leading to the enhancement of J c in the bulk and tape form. Moreover, NiO with size closer to the coherence length, ξ was more effective in enhancing J c. 相似文献
14.
Nahed Moutalbi Asma Ouerghi Ali M��chirgui 《Journal of Superconductivity and Novel Magnetism》2011,24(1-2):165-168
The influence of pinning centers size on the superconducting properties was investigated. Through the addition of three batches of ZrO2 nano-particles with mean size of D 1=13 nm, D 2=21 nm, and D 3=85 nm, we have succeeded in incorporating effective artificial pinning centers within the YBCO matrix of the bulk superconductor. An enhancement in the flux pinning and an improvement in the critical current densities (transport critical current density J ct and magnetic critical current density J cm) were achieved. The results indicate that slight inclusions of ZrO2 can greatly enhance the flux pinning capability of samples. Comparative analyses of the critical current densities and the resulting pinning force F p for the three diameters have shown that pinning centers with finer size are much more efficient than those with a size larger than the coherence length ??. 相似文献
15.
Z. D. Yakinci D. M. Gokhfeld E. Altin F. Kurt S. Altin S. Demirel M. A. Aksan M. E. Yakinci 《Journal of Materials Science: Materials in Electronics》2013,24(12):4790-4797
Y2/3 Se1/3Ba2Cu3Ox compound was fabricated by using solid state fabrication technique. Optimum heat treatments conditions for Y0.77Se0.33Ba2Cu3Ox were investigated. It was determined that the XRD results of these samples were similar to Y-123 phase with some impurities. Magnetization dependence of applied magnetic fields was measured in the range of 0–9 T at 10–50 K. The symmetric and asymmetric M–H loops were obtained for the samples. Magnetization loops obtained from measurements were successfully described by the extended Valkov–Khrustalev model. The temperature and applied magnetic field dependencies of magnetization of sample were estimated and critical current density of samples was calculated by Bean model and pinning force of samples was calculated by using Lorentz force. It is found from critical current density values that Se additions were acted as a pinning center which increased critical current density. 相似文献
16.
To improve on present critical current (J c) performance, multifilamentary Ag/Bi-2223 tapes with a large range of reduction rates were manufactured. The relative core mass density D was calculated, dependent on the measured geometric dimensions of the tapes. Experimental results, D vs. J c, D vs. maximum pinning force density F max , and D vs. irreversible magnetic field B irr, are quantitatively formatted. In particular, the magnetic field dependence of J c is critically dependent on its core density. If the core density increases by 10%, J c of the tapes in this experiment is enhanced by as much as 100%. Therefore, in the present state of the technological process for manufacturing Ag/Bi-2223 tape, increasing the core density is clearly a significant strategy in improving the electronic and magnetic properties of the tapes and enhancing the capacity for carrying current at high magnetic fields. The limit of the bulk self-field-J c can be calculated by the relationships of J c vs. D. The limit is estimated to be on the order of 200 kA/cm2 for multifilamentary Bi-2223 tapes, which was supported by magneto-optical (MO) magnetization measurements results. It is a hard task to approach this limit with the present state of the art in manufacturing Ag/Bi-2223 tape, and it is the time to suggest some new ideals for Bi-2223 tapes to promote large-scale applications. 相似文献
17.
Suchitra Rajput Sujeet Chaudhary 《Journal of Superconductivity and Novel Magnetism》2013,26(7):2375-2381
We report the measurement of magnetoresistance in MgB2 tapes with a varying magnetic field applied perpendicular to the tape surface. Scaling functions for excess conductance suggested by Ullah and Dorsey have been used to analyze the scaling behavior of the resistivity in MgB2 tapes just above their critical region. The fluctuations in the magnetoresistance, R(T,H), behavior is found to follow 3D scaling for the MgB2 tape. From the slope of the upper critical field, H C2 vs. T curve, it is ~68 Å. The zero temperature H C2 that was found following the WHH model was ~5 T, whereas, from linear extrapolation of H C2 versus T yield a value of H C2(0)~24.5 T. 相似文献
18.
The paper deals with the investigation of the impact made by two-dimensional effects on the process of passage of current in a short vacuum arc in an axial magnetic field. A two-fluid mathematical model is used, which is based on hydrodynamic and electrodynamic equations. The axial magnetic field B z affects significantly the magnitude of two-dimensional effects: the two-dimensional effects increase with decreasing B z . The simulation results demonstrate that the contraction of plasma density exceeds that of current density. The distribution of anode drop of potential on the anode surface is nonuniform; in the case of certain (critical) values of current, the anode drop goes to zero on the external boundary of plasma. The dependence of the critical current on B z is determined. The distribution of current density on the starting plane is nonuniform with a maximum on the axis, and the ion trajectories are inclined to the discharge axis. The possibility is discussed of matching the solution in the plasma region of vacuum arc with that for cathode flames. 相似文献
19.
MgB2 films with the thickness of 350 to 1150 nm have been prepared on the Al2O3 (001) single crystal substrates from high purity B and Mg powder by the thermal evaporation method. Films were then heat treated ex-situ under Mg vapor at 950?°C to achieve actual MgB2 stoichiometry. Thickness of the films, so the deposition time, was varied to investigate its influence on critical current density of the films. The films fabricated were analyzed by means of microstructural, transport, and magnetic properties. The best T c and T zero values were obtained to be 39.5 K and 38 K, respectively, and decreased with increasing the thickness. We found that the critical current density of the films prepared is highly thickness dependent. The maximum $J_{c}^{\mathrm{mag}}$ value was calculated to be 3.18×106 A?cm?2 at 10 K and zero field for 1150 nm thick films but dropped drastically by thickness. 相似文献
20.
Cherine David Brinda Arumugam Amuda Rajamani 《Journal of Superconductivity and Novel Magnetism》2014,27(6):1561-1567
Magnetization switching dynamics in a spin valve nanopillar, induced by spin transfer torque in the presence of a periodic applied field is investigated by solving the Landau–Lifshitz–Gilbert–Slonczewski equation. Under steady state conditions, the switching of magnetization occurs in the system, above a threshold current density value J c. A general expression for the critical current density is derived and it is shown that this further reduces when there is magnetic interface anisotropy present in the free layer of the spin valve. We also investigated the chaotic behavior of the free layer magnetization vector in a periodically varying applied magnetic field, in the presence of a constant DC magnetic field and spin current. Further, it is found that in the presence of a nonzero interfacial anisotropy, chaotic behavior is observed even at much smaller values of the spin current and DC applied field. 相似文献