JPH04212401A - Superconducting magnet - Google Patents

Abstract

PURPOSE:To shorten the time necessary for cooling-down, without changing the capacity of a refrigerator, by installing a heat transfer rod for cooling-down composed of good conductor wherein one tip exists outside a vacuum vessel and the other tip reaches the inside of a cryogenic vessel. CONSTITUTION:Heat, which has traveled a protruding part higher than an upper flange 10C of a heat transfer rod 17 for cooling-down and flanges 10B, 10C and permeated from a vacuum vessel 3, travels the rod type part of the heat transfer rod 17, reaches the lower end portion, and heats liquid helium in contact with the lower end of the rod. At the same time, the heat travels connectors inserted in connector holes 30A, reaches a superconducting coil 1, and heats the liquid helium in contact with them. The heat transfer rod for cooling-down is made of good conductor like copper or aluminum having large thermal conductivity, and its shape size is made to coincide almost with that of a current lead 9.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention cools a superconducting magnet operated in persistent current mode, such as a magnet used in a superconducting nuclear magnetic resonance apparatus, particularly a superconducting coil, to an extremely low temperature where the superconducting state is maintained. This invention relates to a cool-down heat transfer rod or current lead used during cool-down.

0002

[Prior Art] A superconducting magnet used in a superconducting nuclear magnetic resonance apparatus is connected to a separate DC power source after the superconducting coil is cooled to an extremely low temperature and the superconductivity is maintained steadily. So-called excitation is performed in which a voltage is applied and a current is supplied. The current flowing through the superconducting coil increases at a rising rate determined by the applied voltage and the inductance of the superconducting coil, but when the current reaches a predetermined value, a persistent current switch built in the same cryogenic container as the superconducting coil is short-circuited. The device is placed in a so-called persistent current mode in which current continues to flow semi-permanently. A superconducting magnet is operated in this persistent current mode.

FIG. 3 is a cross-sectional view of a superconducting magnet. In this figure, the superconducting magnet has a substantially cylindrical shape, and its axis of symmetry is the horizontal line in the center of the figure. The above cross-sectional view also shows a cross-sectional view of the service port 100 which projects into a cylindrical shape.

[0004] The outside of the superconducting magnet is a vacuum container 3, in which a cryogenic container 2 is provided which houses a first heat shield, a second heat shield, and a superconducting coil 1 in order from the outside. A connecting pipe 7 connecting the outside of the vacuum container 3 and the cryogenic container 2 is connected to the service port 100.
The structure is such that the cryogenic container 2 and the atmosphere outside the vacuum container 3 communicate with each other via a pressure relief valve 8 or a valve (not shown). The connecting pipe 7 passes through the first heat shield 4 and the second heat shield 5 on the way, and is mechanically supported and thermally connected to the flange provided on the connecting pipe 7 at each penetration part. is connected to. The connecting pipe 7 is made of stainless steel with low thermal conductivity, and
Vacuum container 3, first heat shield 4, second heat shield 5
A configuration is adopted in which bellows parts shown in the waveforms in the figure are provided at the connecting parts with the cryogenic container 2 and the cryogenic container 2, respectively, and have a heat insulating part that increases the thermal resistance when heat is conducted through the connecting pipe 7. has been done. Since the inside of the cryogenic container 2 is connected to the atmosphere via the connecting pipe 7, the inside thereof is at 1 atmosphere, the same as the atmosphere. On the other hand, since the inside of the vacuum container 3 is maintained in a vacuum to improve the heat insulation effect by the same effect as a thermos flask, the communication tube 7 also has sufficient mechanical strength to withstand the vacuum.

[0005] Liquid helium is sealed in the cryogenic container 2, and the superconducting coil 1 is immersed in this liquid helium to maintain a cryogenic temperature of about 4K. first heat shield 4,
The second heat shield 5 is maintained at approximately 80K and approximately 20K by being cooled by the refrigerator 6, respectively. By providing two layers of heat shields 4 and 5 between the vacuum container 3 and the cryogenic container 2 in this way, heat intrusion from the outside, mainly due to radiation, is reduced and the amount of evaporation of liquid helium is minimized, making it more expensive. A configuration that suppresses helium consumption is adopted.

FIG. 3 shows the current lead 9 installed during excitation. When excitation is completed and the permanent current mode is entered, this current lead 9 is no longer needed and is removed. The connection between the current lead 9 and the superconducting coil 1 is performed at a low temperature connection part 31, as will be described later.

[0007] During operation, the liquid helium evaporates and the helium gas generated rises in the connecting pipe 7 and is discharged into the atmosphere from a valve (not shown). In some cases, it is collected without being released. The so-called quench, in which the superconducting coil 1 suddenly becomes normal conductive for some reason, is an unavoidable phenomenon for superconducting coils, but at that time, the liquid helium in the cryogenic container 2 rapidly evaporates and the internal pressure increases.
In order to avoid this, a pressure relief valve 8 is provided, which operates when the internal pressure exceeds a certain level, and a large amount of helium gas generated by quenching is released from the pressure relief valve 8 into the atmosphere.

FIG. 4 is a cross-sectional view of a conventional current lead. In this figure, the current lead 9 is provided with an outer cylinder 25 and two conductors 22 as reciprocating conductors passing through the outer cylinder 25, and a lower low-temperature connection part 3 connected to the superconducting coil 1.
1 is a support insulator 27, a connector conductor 28, and a connector hole 3
0 and a guide pin 30. The upper part of the conductor 22 in the diagram is connected to a DC power source by a terminal (not shown), and the lower part is electrically connected to the connector conductor 28 of the low-temperature connection part 31, and a connector (not shown) of the superconducting coil 1 is inserted into the connector hole 30. As a result, the superconducting coil 1 is electrically connected to a DC power source. The two connector conductors 28 and the outer cylinder 25 are insulated from each other by a support insulator 27.

The current lead 9 is provided with a flange 10A, and the flange 10A is fixed to the vacuum container 3 by being bolted to a flange 10B provided on the vacuum container 3. Further, several helium gas holes 23 are provided at the same height in the lower part of the outer cylinder 25, and helium gas is guided into the outer cylinder 23 from the connecting pipe 7 to cool the conductor 22. During excitation, when current flows through the conductor 22 and generates heat, the valve that releases the helium gas in the connecting tube 7 to the atmosphere is closed, and all the helium gas generated by evaporation of liquid helium passes through the current lead 9 and is exhausted to the upper part. It is discharged to the atmosphere through the port 16.

[0010] Incidentally, the operation of cooling the superconducting coil 1 and the first and second heat shields 4 and 5 to the operating temperature is called cool-down. The heat shields 4 and 5 of No. 2 are mainly cooled by a refrigerator 6. There is some effect of the helium gas generated by evaporation of liquid helium gas due to the intrusion heat being cooled through the connecting pipe 7 as it rises in the connecting pipe 7, but this effect occurs because the amount of helium gas is small. In reality, we cannot expect much.

[0011]

[Problems to be Solved by the Invention] As mentioned above, during cool down, the first heat shield 4 is heated to about 80K.
It is mainly the refrigerator 6 that cools the second heat shield 5 to about 20K, but the cooling performance of the refrigerator 6 is based on the refrigeration performance necessary to maintain the temperature of these heat shields. The problem is that it takes a lot of time to cool down each of the heat shields 4 and 5 to a predetermined temperature, and in reality it takes several days to cool down the heat shields 4 and 5. be. In order to shorten the time required for cool-down, it is possible to use a refrigerator with a large cooling capacity, but the refrigerator becomes expensive and its size increases, making it difficult to incorporate it into a superconducting magnet. This method is difficult to adopt due to practical problems.

An object of the present invention is to provide a superconducting magnet that can solve these problems and shorten the time required for cool-down without changing the capacity of the refrigerator.

[0013]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a vacuum container whose interior is kept in a vacuum, a cryogenic container housed in the vacuum container and kept at an extremely low temperature, A first and second two-layer heat shield for thermally shielding between the cryogenic container and the vacuum container, a superconducting coil housed in the cryogenic container, and the outside of the vacuum container and the cryogenic container. a connecting pipe that communicates with the inside through the first and second heat shields, and has a heat insulating section between the vacuum container, the first and second heat shields, and the cryogenic container, respectively; A superconducting magnet in which a current lead for electrically and removably connecting the superconducting coil to an external power supply when exciting the superconducting coil is installed in the connecting pipe, and one tip of the superconducting magnet is installed outside the vacuum vessel during cool-down. A cool-down heat transfer rod consisting of a heat transfer body located in the cryogenic container with the other end reaching into the cryogenic container shall be installed in place of the current lead, and the cool-down heat transfer rod shall be installed in the vacuum container. The part has substantially the same shape as the attachment part of the current lead to the vacuum vessel, and the tip of the cool-down heat transfer rod on the cryogenic vessel side is connected to the superconducting coil of the current lead. or a heater to which power is supplied from the outside is provided at the low temperature connection part which is the connection part with the superconducting coil of the current lead, During cool-down, this current lead is attached instead of the heat transfer rod for cool-down, and the low-temperature connection part is heated by the heater.

[0014]

[Operation] In the configuration of this invention, during cooldown,
Instead of a current lead that is installed in the connecting tube and electrically connects the external DC power supply and the superconducting coil during excitation, a good heat conductor is used that has one tip outside the vacuum vessel and the other tip that reaches inside the cryogenic vessel. By attaching the cool-down heat transfer rod, the amount of heat entering into the cryogenic container through the cool-down heat transfer rod increases. Therefore, the amount of evaporation of the liquid helium sealed in the cryogenic container increases, and the amount of helium gas released to the outside through the connecting pipe increases. This helium gas cools the connecting pipes and cools the heat shields through flanges connecting the connecting pipes and each heat shield. When the cool-down heat transfer rods were not provided, the cooling effect was not large because the amount of helium gas was small, whereas the cooling effect was increased by providing the cool-down heat transfer rods. In addition, by making the attachment part of the cool-down heat transfer rod to the vacuum vessel the same structure as the attachment part of the current lead to the vacuum vessel, the support of the cool-down heat transfer rod is ensured, and Thermal coupling between the cool-down heat transfer rods is improved and the amount of heat intrusion from the cool-down heat transfer rods is further increased. Also,
By making the tip of the cool-down heat transfer rod on the side of the cryogenic container the same structure as the connection part with the superconducting coil of the current lead, the thermal coupling between the cool-down heat transfer rod and the superconducting coil is improved. Evaporation of helium is further promoted. Alternatively, a heater that is supplied with power from an external source is provided at the low-temperature connection section where the current lead connects to the superconducting coil.
By attaching this current lead instead of the cool-down heat transfer rod during cool-down and heating the low-temperature connections with a heater, the superconducting coil will be heated by heat conduction from the low-temperature connections, and the superconducting coil will come into contact with these. The evaporation of liquid helium is accelerated.

[0015]

EXAMPLES The present invention will be explained below based on examples. FIG. 1 is a sectional view of a cool-down heat transfer rod showing a first embodiment of the present invention. In this figure, the cool-down heat transfer rod is made of a good heat transfer material with high thermal conductivity, such as copper or aluminum, and has a configuration that almost matches the current lead in FIG. 4 in shape and dimensions. That is, the connection part with the vacuum vessel 3 is a flange 10C having the same dimensions as the flange 10A of the current lead, the diameter of the rod is made to match that of the outer cylinder of the current lead 9, and the connector has the same dimensions as the connector hole 30 of the current lead 9. A hole 30A is provided. The lengthwise dimensions are also included. The difference is that the current lead 9 is provided with an exhaust port 16 at the top end, whereas the cool-down heat transfer rod 17 does not have a corresponding protrusion, and of course there is no need for it. It is. Note that the protruding portion above the flange 10C is not necessarily required.

Heat enters the cryogenic container 2 from the outside through the cool-down heat transfer rod 17 through the following route. The heat that enters from the vacuum container 3 through the protrusion above the flange 10C and the flanges 10B and 10C of the cool-down heat transfer rod 17 is transmitted through the rod-shaped portion of the cool-down heat transfer rod 17 and reaches the lower end. It heats the liquid helium (not shown) that is in contact with this portion, and also heats the liquid helium that is transmitted to the superconducting coil 1 through a connector (not shown) inserted into the connector hole 30A and comes into contact with them. The heated liquid helium evaporates and becomes helium gas, which rises in the connecting pipe 7. Connecting pipe 7 as shown in Figure 3
has a bellows part that suppresses the heat that enters from the outside through the connecting pipe 7, but it is in thermal contact with the first and second heat shields 4 and 5 via flanges in the middle. This portion is cooled by the aforementioned helium gas, and this is transmitted to the first and second heat shields 4 and 5 via the flanges, respectively, for cooling. As mentioned above, in the conventional configuration, the flow rate of helium gas was small, so the cooling effect on the first and second heat shields 4 and 5 was small, but by installing the cool-down heat transfer rod 17. By performing a cool-down, the amount of helium gas generated increases, so the cooling effect of this helium gas on the first and second heat shields 4 and 5 increases, and the time required for cool-down is shortened. .

The amount of heat intrusion by the cool-down heat transfer rod 17 can be adjusted by the attachment structure to the vacuum vessel 3 and the connection structure with the superconducting coil. That is, as shown in FIG. 1, the vacuum container 3 is connected to the flange 10C on the outside air side.
The configuration in which the flange 10B of the cryogenic vessel 2 is fixed with bolts is the configuration that maximizes the amount of heat penetration, and the configuration in which the connector hole 30A is provided on the side of the cryogenic vessel 2 to thermally connect it to the superconducting coil is also the best configuration. This configuration allows heat to be transferred inward. In this way, the cool-down heat transfer rod 1 in Figure 1
7 is the configuration in which the amount of heat penetration is maximized, and in reality, the amount of helium gas generated is adjusted to an appropriate amount, taking into account the fact that the amount of expensive helium consumed is not too large. The amount of heat penetration is adjusted to an appropriate level.

In order to adjust the amount of heat penetration, the flange 1
You can limit heat intrusion from the vacuum container 3 by inserting a heat insulating material between 0C and 10B, or heat transfer rod 1 for cool down.
The configuration on the cryogenic container 2 side of No. 7 is adopted such that the guide pin 29A and connector hole 30A are not provided, and the length is shortened to such an extent that it does not hit the connector of the superconducting coil. Also,
The amount of heat penetration can also be adjusted by changing the diameter of the cool-down heat transfer rod 17. In any case, the configuration shown in FIG. 1 is merely an example of the cool-down heat transfer rod, and any configuration may be adopted as long as it does not contradict the purpose of the present invention.

FIG. 2 is a sectional view of a current lead showing a second embodiment of the present invention, and the same members as those in FIG. 4 are given the same reference numerals and detailed explanations will be omitted. In this figure, support insulator 27 of cold connection 31B of current lead 90
A rod-shaped heater 40 is embedded in B, a lead wire 41 passes through the outer cylinder, and an airtight terminal 43 passes through the outer cylinder 25B.
It is connected to a heater power source 42 provided outside through. During cool-down, this current lead 90 is attached in advance as in the conventional cool-down, and current is supplied to the heater 40 from the heater power source 42 to heat it. The heated heat raises the temperature of the low-temperature connection part 31 and also raises the temperature of the superconducting coil 1 shown in FIG. 3, which is in thermal contact with the connector hole 30 and the guide pin 29. The amount of evaporation of the liquid helium that is in contact with these increases due to the heat. As a result, similarly to the first embodiment, cooling of the first and second heat shields is promoted and the cool-down time can be significantly shortened.

In this figure, the support insulator 2 is used as the heater 40.
Although a rod-shaped heater suitable for being embedded in the 7B is used, the configuration is not limited to this. Furthermore, even if a configuration is adopted in which helium gas is guided to a refrigerator in order to recover it without releasing it into the atmosphere, the air pressure inside the outer cylinder 25B is not much different from the outside air, so the airtight terminal 43 is generally referred to as harmotic and is sold commercially. You can use what you have. The electric power required for heating the heater 40 is the above-mentioned M
In the case of the superconducting magnet of the RI device, the capacity is several kW at most, so the capacity of the heater power supply 42 is not a problem in implementation.
The lead wires 41 may also be thin, and these heaters 40 and related members can be easily implemented within the scope of conventional technology.

[0021]

[Effects of the Invention] As described above, when a superconducting magnet is cooled down, instead of the current lead attached during excitation, one tip is outside the vacuum container and the other tip reaches inside the cryogenic container. By installing a cool-down heat transfer rod made of a good heat conductor, the amount of heat that enters the cryogenic container through the cool-down heat transfer rod increases, and therefore, the temperature inside the cryogenic container is increased. The amount of evaporation of liquid helium increases, and the amount of helium gas released to the outside through the connecting pipe increases. This helium gas cools the connecting pipes and cools each heat shield via a flange connecting the connecting pipe and each heat shield. As a result, the cooling of the heat shield is accelerated and the cool-down time is significantly shortened. In addition, by making the attachment part of the cool-down heat transfer rod to the vacuum vessel the same structure as the attachment part of the current lead to the vacuum vessel, the support of the cool-down heat transfer rod is ensured, and This has the effect of improving the thermal coupling with the heat transfer rod and further increasing the amount of heat intrusion from the cool-down heat transfer rod. In addition, by making the tip of the cool-down heat transfer rod on the side of the cryogenic container the same structure as the connection part of the current lead to the superconducting coil, the thermal coupling between the cool-down heat transfer rod and the superconducting coil is improved. The effect is that the evaporation of liquid helium is further promoted. Alternatively, a heater to which power is supplied from the outside can be installed at the low-temperature connection part where the current lead connects to the superconducting coil, and this current lead can be attached in place of the cool-down heat transfer rod during cool-down, and the heater can reduce the temperature to low temperatures. By heating the connections, the superconducting coils will be heated by heat conduction from these cold connections, which will accelerate the evaporation of the liquid helium that comes into contact with them, significantly reducing the cool-down time for the same reason as mentioned above. This has the effect of shortening the time to .

[Brief explanation of the drawing]

[Fig. 1] A cross-sectional view of a heat transfer rod for cooling down a superconducting magnet showing a first embodiment of the present invention.

[Fig. 2] A cross-sectional view of a current lead of a superconducting magnet showing a second embodiment of the present invention.

[Figure 3] Cross-sectional view of superconducting magnet

[Figure 4] Cross-sectional view of the current lead of a conventional superconducting magnet

[Explanation of symbols]

1 Superconducting coil 2 Cryogenic container 3 Vacuum container 4 First heat shield 5 Second heat shield 7 Connecting pipe 9 Current lead 90 Current lead 17 Heat transfer rod for cool down 25 Outer cylinder 25B outer cylinder 27 Support insulator 27B Support insulator 28 Connector conductor 29 Guide pin 29A Guide pin 30 Connector hole 30A connector hole 31 Low temperature connection 31B Low temperature connection part 40 Heater 41 Lead wire 42 Heater power supply 43 Airtight terminal

Claims (4)

[Claims] Claims: 1. A vacuum container whose interior is kept in a vacuum; a cryogenic container housed in the vacuum container and kept at a cryogenic temperature; a superconducting coil housed in the cryogenic container; the outside of the vacuum container and the inside of the cryogenic container are communicated through the first and second heat shields; The superconducting coil is electrically connected to an external power source when the superconducting coil is excited. A superconducting magnet in which a removably connected current lead is installed in the connecting pipe, the superconducting magnet having one tip outside the vacuum vessel and the other tip reaching inside the cryogenic vessel during cool-down. A superconducting magnet characterized in that a cool-down heat transfer rod is attached in place of the current lead. 2. The superconductor according to claim 1, wherein the attachment portion of the cool-down heat transfer rod to the vacuum vessel has substantially the same shape as the attachment portion of the current lead to the vacuum vessel. magnet. 3. A claim characterized in that the tip of the cool-down heat transfer rod on the side of the cryogenic container has substantially the same shape as the low-temperature connection portion that is the connection portion of the current lead to the superconducting coil. The superconducting magnet according to claim 1 or claim 2. Claim 4: A heater to which power is supplied from the outside is provided at the low-temperature connection part where the current lead connects to the superconducting coil, and this current lead is attached in place of the cool-down heat transfer rod during cool-down. The superconducting magnet according to claim 1, wherein the low temperature connection part is heated by the heater.