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Flux Pinning: Flux Tube diagram

Flux Pinning (Also known as Quantum Locking) is the phenomenon where as a superconductor coated disk is locked in 3 dimensional space above a magnet. The super conductor must be a Type II superconductor due to the fact that Type I superconductors cannot be penetrated by magnetic fields. The act of magnetic penetration is what makes Flux Pinning possible. The superconductor disk ("Wafer") is made up of a base (usually a sapphire disk) coated in a thin layer of superconductor (Yttrium Barium Copper Oxide). If the superconductor layer is less than one micron thin, the magnetic field from the magnet can penetrate through the tiny imperfections in the layer. These sites of penetration are known as Flux Tubes. On a simple 3 inch diameter disk with one micron of nitrogen-cooled superconductor, there are approximately 100 billion Flux Tubes that hold 70,000 times the superconductor's weight. These penetrations are what holds the disk in place thereby "pinning" it. This effect is closely related to the Meissner Effect with one crucial difference, the Meissner Effect works by surrounding the superconductor with magnetic fields creating a wobbly hold unlike the locked state of the superconductor disk. The penetration of the magnetic field through the disk results in the commonly know effect "Quantum Levitation".

Importance of Flux Pinning

Flux pinning is desirable in high-temperature ceramic superconductors to prevent "flux creep", which can create a pseudo-resistance and depress both critical current density and critical field.

Degradation of a high-temperature superconductor's properties due to flux creep is a limiting factor in the use of these superconductors. SQUID magnetometers suffer reduced precision in a certain range of applied field due to flux creep in the superconducting magnet used to bias the sample, and the maximum field strength of high-temperature superconducting magnets is drastically reduced by the depression in critical field.

Flux Pinning in the Future

The worth of flux pinning is seen through many implementations such as lifts, frictionless joints, and transportation. The thinner the superconducting layer, the stronger the locking that occurs when exposed to magnetic fields. Many scientists currently studying flux pinning say that theoretically it is possible for such superconducting disks to hold up to 2,000 pounds making for a perfect dolly-type technology. Since the superconductor is locked above the magnet away from any surfaces there is the potential for a frictionless joint. Transportation is another area flux pinning technology could revolutionize and reform. MagSurf was developed by a french university utilizing flux pinning to create a hovercraft-like effect that could support a human demonstrating the usefulness of the technology. These are a few of the endless possibilities concerning the utilization of flux pinning.

See also

• Flux pumping
• Superconductivity
• Abrikosov vortex
• Pinning force
• Meissner Effect

Other sources

• Future Science introduction to high-temperature superconductors.
• American Magnetics tutorial on magnetic field exclusion and flux pinning in superconductors.
• Cern Lhc documentation Stability of superconductors.
• Quantum Levitation Demonstration of flux pinning.
• Flux-Pinning of Bi₂Sr₂CaCu₂O_{(8 + Delta)} High T_c Superconducting Tapes Utilizing (Sr,Ca)₁₄Cu₂₄O_{(41 + Delta)} and Sr₂CaAl₂O₆ Defects (T. Haugan; et al. AFB OH Propulsion Directorate. Air Force Research Lab Wright-Patterson. Oct 2003)
• Boaz Almog “levitates” a superconductor Boaz Almog from Tel Aviv University demonstrates quantum locking on TED Talks - June 2012.

Category:Magnetic levitation Category:Superconductivity Category:Quantum magnetism