Electricity: electrical systems and devices – Safety and protection of systems and devices – Superconductor protective circuits
Reexamination Certificate
2000-03-21
2002-10-22
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Superconductor protective circuits
C361S115000, C361S143000
Reexamination Certificate
active
06469880
ABSTRACT:
The present invention relates generally to a method and system for transport and removal of trapped magnetic flux, or vortices, in a superconductor device. More particularly, the invention is directed to a method and system for application of an AC current to a superconductor to induce motion of vortices and cause their substantial removal from a superconductor.
A serious obstacle that impedes the utilization of low and high temperature superconductor devices is the presence of trapped flux. Flux lines or vortices are induced by fields as small as the Earth's magnetic field. Once present in a superconductor, vortices dissipate energy and generate internal noise, limiting the operation of numerous superconducting devices. Prior methods used to overcome this difficulty include the pinning of vortices by the incorporation of impurities and defects, the construction of flux dams, slots and holes and also the use of magnetic shields which block the penetration of new flux lines in the bulk of the superconductor or reduce the magnetic field in the immediate vicinity of the superconducting device. The most desirable result would be to remove the vortices from the bulk of the superconductor. There is currently no known phenomenon or process, however, that could form the basis for such a result.
It is therefore an object of the invention to provide an improved method and system for producing supercondutors with enhanced properties.
It is another object of the invention to provide a novel method and system for removal of unwanted magnetic flux trapped in a superconductor.
It is yet a further object of the invention to provide an improved method and system for removal of magnetic vortices in a superconductor by application of an AC field.
It is also an object of the invention to provide an improved method and system for application of a particular AC potential to a superconductor to sweep magnetic vortices out of the superconductor.
It is an additional object of the invention to provide a novel method and system for generating a patterned potential field designed to remove a magnetic flux from a superconductor.
In the present invention, the application to a superconductor of an AC current that is patterned with an asymmetric pinning potential can induce vortex motion whose direction is determined only by the asymmetry of the pattern. This vortex motion can result in their substantial removal from the superconductor. The mechanism responsible for this phenomenon is the well-known ratchet effect, and its working principle applies to both low and high temperature superconductors. We demonstrate that with an appropriate choice of the pinning potential, the ratchet effect can be used to remove vortices from superconductors in the parameter range required for various applications.
The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with the objects and advantages thereof are best understood by reference to the following description taken in conjunction with the accompanying drawings. Provisional Application Ser. No. 601125,706 is also incorporated by reference herein.
REFERENCES:
patent: 5986453 (1999-11-01), Anderson et al.
Falo et al., “Ratchet Potential For Fluxons In Josephson-Junction Arrays”, Mar. 15, 1999,Europhysics Letters, pp. 700-706.
Robilliard et al., “Ratchet For Cold Rubidium Atoms: The Asymmetric Optical Lattice”, Jan. 25, 1999,Physical Review Letters, pp. 851-854.
Linke et al., “A Quantum Dot Ratchet: Experiment And Theory”, Nov. 1, 1998,Europhysics Letters, pp. 343-349.
Derenyi et al., “Ratchet Effect In Surface Eletromigration: Smoothing Surfaces By An AC Field”, Feb. 16, 1998, pp. 1473-1476.
Slater et al., “Bidirectional Transport Of Polyelectrolytes Using Self-Modulating Entropic Ratchets”, Feb. 10, 1997,Physical Review Letters, pp. 1170-1173.
Zapata et al., “Voltage Rectification By A SQUID Ratchet”, Sep. 9, 1996,Physical Review Letters, pp. 2292-2295.
Barabasi Albert-Laszlo
Derenyi Imre
Janko Boldizsar
Lee Choongseop
Jackson Stephen W.
Rechtin Michael D.
University of Notre Dame
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