Stable superconducting magnet

Claim 2

The combination as defined in claim 2 wherein said first means maintains said low-temperature environment substantially as a fluid in contAct with the said first portion of said turns.

Claim 3

The combination as defined in claim 1 wherein said first means directs said low-temperature environment as a liquid to the said first portion of said turns and exhausts said low-temperature environment converted to a gas as a result of contact with said first portion of said turns at a rate sufficient to maintain said superconducting material at less than its critical temperature when said normal metal is carrying current.

Claim 4

In a superconducting coil having a rated current for providing a magnetic field, the combination comprising: a. a conductor forming a plurality of turns comprising a superconducting material in intimate electrically and thermally conductive contact with a normal material having a low-temperature electrical conductivity of at least about the order of copper at superconducting temperatures, the total cross section of said normal material being greater than the total cross section of said superconducting material so that when said conductor is exposed to a low-temperature environment to reduce the temperature of said superconductive material below its critical temperature and current flowing through the said conductor is increased until a voltage is measurable across the ends of said conductor, said voltage will disappear upon reduction of said current to a value not substantially less than said critical current; b. a fluid low-temperature environment for reducing the temperature of said conductor below the critical temperature of said superconducting material; and c. first means for maintaining said low-temperature environment as a fluid in contact with a portion of the surface of each turn of said conductor, said ratio of cross sections, the amount of said surface of each turn in contact with said low-temperature environment, and said first means being selected, arranged and adapted to conduct heat away from said conductor at a rate sufficient to prevent said superconducting material from reaching a temperature in excess of its critical temperature when said normal material is carrying current.

Claim 5

In a superconducting device for providing a given magnetic field when immersed in a low-temperature environment to reduce the temperature of superconducting material below its critical temperature, said device containing superconducting material and having a rated current, the combination comprising: a. a conductor forming a plurality of turns comprising a superconducting material in intimate electrically and thermally conductive contact with a normal material having a high electrical conductivity at superconducting temperatures, said superconducting material having a predetermined critical current in a magnetic field equal to said given magnetic field, the total cross section of said normal material being greater than the total cross section of said superconducting material so that when conductor is exposed to a low-temperature environment to reduce the temperature of said superconductive material below its critical temperature and current flowing through the said conductor is increased until a voltage is measurable across the ends of said conductor, said voltage will disappear upon reduction of said current to a value not substantially less than said critical current; b. electrically nonconductive means electrically insulating said turns one from another; and c. means for maintaining said low-temperature environment in contact with each turn of said conductor and preventing said conductor from increasing in temperature by an amount Delta T less than about the difference between the superconducting temperature of operation and the critical temperature of said superconducting material, said Delta T being substantially equal to Rho I2/h P A, where I is the current in amperes flowing in said conductor; Rho is the resistivity of said normal material in ohm centimeter h is the effective heat transfer coefficient from sAid superconducting material to said low-temperature environment in watts per square centimeter per degree Kelvin; A is the cross-sectional area of said conductor in square centimeters; and P is the portion of the perimeter of the cross section of said conductor in centimeters in contact with said low-temperature environment.

Claim 6

In a superconducting device for providing a magnetic field when immersed in a low-temperature environment to reduce the temperature of superconducting material below its critical temperature, said device containing superconducting material and having a rated current, the combination comprising: a. a conductor forming a plurality of turns and comprising a superconducting material and a normal material having a high electrical conductivity at superconducting temperatures, at least a major portion of the surface of one of said materials being in electrically and thermally conductive contact with said other material, the electrical conductivity between said contacting surfaces at superconducting temperatures being not substantially in excess of the electrical conductivity of said normal material at superconducting temperatures, said turns being wound to place at least a portion of a surface of said conductor forming each turn in communication with said low-temperature environment, the total cross section of said normal material being substantially greater than the total cross section of said superconducting material whereby at the superconducting temperature of application said normal material will carry said rated current of said device; b. electrically nonconductive means insulating said turns one from another, said at least a portion of the surface of each said turn being exposed to said low-temperature environment; and c. means for maintaining said low-temperature environment in contact with said exposed surface of said conductor and preventing said conductor from increasing in temperature by an amount Delta T less than about the difference between the superconducting temperature of operation and the critical temperature of said superconducting material, said Delta T being substantially equal to Rho I2/h P A , where I is the current in amperes flowing in said conductor; Rho is the resistivity of said normal material in ohm centimeters; h is the effective heat transfer coefficient from said superconducting material to said low-temperature environment in watts per square centimeter per degree Kelvin; A is the cross-sectional area of said conductor is square centimeters; and P is the portion of the perimeter of the cross section of said conductor in centimeters in contact with said low-temperature environment.

Claim 7

In a superconducting device for providing a magnetic field when immersed in a low-temperature environment to reduce the temperature of superconducting material below its critical temperature, said device containing superconducting material and having a rated current, the combination comprising: a. a conductor forming a plurality of turns comprising a superconducting material in intimate electrically and thermally conductive contact with a normal material having a high electrical conductivity at superconducting temperatures; b. electrically nonconductive means electrically insulating said turns one from another; and c. means for maintaining said low-temperature environment in contact with at least part of each turn of said conductor and preventing said conductor from increasing in temperature by an amount Delta T the ratio of the total cross section of said superconducting material to the total cross section of said conductor being substantially equal to where Rho is the resistivity of said normal material in ohm centimeters; h is the effective heat transfer coefficient from said superconducting material to said low-temperature environment in watts per square cEntimeter per degree Kelvin; A is the total cross-sectional area of said conductor in square centimeters; P is the portion of the perimeter of the cross section of said conductor in centimeters in contact with said low-temperature environment; Delta T is the rise in temperature in the conductor with all of the current flowing in the normal material and is less than about the difference between the superconducting temperature of application and the critical temperature of the superconducting material; and Jsc is the current density in amperes per square centimeter in the superconducting material when it is carrying the current flowing in said conductor.

Claim 8

In a superconducting device for providing a magnetic field when immersed in a low-temperature environment to reduce the temperature of superconducting material below its critical temperature, said device containing superconducting material and having a rated current, the combination comprising: a. a conductor forming a plurality of turns comprising a superconducting material imbedded in and in intimate electrically conductive contact with a normal material having a high electrical conductivity at superconducting temperatures, said turns being wound to place at least a portion of the surface of said conductor forming each turn in communication with said low-temperature environment; b. electrically nonconductive means electrically insulating said turns one from another, said at least a portion of the surface of each said turn being exposed to said low-temperature environment; and c. means for maintaining said low-temperature environment in contact with said exposed surface of said conductor and preventing said conductor from increasing in temperature by an amount Delta T, the ratio of the total cross section of said superconducting material to the total cross section of said conductor being substantially equal to where Rho is the resistivity of said normal material in ohm centimeters; h is the effective heat transfer coefficient from said superconducting material to said low-temperature environment in watts per square centimeter per degree Kelvin; A is the total cross-sectional area of said conductor in square centimeters; P is the portion of the perimeter of the cross section of said conductor in centimeters in contact with said low-temperature environment; Delta T is the rise in temperature in the conductor with all of the current flowing in the normal material and is less than about the difference between the superconducting temperature of application and the critical temperature of the superconducting material; and Jsc is the current density in amperes per square centimeter in the superconducting material when it is carrying the current flowing in said conductor.

Claim 9

A composite electrical conductor comprising: a. elongated superconductive material, a relatively short sample of said superconductive material having a predetermined rated current in a given magnetic field; and b. a normal metal having a low-temperature electrical conductivity of the order of copper at temperature at which said superconductive material is superconductive, said metal being in intimate electrically and thermally conductive contact with at least a substantial portion of said superconductive material to provide substantially minimum electrical resistance and substantially maximum heat transfer between said normal metal and said superconductive material said metal further having a cross-sectional area that in combination with said electrically and thermally conductive contact, in an environment having a temperature less than the critical temperature of said superconductive material, prevents propagation of a localized normal region resulting from increasing current flow through said sample in said given magnetic field until a constant voltage is measurable across said condUctor.

Claim 10

The combination as defined in claim 10 wherein said cross-sectional area and said thermally and electrically conductive contact causes said normal region to disappear upon reduction of said current to a value not substantially less than said rated current.

Claim 11

A composite electrical conductor comprising: a. elongated superconductive material, a relatively short sample of said superconductive material having a predetermined rated current in a given magnetic field; and b. a normal metal having a low-temperature electrical conductivity of the order of copper at the temperature at which said superconductive material is superconductive, said metal being in intimate electrically and thermally conductive contact with at least a substantial portion of said superconductive material to provide substantially minimum electrical resistance and substantially maximum heat transfer in said normal material and between said normal metal and said superconductive material, and said normal metal having a cross-sectional area substantially greater than the cross-sectional area of said superconductive material so that when said conductor is exposed to a low-temperature environment to reduce the temperature of said superconductive material below its critical temperature and current flowing through said sample is increased until a constant voltage is measurable across said conductor as a result of a localized normal region is said superconductive material, said voltage will disappear upon reduction of said current to a value not substantially less than said rated current.

Claim 12

The combination as defined in claim 10 wherein said normal metal has an essentially rectangular cross section and at least substantially surrounds said superconductive material.

Claim 13

The combination as defined in claim 13 wherein said superconductive material comprises a plurality of superconductive wires spaced one from another, said normal metal at least substantially surrounding each said superconductive wire.

Claim 14

The combination as defined in claim 10 wherein said superconductive material is heat-treated superconductive material.