JP3284656B2 - Current lead using oxide superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current lead using an oxide superconductor for supplying a DC exciting current from an external power supply to a superconducting coil housed in a vacuum insulated container.

[0002]

2. Description of the Related Art Since a superconducting coil of a superconducting magnet device is cooled by a cryogenic refrigerant such as liquid helium and maintains a superconducting state, liquid helium is supplied to a radiation shield using liquid nitrogen or a vacuum heat insulating container having a multilayer heat insulating layer. It is stored in a immersed state. Further, the current lead is cooled by a low-temperature helium gas obtained by evaporating liquid helium, and is configured to prevent intrusion heat from the normal temperature side and Joule heat generated by the current lead from entering the cryogenic portion. Conventionally,
Electric current conductors, such as copper, were used for the current leads.However, copper is both a good conductor and a good heat conductor. There is a disadvantage that the loss increases. Therefore, an oxide superconductor, which is a high-temperature superconductor, is used on the low-temperature side of the current lead to reduce the Joule heat to zero and at the same time use the low thermal conductivity to greatly reduce the heat that enters the cryogenic side. It has been known.

FIG. 8 is a simplified cross-sectional view showing a conventional structure of a current lead of a superconducting magnet device, FIG. 9 is an enlarged cross-sectional view showing an AA portion of FIG. 8, and FIG. 10 is a BB of FIG. It is sectional drawing which expands and shows a part. In these figures, a superconducting coil 1 is housed in a vacuum heat insulating container 2 in a state of being immersed in liquid helium He, and is electrically connected to a low-temperature terminal 5A of a current lead 3 by a lead wire 6. The current lead 3 is configured as a series connection of a high-temperature side lead 4 having a normal-temperature terminal 4A on the upper side and a low-temperature side lead 5 having a low-temperature terminal 5A on the lower side. Low-temperature helium gas GHe passes through the lead and is connected to the normal-temperature terminal 4A side. It is cooled by exiting.

As shown in FIG. 9, the high-temperature side lead 4 accommodates a bundle of electric conductors 8 such as copper or a copper alloy in a hollow tube 7 and cools a helium gas through a cooling passage formed in the gap. When GHe flows, the intrusion heat from the room temperature terminal 4A side and the Joule heat generated by the current flowing through the conductor 8 are exhausted. As shown in FIG. 10, the low-temperature side lead 5 has an oxide superconducting conductor made of an oxide superconducting conductor such as an yttrium-based or bismuth-based conductor inside a hollow tube 7 made of a metal having a low thermal conductivity or an insulating material. The body 9 is stored, and a low-temperature helium gas GH is
e, a cooling passage is formed, and the temperature of the oxide superconductor 9 is cooled to the liquid nitrogen temperature (about 77 K) or less,
The oxide superconductor 9 is in a superconducting state, the Joule heat is reduced to zero, the heat penetrating into the low-temperature terminal 5A side is small, and the consumption of liquid helium is small.
Is obtained.

[0005]

In the current lead 3 configured as described above, the oxide superconductor 9 rarely obtains a stable superconducting state from the beginning of energization.
In general, the current that can be supplied gradually increases while repeating a quenching phenomenon in which the superconducting state is locally broken and transitions to the normal conducting state, and then the superconducting state finally reaches a stable superconducting state. In addition, even when a stable superconducting state is reached, quench may occur at an unexpected time. By the way, the resistivity of the oxide superconductor 9 in the normal conducting state is 3 to 4 orders of magnitude higher than that of the copper material, and the thermal conductivity is 1/100 or less of that of low-temperature copper. When quench occurs in the oxide superconductor 9, excessive Joule heat is generated at the site where the quench occurs, and the oxide superconductor 9 locally overheats and burns because there is no escape of heat due to conduction inside the oxide superconductor 9. Things happen. If the oxide superconductor 9 burns out, not only can the current supply not be sustained, but also a large repair cost is required to disassemble and repair the current lead, and the superconducting coil device cannot be used during the repair period. Problems arise.

As a countermeasure, a bypass circuit including a power diode, a thyristor, a voltage non-linear resistance element and the like is added to both ends of the low-temperature side lead 5, and an increase in the potential drop of the oxide superconductor 9 due to quench is detected. Has been already proposed by the applicant of the present invention (Japanese Patent Application No. Hei.
No. 33269). However, in this method, it is necessary to add a bypass circuit component to the outside of the current lead, and there is a problem that the configuration of the current lead is complicated, and there is a need for improvement.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a current lead having a simple structure in which current supply to a superconducting coil can be continued by avoiding burning due to quenching of an oxide superconductor on a low-temperature side lead, and heat intrusion is reduced. It is in.

[0008]

According to the present invention, an exciting current from an external power supply is passed through a superconducting coil housed in a vacuum insulated container and kept at a very low temperature. The current lead consists of a series connection of a high-temperature side lead made of a good conductive metal and a low-temperature side lead made of an oxide superconductor, and is cooled by a low-temperature refrigerant gas. About 1 / of copper
A bypass conductor made of a low thermal conductive metal as small as 100 or less is provided in parallel with the oxide superconductor, and the bypass conductor is formed of a cylindrical conductor that houses the oxide superconductor, A hollow tube through which a low-temperature refrigerant gas flows is used, and the bypass conductor is a rod-shaped conductor housed in the hollow tube together with the oxide superconductor. Is made of a conductor wound on the outer diameter side of the hollow tube containing the oxide superconductor.

[0009]

In the structure of the present invention, a low-thermal-conductivity bypass conductor is provided on the low-temperature side lead in parallel with the oxide superconductor, so that the oxide superconductor maintains a superconducting state. In the flowing state, current flows only in the oxide superconductor, and since the bypass conductor has low thermal conductivity, heat entering from the high-temperature side lead side is suppressed. If the quench occurs in the oxide superconductor for some reason and the resistance of the oxide superconductor increases rapidly, the current is commutated to the bypass conductor side and the current of the oxide superconductor is drastically reduced. As a result, heat generation of the oxide superconductor is suppressed and its burning is avoided.

[0010] Further, if a cylindrical low thermal conductivity metal surrounding the oxide superconductor is used as the bypass conductor and a low-temperature refrigerant gas is circulated therein, the bypass conductor also serves as a hollow tube. The configuration of the current lead can be simplified.
The same effect as described above can also be obtained by adopting a configuration in which the bypass conductor is made of a rod-shaped low heat conductive metal and housed in a conventional hollow tube together with the oxide superconductor.

In addition, the same function as described above can be obtained by forming the bypass conductor with a low thermal conductive metal in the form of a coil spring wound on the outer diameter side of a hollow tube containing the oxide superconductor. By arbitrarily selecting the cross-sectional area and the number of turns, it is possible to set the optimum electric resistance value and heat resistance value. In addition, when stainless steel is used as the low thermal conductive metal, the electrical resistivity of the stainless steel is one to two orders of magnitude lower than that of the oxide superconductor in a normal temperature state, and the thermal conductivity is about one hundredth smaller than that of copper. It can be an ideal bypass conductor.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
FIG. 1 is a sectional view schematically showing a current lead using an oxide superconductor according to an embodiment of the present invention, and FIG.
FIG. 9 is a cross-sectional view at a position C, and the same components as those in the related art are denoted by the same reference numerals, and redundant description is omitted. In these figures, a current lead 13 is formed as a series connection of a high-temperature side lead 4 and a low-temperature side lead 15, and a low-temperature helium gas GHe flowing therethrough from the low-temperature terminal 5A to the normal-temperature terminal 4A. Cooled. The low-temperature side lead 15 is composed of, for example, an oxide superconductor 9 divided into a plurality of strips and a cylindrical bypass conductor 17 surrounding the same.
A and 15B are electrically conductively coupled to each other, and a cooling passage made of low-temperature helium gas GHe is formed in a gap between the two. As described above, the bypass conductor 17 also has the function of the hollow tube 7 in FIG. Further, by using a stainless steel material, which is a metal having a small thermal conductivity, as the cylindrical bypass conductor 17, the resistivity is lower by one to two orders of magnitude than that of the oxide superconductor in a normal conducting state, and the thermal conductivity is reduced. Is formed about two orders of magnitude lower than that of the copper material.

Therefore, the obtained low-temperature lead 15 is
Since the bypass conductor 17 also serves as a hollow tube, the configuration of the current lead can be simplified. Also, utilizing the fact that the resistivity of the stainless steel material is one or two orders of magnitude lower than that of the oxide superconductor 9 in the normal conducting state, the quenching corresponds to the increase in the resistance of the oxide superconductor 9 and Most of the current flowing to the bypass conductor 17 is reduced to reduce heat generation at the quench portion of the oxide superconductor 9 and avoid burning of the oxide superconductor 9. Furthermore, the bypass conductor 17 also serves as a hollow tube, and the thermal conductivity of stainless steel is 1/1 times that of copper.
Since the temperature is not more than 00, the infiltration heat from the high-temperature side lead 4 side due to the provision of the bypass conductor 17 is suppressed, so that burning of the oxide superconductor 9 due to quench is prevented and current is supplied to the superconducting coil. Can be obtained, and a current lead with less intrusion heat and a simple configuration can be obtained.

FIG. 3 is a sectional view of a low-temperature side lead portion showing a different embodiment of the present invention. An oxide superconductor in which a low-temperature side lead 25 is housed in a hollow tube 7 and both ends are conductively coupled to each other. 29 and a bypass conductor 27 made of a stainless steel material in the form of a round bar, which is different from the above-described embodiment. Even if a quench occurs in the oxide superconductor 29 of the low-temperature side lead 25, the bypass conductor 27 By this, the burnout of the oxide-based superconductor 29 can be prevented, the supply of current to the superconducting coil can be continued, and a current lead with less heat intrusion and a simple configuration can be obtained.

FIG. 4 is a cross-sectional view of a low-temperature side lead portion showing another embodiment of the present invention. A low-temperature side lead 35 is housed in a hollow tube 7 and has a rectangular rod shape in which both ends are electrically connected to each other. This embodiment is different from the above-described embodiment in that it is constituted by an oxide superconductor 39 and a bypass conductor 37 made of a rectangular rod-shaped stainless material, and the same operation and effect as in the above-described embodiment can be obtained. .

FIG. 5 is a sectional view schematically showing a current lead using an oxide superconductor according to another embodiment of the present invention.
FIG. 6 is a longitudinal sectional view of the low-temperature lead of FIG. 5, and FIG.
FIG. 9 is a cross-sectional view of D, and the same members as those in FIG. The current lead 43 includes a high-temperature side current lead 4 and a low-temperature side current lead 45, and the low-temperature side current lead 45 is a low-temperature side current lead 5 shown in FIG.
A bypass conductor 47 in the form of a spring coil is wound around the outer diameter side of the coil. The bypass conductor 47 is also made of stainless steel similarly to the aforementioned bypass conductors 17, 27 and 37, and the upper portion thereof is a conductive coupling portion 15A. The lower portion is connected to the low-temperature terminal 5A.

The bypass conductor 47 is wound around the outer diameter side of the hollow tube 7 containing the oxide superconductor 9 and through which the helium gas GHe is passed with a predetermined number of turns to form a spring coil. By selecting an appropriate value for the cross-sectional area and the number of turns of the conductor, the electric resistance value and the heat resistance value thereof can be set to optimal values. In these figures, the bypass conductor 47 is made of a single stainless steel material having a circular cross section, but this is not a limitation.
The cross-sectional shape may be a plate shape. Further, the number of conductors may be plural.

Although the above-described bypass conductors are all described as using stainless steel, this stainless steel has a much lower thermal conductivity than copper, as described above.
The resistivity is much smaller than that of the oxide superconductor at room temperature, which is a characteristic necessary for a bypass conductor. Therefore, the function as the bypass conductor can be sufficiently exhibited by adopting the stainless material as the material of the bypass conductor. However, the material of the bypass conductor is not limited to stainless steel, and any metal material other than stainless steel can be used as long as the metal material satisfies the small amount of heat and small electric resistance required for the bypass conductor. .

[0019]

As described above, according to the present invention, by providing a bypass conductor made of a metal having low thermal conductivity in parallel with the oxide superconductor of the low-temperature side lead, the oxide superconductor maintains the superconducting state. Under normal flow conditions, current flows only through the oxide superconductor.However, if the resistance of the oxide superconductor suddenly increases due to quenching, the resistance of the bypass conductor is much smaller than the resistance. The flowing current is diverted to the bypass conductor, the current flowing in the oxide superconductor is drastically reduced, the heat generation is suppressed, and the burning can be avoided.In a normal state, the bypass conductor has low thermal conductivity, so high temperature The effect is obtained that the heat entering from the side of the side lead can be suppressed.

The bypass conductor is made of a cylindrical low heat conductive metal surrounding the oxide superconductor, a low-temperature refrigerant gas is circulated inside the bypass superconductor, and both ends of the bypass conductor are connected to both ends of the oxide superconductor. With the configuration of conducting coupling, the effect that the configuration of the current lead can be simplified because the bypass conductor also serves as the hollow tube is obtained. Also,
The same effect as described above can be obtained by adopting a configuration in which the bypass conductor is made of a rod-like low heat conductive metal such as a round bar or a square bar and provided in the hollow tube together with the oxide superconductor. In addition, by forming the bypass conductor from a coil spring-like low thermal conductive metal wound on the outer diameter side of the hollow tube containing the oxide superconductor, the same effect as described above can be obtained, and the cross-sectional area can be reduced. By arbitrarily selecting the number of turns, it is possible to obtain an effect that an optimal electric resistance value and thermal resistance value can be set.

Further, by adopting stainless steel as the low thermal conductive metal, the electrical resistivity is one to two orders of magnitude lower than that of the oxide superconductor in a normal temperature state, and the thermal conductivity is about one hundredth smaller than that of copper. Therefore, since the material is suitable for the bypass conductor, the bypass conductor can more reliably obtain the above-described effects.

[Brief description of the drawings]

FIG. 1 is a simplified cross-sectional view of a current lead using an oxide superconductor according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line CC in FIG.

FIG. 3 is a sectional view of a low-temperature side lead portion showing a different embodiment of the present invention.

FIG. 4 is a cross-sectional view of a low-temperature side lead portion showing another embodiment of the present invention.

FIG. 5 is a simplified sectional view of a current lead using an oxide superconductor according to another embodiment of the present invention.

FIG. 6 is a longitudinal sectional view of the low-temperature side lead of FIG. 5;

FIG. 7 is a sectional view taken along line DD of FIG. 6;

FIG. 8 is a simplified cross-sectional view showing a conventional structure of a current lead of a superconducting magnet device.

FIG. 9 is an enlarged cross-sectional view showing an AA part of FIG. 8;

FIG. 10 is an enlarged cross-sectional view showing a BB portion of FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Superconducting coil 2 Vacuum heat insulation container 3,13,43 Current lead 4 High temperature side lead 5,15,25,35,45 Low temperature side lead 15A, 15B Conductive coupling part 17,27,37,47 Bypass conductor 7 Hollow tube 8 Good electric conductor 9,29,39 Oxide superconductor 13 Vacuum insulated container GHe Helium gas He Liquid helium

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Ikuo Ito 1-1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Toshio Ude 1, Tanabe Nitta, Kawasaki-ku, Kawasaki-ku, Kanagawa Prefecture No. 1 Fuji Electric Co., Ltd. (56) References JP-A-63-292610 (JP, A) JP-A-1-109612 (JP, A) JP-A-5-343375 (JP, A) JP-A-5 −167107 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01L 39/02-39/04 H01L 39/14-39/16 H01F 6/00

Claims (4)

(57) [Claims] A current lead for passing an exciting current from an external power supply into a superconducting coil housed in a vacuum insulated container and kept at a cryogenic temperature comprises a high-temperature side lead made of a good conductive metal; A series member connected to a low-temperature side lead made of a body and cooled by a low-temperature refrigerant gas.
A current lead using an oxide superconductor, characterized in that a bypass conductor made of a low thermal conductive metal having a size as small as described below is provided in parallel with the oxide superconductor. 2. The method according to claim 1, wherein the bypass conductor is formed of a tubular conductor containing the oxide superconductor and serves as a hollow tube through which a low-temperature refrigerant gas flows. Current lead using oxide superconductor. 3. The current lead using an oxide superconductor according to claim 1, wherein the bypass conductor is formed of a rod-shaped conductor housed in a hollow tube together with the oxide superconductor. 4. The current using an oxide superconductor according to claim 1, wherein the bypass conductor comprises a conductor wound around the outer diameter side of the hollow tube containing the oxide superconductor. Lead.