scholarly journals Effect of geometry and interfacial resistance on current distribution and energy dissipation at metal/superconductor junctions

1989 ◽  
Vol 4 (3) ◽  
pp. 530-538 ◽  
Author(s):  
Meilin Liu ◽  
Lutgard C. De Jonghe
Keyword(s):  
Energy Dissipation ◽  
Critical Current Density ◽  
Contact Resistance ◽  
Critical Current ◽  
Current Distribution ◽  
Current Density ◽  
Power Dissipation ◽  
Superconducting Phase ◽  
Total Power ◽  
Interfacial Resistance

Potential and current distributions and local energy dissipation due to Joule heating in metal-superconductor junctions have been computed as a function of geometric parameters and interfacial resistance. The primary current distribution and power dissipation are highly nonuniform in the system. The secondary current distribution and power dissipation, however, become more uniform as the interfacial resistance increases. Analysis indicates that zero contact resistance is not a stable situation since the primary distribution leads to local current densities exceeding the critical current density of the superconducting phase near the corner of the junction. Local contact failure might then initiate. A finite contact resistance is necessary for a practical application, and the minimum value of the contact resistance can be estimated from the operating current density (javg) of the device and the critical current density (jcri) of the superconducting phase. To obtain an optimum value of the contact resistance, however, one further has to take into consideration the stability and reliability of the device performance, which is, in turn, directly related to the uniformity of the current distribution and power dissipation, to temperature fluctuation of the superconducting phases brought about by local power dissipation, and to the thermal management of the system. Furthermore, a nonuniform contact resistance layer of appropriate profile can redistribute the current more effectively and more uniformly and hence reduce the total power dissipation in the system for a given jmax/javg ratio obtained by a uniform resistance layer.

scholarly journals Mathematical modeling of the magnetic properties of axisymmetric hard superconductors of the second kind in the Kim model

2020 ◽  
Vol 22 (4) ◽  
pp. 456-462
Author(s):  
Nikolay D. Kuzmichev ◽  
Aleksey A. Shushpanov ◽  
Mihail A. Vasyutin
Keyword(s):  
Mathematical Modeling ◽  
Magnetic Field ◽  
Magnetic Properties ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Distribution ◽  
Current Density ◽  
Local Magnetic Field ◽  
Aspect Ratios ◽  
Kim Model

Authors perform mathematical modeling of magnetic properties, such as current distribution, intrinsic magnetic field and magnetization of a number of axisymmetric superconductors of the second kind, for example, of a sphere with the dependence of the critical current density on the local magnetic field in the Kim model. The simulation is based on equation that is integral with respect to coordinate and differential with respect to time. The equation describes time evolution of the critical current density and is solved numerically for a uniformly varying external magnetic field. The shape of the sample is set using a distorted rectangular irregular mesh with compaction to the edges of the sample. While solving the equation of current motion, the total magnetic field iscalculated at the points of the superconductor to calculate the value of the critical current density. In the article, the obtained solutions are used to visualize the current distribution in the volume of a superconductor and to construct magnetization hysteresis loops. Also, thanks to the calculations of the magnetic field in the center of the sample, the dependencies of the total penetration field for samples with different aspect ratios are obtained.

Effects of Tin Addition to the Tl-Based 1223 Superconducting System

1998 ◽  
Vol 12 (04) ◽  
pp. 131-141 ◽  
Author(s):  
Y. T. Wang ◽  
A. M. Hermann
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Temperature Drop ◽  
Superconducting Phase ◽  
Transport Critical Current Density ◽  
X Ray Diffraction ◽  
Pinning Centers ◽  
Magnetization Data ◽  
A Minor

Polycrystalline samples of Tl-based-1223 superconducting system were prepared with tin-addition to form ( Tl 0.5 Pb 0.5) Sn x Sr 1.6 Ca 2.4 Cu 3 O y, for x=0–0.3. X-ray diffraction data showed the presence of a minor 1212 phase and impurities which increased with increasing x while the samples without addition of tin, x=0, were nearly single phase of Tl,Pb-1223. The effects of tin addition to Tl,Pb-1223 on the magnetic properties were studied by dc susceptibility and hysteresis magnetization measurements. The magnetic results revealed a significant enlargement of hysteresis magnetization in tin-added samples with an onset transition temperature drop of only 1–4 K. According to recent measurements, the intragrain Jc reflects the transport critical current density in high field region. The critical current density in Tl,Pb-1223 was enhanced by as much as ten-times by tin-addition. An electron micro-probe technique was employed to locate the added tin in the samples, but Sn incorporated into the superconducting phase was below detectability. The variation in Tc with Sn addition and a reduction in pinning strength at Sn concentration above x=0.05 show that the enhanced pinning is due to introduction of pinning centers into the superconducting phase even though micro-probe analysis indicates that most of the Sn is present in a nonsuperconducting phase. The field dependence and time dependence of the magnetization data showed an increased concentration of pinning centers without a change in pinning energy.

Mechanism of Je Enhancement of YBa2Cu3O7-α Due to Ag-Doping

1987 ◽  
Vol 99 ◽  
Author(s):  
J. H. Kung ◽  
H. H. Yen ◽  
Y. C. Chen ◽  
C. M. Wang ◽  
P. T. Wu
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Crystal Orientation ◽  
Superconducting Phase ◽  
Optimum Level ◽  
Chemical Forms ◽  
Ag Doping ◽  
Ceramic Superconductors

ABSTRACTAg-doping was found to enhance the critical current density of the ceramic superconductors by as much as a factor of 15. This Jc enhancement is due to both the increased amount of the superconducting phase and the resulting preferred crystal orientation. The optimum level of dopant may vary according to the chemical forms of Ag dopants.

EFFECT OF THE SECOND PHASE ON CRITICAL CURRENT DENSITY IN Nb-ADDED YBCO FILMS

1995 ◽  
Vol 09 (07) ◽  
pp. 439-443 ◽  
Author(s):  
JUN-HUI JIA ◽  
ZHEN-ZHONG QI
Keyword(s):  
Thin Films ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Superconducting Films ◽  
Superconducting Phase ◽  
Second Phase ◽  
Dc Magnetron Sputtering ◽  
Ybco Films ◽  
Crystalline Substrate

Thin films of YBCO with or without Nb added were prepared on (100) ZrO 2 single crystalline substrate by dc magnetron sputtering method. A phase of YBa 2 NbO 6 was found to form not only in the target materials of YBCO but also in the sputtered thin films. The second phase of YBa 2 NbO 6 in the superconducting films destroyed a match relation between the lattice of YBCO and the lattice of ZrO 2 substrate. The measurements of critical current density J c under magnetic field (H // c axis, up to 5T) showed that the J c in Nb-added YBCO films reduced more apparently than that in YBCO films. It is concluded that the existence of second phase of YBa 2 NbO 6 in superconducting phase does not play a rule of flux pinning.

THE NATURE OF TRANSPORT CRITICAL CURRENT DISTRIBUTION IN CERAMIC SAMPLE

2008 ◽  
Vol 22 (06) ◽  
pp. 645-650
Author(s):  
N. A. BOGOLYUBOV
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Cross Section ◽  
Current Distribution ◽  
Current Density ◽  
Ceramic Sample ◽  
Homogeneous Function ◽  
Transport Critical Current Density

It is shown that the transport critical current density in a ceramic sample having any cross-section is a homogeneous function of coordinates.

Microstructural characterization of YBa2Cu3O7-x thin films formed by metalorganic CVD

1991 ◽  
Vol 49 ◽  
pp. 1080-1081
Author(s):  
P. Lu ◽  
W. Huang ◽  
C.S. Chern ◽  
Y.Q. Li ◽  
J. Zhao ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Film Growth ◽  
Chemical Vapor ◽  
Microstructural Characterization ◽  
Ion Milling ◽  
Conventional Grinding

The YBa2Cu3O7-x thin films formed by metalorganic chemical vapor deposition(MOCVD) have been reported to have excellent superconducting properties including a sharp zero resistance transition temperature (Tc) of 89 K and a high critical current density of 2.3x106 A/cm2 or higher. The origin of the high critical current in the thin film compared to bulk materials is attributed to its structural properties such as orientation, grain boundaries and defects on the scale of the coherent length. In this report, we present microstructural aspects of the thin films deposited on the (100) LaAlO3 substrate, which process the highest critical current density.Details of the thin film growth process have been reported elsewhere. The thin films were examined in both planar and cross-section view by electron microscopy. TEM sample preparation was carried out using conventional grinding, dimpling and ion milling techniques. Special care was taken to avoid exposure of the thin films to water during the preparation processes.

Facet Topography and Dislocation Structure as a Possible Source for Electrical Heterogeneity in [001] TILT Bicrystals of YBa2Cu3O7-δ

1996 ◽  
Vol 54 ◽  
pp. 338-339
Author(s):  
I-Fei Tsu ◽  
D.L. Kaiser ◽  
S.E. Babcock
Keyword(s):  
Grain Boundary ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Electromagnetic Properties ◽  
Length Scale ◽  
Density Values ◽  
Current Densities ◽  
Applied Fields ◽  
A Current

A current theme in the study of the critical current density behavior of YBa2Cu3O7-δ (YBCO) grain boundaries is that their electromagnetic properties are heterogeneous on various length scales ranging from 10s of microns to ˜ 1 Å. Recently, combined electromagnetic and TEM studies on four flux-grown bicrystals have demonstrated a direct correlation between the length scale of the boundaries’ saw-tooth facet configurations and the apparent length scale of the electrical heterogeneity. In that work, enhanced critical current densities are observed at applied fields where the facet period is commensurate with the spacing of the Abrikosov flux vortices which must be pinned if higher critical current density values are recorded. To understand the microstructural origin of the flux pinning, the grain boundary topography and grain boundary dislocation (GBD) network structure of [001] tilt YBCO bicrystals were studied by TEM and HRTEM.

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