JPH06231951A - Current lead of superconducting magnet - Google Patents

Abstract

PURPOSE:To realize a conductor constitution which makes possible the reduction of the sum of heat penetration by Joule heat and heat penetration by heat conduction. CONSTITUTION:Each of a plurality of conductors 39A constituting a main body part 34A of a current lead 3A is divided into a room temperature side conductor 391 and a low temperature side conductor 392 in a longitudinal direction, and each thereof is connected by a connection part. Thereby, different materials can be used for conductors 391, 392. There is a tendency that heat penetration through the conductors 39A by heat conduction is large at a temperature side, and that by Joule heat is large at a low temperature side. Heat conduction rate and residual resistivity are in a proportional relation: therefore, if a material of a small residual resistivity is used for the room temperature side conductor 391, heat penetration due to heat conduction is reduced because of small heat conduction rate, and if a material of large residual resistivity is used for the low temperature side conductor 392, Joule heat is reduced because of small resistivity at a low temperature. General amount of heat penetration is reduced in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current lead of a superconducting magnet for supplying electric power to the superconducting magnet in a cryogenic container from the outside.

[0002]

2. Description of the Related Art Generally, since a superconducting magnet is cooled by a cryogenic refrigerant such as liquid helium, it is housed in a vacuum container insulated by a liquid nitrogen shield or vacuum. Since the current lead supplies electric power to the superconducting coil maintained at a cryogenic temperature from the room temperature part, the Joule heat generation that generally occurs in the lead conductor and the so-called heat intrusion that penetrates from the room temperature part to the internal cryogenic part by heat conduction. In order to reduce the amount, a method of cooling by using low temperature helium gas in which liquid helium is evaporated is adopted. Therefore, if the amount of heat intrusion such as Joule heat or conduction heat is large, not only the amount of expensive liquid helium consumed becomes large, but also the characteristics of the superconducting magnet may be adversely affected.

FIG. 4 is a vertical sectional view of a general superconducting magnet. In this figure, the vacuum heat insulating container 1 includes a vacuum container 11, a liquid nitrogen shield 12, and a liquid helium container 13 from the outside.
The inside of the vacuum container 11 is maintained in vacuum, and the liquid nitrogen shield 12 is filled with liquid nitrogen.
Liquid helium 4 is enclosed in the liquid helium container 13, and the superconducting coil 2 is immersed therein. The current lead 3 is attached by penetrating the upper lid 15 in the service port 14 provided between the liquid helium container 13 and the vacuum container 11, and the upper end thereof is in the atmosphere and the terminal plate 33.
Is attached, and the lower end thereof is inside the liquid helium container 13 and is connected with the connection lead 21. The terminal plate 31 is connected to an external power source (not shown), and the connection lead 21 electrically connects the current lead 3 and the superconducting coil 2.

As will be described later, the current lead 3 is composed of the hollow tube shown in this figure and a plurality of conductors passing through it, and the helium gas 42 flowing from the lower end into the gap between them. The conductor cools as it rises through and discharges from the top. FIG. 5 is an elevational view including a rotation-illustrated sectional view showing details of the current lead 3 in FIG. In this figure, the current lead 3 is composed of a gas discharge pipe 32, a terminal plate 33, a main body portion 34, a low temperature side connection portion 35, and a low temperature terminal plate 36 from the top. As shown in the rotational sectional view, the main body 34 includes an insulating tube 37, a hollow tube 38, and a plurality of conductors 39 passing through the hollow tube 38 from the outer diameter side.
The helium gas 42 that has flowed in through a hole (not shown) of the low temperature connection portion 35 passes through the gap 381 between the conductors 39 and the conductor 3
Cool 9. The insulating tube 39 is the two current leads 3 of FIG.
It is provided to avoid electrical contact between or with the service port 14. The helium gas 42 flowing upward through the gap 381 in the hollow pipe 38 is discharged from the discharge pipe 32 to the atmosphere.

The conductor 39 is composed of a plurality of thin conductors in order to increase the contact area with the helium gas and enhance the cooling effect. The number of conductors 39 is determined by the current value and the length. That is, there are many
In other words, if the total cross-sectional area is large, the resistance value of the current lead decreases and the Joule heat generation amount decreases, but the heat penetration amount due to heat conduction from the room temperature portion increases. On the contrary, if the number is small, the amount of heat penetration from the room temperature portion can be reduced, but the resistance increases and the Joule heat generation amount increases. Conductor 39
In determining the number of lines, the optimum number and length are determined by comprehensively considering two contradictory matters.

[0006]

As the material of the conductor 39, copper, which is a good conductive metal, and, in particular, electrolytic copper having a large residual resistance ratio is used. The residual resistance ratio is the ratio of the electrical resistivity at room temperature to the electrical resistivity at extremely low temperature (4.2K). That is, the larger the residual resistance ratio of the metal, the smaller the electric resistance at cryogenic temperature, and the smaller the heat penetration due to Joule heat generation. The residual resistance ratio of copper greatly changes depending on the amount of impurities, and increases as the purity increases. In the case of electrolytic copper,
The range of 30 to 30,000 varies depending on the amount of impurities.

On the other hand, electrolytic copper has good electrical conductivity as well as good thermal conductivity. The thermal conductivity that determines the amount of heat penetration due to heat conduction has a correlation with the above-described residual resistance ratio, and a metal having a larger residual resistance ratio has a larger thermal conductivity. In order to minimize the amount of heat penetration from the conductor 39 of the current lead 3, it is ideal to reduce both the amount of heat penetration due to Joule heat generation and the amount of heat penetration due to heat conduction. That is,
As a material, a metal having a large residual resistance ratio and a small thermal conductivity is ideal, but as described above, the ideal residual metal does not exist due to the correlation between the residual resistance ratio and the thermal conductivity. is there.

An object of the present invention is to solve the above problems and provide a current lead having a conductor structure capable of minimizing the sum of heat intrusion due to Joule heat generation and heat intrusion due to heat conduction.

[0009]

In order to solve the above-mentioned problems, according to the present invention, a superconducting magnet for electrically connecting a superconducting coil housed in a vacuum heat insulation container and immersed in liquid helium to an external power source. In the current lead of, each of the plurality of conductors forming the main body of the current lead of this superconducting magnet is divided into a room temperature side conductor and a low temperature side conductor in the longitudinal direction, and these are connected by a connecting portion, It is assumed that a material with a small residual resistance ratio is used for the room temperature side conductor and a material with a large residual resistance ratio is used for the low temperature side conductor, and the number of conductors for the room temperature side conductor and the low temperature side conductor is different. , The normal temperature side conductor and the low temperature side conductor are connected via a connecting piece, and the normal temperature side conductor and the low temperature side conductor have the same number of conductors, and the connecting portions correspond to each other one to one. Made by pressure welding To.

[0010]

In the structure of the present invention, each of the plurality of conductors forming the main body of the current lead is divided into a room temperature side conductor and a low temperature side conductor in the longitudinal direction, and these are connected by a connecting portion. Allows different materials to be used for each conductor. When the conductors of the same material are used, the amount of heat penetration tends to be large due to heat conduction at room temperature and large due to Joule heat generation at low temperature, so the thermal conductivity is large when the residual resistance ratio is large. Therefore, if a material with a small residual resistance ratio is used for the room temperature side conductor, the thermal conductivity is small and the amount of heat penetration due to heat conduction is greatly reduced.
By using a material having a large residual resistance ratio for the low temperature side conductor, the resistivity at a low temperature is small, so the Joule heat generation is greatly reduced, and the amount of heat intrusion is comprehensively reduced.

Further, by setting the number of conductors of the room temperature side conductor and the temperature of the low temperature side conductor to be different from each other, it is possible to set a condition in which the amount of heat penetration is further reduced as compared with the case where the restriction that the number is the same is provided. . Further, by adopting the structure of the connecting portion that connects the room temperature side conductor and the low temperature side conductor via the connecting piece, it is possible to connect even if the number of both conductors is the same or different. Further, when the number of conductors of the room temperature side conductor and the number of conductors of the low temperature side are the same, the respective conductors can be pressure-welded at the connection portion in a one-to-one correspondence.

[0012]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is an elevational view of a current lead showing an embodiment of the present invention. The same members as those in FIG. 5 are designated by the same reference numerals and their detailed description will be omitted. The difference between the current lead 3A of FIG. 1 and the current lead 3 of FIG. 5 is that the conductor 39A passing through the main body 3A is the conductor 391 and 392 at the portion A of the figure as shown in the sectional view at the portion A.
The point is that it is connected to and. The conductor 391 on the normal temperature side, which is the upper side of the figure, uses electrolytic copper with a small residual resistance ratio, and the conductor 392 on the low temperature side, the lower side of the figure, uses electrolytic copper with a large residual resistance ratio.

FIG. 2 is an enlarged view of portion A in FIG. In this figure, only six conductors 39A are shown in the portion A, but in reality, the number is much larger as shown in FIG. In this figure, conductor 39A is conductors 391 and 39.
2 are connected to each other at a connecting portion 393. A suitable method for connecting the connection portion 393 is, for example, a pressure welding method in which both conductors are pressed and joined.

Assuming that the residual resistance ratio of the material of the conductor 391 is 3
0, the residual resistance ratio of the material of the conductor 392 is 100, and the total length of the conductor 39A is 700 mm,
The distribution of the lengths of the conductors 391 and 392 that minimizes the total heat intrusion amount can be easily obtained by calculation.
When 1 is 550 mm and the conductor 392 is 150 mm, the amount of heat penetration is minimum, and the amount of heat penetration of the current lead 3A is reduced to about 90% of the conventional case.

Since the numbers of the conductors 391 and 392 are the same in FIGS. 1 and 2, it is possible to connect each one. However, it is not inevitable that the numbers of the two must be the same, and different numbers can be adopted to further reduce the amount of heat penetration. FIG. 3 is an enlarged view of part A showing an embodiment of the present invention different from that of FIG. 2 is different from FIG. 2 in that the number of conductors 391 and the number of conductors 392 are different from each other, so that one-to-one connection cannot be made as in FIG. Therefore, a connection piece 394 is provided between the conductor 391 and the conductor 391 on the upper end surface of the connection plate 394.
2 is connected to the lower end surface of the connection piece 394, and the connection piece 3 is connected.
The configuration is such that the conductors 391 and 392 are connected via 94. With such a configuration, the conductor 3
The number of 91 and 392 can be freely selected.
Especially when the rated current is as large as 10 kA or more, the conductor 3
If the numbers of 91 and 392 are the same, it may not be possible to reduce the amount of heat penetration even if two types of conductors with different residual resistance ratios are used. Can be set, so that the configuration shown in FIG. 3 is adopted. Normally, as shown in FIG. 3, it is appropriate to make the number of conductors of the room temperature side conductor 391 smaller than that of the low temperature side conductor 392. In addition,
As a matter of course, even if the number is the same, as shown in FIG.
It is also possible to adopt a configuration in which the conductors 391 and 392 are connected via 94, and the selection is mainly determined in terms of manufacturing man-hours. Since the influence of the connection piece 394 on the heat penetration is small, ordinary electrolytic copper may be used, and the value of the residual resistance ratio does not pose a problem.

The number of different residual resistance ratios of the conductor 39 is not limited to two. It is also possible to adopt a configuration in which the amount of heat penetration is further reduced by using conductor materials having three or more different residual resistance ratios. However, increasing the number of different materials increases the number of connecting parts, increasing the number of manufacturing steps and eventually increasing the cost of the current lead. Therefore, it is necessary to consider not only the amount of heat intrusion but also comprehensive consideration.

When a different number of conductors is used, the gap 381 with the hollow tube 38 becomes large and the flow rate of the helium gas decreases at the conductor with the smaller number of conductors, and the cooling effect decreases to a nonnegligible level. Problems can arise. In such a case, in order to reduce the total cross-sectional area of the gap, a configuration is adopted in which a dummy metal such as a stainless steel rod that is not related to electricity conduction or heat conduction is arranged along the portion of the conductor having a small number of conductors. .

[0018]

As described above, according to the present invention, each of the plurality of conductors forming the main body of the current lead is divided into a room temperature side conductor and a low temperature side conductor in the longitudinal direction, and these are connected by a connecting portion. By configuring, the materials used for each conductor can be different. The heat invasion through these conductors tends to be largely due to heat conduction at room temperature and due to Joule heat generation at low temperature, so the thermal conductivity and residual resistance ratio have the above-mentioned correlation. Therefore, if a material with a small residual resistance ratio is used for the room temperature side conductor, the thermal conductivity is small, so the amount of heat penetration due to heat conduction is greatly reduced, and if a material with a large residual resistance ratio is used for the low temperature side conductor, Since the resistivity at that time is small, the amount of heat intrusion due to Joule heat generation is greatly reduced, and as a result, the overall amount of heat intrusion is reduced.

Further, by making the number of conductors of the room temperature side conductor and the number of conductors of the low temperature side different, it is possible to obtain an effect that the amount of heat penetration can be further reduced as compared with the case where the limitation that the number is the same is provided. . Further, by adopting the configuration of the connecting portion that connects the room temperature side conductor and the low temperature side conductor through the connecting piece, it is possible to easily connect both the same number or different number of conductors, and When the numbers are the same, it is possible to adopt a connection by pressure welding by associating the respective conductors in the connecting portion in a one-to-one correspondence.

[Brief description of drawings]

FIG. 1 is an elevation view of a current lead showing an embodiment of the present invention.

FIG. 2 is an enlarged view of part A of FIG.

FIG. 3 is an enlarged view of part A showing an embodiment of the present invention different from that of FIG.

FIG. 4 is a vertical sectional view of a general superconducting magnet.

FIG. 5 is an elevational view including a rotational sectional view showing details of the current lead in FIG.

[Explanation of symbols]

 1 Vacuum Insulation Container 11 Vacuum Container 12 Liquid Nitrogen Shield 13 Liquid Helium Container 14 Service Port 2 Superconducting Coil 3 Current Lead 34 Main Body 34A Main Body 34B Main Body 38 Hollow Tube 381 Gap 39 Conductor 39A Conductor 391 Normal Temperature Side Conductor 392 Low Temperature Side Conductor 393 Connection part 394 Connection piece

Claims (4)

[Claims] 1. A current lead of a superconducting magnet for electrically connecting a superconducting coil housed in a vacuum heat insulating container and immersed in liquid helium to an external power source, wherein a plurality of main parts of the current lead of the superconducting magnet are formed. Each of the conductors is divided into a room temperature side conductor and a low temperature side conductor in the longitudinal direction, and these are connected at the connecting part. A material with a small residual resistance ratio is used for the room temperature side conductor, and a low resistance for the low temperature side conductor. A current lead for a superconducting magnet, which is made of a material having a large ratio. 2. The current lead for a superconducting magnet according to claim 1, wherein the number of conductors of the room temperature side conductor is different from that of the low temperature side conductor. 3. The current lead for a superconducting magnet according to claim 1, wherein the room temperature side conductor and the low temperature side conductor are connected via a connecting piece. 4. The superconducting magnet according to claim 1, wherein the room temperature side conductor and the low temperature side conductor have the same number of conductors, and the connecting portions are pressure-welded so as to correspond to each other one to one. Current lead.