Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Superconductive type
Reexamination Certificate
2000-06-13
2003-09-16
Barrera, Ramon M. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Superconductive type
C505S879000
Reexamination Certificate
active
06621395
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to superconducting materials, and more particularly, to methods of charging superconducting materials.
BACKGROUND OF THE INVENTION
Many electrical conductors, which can include metallic elements, compounds, and alloys, undergo phase transitions and become superconducting when temperature is reduced below a critical temperature (T
c
). Superconducting materials may be characterized by no resistance to the flow of electric current, the tendency to exclude magnetic fields, amongst other interesting magnetic, thermal and electrical properties. Such properties make superconductors potentially useful in a large number of areas including power transmission, digital circuitry, magnets, motors, and many others.
High-temperature superconducting (HTS) materials are generally considered those materials which have a critical temperature of greater than about 20 K. The development of such materials has enabled an increase in the operation temperature of superconducting devices from the liquid helium range (4 K-20 K) to the liquid nitrogen range (60 K-120 K) which has drastically reduced the cost and increased the viability of operating such devices. High-temperature superconducting materials are generally ceramic compounds.
In certain applications, for example when used as magnets, it is necessary to charge superconducting materials. Charging involves inducing a non-decaying electrical current in the superconductor that persists even in the absence of an externally applied magnetic field. The electrical currents flowing in the superconductor generate a magnetic field which may be utilized for a variety of applications. Conventionally, high-temperature superconducting materials may be charged by non-isothermal methods which involve exposing the material to an external magnetic field when the material is not superconducting, decreasing the temperature until the material becomes superconducting (i.e., below the critical temperature), and then removing the externally applied field. In some cases, such conventional charging methods may require that the sample needs to be cooled quickly which may result in large thermal stresses that can cause cracks in the superconducting material. Furthermore, the external magnetic field may need to be applied for relatively long times (i.e., on the order of seconds) which can complicate the design of the charging coils which provide the charging magnetic field. Accordingly, other methods for charging superconducting materials, and in particular near-isothermal methods, may be desirable.
SUMMARY OF THE INVENTION
The invention provides methods of charging superconducting materials and, in particular, methods of charging high-temperature superconducting materials. The methods generally involve cooling a superconducting material to a temperature below its critical temperature. Then, an external magnetic field is applied to charge the material at a nearly constant temperature. The external magnetic field first drives the superconducting material to a critical state and then penetrates into the material. When in the critical state, the superconducting material loses all the pinning ability and therefore is in the flux-flow regime. In some embodiments, a first magnetic field may be used to drive the superconducting material to the critical state and then a second magnetic field may be used to penetrate the superconducting material. When the external field or combination of external fields are removed, the magnetic field that has penetrated into the material remains trapped. The charged superconducting material may be used as solenoidal magnets, dipole magnets, or other higher order multipole magnets in many applications.
In one aspect, the invention provides a method of charging a superconducting material. The method includes providing a superconducting material and charging the superconducting material without decreasing the temperature of the superconducting material.
In another aspect, the invention provides a method of charging a superconducting material. The method includes providing a superconducting material, and charging the superconducting material, while the temperature of the superconducting material varies by less than 15 K.
In another aspect, the invention provides a method of charging a superconducting material. The method includes cooling a superconducting material to a temperature below the critical temperature in the absence of an external magnetic field, and charging the superconducting material.
In another aspect, the invention provides a method of charging a superconducting material. The method includes driving a superconducting material into the critical state by one of applying a first external magnetic field, imposing a current in the superconducting material, or a combination of applying a first external magnetic field and imposing a current in the superconducting material. The method further includes applying a second external magnetic field to penetrate into the superconducting material.
Other advantages, aspects, and features of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.
REFERENCES:
patent: 4190817 (1980-02-01), Rabinowitz
patent: 4954727 (1990-09-01), Hilal
patent: 5132278 (1992-07-01), Stevens et al.
patent: 5276419 (1994-01-01), Griffin et al.
patent: 5289150 (1994-02-01), Rabinowitz
patent: 5298875 (1994-03-01), Laibowitz et al.
patent: 5306701 (1994-04-01), Israelsson et al.
patent: 5328893 (1994-07-01), Sun et al.
patent: 5339061 (1994-08-01), Reick
patent: 5659278 (1997-08-01), Yanagi et al.
Japanese Abstract No. 7-111213, 4/95.
Japanese Abstract No. 7-211546, 8/95.
Blohowiak et al., “Evaluation of YBa2Cu3O7-xBulk Superconductors for High Field Magnet Applications,” Aug. 24, 1992.
Chen et al., “Characterizatio of YBa2Cu3O7, including critical current density Jc, by Trapped Magnetic Field,” Institute for Beam Particle Dynamics and Texas Center for Superconductivity, University of Houston, Houston, Texas, Jan. 21, 1992.
Chen et al., “Improvement of Persistent Magnetic Field Trapping in Bulk Y-Ba-Cu-O Superconductors,” Institute for Beam Particle Dynamics and Texas Center for Superconductivity, University of Houston, Houston, Texas, 1992.
Chen et al., “Quasipermanent Magnets of High Temperature Superconductor: Temperature Dependence,” Appl. Phys. Lett. 62. (25), Jun. 21, 1993, pp. 3366-3368.
Gao et al., “Unusually Large Shielding Fields in Single-Grain YBa2Cu3O7-&dgr;,” Texas Center for Superconductivity, University of Houston, Houston, Texas, Feb. 7, 1994.
Itoh, “Influence of Wall Thickness on Magnetic Shielding Effects of BPSCCO Cylinders,” Advances in Cryogenic Engineering, vol. 40, pp. 261-270, 1994.
Liu et al., “Studies of Magnetization Currents in YBa2Cu3O7-xSuperconductors,” J. Appl. Phys. 73 (10), May 15, 1993, pp. 6530-6532.
Ohyama et al., “Improvement in Magnetic Shielding by Use of Triple-Cylinder Configuration of a Superconducting BPSCCO,” Advances in Cryogenic Engineering, vol. 40, 1994, pp. 245-252.
Ren et al., “Quasi Permanent Superconducting Magnet of Very High Field,” J. Appl. Phys. 74 (1), Jul. 1, 1993, pp. 718-719.
Weinstein et al., “Permanent Magnets of High-TcSuperconductors,” J. Appl. Phys. 73 (10), May 15, 1993, pp. 6533-6535.
Weinstein et al., “Progress in Jc, Pinning, and Grain Size, for Trapped Field Magnets,” Presented at International Symposium on Superconductivity, Hiroshima, Japan, Oct. 1993.
Barrera Ramon M.
Massachusetts Institute of Technology
Wolf Greenfield & Sacks P.C.
LandOfFree
Methods of charging superconducting materials does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods of charging superconducting materials, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods of charging superconducting materials will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3019510