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1.
High-T c superconducting joints between Ag-clad Bi-2223 tapes have been developed for persistent current applications. Two presintered tapes with one side of the silver stripped were lapped and then wrapped by a silver foil. The complex was uniaxially pressed followed by appropriate sintering to form a high-T c superconducting tape joint. It was found that the ratio of critical currents through the joint to that of the tape,I cj/Ic, depended on the uniaxial pressure and the sintering conduction. At liquid-nitrogen temperature 77 K,I cj/Ic=99% has been achieved. Persistent current loops formed by Bi-2223 tapes have also been fabricated and tested. Joint resistance of a loop was determined to be ~4×10?13 Ω between the decay time of 120 and 3600 sec. 相似文献
2.
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
3.
A practical Bi-2223 superconducting magnet, working in liquid nitrogen (L.N2), was designed and fabricated. Bi-2223 tape with a critical current of 147 A was prepared by a controlled overpressure (CT-OP) process at 77.3 K in self-field. Ten double-pancake coils were resistively connected by copper terminals. The bore diameter was 54 mm?, the magnet outer diameter was 122 mm?, the height of the magnet was 124 mm, and the weight of the magnet was about 3 kg. The maximum magnetic field at the center of the bore was 0.48 T with an operating current of 50 A. The experimental results agree well with design predictions calculated by finite element method. AC operation was also performed, and no distortion of the voltage waveform was observed. Therefore, this Bi-2223 superconducting magnet is a suitable replacement for copper magnets designed for applications in science and technology. 相似文献
4.
N. V. Vo C. C. Neo A. J. Bourdillon S. X. Dou H. K. Liu 《Journal of Superconductivity》1996,9(6):605-614
It has been found that the degree of thermal stability of Bi(Pb)-2223/Ag pancake-shaped coils at 77 K can be determined by controlling the amount of matrix and superconducting materials during processing. The intermediate deformation step between sintering stages has been found to be crucial in optimizing the performance of the processed composite tapes as well as governing the thermal stability of the subsequently made pancake-shaped coils. Results obtained from numerical analysis of the finite element method has shown that monolayer coils produced from Bi(Pb)-2223/Ag composite tapes are thermally very stable with high values of the fill factor. However, increasing the number of co-wound tapes would require either a reduction in the fill factor or an increase in cooling rate for thermal stability to be sustained as would otherwise be achieved with the metallurgically same single tape. 相似文献
5.
This paper presents the electric insulated type detection method of the temperature rise in the Bi2223/Ag tape using the time-frequency visualization of AE signals based on the wavelet transform. At the high operation temperature, the specific heat and the normal zone propagation velocity of the Bi2223/Ag tape are high and low, respectively, and therefore the local and excessive temperature rise is easy to generate in the superconducting-to-normal transition. As a result, the Bi2223/Ag tape is degraded or burned. In the proposed method, AE signals accompanying with the temperature rise are measured by an AE sensor, and furthermore AE signals are precisely and visually measured and estimated by the time-frequency visualization using the wavelet transform. Experimental results show the feasibility of the proposed method as the detection method of the temperature rise in the Bi2223/Ag tape. 相似文献
6.
O. Ozogul 《Journal of Superconductivity》2004,17(4):513-517
The Anderson–Kim model for a granular superconductor was employed to calculate both temperature and magnetic field dependencies of the AC susceptibility of a Bi-2223 superconductor. Moreover, similar calculations were performed for the magnetization. The prediction of the model, including the intergranular and intragranular contribution, for susceptibilities and magnetizations was consistent with experimental data very well by considering the temperature-dependent effective volume fraction. The temperature-dependence of fitting parameters was shown to obey almost quadratic power relation (1–T/T
c)
with 2. 相似文献
7.
A similarity in the dc voltage-current (V-I) curves for both direct and alternating transport currents is used to propose that unpinned flux vortices are generated above theI
ctransition for dc transport currents, when Abrikosov flux vortices begin to penetrate the superconductor. Two methods can be used to give a dc voltage drop for an ac transport current: (1) if there is a slight dc offset voltage in the ac current which favors vortex loop collapse as in a traditional dcI
ctest, or (2) if an asymmetric transverse magnetic field is present which favors vortex loop collapse for current in one direction over the reverse direction. 相似文献
8.
For the endurance evaluation of High Temperature Superconductors (HTS), the mechanical and transport properties of multifilamentary Bi2Sr2Ca2Cu3O10+x (Bi-2223) superconducting tapes with different reinforcements subjected to high-cycle axial fatigue loading were investigated at 77 K in the self-field. The mechanical fatigue limits based on the relations between the applied stress amplitude and the numbers of cyclic steps to reach failure (S-Nf curves) were obtained. The transport properties were evaluated with the increase of repeated cycles, N, at different applied stress amplitudes which eventually leads to the electric fatigue limit. The influence of reinforcement on the mechanical and transport properties of Bi-2223 tapes were discussed. Fractographic observation was performed in order to understand the Ic degradation mechanism in fatigue tested Bi-2223 tapes. 相似文献
9.
W. M. Chen F. Wang F. Lin S. S. Jiang Y. C. Guo H. K. Liu S. X. Dou 《Journal of Superconductivity》2000,13(3):441-446
For polycrystalline Ag/Bi-2223 tapes, the preferential orientation of grains is a very important issue. The platelike grains in the tapes are generally believed in a high-order alignment. However, microstructural observation by SEM shows that the grain alignment is far from perfect. Theoretically, upper critical field, H
c2, for H parallel to ab plane and c axis was calculated form the relation of M(H). However, the ratio of H
c2 (H//ab) to H
c2(H//c) depends on the angle () between the ab plane of grains and the broad surface of the tapes. Based on the ratio, the orientation distribution of grains is obtained. The results show that grains in Ag/Bi-2223 tapes can grow with ab plans at any angle between 75° > > –75°, but no grain can grow with its ab plane perpendicular to the tape broad surface. The overall distribution is that: >90% grains orient in the angle range of || < ± 75°, about 5% grains at ±75° || ±85°, and no grains at || > ±85°. 相似文献
10.
对4种Bi系2223高温超导带材77 K下的力学性质进行了实验研究.通过选择合适的合金包套替代传统的银包套,带材的机械性能能有所提高,但电学性质有所降低,尤其是内包套采用合金、外包套采用银,其机械性能反而低于纯银包套带材.通过X射线衍射图谱发现,当包套采用合金材料,尤其是内包套采用合金、外包套仍采用纯银,会大大降低样品中2223相的体积含量.相比较临界电流密度,n值对材料的破坏更为敏感.利用X光同步辐射技术初步探讨了银包套带材在室温和77 K下的损伤破坏过程. 相似文献
11.
12.
With high upper critical fields, high temperature superconductors (HTSC) have been recognised as candidate materials for coil and magnet applications. High field devices, at one time or another, when operated close to their rated limits are often faced with instability problems which normally are electrical, magnetic or mechanical in nature. The determination of stability parameters, therefore, is of interest to the conductor designer which very much assists in the processing aspect of long length production of wires and tapes. Due to the morphology of the superconductor most HTSC devices made with Bi(Pb)—2223 precursor exist in tape form. Here the determination of stability parameters (for flux-jump and cryogenic stability) for multifilamentary Bi(Pb)—2223/Ag tapes are presented. Processing parameters such as intermediate deformation and filling factors have been found to play a crucial role, not only on the critical current density of the tapes but on the stability aspect in conductor design as well. 相似文献
13.
Y. B. Huang M. Dhallé G. Witz F. Marti E. Giannini E. Walker R. Passerini A. Polcari S. Clerc K. Kwasnitza R. Flükiger 《Journal of Superconductivity》1998,11(5):495-505
A significant reduction of ac losses in twisted Bi(2223) multifilamentary tapes with Ag sheaths has been achieved by using oxide (BaZrO3 and SrZrO3) barriers between filaments. These barriers have two important effects: they increase the transverse resistivity, which suppresses induced coupling currents, and they reduce filament bridging, which in pure Ag sheath tapes largely cancels the beneficial effect of filament twisting. The decoupling can be gauged by the frequency at which loss shows a maximum in a low-amplitude ac field applied perpendicular to the tape. So far, the frequency of the loss maximum, f
m, in Ag-sheathed tapes has been enhanced from 5 Hz (untwisted) to 82 Hz (11 mm in twist pitch length). Different ways to introduce oxide barriers in tapes with 19–95 filaments are presented. The critical current density in the filaments varied between 10,000 and 20,000 A/cm2. Ac loss measurements as well as the electrical and mechanical characterization are discussed in detail. The variation of the critical current density with bending strain is shown to be similar to that of tapes without barriers. 相似文献
14.
15.
采用SEM和TEM观测了经热压处理后的Ag/Bi(2223) 带材(Jc=56000A/cm2,在77K、自场)和只经过室温轧制处理的带材.与室温轧制的带材比较发现:即使在临近第二相的区域,热压处理后的带材结构也非常密实;热压处理后,晶体缺陷诸如裂缝、亚晶界、残余无定形态和中间相等,易阻碍或中断电流传输的缺陷显著减少;热压处理后带材的位错密度基本相同,但在某些区域分布不均匀或呈网状结构;在一定方向上晶界能捕获途经它的位错;热压过程促使第二相部分转变为超导相Bi(2223),进而提高带材的载流能力. 相似文献
16.
The alternating current losses have been investigated at 77 K on the silver-sheathed (Bi, Pb)-2223 multifilamentary tape having 37 filaments using an inductive technique under ac magnetic field with frequencies between 100 and 510 Hz. The measured data on the multifilamentary tape have been discussed vis-à-vis that reported for monofilamentary tapes. The results obtained could be accounted fairly well by considering contributions from the eddy current losses in the silver matrix along with the hysteresis losses in the superconducting filaments. 相似文献
17.
C. H. Stoessel R. F. Bunshah S. Prakash H. R. Fetterman 《Journal of Superconductivity》1993,6(1):1-17
This review of high-T
c superconducting thin-film processing focuses on the developments in thin-film deposition technologies since 1987. The common deposition processes are described with reference to their effects on superconductor film performance. A comparative evaluation of the potential of the technologies is also given. The development of multilayers and heterostructures is an important requirement for future device applications and is also described. The latest results of the deposition of novel superconducting materials and deposition on uncommon substrates are discussed. The outlook on some imminent topics of future development in process technologies for high-T
c superconducting thin films is discussed. 相似文献
18.
Multifilamentary HTSC tapes are important for their applications in various electrical devices. Powder-in-tube technique with
improved optimized synthesis parameters is regarded as one of the most promising ways to prepare long-length multifilamentary
Bi-2223/Ag tapes. Nevertheless, usefulness of such tapes depends on their electrical and mechanical properties. Critical current
density of a Bi-2223/Ag tape with 37 filaments has been studied at 77 K with field, field orientation, thermal cycling and
bending strain as parameters. Results have been discussed in light of various mechanisms and models. A small pancake coil
has been fabricated out of the same tape and the test results presented. 相似文献
19.
V. A. Cherenkov 《Journal of Superconductivity》1991,4(3):213-217
The high-temperature superconductor glass state in the Josephson weak-link model is studied. Reversibility phenomena in weak magnetic fields are outlined. 相似文献
20.
We investigate the specific heat properties of a high-T
c superconductor model, the two-carrier model which includes an electron-phonon interaction driven by lattice defects such as oxygen deficiencies in the otherwise conventional BCS superconductor. The normal state is identified as a two-carrier model system which is composed of two groups of charge carriers: the normal and the renormalized Bloch carriers. An enhanced normal-state electronic specific heat is obtained, and there is good agreement between theoretical predictions about the specific heat anomalies at and aboveT
c and experimental data. 相似文献