WO2019239650A1

WO2019239650A1 - Superconducting electromagnet device

Info

Publication number: WO2019239650A1
Application number: PCT/JP2019/008439
Authority: WO
Inventors: 学青木
Original assignee: 株式会社日立製作所
Priority date: 2018-06-15
Filing date: 2019-03-04
Publication date: 2019-12-19
Also published as: JP2019220495A

Abstract

Provided are novel cooling system for a superconducting electromagnet, and a superconducting electromagnet device in which the cooling system is used. The superconducting electromagnet device according to the present invention comprises a vacuum container, a radiation shield contained within the vacuum container, a plurality of superconducting coils contained within the radiation shield, and a coil container that accommodates the superconducting coils, wherein the superconducting electromagnet device is characterized by comprising a cooling system for superconducting coils, the cooling system including the coil container, a refrigerant container in which a refrigerant accumulates, refrigerant piping through which the coil container and the refrigerant container communicate, a trap member to which the refrigerant is supplied from the refrigerant piping, and a refrigerator provided to the refrigerant container, and the trap member being provided between the inner wall of the coil container and the surface of the superconducting coils. The superconducting electromagnet device is further characterized in that the trap member is a transcalent body having a gap through which the refrigerant can penetrate.

Description

Superconducting magnet system

The present invention relates to a superconducting electromagnet apparatus.

The superconducting electromagnet device is composed of a superconducting coil and a permanent current switch installed in parallel to the superconducting coil, and supplies the current from the exciting power source to the superconducting coil with the permanent current switch open, and then closes the permanent current switch. In this state, the current supplied from the exciting power supply is reduced to zero, so that a permanent current operation in which the current continues to flow through the superconducting closed circuit composed of the superconducting coil and the permanent current switch with almost no attenuation is obtained. Thereby, the superconducting electromagnet apparatus can hold the magnetic field for a long time.

On the other hand, a phenomenon called quench is also known as a phenomenon in which the superconducting coil loses the superconducting state due to some abnormality. Various studies have been conducted on the reason and mechanism of the occurrence of the quenching phenomenon, and it is considered that mechanical disturbance generated in the superconducting coil is included in one of the factors through experiments and the like. That is, when a temperature rise exceeding the critical temperature occurs in the superconducting member constituting the superconducting coil due to mechanical disturbance, more specifically, a part of the superconducting coil undergoes normal conducting transition due to the mechanical disturbance, and at that site. There may be a case where Joule heat generation exceeds the cooling capacity of the cooling means. In this case, the normal conducting region is expanded, and the magnetic energy in the superconducting coil is consumed as thermal energy in the normal conducting region, and as a result, the superconducting coil is in the normal conducting transition and cannot maintain the magnetic field.

Conventional superconducting electromagnet devices have many immersion cooling systems that are used by immersing them in a refrigerant typified by liquid helium or liquid nitrogen in order to keep the constituent elements typified by the above superconducting coil and permanent current switch in a superconducting state. It has been adopted. Therefore, when the quench phenomenon occurs, the liquid helium that has been filled for cooling is vaporized and released outside the apparatus, resulting in a burden of cooling costs necessary for refilling, and until refilling and re-excitation. There is a problem that the device becomes unusable for a period of time. In addition, helium, which is one of the refrigerants used for cooling, has a problem of resource depletion, and reduction of the amount of use has been a problem. Therefore, a cooling system that cools the refrigerator and components by thermally connecting them with a metal with good thermal conductivity, or an indirect system that cools by bringing the pipe in which liquid helium is circulated into contact with the object to be cooled. Cooling methods have been proposed. (For example, Patent Documents 1 and 2)

JP 2009-188065 A Japanese Patent Application Laid-Open No. 06-342721

A superconducting electromagnet apparatus that employs a conductive cooling system or an indirect cooling system has the advantage of reducing the amount of helium used. However, compared with immersion cooling, it is less susceptible to frictional heat generated by the displacement of the superconducting coil due to electromagnetic force when energized and the release of thermal energy due to mechanical disturbances such as cracking of the resin that fixes the superconducting wire. The degree is small.

For example, the heat capacity per unit volume of liquid helium in a cryogenic region of 5K or less is larger than that of metal, and is about 600 times that of oxygen-free copper, for example. This fact means that when the same mechanical disturbance occurs, the temperature increase in the conduction cooling method or the indirect cooling method tends to increase in principle with respect to the temperature increase in the immersion cooling method.

As described above, the conventional superconducting electromagnet apparatus has a strong connection between the amount of refrigerant used and the cooling performance, and it has been difficult to achieve both reduction of the refrigerant usage fee and maintenance of the cooling performance.

Therefore, a main object of the present invention is to provide a novel superconducting electromagnet cooling system and a superconducting electromagnet apparatus using the same.

In order to solve the above problems, the present invention provides a vacuum vessel, a radiation shield contained in the vacuum vessel, a plurality of superconducting coils contained in the radiation shield, and a coil vessel that houses the superconducting coil, A superconducting electromagnet apparatus comprising: the coil container; a refrigerant container that stores the refrigerant; a refrigerant pipe that communicates the coil container and the refrigerant container; a trap member that is supplied with refrigerant from the refrigerant pipe; and the refrigerant A cooling system for a superconducting coil including a refrigerator provided in the container, wherein the trap member is provided between the inner wall of the coil container and the surface of the superconducting coil.

According to the present invention, it is possible to provide a superconducting electromagnet cooling system with high cooling performance while reducing the amount of refrigerant used, and a superconducting electromagnet apparatus using the same.

It is the figure which showed the cross section of the superconducting electromagnet apparatus which concerns on 1st Embodiment. It is the figure which showed typically the circuit structure concerning 1st Embodiment. It is a partial enlarged view of a device cross section according to the first embodiment. It is the figure which showed the member which comprises the coil container which concerns on 1st Embodiment. It is the figure which showed the apparatus cross section which concerns on 2nd Embodiment. It is the figure which showed the apparatus cross section which concerns on 2nd Embodiment. It is the figure which showed the apparatus cross section which concerns on 3rd Embodiment. It is the figure which showed typically the circuit structure concerning 3rd Embodiment.

Embodiments of the present invention will be described in detail with reference to the drawings as appropriate. The following are only examples, and are not intended to limit the embodiments of the present invention to the following specific contents.

[First embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 3, and FIG.

FIG. 1 schematically shows a cross section of the superconducting electromagnet apparatus 1 according to the first embodiment. The main elements constituting the superconducting electromagnet apparatus 1 include a vacuum vessel 2, a radiation shield 3 contained in the vacuum vessel 2, a coil vessel 11 contained in the radiation shield 3, and a superconducting coil 4 contained in the coil vessel 11. Can be mentioned.

In addition, the superconducting coil 4 in this embodiment has a central axis 21 corresponding to the center line of the coil winding oriented in the vertical direction. Here, the central axis 21 of the superconducting coil 4 may be oriented in the horizontal direction, and there is an opening 24 that penetrates the vacuum vessel 2 and the radiation shield 3. A plurality of vacuum containers 2 and coil containers 11 may be provided, and the superconducting coils 4 may be provided according to the number of them. A plurality of superconducting coils 4 may be provided inside one coil container 11. In the example shown in FIG. 1, two superconducting coils 4 are housed in one coil container 11 to constitute one superconducting electromagnet, and the superconducting electromagnet apparatus 1 is provided with four superconducting magnets.

Further, when the superconducting electromagnet apparatus 1 is applied as a static magnetic field generation source of a magnetic resonance imaging apparatus, a space for inserting a subject is changed by changing the arrangement and structure of the vacuum vessel 2 and a refrigerant pipe 6 described later. It is good to form.

Inside the coil container 11, in addition to the superconducting coil 4, a trap member 5 that temporarily traps the refrigerant and a refrigerant pipe 6 that is a refrigerant circulation channel are provided. The trap member 5 is made of a good thermal conductor (for example, aluminum), and is placed so as to face the inner diameter surface of the superconducting coil 4 as shown in the figure. Moreover, the trap member 5 is provided with a gap through which liquid helium permeates, a groove or a dent that stays in the interior or surface of the trap member 5. In addition to these, the trap member 5 can adopt a porous shape such as a porous member, or a slit or groove shape provided along the circumferential direction of the superconducting coil 4 and can trap the refrigerant. Any form can be used.

The refrigerant pipe 6 is provided so that the refrigerant is supplied to the trap member 5. The refrigerant pipe 6 includes an introduction path for introducing the refrigerant into the coil container 11 and a discharge path for discharging the refrigerant from the coil container 11, and has a refrigerant pipe 6 corresponding to both flow paths. This constitutes the refrigerant circulation path. For example, in FIG. 1, the refrigerant pipe 6 connected from the lower side in the vertical direction of the coil container 11 may pass through the introduction path and the refrigerant pipe 6 connected from the upper side of the coil container 11. That is, the expressions “introduction path” and “discharge path” are names that are simply called from the main circulation direction of the refrigerant.

The refrigerant pipe 6 is connected to a refrigerant container 31 that stores the refrigerant, and basically, the refrigerant circulation path is configured by the refrigerant container 31, the refrigerant pipe 6, and the coil container 11. The refrigerant container 31 is provided with the refrigerator 12 so that the temperature of the refrigerant circulating by the refrigerator 12 is maintained, while the vaporized refrigerant is liquefied again.

Further, if it is assumed that the superconducting electromagnet apparatus 1 operates in a so-called permanent current mode, a permanent current switch 9 may be installed in the refrigerant container 11 as shown in FIG. By installing the permanent current switch 9 so as to be immersed in the refrigerant stored in the refrigerant container 31, it is possible to stabilize the circuit through which the permanent current flows. Note that the permanent current switch 9 may not be installed in the case of not operating in the permanent current mode, for example, in the case of the power supply type. In addition, the internal space of the refrigerant container 31 is not limited to a permanent current switch, an energization cable for drawing current from the outside during excitation, a pressure sensor for measuring the internal pressure of the refrigerant container 31, and a temperature monitoring function. A temperature sensor or the like may be provided.

The superconducting electromagnet apparatus 1 is further connected to an external communication pipe 32 for supplying or discharging the refrigerant from the outside to the refrigerant circulation system including the refrigerant container 31, the refrigerant pipe 6 and the coil container 11. Is done. The supply and discharge pipes may be common or may be provided as individual pipes depending on their roles.

The external communication pipe 32 is provided so as to penetrate the vacuum vessel 2 and the radiation shield 3 as shown in FIG. The external communication pipe 32 is provided with a valve 72 and a valve 73 so that the connection between the refrigerant container 11 and the external space can be switched as necessary. Further, the external communication pipe 32 may be configured to be connected to the refrigerant pipe 6 connected to the coil container 11 or to be connected to the coil container 11. Since the external communication pipe 32 has a structure that connects a cryogenic environment and a room temperature environment, it is preferable to use a member having low thermal conductivity so that heat penetration through the pipe is minimized.

FIG. 2 is a schematic diagram of a circuit configuration of the superconducting electromagnet apparatus 1. The superconducting electromagnet apparatus 1 includes eight superconducting coils 4, and these superconducting coils 4 are connected in series.
Protection resistors 10 are connected in parallel to these superconducting coils 4. In the example shown in FIG. 2, one protective resistor 10 is provided in parallel to the four superconducting coils 4 connected in series, so that the magnetic energy of the superconducting coil 4 can be consumed as needed. Consists of.

When the current breaker 14 is cleaved, the superconducting coil 4 and the permanent current switch 9 constitute a closed circuit. The permanent current switch 9 is also formed of a superconducting member in the same manner as the superconducting coil 4 and can be kept at a critical temperature or less to be in a superconducting state.

In order to supply a current necessary for excitation to the superconducting coil 4 having the above circuit configuration, an excitation power source 13 and a current breaker 14 are installed outside the vacuum vessel 2.

The following steps are executed to energize a current in a superconducting circuit composed of the superconducting coil 4 and the permanent current switch 9. First, in a state where the permanent current switch 9 is in an electric resistance state (open state) due to heating or the like, the electric circuit breaker 14 is closed, and current is supplied from the excitation power supply 13 to the superconducting coil 4. When the energization amount is gradually increased and the target current value is reached, the heating of the permanent current switch 9 is then stopped and cooled. When the cooled permanent current switch 9 transitions to the superconducting state and becomes a state where the electric resistance is minimized (closed state), the current supplied from the excitation power supply 13 is subsequently made zero and the current breaker 14 is opened. As a result, the operation is a permanent current operation in which the current continues to flow in the superconducting closed circuit including the superconducting coil 4 and the permanent current switch 9 with almost no attenuation. As described above, the superconducting electromagnet apparatus 1 can hold a magnetic field for a long time.

FIG. 3 is an enlarged view of a part of the schematic cross-sectional view of the apparatus centering on the superconducting coil 4 of the superconducting electromagnet apparatus 1. The superconducting coil 4 is cooled while being accommodated in the coil container 11, and the conducting wire (superconducting wire 34) that supplies current to the superconducting coil 4 is also cooled. That is, the superconducting wire 34 is drawn into the refrigerant container 31 through the refrigerant pipe 6 connecting the coil container 11 and the refrigerant container 31. Also for the superconducting wires 34 that supply current to the other superconducting coils 4, the plurality of superconducting wires 34 drawn into the refrigerant container 11 are connected as in the circuit shown in FIG.

Here, the trap member 5 is provided between the superconducting coil 4 and the wall surface of the refrigerant container 11. The position where the trap member 5 is provided is on the inner diameter side of the superconducting coil 4 in the example shown in FIG. 3, but is not limited thereto, and may be on the outer diameter side, the upper surface side, or the lower surface side. The trap member 5 has a space through which liquid helium permeates, and is preferably made of metal from the viewpoint of heat transfer. For example, it is conceivable as a candidate to form a coiled metal member made of an aluminum wire along the inner diameter surface of the superconducting coil 4.

In order to realize such a coil structure, the following coil molding process can be considered. First, an aluminum wire is wound around a winding frame (not shown). Subsequently, a superconducting wire is wound so as to cover the winding of the aluminum wire, and each is integrated with a resin or the like. In addition, the process of integration with resin or the like is preferably a process other than the resin impregnation molding method. The resin impregnation molding method fills the voids inside the aluminum winding with the resin, and reduces the gap through which liquid helium penetrates. Therefore, as a forming method, a superconducting wire and an aluminum wire previously coated with a self-bonding resin are employed, and a self-bonding method in which a wire coated with a resin is wound and then heated to be integrated is effective. As a method. In the self-bonding method, as a resin impregnation method, a gap is easily secured between the wires, and a flow path for liquid helium to pass is easily secured.

After the formation of the coil is completed, the trap member 5 and the superconducting coil 4 are separated from a winding frame (not shown) and accommodated in the coil container 11. In addition, for such accommodation operation, the coil container 11 is configured by a combination of a plurality of members, and is integrated by welding or the like after the trap member 5 and the superconducting coil 4 are installed. For example, in the example shown in FIG. 3, the upper part of the coil container 11 is constituted by a container member 11a, the lower part is constituted by a container member 11c, and the outer surface and the partition surface of the two superconducting coils 4 are constituted by the container member 11b. The inner diameter surface of the coil container 11 may be provided integrally with either the container member 11a or the coil container 11c. In addition, the pattern of the member which comprises this coil container 11 is not restricted to what was mentioned above, A free structure can be employ | adopted.

Further, when two superconducting coils 4 as shown in FIG. 3 are housed in one coil container 11, an opening through which liquid helium passes as shown in FIG. 4 is formed in a portion corresponding to a partition plate sandwiched between both coils. A part 51 is provided. Further, grooves 52 as shown in FIG. 4 are provided in the

members

11a and 11b which contact the upper surface in the vertical direction of the superconducting coil.

The helium gas vaporized when the superconducting coil 4 is cooled by the opening 51 and the groove 52 does not stay in the coil container, moves to the trap member 5 side through the groove 52, and passes through the refrigerant circulation path 6 to form the refrigerant container. It returns to 31 and it becomes possible to reliquefy with the refrigerator 12. FIG.

Here, the external communication pipe 32 can be used not only for supplying liquid helium into the apparatus but also for cooling the superconducting coil 4 from room temperature. At that time, the superconducting coil 4 can be cooled as described above by supplying and discharging the refrigerant in the direction of the arrow 20 and allowing the refrigerant to pass through the trap member 5. When quenching occurs, the vaporized helium is discharged out of the apparatus through the check valve 72 provided in the external communication pipe 32, thereby preventing the apparatus from being damaged by the vaporized helium. .

As described above, the superconducting electromagnet apparatus 1 described in the present embodiment reduces the amount of helium used by limiting liquid helium to the refrigerant container 31, the refrigerant circulation path 6, and the coil container 11. Furthermore, in the coil container 11, the volume occupied by the liquid helium is reduced by providing the trap member 5 in a region other than the superconducting coil 4. Thereby, the usage-amount of helium can be reduced compared with the conventional immersion cooling. In addition, by adopting a structure in which the liquid helium that has passed through the trap member 5 is in direct contact with the superconducting coil 4, it is possible to reduce the amount of helium used and suppress an increase in coil temperature when a mechanical disturbance occurs. Become.

[Second Embodiment]
FIG. 5 shows a cross section of the superconducting electromagnet apparatus 1 according to the second embodiment. The second embodiment is different from the first embodiment shown in FIG. 1 in that the central axis 21 of the superconducting electromagnet 4 faces the horizontal direction. Moreover, the surface which the superconducting coil 4 and the coil container 11 contact differs in that the groove | channel 52 which is 1st Embodiment is not provided.
FIG. 6 shows a cross-sectional view of the superconducting electromagnet apparatus 1 shown in FIG. The liquid helium circulates in the external communication pipe 32 in the direction of the arrow 20 and cools the superconducting coil 4 through the trap member 5.

By adopting such a structure, the same effect as that of the first embodiment can be obtained even in the superconducting electromagnet apparatus 1 in which the central axis 21 faces the horizontal direction. Further, since the helium gas vaporized when the superconducting coil 4 is cooled moves upward in the trap member 5 by buoyancy, the helium gas can be obtained without providing the coil container 11 with the groove 52 for preventing the helium gas from staying. It is possible to reach the refrigerant container 31 without stagnation and re-liquefy.

[Third Embodiment]
FIG. 7 shows a cross section of the superconducting electromagnet apparatus 1 according to the third embodiment. FIG. 8 schematically shows a circuit of the superconducting electromagnet apparatus 1. In the third embodiment, a plurality of superconducting coils 8 having a higher critical temperature than that of the superconducting coil 4 used in the first embodiment shown in FIG. 1 are additionally installed inside the apparatus. It is different in that it is thermally connected by a high thermal conductor 80 having a high height. Further, the superconducting coil 8 having a high critical temperature is different in that it is energized from an excitation power source 13b different from the superconducting coil 4.

Here, when the superconducting coil 4 is maintained below the critical temperature, the superconducting coil 8 connected to the refrigerant circuit 6 and having a high critical temperature is also maintained in the superconducting state.

By adopting such a structure, it is possible not only to obtain the same effect as in the first embodiment, but also to add a new superconducting coil without adding a refrigerator, and to install a superconducting electromagnet apparatus. It becomes possible to introduce a superconducting electromagnet apparatus capable of generating a stronger magnetic field later.

DESCRIPTION OF SYMBOLS 1 Superconducting magnet apparatus 2 Vacuum vessel 3 Radiation shield 4 Superconducting coil 5 Trap member 6 Refrigerant piping 7 Refrigerant 8 Superconducting coil 9 with high critical temperature Permanent current switch 10 Protection resistor 11 Coil vessel 12 Refrigerator 13 DC power supply 14 Current breaker 20 Vaporization Arrow indicating the direction of travel of the cooled refrigerant Central axis 24 opening 31 refrigerant container 32 external communication pipe 34 superconducting wire guiding electromagnetic device 51 opening 52 groove 72 check valve 73 valve 81 the high thermal conductive body

Claims

In a superconducting electromagnet apparatus comprising: a vacuum vessel; a radiation shield contained in the vacuum vessel; a plurality of superconducting coils contained in the radiation shield; and a coil vessel containing the superconducting coil.
The coil container, a refrigerant container for storing refrigerant, a refrigerant pipe for communicating the coil container and the refrigerant container, a trap member to which a refrigerant is supplied from the refrigerant pipe, and a refrigerator provided in the refrigerant container; A superconducting coil cooling system including
The superconducting electromagnet apparatus according to claim 1, wherein the trap member is provided between an inner wall of the coil container and a surface of the superconducting coil.
The superconducting electromagnet apparatus according to claim 1, wherein the trap member is a good thermal conductor having a gap through which a refrigerant can permeate.
The refrigerant container supplies the refrigerant to the coil container through the refrigerant pipe, collects the refrigerant vaporized in the coil container through the refrigerant pipe,
The superconducting electromagnet apparatus according to claim 1, wherein the refrigerator liquefies the vaporized refrigerant collected by the refrigerant container.
4. The superconducting wire of the superconducting coil is introduced into the refrigerant container through the refrigerant pipe, and is connected to a permanent current switch or a superconducting wire of another superconducting coil in the refrigerant container. The superconducting electromagnet apparatus according to any one of the above.
A pipe for supplying a refrigerant from outside the apparatus through the refrigerant container to the inside of the coil container and discharging the refrigerant to the outside of the apparatus is further provided, and the refrigerant penetrating the trap member is supplied from the pipe. Item 5. The superconducting electromagnet device according to any one of Items 1 to 4.
The superconducting electromagnet apparatus according to any one of claims 1 to 5, further comprising a superconducting coil having a higher critical temperature than the superconducting coil, wherein the superconducting coil is in thermal contact with the refrigerant pipe.
The said coil container has a groove | channel on the surface which contacts the perpendicular direction upper surface of the said superconducting coil, The said groove | channel is a shape which contacts the said superconducting coil and the said trap member, Any one of Claim 1 thru | or 6 characterized by the above-mentioned. The superconducting electromagnet apparatus according to claim 1.
The superconducting electromagnet apparatus according to any one of claims 1 to 7, wherein a central axis of the superconducting coil faces a vertical direction, and the superconducting coil is disposed across an opening provided in a horizontal direction. .
The superconducting electromagnet device according to any one of claims 1 to 6, wherein a central axis of the superconducting coil is oriented in a horizontal direction.