JP6491828B2 - Superconducting magnet system - Google Patents

Description

  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.

  In the conventional superconducting electromagnet apparatus, in order to keep the constituent elements typified by the superconducting coil and the permanent current switch in a superconducting state, an immersion cooling method used by immersing them in a refrigerant typified by liquid helium or liquid nitrogen, In many cases, a conduction cooling method is employed in which a refrigerator and a component are thermally connected to each other with a metal having good thermal conductivity for cooling. Among these cooling systems, the immersion cooling system is also used for recondensing the refrigerant vaporized by heat intrusion into the apparatus, such as the MRI apparatus and the NMR apparatus, operating for a long period of several months to one year. A refrigerator is provided.

  With a superconducting magnet equipped with a refrigerator as described above, the superconducting state can be maintained for a long time as long as power is supplied, but when the refrigerator stops due to a power failure etc., a superconducting coil or permanent current switch There is a risk that the temperature will rise and normal conduction transition will occur and the magnetic field cannot be maintained. In particular, in the conduction cooling method, the heat capacity of a refrigerant such as liquid helium used in the immersion cooling method cannot be expected, so that the temperature rises immediately after the refrigerator is stopped.

  Therefore, compared to metals such as copper and aluminum, a refrigerant with a high specific heat and a low density is kept in the solid state in the cryogenic temperature range of 60K or less, and the heat capacity is used to suppress the temperature rise during power outages. A method has been proposed. Nitrogen is a typical example of the refrigerant used for such applications. (For example, Patent Documents 1, 2, and 3). Nitrogen liquefies at 77K under 1 atm and solidifies at 64K or less.

JP 2007-321050 A JP 2002-208512 A JP 2011-082229 A

  As a method of suppressing the temperature rise at the time of a power failure using a solid refrigerant as described above, a method of providing a refrigerant container in thermal contact for each of a plurality of superconducting elements is conceivable.

  However, since the thermal conductivity of solid refrigerant typified by nitrogen is as low as that of stainless steel and the thermal diffusion time is long, heat is propagated to the solid refrigerant at a position away from the heat transfer surface between the container and the solid refrigerant. There was a problem that it was difficult to use the heat capacity of the individual refrigerant away from the hot surface within a predetermined time. Also, since the volume is reduced when the refrigerant solidifies and a gap is created between the container and the solid refrigerant, the solid refrigerant can be expected to be in thermal contact only on the surface where it falls and contacts according to gravity. It is considered effective to provide a wide refrigerant container, limit the thickness of solid nitrogen in the refrigerant container, and secure a thermal contact surface between the refrigerant container and the superconducting element. However, in order to adopt this method, it is necessary to secure a space for newly arranging a refrigerant container having a large bottom area in the heat insulating container of the apparatus, and there is a problem that the apparatus cannot be increased in size.

In view of the above, an object of the present invention is to provide a superconducting electromagnet apparatus including a refrigerant container that can efficiently use the heat capacity of a solid refrigerant without increasing the size of the apparatus.

  The present invention relates to a superconducting magnet device having a refrigerant container containing a solid refrigerant, wherein the refrigerant container has a shape in which a metal tube is spirally wound, and the refrigerant container and the superconducting coil are in thermal contact with each other. Take. In addition, the refrigerant container has a structure arranged in the middle of the heat conduction path from the refrigerator to the superconducting coil.

  By using such a superconducting electromagnet device, it is possible to limit the thickness of the solid refrigerant in the refrigerant container, and to ensure a wide thermal contact surface between the solid refrigerant and the refrigerant container, and the heat capacity of solid nitrogen Can be used within a predetermined time.

It is the figure which showed the apparatus structure which concerns on 1st Embodiment. 1 is a diagram schematically showing a circuit configuration according to a first embodiment. FIG. FIG. 3 is a diagram schematically showing a cross-sectional structure of a refrigerant container according to the first embodiment. It is the figure which showed the apparatus structure which concerns on 2nd Embodiment. It is the figure which showed typically the cross-section of the refrigerant | coolant container which concerns on 2nd Embodiment. It is the figure which showed typically the cross-section of the refrigerant | coolant container which concerns on 3rd Embodiment.

Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
(First embodiment)
A first embodiment to which the present invention is applied will be described below with reference to FIG. 1, FIG. 2, and FIG. FIG. 1 schematically shows a cross section of a superconducting electromagnet apparatus 1 according to the first embodiment.

  The superconducting electromagnet apparatus 1 includes a vacuum vessel 2, a radiation shield 3 contained in the vacuum vessel 2, and a plurality of superconducting coils 4 arranged in a space contained in the radiation shield 3. The radiation shield 3 has a structure including a plurality of refrigerant containers 5, the refrigerant 6 is stored in these refrigerant containers 3, and the superconducting coil 4 is in contact with the refrigerant container 5 in which the refrigerant 6 is stored.

  The superconducting magnet device 1 includes a conducting wire that leads current from an external power source called a power lead in order to supply current to the superconducting coil 4. In this embodiment, it is connected to an external power supply, and is disposed in a space enclosed by a normal conducting power lead 7 penetrating the vacuum vessel 2 and the radiation shield 3 and the radiation shield 3, such as the superconducting coil 4 and the permanent current switch 9. A superconducting power lead 8 that connects the superconducting element and the normal conducting power lead 7 is used. The permanent current switch 9 is a mechanism for generating a permanent current in the superconducting coil 4.

  The refrigerator 12 shown in FIG. 1 has the role of operating the superconducting magnet device 1 stably by maintaining the superconducting state of the superconducting coil 4. Specifically, the second stage 12 b of the refrigerator 12 is connected to each refrigerant container 5 via the heat conduction path 11, and the first stage 12 a of the refrigerator 12 is in contact with the radiation shield 3. Since each refrigerant container 5 is in contact with the permanent current switch 9, each superconducting coil 4, and the low temperature end 8 b of the superconducting power lead 8, these members are cooled by the second stage 12 b via the refrigerant container 5.

  Since the normal power lead 7 is in contact with the radiation shield 3, the first stage 12 a is cooled through the radiation shield 3. Further, the high-temperature end 8 a of the superconducting power lead 8 is cooled by the first stage 12 a of the refrigerator 12 by being connected to the normal power lead 7 in contact with the radiation shield 3.

  The central axis 21 of the superconducting coil 4 of the present embodiment is oriented in the vertical direction, and there is an opening 24 that penetrates the vacuum vessel 2 and the radiation shield 3. That is, the superconducting coils 4 are arranged to face each other at a predetermined interval in the vertical direction, and the superconducting magnet device 1 has an opening 24 between the superconducting coils 4 arranged to face each other. The plurality of refrigerant containers 5 are connected in series by connecting pipes 32, respectively, so that the refrigerant 6 is supplied from the refrigerant introduction pipe 30 and can be discharged from the refrigerant discharge pipe 31. In the present embodiment, the refrigerant introduction pipe 30 and the refrigerant discharge pipe 31 are configured with members having low thermal conductivity represented by stainless steel to limit the amount of heat penetration.

Although FIG. 1 shows an example in which the superconducting coil 4 is arranged to face the vertical direction, the present invention is not limited to this, and the central axis 21 of the superconducting coil 4 may face the horizontal direction. In this case, the superconducting coils 4 are arranged facing each other at a predetermined interval in the horizontal direction, and the superconducting magnet device 1 has an opening 24 between the superconducting coils 4 arranged facing each other.
FIG. 2 schematically shows a circuit configuration of the superconducting electromagnet apparatus 1. A plurality of protective resistors 10 are connected in parallel to a plurality of superconducting coils 4. The excitation power supply 13 and the current breaker 14 are installed outside the vacuum vessel 2.
The superconducting magnet device 1 of the present embodiment shifts to the permanent current operation mode by the following mechanism. Note that before the transition to the permanent current operation mode, the superconducting coil 4 and the permanent current switch 9 are kept in the superconducting state by being kept below the critical temperature.

  First, a current is supplied from the exciting power supply 13 to the superconducting coil 4 with the permanent current switch 9 in the “open” state. Thereafter, when the supply current of the exciting power source 13 is made zero while the permanent current switch 9 is “closed” and the current breaker 14 is “open”, the superconductivity comprising the superconducting coil 4 and the permanent current switch 9 is established. In the closed circuit in the state, the current supplied from the excitation power supply 13 continues to flow with almost no attenuation. This state is called a permanent current operation mode.

  By shifting to the permanent current operation mode, the superconducting electromagnet apparatus 1 can maintain a magnetic field for a long period of time. In addition, the permanent current switch 9 is brought into an “open” state by being normally conducted by being heated by a heater or the like (not shown). To “closed” state.

  As described above, the opening / closing control of the permanent current switch 9 is executed by a heater or the like. However, in the superconducting magnet device 1 of this embodiment, the connecting pipe 32 is formed of a member having low thermal conductivity, typified by stainless steel, and heat flux. Is limiting. Therefore, even when the opening / closing control of the permanent current switch 9 is performed by the heater or the like by the heater or the like, the superconducting coil 4 is not heated and transited to the normal conducting state via the connecting pipe 32 and the refrigerant container 5, and the superconducting coil 4 can be effectively kept below the critical temperature.

  Next, the refrigerant | coolant container 3 with which the superconducting magnet apparatus 1 of this embodiment is provided is demonstrated.

  As shown in FIG. 3, the refrigerant container 5 does not change the position of the metal tube 16 in the direction of the central axis 21 from the inner peripheral side to the outer peripheral side with respect to the central axis 21, in other words, the central axis direction is the same. It is manufactured so as to have a so-called single pancake coil shape formed by winding in a spiral shape while maintaining the position.

  In addition, the spiral here means a curve that moves away from the center point while swirling like a spiral on a two-dimensional plane, or that approaches the center point from a far point toward the center point, The three-dimensional vertical component, in this embodiment, is different from a spiral curve that continues to be displaced during turning in the direction of the central axis of the superconducting coil 4.

  The refrigerant container 5 is a position where the superconducting coil 4 communicates with the heat conducting path from the refrigerator 12 to the superconducting coil 4, that is, the second stage 12b and the heat conducting path 11 connected to the second stage 12b. Placed in.

  An example of a specific arrangement relationship is shown in FIG. The refrigerant container 5 is fixed by a heat transfer plate 17 from above and below. The refrigerant container 5 is in thermal contact with the refrigerator 5 through the heat conduction path 11 and the heat transfer plate 17a, and is in thermal contact with the superconducting coil 4 through the heat transfer plate 17b.

  Since the metal tube 16 has a so-called single pancake coil-shaped structure, the solid refrigerant 6 enclosed in the plurality of refrigerant containers 5 is limited in thickness (volume), falls according to gravity, and is separated from the inner wall of the metal tube 16. Since a wide thermal contact surface can be secured, heat propagates to the solid refrigerant 6 within a predetermined time, and a heat capacity for suppressing temperature rise can be used.

  Moreover, since the refrigerant container 5 provided in the superconducting magnet device 1 of the present embodiment has a single pancake coil shape formed by winding the metal tube 16 in a spiral shape, the side wall of the metal tube 16 is twice the number of turns. Exists. The side walls of these metal tubes 16 are in contact with the heat transfer plate 17a through the upper surface of the metal tube 16, and are in contact with the superconducting coil 4 through the bottom surface of the metal tube 16 and the heat transfer plate 17b. It serves as a path for communicating heat conduction between the plate 17a and the heat transfer plate 17b.

  Here, if the refrigerant container 5 does not have a plurality of separated spaces in the radial direction as shown in FIG. 3, but is a refrigerant container having only a single space, the side walls connecting the upper and lower surfaces are Since there is only one, compared to such a refrigerant container, the refrigerant container 5 as shown in FIG. 3 can realize high cooling performance by having many heat conduction paths.

  That is, the refrigerant container 5 included in the superconducting magnet device 1 of this embodiment has a role as a tank for storing the solid refrigerant 6 and a role as an efficient heat conduction path by taking a single pancake coil shape. It is possible.

  Further, the refrigerant container 5 also serves as a cooling path structure for cooling the superconducting coil 4 in the circumferential direction, and it is not necessary to secure a space for newly installing the refrigerant container in the apparatus. Therefore, the superconducting electromagnet apparatus 1 according to the present embodiment has the refrigerant container 5 that can effectively use the heat capacity of the solid refrigerant 6, and can avoid an increase in size due to the provision of the refrigerant container 5. .

The metal tube 16 constituting the refrigerant container 5 uses a hollow conductor obtained by forming a gap in a metal structure having high thermal conductivity such as copper and then performing steel drawing. By using the hollow conductor, the number of joints can be reduced from the metal tube 16, and the possibility of vacuum leakage and refrigerant leakage is reduced. As a result, the reliability of the superconducting magnet device 1 can be improved. Is possible.

(Second Embodiment)
4 and 5 show a cross section of the superconducting electromagnet apparatus 1 and the cross section of the refrigerant container 5 according to the second embodiment. Compared with the first embodiment shown in FIG. 1, the second embodiment has a structure in which a plurality of refrigerant containers 5 are connected in parallel by a connecting pipe 32.

  In the refrigerant container 5, the metal tube 16 is spirally wound from the outer peripheral side toward the inner peripheral side, and then the metal tube 16 is arranged in the center axis direction of the apparatus on the inner peripheral side with respect to the height direction width. This is a so-called double pancake coil that is shifted in a spiral manner from the inner periphery to the outer periphery.

  The superconducting coil 4 and the refrigerant container 5 are held by a coil bobbin 40, the heat conduction path 11 is in direct thermal contact with the refrigerant container 5, and the superconducting coil 4 is in direct thermal contact with the refrigerant container 5.

  Such a structure not only obtains the same effect as the first embodiment, but also has the coil bobbin 40 with the refrigerant inlet 35 and the refrigerant outlet 36 to the refrigerant container 5 arranged on the outer peripheral surface side. Even in this case, the refrigerant can be introduced into the refrigerant container 5 without interference.

  This is because if the single pancake coil shape is used, in order to accumulate the solid refrigerant 6 over the entire metal tube 16, the refrigerant inlet 35 is formed at one end of the metal tube 16, and the refrigerant discharge port 36 is formed at the other end. , Either one is located in the vicinity of the central axis of the single pancake coil formed in a spiral shape. Then, in order to hold the refrigerant container 5 by the coil bobbin 40 as in this embodiment, it is necessary to process the coil bobbin 40 in order to pass either the refrigerant introduction port 35 or the refrigerant discharge port 36.

  In that regard, if the refrigerant container 5 has a double pancake coil shape, both ends of the metal tube 16 are positioned on the outer peripheral surface of the refrigerant container 5, so that the coil bobbin 40 can be used without complicated processing. It becomes possible to do.

  Further, the heat transfer plate 17 can be omitted by fixing the metal tube 16 with the coil bobbin 40. In this structure, the lower part of the double pancake coil-shaped refrigerant container 5 is filled with the solid refrigerant 6.

Then, if only a part of the refrigerant containers 5 rise in temperature and the refrigerant is vaporized, and the other individual refrigerants 6 do not rise in temperature and are kept in a solid state, the vaporized refrigerant cannot pass through the refrigerant container 5. It is possible. Therefore, when a plurality of refrigerant containers 5 are connected in parallel as in the present embodiment, and the vaporized refrigerant is discharged without passing through the other refrigerant containers 5, the vaporized refrigerant is freely contained in the refrigerant container 5. Since it can move to the upper stage, it is possible to reduce the possibility that the pressure is concentrated in one place of the refrigerant container 5 to cause damage or the like.

(Third embodiment)
FIG. 6 shows a cross section of the refrigerant container 5 according to the third embodiment. Compared with the first embodiment shown in FIG. 1, the third embodiment has a structure in which the refrigerant container 5 is made up of two layers of metal pipes 16 a and 16 b with different winding directions and connected by a connecting pipe 32 a. It has become. The superconducting coil 4 and the refrigerant container 5 are held by the coil bobbin 40, the heat transfer plate 17 is omitted, the heat conduction path 11 is in direct thermal contact with the refrigerant container 5, and the superconducting coil 4 is directly in contact with the refrigerant container 5. The structure is in thermal contact.

  By adopting such a structure, not only the same effects as in the first and second embodiments can be obtained, but also the polarity of the induced voltage generated in the refrigerant container 5 due to the magnetic field change at the time of excitation and demagnetization of the superconducting coil 4 can be achieved. Since the metal tubes 16a and 16b are reversed, the induced current can be suppressed, and the Joule heat generated by the induced current can be suppressed.

  As mentioned above, although several embodiment of this invention was described, this invention is not limited to the structure described in the said embodiment, unless it deviates from the summary of this invention described in the claim. The configuration can be changed as appropriate.

The above-described exemplary embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. . Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each exemplary embodiment.

1 Superconducting magnet device 2 Vacuum vessel 3 Radiation shield 4, 4a, 4b Superconducting coil 5, 5a, 5b, 5c, 5d Refrigerant vessel 6 Refrigerant 7 Normal conducting power lead 8 Superconducting power lead
8a Superconducting power lead hot end
8b Superconducting power lead cold end
9 Permanent current switch
10, 10a, 10b Protection resistance
11 Heat conduction path
12 Refrigerator
13 DC power supply
14 Current breaker
16 Metal pipe
17, 17a, 17b Cooling copper plate
21 Central axis of superconducting electromagnet
24 opening
30 Refrigerant introduction piping
31 Refrigerant discharge piping
32 Connection piping
35 Refrigerant inlet
36 Refrigerant outlet
40 coil bobbin

Claims (8)

A superconducting coil;
A permanent current switch connected to the superconducting coil;
A plurality of refrigerant containers in thermal contact with each of the superconducting coil and the permanent current switch;
A refrigerator that cools the plurality of refrigerant containers;
With
At least one of the refrigerant containers is
Formed from a metal tube wound in a spiral around the central axis of the superconducting coil;
Having a thermal contact surface with the surface of the superconducting coil in the central axis direction, and disposed at a position communicating a heat conduction path from the refrigerator to the superconducting coil;
A superconducting magnet device in which a solidified refrigerant is accommodated in the metal tube. The superconducting magnet device according to claim 1,
The refrigerant container is
The metal tube wound in a spiral shape has a structure in which two layers are laminated in the direction of the central axis of the spiral,
The superconducting magnet device is characterized in that the metal pipes constituting the two layers are wound in opposite directions and connected at least at one place. The superconducting electromagnet apparatus according to claim 1,
The refrigerant container is
The metal tube wound in a spiral shape has a structure in which two layers are laminated in the direction of the central axis of the spiral,
The superconducting electromagnet apparatus characterized in that the metal tube constituting the two layers is a single metal tube formed so as to displace in the central axis direction on the innermost circumference of the spiral. The superconducting electromagnet device according to claim 1 or 2,
A superconducting electromagnet apparatus comprising a plurality of the refrigerant containers connected in series to each other. In the superconducting electromagnet apparatus according to any one of claims 1 to 3,
A superconducting electromagnet apparatus comprising a plurality of the refrigerant containers connected in parallel to each other. The superconducting electromagnet apparatus according to any one of claims 1 to 5,
The superconducting magnet device, wherein the metal tube is a hollow conductor. The superconducting electromagnet apparatus according to any one of claims 1 to 6,
The central axis direction of the superconducting coil is a vertical direction,
A vacuum vessel containing the superconducting coil and a radiation shield are provided;
The superconducting electromagnet apparatus, wherein the superconducting coils are arranged to face each other at a predetermined interval in the vertical direction. The superconducting electromagnet apparatus according to any one of claims 1 to 6,
The central axis direction of the superconducting coil is a horizontal direction,
A vacuum vessel containing the superconducting coil and a radiation shield are provided;
The superconducting magnet device, wherein the superconducting coils are arranged to face each other at a predetermined interval in the horizontal direction.