JPH08195309A - Superconducting current lead - Google Patents

Abstract

PURPOSE: To increase the critical current density of the main body of a superconducting current lead by providing the connecting part of a copper lead element and a high temperature conducting lead element at the main body of the superconducting current lead between a cooling means and the terminal on the side of a superconducting coil. CONSTITUTION: A connecting part 13 of a copper lead element 11a and a high temperature superconducting lead element 11b in a main body 11 of a superconducting current lead contained inside a gas pipe 5b is provided at a part lower than a bottom part of a liquid nitrogen container 12. The connecting part 13 is connected by, e.g. solder and cooled by helium gas 9 generated by the evaporation of liquid helium contained in a liquid helium container 2. Therefore, the temperature of the high-temperature end of the high-temperature superconducting lead element 11b, i.e., the connecting part 13, during the operation becomes the temperature lower than 77k, which is the temperature in the liquid nitrogen container 12. Thus, the critical current density of the main body of the superconducting current lead can be increased, and the magnetic-field characteristics of a superconducting coil can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting current lead for supplying an electric current from an exciting power source placed in a room temperature environment to a superconducting coil immersed in liquid helium contained in a liquid helium container. In particular, the present invention relates to a superconducting current lead that can cope with an increase in current capacity.

[0002]

2. Description of the Related Art Generally, a superconducting current lead is used as a means for supplying an electric current to a superconducting coil that is immersed and cooled in a liquid helium container from an exciting power source placed in a room temperature environment.

A conventional example of a superconducting current flow lead will be described below with reference to FIG. Superconducting coil 1 is immersed in liquid helium 3 contained in liquid helium container 2. The liquid helium container 2 is housed in an adiabatic vacuum container 4 made of stainless steel or the like. Further, a gas pipe 5b is connected to the liquid helium container 2, and the helium gas 9 generated by the liquid helium 3 in the liquid helium container 2 being vaporized is released from the gas pipe 5b to the outside of the adiabatic vacuum container 4. A branch pipe 18 is provided for this purpose. The gas pipe 5b is also connected to the liquid nitrogen container 12, and the liquid nitrogen container 12 is further provided with a gas pipe 5a communicating with the outside of the heat insulating vacuum container 4.

The superconducting current lead body 11 has a high temperature superconducting lead element 11b connected to the superconducting coil side terminal 8 and a copper lead element 11a connected to the room temperature side environmental terminal 7. The high temperature superconducting lead element 11b is made of a high temperature superconducting material which exhibits a superconducting state at a liquid nitrogen temperature or higher, while the copper lead element 11a is made of copper or a copper alloy material.

The high temperature superconducting lead element 11b connected to the superconducting coil side terminal 8 is cooled by the helium gas 9 which evaporates in the gas pipe 5b, and then the liquid nitrogen container 12
Among them, it is connected to the copper lead element 11a at the connecting portion 13. On the other hand, the copper lead element 11a is housed in the gas pipe 5a, guided to the ambient temperature side environmental terminal 7 while being cooled by the nitrogen gas 14 supplied from the liquid nitrogen container 12, and connected to a power cable (not shown).

In this case, the high temperature superconducting lead element 11b maintains the superconducting state, does not generate Joule heat and uses the ceramic material which is the high temperature superconducting material. Also few. Therefore, the amount of heat entering the superconducting coil is greatly reduced in the superconducting current lead body using the high-temperature superconducting lead element 11b, as compared with the whole body composed of the copper lead element 11a. A superconducting current lead using such a high temperature superconducting lead element 11b has already been disclosed in Japanese Patent Publication No. 5-11.
It is also disclosed in Japanese Patent No. 647.

[0007]

In the conventional superconducting current lead described above, the intermediate connecting portion 13 is placed in the liquid nitrogen 10.
Although it is possible to prevent heat from entering from the room temperature side environment terminal 7 side by setting the critical temperature density of the high temperature superconducting lead element when a magnetic field is applied as long as the operating temperature is up to 77K which is the liquid nitrogen temperature. Is too small. The critical current density is the maximum current density that can flow in the superconducting material under a certain operating temperature and operating magnetic field. When this critical current density becomes small, a thick read element is required to pass a current for generating a necessary superconducting magnetic field, which increases heat penetration due to heat conduction.

FIG. 5 shows an example of temperature characteristics of the critical current density jc of the high temperature superconducting lead element when the operating magnetic field is used as a parameter. According to FIG. 5, jc is about 10000 A / cm ² when the operating magnetic field is 0 Tesla at 77 K, but is significantly reduced at 0.5 Tesla, and is below 500 A / cm ² . That is, it can be seen that the critical current density jc decreases as the strength of the operating magnetic field increases. Therefore, for the critical current density jc of the high-temperature superconducting lead element, as long as the operating temperature is fixed at 77K, for example, when the strength of the leakage magnetic field from the superconducting coil exceeds 0.5 tesla, the critical current density becomes small, and in practice Designing superconducting current lead becomes difficult.

On the other hand, the leakage magnetic field value generated by the superconducting coils manufactured up to now is more than 0.5 tesla in many cases, and it can be said that it is rather general. Therefore, the superconducting current flow lead to which the high temperature superconducting lead element 11b is currently applied has a drawback that it can be applied only to a special coil having a small leakage magnetic field, that is, a small magnetic energy.

The present invention has been made in view of the above conventional circumstances, and an object thereof is to make it possible to keep the critical current density of the superconducting current lead body large even if the leakage magnetic field value of the superconducting coil is large. An object of the present invention is to provide a superconducting current lead capable of improving the magnetic field characteristics of the superconducting coil.

[0011]

In order to achieve the above-mentioned object, the superconducting current lead of the present invention is a room temperature environment for a superconducting coil immersed in liquid helium contained in a liquid helium container. In order to supply a current from the excitation power source placed below, a copper lead element made of copper or a copper alloy material connected to the room temperature environment side terminal and a superconducting coil side terminal provided in the liquid helium container are connected. A superconducting current lead having a high-temperature superconducting lead element made of a high-temperature superconducting material that exhibits a superconducting state at a liquid nitrogen temperature or higher. Cooling means for cooling the main body using liquid nitrogen, and connecting this cooling means and the liquid helium container to store the superconducting current lead body. And a gas pipe for cooling the superconducting current flow lead body by flowing liquid helium from the liquid helium container to the branch pipe along the way, and the liquid helium container copper lead element and high temperature superconducting lead element The superconducting current lead is provided with a connecting portion on the superconducting current lead body between the cooling means and the terminal on the superconducting coil side.

According to a second aspect of the present invention, the cooling means according to the first aspect is a superconducting current lead which is a liquid nitrogen container for containing liquid nitrogen. The invention described in claim 3 is claim 1
The described cooling means is a superconducting current lead which is a cooling pipe for circulating and circulating the liquid nitrogen refrigerant generated in the refrigerator. The invention according to claim 4 is the superconducting current lead according to any one of claims 1 to 3, wherein a cooling fin is provided in the connecting portion.

[0013]

In the superconducting current lead of the above construction, since the connecting portion between the copper lead element and the high temperature superconducting lead element is provided closer to the superconducting coil side terminal than the cooling means is arranged, the liquid supplied into the gas pipe is The helium gas from the helium container cools the high temperature superconducting lead element to a temperature equal to or lower than the temperature of the liquid nitrogen contained in the liquid nitrogen container.

[0014]

The first embodiment of the superconducting current lead according to the present invention will be described below.
The embodiment will be described with reference to FIG. FIG. 1 is a sectional view showing a first embodiment of a superconducting current lead according to the present invention,
The same parts as those in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted. In the superconducting current lead body 11 housed inside the gas pipe 5b, the connecting portion 13 between the copper lead element 11a and the high temperature superconducting lead element 11b is provided below the bottom of the liquid nitrogen container 12. The connection portion 13 is connected by, for example, solder, and is cooled by the helium gas 9 generated by evaporation of the liquid helium 3 contained in the liquid helium container 2. The helium gas 9 circulates in the gas pipe 5b and is discharged from the branch pipe 18 to the outside of the adiabatic vacuum container 4. Therefore, the high temperature end of the high temperature superconducting lead element 11b, that is, the operating temperature of the connecting portion 13 is lower than the temperature in the liquid nitrogen container 12, which is 77K.
The detailed position of the connection portion 13 is determined by the design of the entire superconducting current lead body based on the critical current density characteristics and the leakage magnetic field value of the high temperature superconducting lead element 11b to be used.

In the superconducting current flow lead thus constructed, the operating temperature of the connecting portion 13 can be made lower than before, and therefore, a large critical current density Jc value can be obtained even in a leakage magnetic field generated by a large-scale coil. It is possible to obtain.

In this case, as in the prior art, as shown in FIG. 4, the connecting portion 13, that is, the high temperature superconducting lead element 11b is used.
A larger amount of helium gas 4 for cooling is required than in the case where the high temperature end of is maintained at the liquid nitrogen temperature of 77K. Therefore, the cooling cost as a current lead increases accordingly. However, as shown in FIG. 5, in general, the high temperature superconducting material can significantly increase the critical current density Jc by slightly lowering the operating temperature from 77K. Therefore, even if the above cooling cost increase is taken into consideration, an effective superconducting current lead can be obtained. It can be realized. Furthermore, it is possible to improve the magnetic field characteristics of the superconducting coil by increasing the critical current density.

Next, the second superconducting current lead according to the present invention will be described.
The embodiment will be described with reference to FIG. FIG. 2 is a sectional view showing a second embodiment of the superconducting current flow lead according to the present invention. The same parts as those in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, a cooling fin 15 is provided in the copper lead element 11a housed inside the gas pipe 5b, and the cooling effect of the helium gas 9 against the Joule heat generated in this portion and the invasion heat due to heat conduction is enhanced to thereby improve the superconducting current flow lead. The cooling efficiency of the main body 11 is improved. Since the cooling efficiency of the superconducting current lead body 11 is improved, the critical current density of the high temperature superconducting lead element 11b can be increased as in the first embodiment, and the magnetic field characteristics of the superconducting coil 1 can be improved. You can

Next, the third superconducting current lead according to the present invention will be described.
The embodiment will be described with reference to FIG. FIG. 3 is a sectional view showing a third embodiment of the superconducting current flow lead according to the present invention. The same parts as those in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, instead of the liquid nitrogen container 12, a cooling pipe 17 is wound around the copper lead element 11a,
In this method, the liquid nitrogen refrigerant 16 generated by an external refrigerator is circulated and cooled. In this case, since the liquid nitrogen container 12 is not used, the structure is simplified, and at the same time, it is not necessary to supplement the liquid nitrogen 10. Also in this embodiment, as in the first and second embodiments, it is possible to improve the magnetic field characteristics of the superconducting coil 1 as the critical current density of the high temperature superconducting lead element 11b increases.

[0019]

As described above, in the superconducting current lead of the present invention, the decrease of the critical current density of the superconducting current lead body due to the magnetic field leaking from the superconducting coil is suppressed, and the critical current density of the superconducting current lead body is increased. By doing so, the magnetic field characteristics of the superconducting coil can be improved.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view showing a first embodiment of a superconducting current lead according to the present invention.

FIG. 2 is a schematic vertical sectional view showing a second embodiment of a superconducting current lead according to the present invention.

FIG. 3 is a schematic vertical sectional view showing a third embodiment of a superconducting current lead according to the present invention.

FIG. 4 is a configuration diagram showing a conventional example of a superconducting current lead.

FIG. 5 is a temperature characteristic diagram of the critical current density of the high temperature superconducting lead element using the operating magnetic field as a parameter.

[Explanation of symbols]

1 ... Superconducting coil 2 ... Liquid helium container 3 ... Liquid helium 4 ... Adiabatic vacuum container 5a, 5b ... Gas pipe 7 ... Room temperature side environment terminal 8 ... Superconducting coil side terminal 9 ... Helium gas 10 ... Liquid nitrogen 11 ... Superconducting current lead body 11a ... Copper lead element 11b ... High temperature superconducting lead element 12 ... Liquid nitrogen container 13 ... Connection part 14 ... Nitrogen gas 15 ... Cooling fin 16 ... Refrigerant 17 ... Cooling pipe 18 ... Branch pipe

Claims (4)

[Claims] 1. A superconducting current lead body is connected to the room temperature environment side terminal as a superconducting current lead body in order to supply a current from an exciting power supply placed in a room temperature environment to a superconducting coil immersed in liquid helium contained in a liquid helium container. A copper lead element made of copper or a copper alloy material and a high temperature superconducting lead element made of a high temperature superconducting material connected to the superconducting coil side terminal provided in the liquid helium container and exhibiting a superconducting state at a liquid nitrogen temperature or higher. In the superconducting current lead, cooling means is provided on the way from the room temperature environment side terminal of the superconducting current lead body to the superconducting coil side terminal to cool the copper lead element using liquid nitrogen, and the cooling means and the liquid helium. The container is connected to accommodate the high temperature superconducting lead element, and a branch pipe is provided in the middle thereof, and the liquid helium is placed in the branch pipe. A gas tube for cooling the high temperature superconducting lead element by circulating liquid helium from the container, and connecting the copper lead element and the high temperature superconducting lead element to the superconducting current lead between the cooling means and the superconducting coil side terminal. A superconducting current lead that is provided on the main body. 2. The superconducting current lead according to claim 1, wherein the cooling means is a liquid nitrogen container containing liquid nitrogen. 3. The superconducting current lead according to claim 1, wherein the cooling means is a cooling pipe for circulating and circulating a refrigerant generated in a refrigerator. 4. The superconducting current lead according to claim 1, wherein the connecting portion is provided with a cooling fin.