JPH07335422A - Current lead for superconductive device - Google Patents

Abstract

PURPOSE:To eliminate a manufacturing step such as a step to make a new outer bypass. CONSTITUTION:A superconducting current lead is composed of a bar lead conductor 1 and a pipe 2 in larger diameter than the conductor to pass herium between them. Besides, a thermal anchor 18 using a liquid nitrogen is provided on a part of the current lead 1, the pipe 2 is covered with a metallic member 6 so that liquid nitrogen running from a liquid nitrogen piping 5a to 5b may be circulated between another metallic member 4 to cool down the pipe 2. On the other hand, the inside part of the current lead increasing the thickness of the lead conductor 1 is made closely adhere to the pipe 2 through the intermediary of an insulating material 3, besides, a vent hole 8 is provided as a path of helium to the thermal anchor part 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a current lead for a superconducting device, which is required to have little heat intrusion because it is operated for a long time such as an MRI device.

[0002]

2. Description of the Related Art Since a superconducting device is mainly used in a laboratory, it consumes a large amount of expensive liquid helium when it is operated for a long time, and it has been experimented at a huge cost.
However, in recent years, due to the commercialization of superconducting magnets such as MRI devices, cost reduction is also required for superconducting technology. As a result, there is more opportunity for the superconducting device to be disconnected from the power supply and used in persistent current mode. In these devices, liquid helium, which is cumbersome to handle, cannot be supplied from the outside during operation, so it is necessary to reduce the evaporation amount of liquid helium for long-term continuous operation.

In a superconducting device, a current lead is used as a means for supplying a current from an exciting power supply placed at room temperature to a superconducting coil that is immersed and cooled in liquid helium. It is well known that in a superconducting device, most of the invasion of heat from the outside is the intrusion of heat from the current leads.

Conventionally, in order to reduce the invasion of heat from the current lead, a method of installing the lead conductor inside the pipe and passing the vaporized helium gas between the lead conductor and the pipe to cool the lead conductor has been proposed. Are known. Further, a method of cooling the lead conductor by forming the lead conductor itself into a pipe shape and passing the evaporated helium gas into the pipe is also well known.

As a modification of this method, Japanese Patent Publication No.
FIG. 5 shows an example disclosed in Japanese Patent Laid-Open No. 11647. There is a liquid helium container 12 in the cryostat 19,
Superconducting coil 10 is immersed in liquid helium 11. A current is supplied to the superconducting coil 10 from the lead conductor 1. The lead conductor 1 is covered with a pipe 2, and a liquid nitrogen container 14 containing liquid nitrogen 15 in the middle thereof is provided.
Is installed. On the higher temperature side than the liquid nitrogen container 14, the nitrogen gas 17 passes between the lead conductor 1 and the pipe 2 to cool the lead conductor 1. Helium gas 16 is passed from the end on the side of the superconducting coil to the nitrogen container 14, and is discharged from the helium gas pipe 13.

This method aims at reliably lowering the temperature of liquid nitrogen at a certain portion of the lead conductor. If the lead conductor is cooled with vaporized helium gas only, as in the first method, the gas is below the liquid nitrogen temperature,
Since the heat capacity of helium gas is small, the temperature difference between the lead conductor and helium gas is large, and when the heat generation of the lead conductor is large, the temperature of the lead conductor becomes higher than the liquid nitrogen temperature. Therefore, in the example shown in FIG. 5, liquid nitrogen having a large heat capacity is used to surely lower the temperature of the lead conductor to the temperature of liquid nitrogen, thereby reducing the penetration of heat from the lead conductor.

[0007]

In the case of a superconducting device that operates for a long time, the evaporation amount of liquid helium regulates the operating time of the product, so the less heat that enters the liquid helium system, the better. Since it is not enough to cool the current lead with the evaporated helium gas, it is necessary to provide a thermal anchor using liquid nitrogen in the middle of the lead.

However, the example introduced in Japanese Patent Publication No. 5-11647 has the following problems. Putting a liquid nitrogen container in the middle of the lead as shown in Fig. 5 makes the product easier to use,
It is disadvantageous in terms of reliability and miniaturization. Further, in this method, since the helium gas bypass is not provided in the anchor portion, the lead conductor on the higher temperature side than the cooling point by liquid nitrogen is cooled with nitrogen gas. Although the helium gas 16 has a lower temperature than the nitrogen gas 17, it does not contribute to the cooling of the high temperature side of the lead conductor 1 and is released to the outside, so that the cooling efficiency is poor.

Therefore, in order to keep the cooling by both the helium gas and the thermal anchor, it is necessary to indirectly cool the lead conductor inside the pipe with a metal member cooled with liquid nitrogen and to provide a helium gas bypass. is there. However, this causes the structure of the thermal anchor portion to become very complicated, leading to a decrease in reliability. Further, if the bypass is provided outside the pipe, the helium gas passes through the outside of the reed and is warmed up, and the anchor portion cannot be cooled by the helium gas.

The object of the present invention is to secure a cooling capacity,
An object of the present invention is to provide a current lead for a superconducting device having a simple structure.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and is characterized in that a lead conductor is passed through a pipe having a larger diameter, and a space between the pipe and the lead conductor is provided. This is because a thermal anchor having the structure described below is provided in the middle of the current lead configured so that a coolant such as helium gas passes.

(1) The thickness of a part of the lead conductor is increased to make contact with the outer pipe through an insulating material. A coolant passage is provided in the thickened portion of the lead conductor, and the pipe on the outside thereof is cooled with a metal member cooled with liquid nitrogen.

(2) A pipe-shaped lead conductor is used. The thickness of a part of the lead conductor is increased to make contact with the outer pipe through an insulating material. Holes are made in the pipe-shaped lead conductors at both ends of the portion. Further, a plug is provided on the outer side of the hollow portion of the pipe-shaped lead conductor. The pipe outside the thickened portion is cooled with a metal member cooled with liquid nitrogen.

(3) A part of the outer pipe is cut out,
The inner lead conductor is directly cooled by the metal member cooled by liquid nitrogen through the insulating material. The outer pipe and its metal member are joined together, and a coolant passage is provided in the metal member.

(4) A pipe-shaped lead conductor is used. A part of the outer pipe is cut out, and the inner lead conductor is directly cooled by a metal member cooled with liquid nitrogen through an insulating material. The outer pipe and the metal member are joined. Holes are made in the pipe-shaped lead conductors at both ends of the metal member. Further, a plug is provided on the outer side of the hollow portion of the pipe-shaped lead conductor.

[0016]

In the present invention, attention was paid to bypassing the refrigerant such as helium gas in the thermal anchor portion. In a normal current lead, the refrigerant passes between the lead conductor and the outer pipe, but at the anchor part, the cooling metal member covers the lead conductor, so there is no ventilation passage, and the structure becomes complicated if a bypass is provided. Become. Therefore, in the present invention, the refrigerant bypass is provided by the method described above.

In (1), since the thickness of the lead conductor is increased and brought into contact with the outer pipe and the pipe is cooled by the metal member, cooling by the thermal anchor can be secured. Moreover, since an insulating material is interposed between the conductor and the outer pipe, no current flows in the outer pipe. Further, since the vent passage of the coolant such as helium gas is provided in the lead conductor in the portion where the thickness of the metal member is increased, the coolant such as helium gas cools the anchor portion and bypasses to the high temperature side without warming in the anchor portion. be able to. As a result, cooling of the conductor with a coolant such as helium gas can be ensured. Further, since the ventilation hole is simply provided as a bypass for the refrigerant, it is not necessary to newly make a bypass and it is not necessary to process the outer pipe, so that the structure of the thermal anchor portion can be simplified.

In (2), since the thickness of the lead conductor is increased and brought into contact with the outer pipe and the pipe is cooled by the metal member, the cooling by the thermal anchor can be secured. Moreover, since an insulating material is interposed between the conductor and the outer pipe, no current flows in the outer pipe. Further, since the pipe-shaped lead conductor is used, the coolant such as helium gas can pass through the hollow portion of the lead conductor to cool the anchor portion, and can be bypassed to the high temperature side without being warmed in the anchor portion. As a result, cooling of the conductor with a coolant such as helium gas can be ensured. Also,
Since the hollow portion of the pipe-shaped conductor was provided with plugs before and after the anchor portion, the refrigerant did not flow out. Further, since the hollow portion of the lead conductor is used as the bypass of the refrigerant, it is not necessary to newly make a bypass and it is not necessary to process the outer pipe, so that the structure of the thermal anchor portion can be simplified.

In (3), since a part of the outer pipe is cut out and the lead conductor is cooled by the metal member, cooling by the thermal anchor can be secured. Since an insulating material is interposed between the cooling metal member and the lead conductor, no current flows in the outer pipe. Also, since the metal member and the outer pipe are joined and a vent passage for the refrigerant is provided in the metal member, the refrigerant such as helium gas should cool the anchor part and bypass to the high temperature side without warming in the anchor part. You can As a result, cooling of the conductor with a coolant such as helium gas can be ensured. Further, since only the vent hole is provided as a bypass for the refrigerant, it is not necessary to newly create a bypass, and the structure of the thermal anchor portion can be simplified.

In (4), since a part of the outer pipe is cut out and the lead conductor is cooled by the metal member, cooling by the thermal anchor can be secured. Since an insulating material is interposed between the cooling metal member and the lead conductor, no current flows in the outer pipe. Further, since the pipe-shaped lead conductor is used, the coolant such as helium gas can pass through the hollow portion of the lead conductor to cool the anchor portion, and can be bypassed to the high temperature side without being warmed in the anchor portion. As a result, cooling of the conductor with a coolant such as helium gas can be ensured. In addition, since the plug is provided in the hollow portion of the pipe-shaped conductor before and after the anchor portion, the refrigerant does not flow out. Further, since the hollow portion of the lead conductor is used as the bypass of the refrigerant, it is not necessary to newly make a bypass, and the structure of the thermal anchor portion can be simplified.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a vertical sectional view of a thermal anchor portion of the current lead of the present invention.

In the present embodiment, the lead conductor 1 is cooled by passing helium gas between the lead conductor 1 and the pipe 2. In the thermal anchor portion 18, the liquid nitrogen flows from the liquid nitrogen pipe 5a, and the liquid nitrogen flows around the cylindrical space surrounded by the metal member 6 and the metal member 4 for cooling the lead conductor, and the liquid nitrogen pipe 5b. Drained from. The thermal anchor portion 18 makes a cylindrical conductor 9 made of the same material as the lead conductor 1 closely adhere to the lead conductor 1. Further, the cylindrical insulating material 3 is brought into close contact with the conductor 9 so as to come into close contact with the pipe 2. The insulating material 3 is provided so that the inner lead conductor and the outer pipe are not electrically short-circuited. The conductor 9 is provided with a ventilation hole 8 for helium gas. The metal member 6 is attached to the outside of the conductor 9 in close contact with the pipe 2. By providing the ventilation hole 8 in the thickened portion of the conductor 9, the helium gas is removed from the thermal anchor 18
Can be passed through to the high temperature side.

In the current lead thus constructed, the portion having the lead conductor can be surely cooled to the liquid nitrogen temperature by the thermal anchor 18, so that the same effect as the known example can be obtained, and further the thermal anchor can be obtained. 18
The lead conductor portion located on the higher temperature side can be cooled with helium gas. Further, since the vent hole for the refrigerant is provided inside the pipe, the helium gas is prevented from being heated in the anchor portion, and further, the anchor portion can be cooled by the helium gas.

Next, it will be shown below that helium gas is superior to nitrogen gas as the cooling medium. The heat transfer to the lead conductor 1 by the flow of the refrigerant in the pipe depends on the flow state. The Reynolds number R that determines the flow state such as turbulent flow and laminar flow is determined by R = ρvd / η. Where ρ is the density, v is the flow velocity, d is the coefficient that depends on the shape of the pipe, and η is the viscosity coefficient of the refrigerant. When the Reynolds number exceeds a certain value, turbulent flow with good heat transfer occurs, and when it is small, laminar flow occurs.
When helium gas and nitrogen gas flow in the same tube at the same flow rate, the Reynolds coefficient ratio is RHe / RN2≈0.1 when the physical properties of the gas of 100K are used. In a general cryostat, since the heat penetration into the liquid helium system is larger than the heat penetration into the liquid nitrogen system, the evaporation amount of the helium gas is 10 times or more that of the nitrogen gas. Therefore, when nitrogen gas and helium gas are used as the refrigerant of the lead conductor 1, the gas flow rate will be about 10 times different,
As a result, as can be seen from the above equation, the Reynolds numbers in the two cases are almost equal, and the flow conditions are the same. In this case, the heat transfer of cooling depends on the thermal conductivity of the refrigerant. The thermal conductivity of helium gas is more than 6 times that of nitrogen gas in the region of 300K or less, so the cooling efficiency by gas is also 6
It will be doubled. As a result, the invasion of heat can be reduced, and the consumption of expensive liquid helium can be reduced. Next, as a structural effect, there is no need to make a helium gas bypass outside the pipe. Further, since it is not necessary to process the pipe 2, and the structure of the metal member 6 is simplified, it is possible to reduce the cost by reducing the manufacturing process. Reliability is also improved by reducing these manufacturing processes. In addition, since no external bypass is provided, the thermal anchor part can be manufactured compactly.

FIG. 2 shows a second embodiment of the present invention. The structure is almost the same as that of FIG. 1, but the difference is that the lead conductor 1a is a pipe, and helium gas flows in from the vent holes 8a and 8c and flows out from 8b and 8d. Helium gas in the lead conductor 1a is closed by plugs 7a and 7b so as not to flow out.

Also in this structure, the helium gas can pass through the inside of the thermal anchor 18, and the feature that the helium gas flows to the high temperature side is the same as described above, and the same effect as the first embodiment can be obtained in terms of cooling. Also in terms of structure, since the helium gas is configured to pass through the inside of the thermal anchor, it can be simplified as in the first embodiment.

FIG. 3 shows a third embodiment of the present invention. In this embodiment, the pipe 2 is cut out and the metal member 6 for cooling is used.
The lead conductor is directly cooled via the cylindrical insulating material 3. In addition, the outer pipe 2 is connected by the metal member 6,
A helium gas passage was provided in the metal member 6 as in the above example. Since it is not necessary to provide an external bypass, the same effect as described above can be obtained. Since the pipe 2 needs to be processed, it takes a little more work than the first and second embodiments, but by constructing the metal member 6 in one piece, the work such as welding can be omitted. Further, since the metal member 6 directly cools without using a pipe, it is advantageous in terms of cooling surface over the first and second embodiments.

FIG. 4 shows a fourth embodiment of the present invention. The thermal anchor 18 that is almost the same as that of the third embodiment is constructed, and the helium gas flow path uses a pipe-shaped lead conductor as in the second embodiment, and the hollow portion thereof is used as a helium gas bypass. The current lead thus configured can also obtain the same effect as that of the third embodiment.

FIG. 6 shows an application of the invention to a superconducting magnet device. Since the structure of the cryostat is almost the same as that of FIG. 5, only the difference will be described here. If the liquid nitrogen container 14 cannot be installed near the current lead,
The liquid nitrogen pipe 5 is connected to the thermal anchor 18. For current lead, lead conductor 1 with helium gas 16 up to room temperature end
Can be cooled. As a result, it is possible to ensure the same cooling capacity with helium gas as in the case without a thermal anchor. Moreover, since the helium gas bypass is not provided outside, the structure of the anchor portion is simplified. Further, the nitrogen gas pipe 16 is also unnecessary.

[0031]

According to the first aspect of the present invention, since the cooling metal member is provided with the ventilation passage as a bypass through which the refrigerant passes through the thermal anchor portion, the refrigerant such as helium gas can pass through the inside of the anchor. The structure of the thermal anchor has been simplified while ensuring cooling with helium gas. Further, since the cooling metal member is configured to cover the outside of the pipe, it is not necessary to process the pipe,
Easy to make.

According to the second aspect of the invention, since the hollow portion of the pipe-shaped lead conductor is used as a bypass through which the refrigerant passes through the thermal anchor portion, the refrigerant such as helium gas can pass through the inside of the anchor. The structure of the thermal anchor part has been simplified while ensuring the cooling by. Further, since the cooling metal member is configured to cover the outside of the pipe, it is not necessary to process the pipe, which facilitates the production.

According to the third invention, since the cooling metal member is provided with the ventilation passage as a bypass for allowing the refrigerant to pass through the thermal anchor portion, the refrigerant such as helium gas can pass through the inside of the anchor. The structure of the thermal anchor part has been simplified while ensuring the cooling by.

According to the fourth aspect of the invention, since the hollow portion of the pipe-shaped lead conductor is used as a bypass for the refrigerant to pass through the thermal anchor portion, the refrigerant such as helium gas can pass through the inside of the anchor. The structure of the thermal anchor has been simplified while ensuring cooling with helium gas.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment showing a thermal anchor portion of a current lead for a superconducting device according to the present invention.

FIG. 2 is a sectional view of a second embodiment of a thermal anchor portion of a current lead for a superconducting device according to the present invention.

FIG. 3 is a sectional view of a third embodiment of a thermal anchor portion of a current lead for a superconducting device according to the present invention.

FIG. 4 is a sectional view of a thermal anchor portion of a current lead for a superconducting device according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view showing a superconducting device to which a conventional current supply lead is applied.

FIG. 6 is a sectional view showing a superconducting device to which a current lead according to the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lead conductor, 2 ... Pipe, 3 ... Insulating material, 4, 6 ... Metal member, 5a, 5b ... Liquid nitrogen piping, 8 ... Helium gas vent, 9 ... Conductor, 18 ... Thermal anchor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Shibata 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Kenichi Hattori 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 in Hitachi, Ltd. Hitachi Research Laboratory

Claims (4)

[Claims] 1. In a current lead for a superconducting device, wherein a rod-shaped conductor is passed through a pipe having a larger diameter, and a refrigerant passes between the pipe and the conductor, the thickness of a part of the conductor is increased. A thermal anchor configured to be in close contact with the outer pipe through an insulating material and covering that portion with a metal member cooled with liquid nitrogen from the outer side of the pipe is provided inside the thermal anchor of the conductor. A current lead for a superconducting device, characterized in that an air passage for passing the refrigerant is provided in a portion having an increased thickness. 2. In a current lead for a superconducting device, wherein a pipe-shaped conductor is passed through a pipe having a larger diameter, and a refrigerant passes between the pipe and the conductor, the thickness of a part of the conductor is increased. A thermal anchor configured to be in close contact with the outer pipe via an insulating material and to cover the portion from the outer side of the pipe with a metal member cooled with liquid nitrogen, and the conductor is provided inside the thermal anchor. A current lead for a superconducting device, characterized in that a hole is provided in each of the holes, the holes are located on both outer sides of a portion having an increased thickness, and a plug for closing a hollow portion of the conductor is provided on the outer side thereof. 3. In a current lead for a superconducting device, wherein a rod-shaped conductor is passed through a pipe having a larger diameter, and a refrigerant passes between the pipe and the conductor. An anchor is installed, and the thermal anchor is configured to connect the pipe and the metal member by sandwiching a metal member cooled with liquid nitrogen, and the metal member is closely adhered to the conductor via an insulating material to directly cool the conductor. A current lead for a superconducting device, wherein the thermal anchor is provided with an air passage for passing the refrigerant through the metal member. 4. In a current lead for a superconducting device, wherein a pipe-shaped conductor is passed through a pipe having a larger diameter, and a refrigerant passes between the pipe and the conductor, a part of the pipe is cut out. A thermal anchor is installed, the thermal anchor connects the pipe and the metal member with a metal member cooled with liquid nitrogen sandwiched therebetween, and the metal member is brought into close contact with the conductor via an insulating material to directly cool the conductor. In the thermal anchor, holes are provided in the conductor, the holes are located on both outer sides of the metal member, and the outer side is provided with a plug for closing the hollow portion of the pipe-shaped conductor. Characteristic current lead for superconducting device.