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Topic: Flux pinning


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In the News (Thu 23 May 19)

  
  Flux
Flux is the flow that occurs as a result of a energy.
Latent heat flux Latent heat flux is the flux of heat from the earth's surface to the atmosphere that is associated with...
Luminous flux Luminous flux is the amount of light that falls on a unit area at unit distance from a source of one cande...
www.brainyencyclopedia.com /topics/flux.html   (288 words)

  
 Magneto-Optic Imaging of High Temperature Superconductors   (Site not responding. Last check: 2007-10-16)
High flux pinning densities are needed for increasing the electrical current carrying capabilities of high temperature superconductors.
Microscopic flux flow in undoped and Li-doped BSCCO cast tapes before and after neutron irradiation was studied by means of a magneto-optical imaging technique in order to correlate flux flow with the microstructure.
Flux penetration was very nonuniform, indicating that current flow in the specimens is inhomogeneous.
www.msel.nist.gov /structure/ceramics/techactv95/magneto.html   (414 words)

  
 Meissner effect - Wikipedia, the free encyclopedia
In the effect, there is an exclusion of magnetic flux brought about by electrical "screening currents" that flow at the surface of the superconducting metal and which generate a magnetic field that exactly cancels the externally applied field inside the superconductor.
The Meissner effect is one of the defining features of superconductivity, and its discovery served to establish that the onset of superconductivity is a phase transition.
Superconducting magnetic levitation is due to the Meissner effect (which repels a permanent magnet) and flux pinning, which stops the magnet from sliding away.
en.wikipedia.org /wiki/Meissner_effect   (187 words)

  
 Measurement of the Vortex Pair Interaction Potential in a Type-II Superconductor
Although flux flow is driven by gradients in the vortex density, such gradients also are negligibly small over the field of view.
Nevertheless, an ensemble average of statistically independent flux line distributions on the fixed pinning potential closely resembles the more familiar annealed average and may be interpreted to reveal similar aspects of the system's interactions.
The Lorentz force redistributing vortices among the pinning centers is sufficiently strong that none of the vortices remains completely pinned throughout the experiment.
www.physics.nyu.edu /grierlab/potential6b/potential6b.html   (1978 words)

  
 simpson   (Site not responding. Last check: 2007-10-16)
We attempted to increase the flux pinning capabilities of YBCO by doping it with the rare earths Sm, Nd, Eu, Dy, Ho, and Gd.
Flux pinning properties are somewhat independent of transition widths, so even if the susceptibility suggests that a sample is inhomogeneous, we can still draw meaningful conclusions about flux-pinning.
However, superconductors are resistant to a changes in their flux density, thus there is a difference in the flux density of the sample when pushing flux in and pulling flux out.
www.physics.ncat.edu /~michael/vsta/vsstg/project/simpson   (1533 words)

  
 Jahrbuch-CD der MPG 2003 - Magneto-optical studies of flux
Quantitative magneto-optical imaging of magnetic flux distributions has developed in a powerful tool for the analysis of the local transport properties of superconductors.
Based on these tools, in this paper we present a systematic comparison of vortex pinning, vortex movement and current transfer of two kinds of planar defects which are typically present in high-temperature superconducting thin films: low-angle grain boundaries and antiphase boundaries.
Special attention is drawn to the local magnetic field dependence of the critical current density and to the spatial distribution of E, giving insight into the collective behavior of vortices at planar defects.
www.mpg.de /forschungsergebnisse/wissVeroeffentlichungen/archivListenJahrbuch/2002/31/publZIM378.html   (175 words)

  
 Theoretical Description
Because of the short-range nature of the flux line interactions, this assumption is justified in the limit of low flux line concentration, where the average flux line separation, as well as fluctuations around it, are much larger than the London penetration depth.
This is consistent with our expectation that an isolated flux line, or one that is effectively isolated, is more likely to be in the domain of attraction of a strong pin in its vicinity.
This resemblance is particularly close for pinned flux lines because their interaction force, f(r), is proportional to the potential, U(r), to logarithmic accuracy in the regime of interest.
www.physics.nyu.edu /grierlab/LQb/node5.html   (1107 words)

  
 M. Marchevsky: Research
The "peak effect" phenomenon in the vortex lattice is characterized by a sudden increase of the pinning strength that reaches a sharp maximum just before vanishing at the superconducting ttansition.
It was recently discovered that the peak effect phenomenon is characterized by the two distinct phases with different pinning strenght that coexist in the superconductor at the macroscopic scale.
As the temperature is lowered, the pinning barriers for rearrangement of the flux quanta become large and the system exhibits an activated behavior.
www.phy.syr.edu /~marchev/research.htm   (601 words)

  
 Forschungsgebiet 07 | Abteilung Schütz | Max-Planck-Institut für Metallforschung | Stuttgart   (Site not responding. Last check: 2007-10-16)
Our goal is the artificial generation of pinning sites to enlarge the appearing current densities by growing the films on modified substrates.
The super-conductor is in the remanent state, the diagonal white lines correspond to the frozen magnetic flux in the sample and the solid lines give the path of the supercurrents.
These high currents correspond to a very effective pinning of flux lines at the generated defects, which can be directly proven by local measurements of the activation enthalpy of thermally activated flux jumps, a method we developed from measurements of the time relaxation of supercurrents.
wwwmf.mpi-stuttgart.mpg.de /de/abteilungen/schuetz/07.html   (337 words)

  
 ASC 2004: Technical Program   (Site not responding. Last check: 2007-10-16)
Pinning centers were introduced into Nb-Ti filaments, consisting of Cu-Ni, Cu, Nb and Nb+Ti rods with the triangular arrangement and the volume fraction of 17 %.
In the Cu-Ni and Cu APC, Kirkendall voids were produced at the interface of pins by diffusion during drawing processes.
We discuss correlation between flux pinning properties and observed heterogenous nano-structures of pins.
www.ascinc.org /asc04/Format.asp?paperNumber=5MM04&Category=2   (202 words)

  
 Vortices in Superconductors
An applied current excerpts a force on the flux lines which start to move unless there is another force counter-acting the first one.
Flux lines moving with an average velocity v on the other hand result in an induced electrical field E proportional to v in such a way that it reduces the applied current.
That resistance can be overcome by pinning the flux lines at intrinsic or artificially introduced defects in the atomic structure of the superconductor.
home.arcor.de /dr.engel/thesis.htm   (356 words)

  
 The Superconductivity Research Group at NTNU   (Site not responding. Last check: 2007-10-16)
Flux pinning in Bi2212 by artificially engineered materials where nanoparticles were introduced.
Flux pinning in Bi2212 by introduction of nanoparticles
This allows us to image the flux distribution in the sample, and from that to calculate critical current densities in the sample on the basis of recorded flux gradients.
www.phys.ntnu.no /brukdef/grupper/materialfysikk/srg/exper_e.shtml   (1291 words)

  
 Powell's Books - Flux Pinning in High Temperature Superco by A. V. Narlikar
The problem of flux pinning holds direct relevance to the development of commercial superconductors, which would sustain a high loss-less current density in a strong magnetic field.
This volume has 7 chapters focussing on a host of topics linked with different aspects of flux pinning, such as the microstructural effects, the role of radiation induced damage and the chemical substitutions, vortex depinning effects intricacies of flux motion, including jumps in magnetization behaviour.
Addressing the frontal issue of the flux hindrance in high temperature superconductors, contributors to this volume focus on topics linked with different aspects of flux pinning, including the microstructural effects, the role of radiation induced damage and the chemical substitutions, vortex depinning effects, intricacies of flux motion, and other topics.
www.powells.com /cgi-bin/biblio?inkey=16-156072790x-0   (188 words)

  
 Images SI, Inc.
Flux pinning occurs in tiny defects in the crystalline structure of the superconducting material.
A smaller portion of the lines of force become trapped in the defects in the superconductor matrix, and are held in place.
These trapped lines of force (flux pinning) are the reason the magnet doesn't slide fall off the superconductor.
www.imagesco.com /articles/supercond/04.html   (126 words)

  
 WFU Physics Seminars   (Site not responding. Last check: 2007-10-16)
For example, these superconductors are characterized by unusually low flux pinning energies.
As a result, the flux vortices, present in a superconductor placed in a magnetic field, move easily in the presence of a current, giving rise to dissipation of energy.
First, it could provide insights into the basic phenomena of high tempera ture superconductivity by addressing issues such as the temperature and magnetic field range over which these materials are really superconducting (zero resistance), and the nature and mechanism of pinning of flux lines.
www.wfu.edu /physics/seminars/2000_Spring/almasan.html   (248 words)

  
 Ovid: Citation display
A hollow superconductor in its critical state with magnetic flux trapped in the hole is proposed to be used for optical signal detection and storage in a wide spectral range.
The sensitivity arises from the temperature dependence of the critical magnetic field in type I superconductors or that of the volume pinning force in hard type II superconductors.
With the use of the effect of low magnetic field microwave absorption the authors have demonstrated the flux trapping in a thin hollow disk which could serve as a basic element of planar structures for the detection of two-dimensional optical information.
wwwrsphysse.anu.edu.au /~ask107/INSPEC/KVP91.html   (168 words)

  
 [No title]   (Site not responding. Last check: 2007-10-16)
Flux Lattice Melting, Flux Pinning, and Superfluid Density Tensor of YBa2Cu3O(7-delta)
We calculate the flux lattice melting curve T_M(H) of YBa2Cu3O(7-delta) for a magnetic field H parallel to c, in good agreement with experiment without any free parameters.
With no pinning, the c component of the superfluid density tensor jumps to a finite value at the transition, but the transverse components remain zero, corresponding to the sliding freedom of the flux lattice.
www.physics.ohio-state.edu /~stroud/Ybco.html   (127 words)

  
 Anderson Theory of Flux-Creep in the Presence of a Pinning Strength Distribution for the Washboard-Type Potential ...
Abstract: Anderson theory is modified to explain the scaling behavior of the E-J curves, the logarithmic dependence of the potential barrier as a function of the transport current, the decrease of the barrier as the temperature goes to zero, and other results of the studies of flux creep in high-T c superconductors.
Moreover, the method provides the possibility of estimating the main pinning parameters of superconductors by fitting the calculated and experimental data.
1 Flux creep in the critical state of a high-temperature super..
citeseer.ist.psu.edu /168136.html   (297 words)

  
 super2
The improvement of flux pinning was achieved by externally added ball-milled secondary phase particles that partially transformed during the technological process to new type of nanometer-scale Zr-rich particles.
The rate of flux penetration into the inter-granular space was an inversal function of the bridge width and was significantly faster than penetration into the grains.
Effective pinning energy of thermally activated flux creep was determined in a range of temperatures from relaxation measurements on samples without antidots and with antidots of different sizes (1.4–2.4 micrometers).
www.fzu.cz /~jirsa/htm/super2.htm   (13850 words)

  
 Flux pinning by regular nanostructures in $\chem{Nb}$ thin films: Magnetic vs. structural effects
Flux pinning by regular nanostructures in $\chem{Nb}$ thin films: Magnetic vs. structural effects
Pinning effects can be observed in the evolution of resistivity and critical current with the applied magnetic field, showing the same qualitative behavior, for both types of samples.
The analysis and comparison of these results allows determining the pinning as due to superconductivity suppression around the nanostructures (indentations or dots) due to a thickness reduction.
www.edpsciences.org /articles/epl/abs/2003/13/7690/7690.html   (181 words)

  
 MAGNETIC MEASUREMENTS OF SUPERCONDUCTORS   (Site not responding. Last check: 2007-10-16)
Study the flux pinning properties of high temperature superconductors as a function of their microstructure and processing variables.
Better control over the flux pinning properties of materials used in shielding and levitation bearings.
Such measurements are important for assessing the flux pinning properties high-temperature superconductors.
www.metallurgy.nist.gov /techactv1995/magsupr.html   (384 words)

  
 Superconductor Terms
The smallest magnetic flux (flux quantum) that exists in nature.
This pinning binds the superconductor to the magnet at a fixed distance.
The Mott transition is the shift from an insulating to a metallic state in a material.
superconductors.org /terms.htm   (4425 words)

  
 World Intellectual Property Organization   (Site not responding. Last check: 2007-10-16)
It is evident that the additive pinning is more effective at low temperatures while the additives at the grain boundaries decouple the grains at high temperatures.
The first is intrinsic pinning due to substitution and impurity pinning (or a combination thereof).
Nano-particle inclusions and substitution, both observed by transmission electron microscopy, are proposed to be responsible for the enhancement of flux pinning in high fields.
www.wipo.int /ipdl/IPDL-CIMAGES/view/pct/getbykey5?KEY=03/106373.031224&ELEMENT_SET=DECL   (4555 words)

  
 Superconductivity   (Site not responding. Last check: 2007-10-16)
This phenomenon, known as flux pinning, causes a field gradient in the superconductor and gives rise to a net current in the material.
Since the pinning force is small, fluxoids can be broken loose from their pinning centers, resulting in a net creep of the flux through a conductor as a function of time.
If the current density is low and the magnetic field is not intense, flux creep is insignificant and the induced voltage and effective resistance of the conductor will be essentially zero.
www.americanmagnetics.com /tutorial/supercon.html   (559 words)

  
 [No title]
We study a one-dimensional mean field model of superconducting vortices with a finite London penetration depth, flux pinning and nucleation of vorticity at inflow boundary sections.
A numerical discretization of the model is derived and it is shown that as the time step and the mesh size tend to zero, the discrete solution converges to the unique weak solution of the continuous model.
Some numerical computations are presented which illustrate the effects of flux pinning and the finite penetration depth.
www.maths.sussex.ac.uk /Staff/VS/abs2.html   (1095 words)

  
 Amazon.ca: Books: A.C. Losses and Flux Pinning in High Temperature Superconductors   (Site not responding. Last check: 2007-10-16)
In this book, Volume 32 of the series, forms the sequel to the previous volume on Flux Pinning in HTS, the focus is on the prominent issue of the AC losses in wires and tapes.
It is understood that the studies and understanding of AC losses hold the master key to unlock the problem of large scale power applications of high temperature superconductors.
Whenever the AC losses are discussed, the topic of flux pinning in superconductors perhaps cannot be left out.
www.amazon.ca /exec/obidos/ASIN/1560727896   (245 words)

  
 Flux ? Info - Knowledge Scout Results [Information for those who really want to know].
AC Losses and Flux Pinning and Formation of Stripe Phase (Studies of High Temperature Superconductors, Volume 33) by A. Narlikar
flux -- (excessive discharge of liquid from a cavity or organ (as in watery diarrhea))
=> flux -- (excessive discharge of liquid from a cavity or organ (as in watery diarrhea))
www.omega23.com /beyond_web_hosting_servers/Flux.html   (3566 words)

  
 Flux pinning in superconducting 123 materials   (Site not responding. Last check: 2007-10-16)
It is speculated that these regions work as strong repulsive pinning centres resulting from the kinetic energy of the order parameter under a significant proximity effect.
This pinning mechanism is different from the usual attractive condensation energy interaction which occurs in 211 or 422 particles.
General guiding principles for the improvement of the flux pinning property will also be discussed.
stacks.iop.org /0953-2048/13/730   (280 words)

  
 [No title]   (Site not responding. Last check: 2007-10-16)
The authors show that surface damage in these samples is by far the most important source of flux pinning, and that substantial shifts in the irreversibility line can be controlled by the number and type of defects added to the surface.
The authors find that the frequency of these oscillations is proportional to the sweep rate of the external magnetic field and is inversely proportional to the square root of the heat capacity.
The following subjects will be covered: fundamental flux pinning mechanisms and properties; artificially introduced pinning centers, including irradiation defects; direct observations of flux dynamics, flux distributions, and current distributions; exotic properties in artificial multilayers; intergranular critical currents in weakly coupled superconductors; phase diagrams of flux-line systems; irreversibility line; and flux dynamics and electromagnetic phenomena.
www.iitap.iastate.edu /htcu/files/95may1em.txt   (6102 words)

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