JPS61116250A - Superconductive device and cooling method thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] - The present invention relates to a superconducting device and a cooling method thereof, and in particular,
The present invention relates to a superconducting device equipped with a refrigerator suitable for use in nuclear magnetic resonance devices, etc., and a cooling device therefor.

[Background of the Invention] A conventional superconducting device equipped with a cryostat for cooling a superconducting coil is! @L shown in Figure 5 and Figure 6
Common and rare.

The figure shows a nuclear magnetic resonance apparatus (usually NM) using a superconducting coil.
It is called R. ) shows a superconducting device for use in a helium container (1) which stores a superconducting coil and is immersed in liquid helium, (1) a helium container (1) which stores a superconducting coil and which is immersed in liquid helium (1), (1) "+7" container (1) which stores a superconducting coil and which is immersed in liquid helium.
The body nitrogen reactor 2 for heat shielding at liquid nitrogen temperature, the liquid nitrogen container 2 and the helium container 1 are housed, and the space between them is maintained in a vacuum to reduce the amount of heat intrusion from the outside. Insulated vacuum container 3. The general configuration includes a service port 4 used for injection and exhaust of refrigerant, insertion of power leads, etc., a helium refrigerator 4L for cooling a helium container 1, and a liquid nitrogen container 2.

Next, various cooling methods in the superconducting device configured as described above will be explained.

The one shown in Figure 7 is called the open method.
Without a refrigerator attached to the cryostat, liquid nitrogen container 2,
A liquid helium container 1 and an evaporative gas helium cooling shield plate 6L are roughly constructed, and liquid nitrogen ('
LNz) and liquid helium (LHe) are sealed and cooled. In this open system, the price of the device is low since there is no refrigerator, but the amount of refrigerant evaporation is L He ≧ 0
．． 5 [t/Hr)1. LN2 b ZO [L/Hr]
As a result, additional LN2 must be injected every few weeks, and operating costs are increased due to the use of refrigerant.

On the other hand, the method shown in Figure 48 is said to be a semi-closed method, in which a refrigerator 7 is installed in the cryostat.
The refrigerator 7 is used to cool the liquid nitrogen container 2 and the gas helium shield 20. This semi-closed system has L
It is possible to reduce the evaporation amount of He + L N 2 to t115 or less, and the refrigerant refill interval is about 6 months or more in the semi-closed system, compared to several weeks in the open system. However, even in this semi-closed system, there is an amount of evaporation of LHe z 0.1 [t/Hr].

Incidentally, in recent years, a so-called closed method, which is a further improvement of the open method and semi-closed method described above, has been considered. In other words, the closed system means L shown in FIG.
The refrigerator 7 installed in the cryostat cools the liquid helium in the liquid helium container 1 and the liquid nitrogen container 2.
By directly cooling the liquid nitrogen inside the cryostat, a cryostat with no evaporation of LHe or LNz can be realized.

For example, for a cryostat that uses a refrigerator to cool liquid helium and liquid nitrogen.

JP-A-59-32758 and JP-A-59-86
It is disclosed in Japanese Patent No. 870.

With the above-mentioned closed system, once LHe and LNx are stored in the liquid helium container 1 and liquid nitrogen container 2, there is no need to refill them. This eliminates the need for tedious work.

What is the advantage of this L? The closed type cryostat has a refrigerator like the semi-closed type, and the equipment price is correspondingly higher, but it is an alternative to the semi-closed type cryostat, which cannot completely reduce LHe evaporation to zero. This will become the mainstream cooling method for medical superconducting devices in the future.

However, the currently proposed closed type cryostats also have some drawbacks.

FIG. 10 shows a typical example of a super-[4] device that employs the closed system currently being considered.

The superconducting ric shown in the diagram houses superconducting coils,
A helium container 1 immersed in liquid helium, a liquid nitrogen container 2 for storing liquid nitrogen and heat shielding the helium container 1 at the liquid nitrogen temperature, and a liquid nitrogen container 2 for storing liquid nitrogen and heat shielding the helium container 1 at liquid nitrogen temperature, and for reducing heat intrusion from the outside. an insulated vacuum container 3 that maintains vacuum;
It is generally constructed of a helium refrigerator 7 for cooling and condensing vaporized gases of liquid helium and liquid nitrogen, and a helium compressor 9 for supplying high-pressure helium to operate the helium refrigerator 7.

In a superconducting device that employs a closed method with such a configuration, when the helium refrigerator 7 is operated, the liquid helium evaporated in the helium container 1 and the liquid nitrogen container 2, and the evaporated gas of liquid nitrogen are A condensing pipe 10.1 provided in the container 1 and 2 is used to absorb heat from the cooling helium gas sent to the helium refrigerator 7 and liquefy it, contributing to cooling. It is something. The helium container 1 and the liquid nitrogen container 2 are usually isolated from the atmosphere by valves 12, respectively, as shown in FIG. It is designed to improve liquefaction efficiency.

However, the above-mentioned closed cooling system has particular safety problems. That is, as mentioned above, since liquid helium and liquid nitrogen are used in a sealed state in each container, if the helium refrigerator 7 breaks down, or for some reason in particular, the adiabatic vacuum inside the cryostat will be destroyed. In this case, heat intrusion into the helium container 1 and the liquid nitrogen container 2 increases, and the pressure inside each container increases due to a rapid increase in the amount of evaporation of the liquid helium and liquid nitrogen. Usually a safety valve,
Although the design is such that the pressure does not rise above a certain level due to the rupture plate, etc., there is a possibility that the pressure inside each container will rise and cool helium and nitrogen gas will blow out to the outside.
When used for medical or industrial purposes, safety is a major issue.

Cooling using an indirect cooling power method can be considered as a method for eliminating the two dangers of pressure rise due to evaporation of liquid helium and liquid nitrogen, and refrigerant blowout.

FIG. 11 shows an example of this indirect cooling method. This method is often used in superconducting devices with high energy physical quantities, and the superconductor to be cooled is provided with a cooling pipe 14 around a conductive coil or a heat shield plate 13. The helium refrigerant connected to the tip of the helium refrigerator 15 times is fed with cooled helium refrigerant, and the helium refrigerant is
The temperature is constantly maintained at a required temperature (for example, 4.5 (K), 77 (K)) by absorbing heat.

If this method is adopted, liquid helium and liquid nitrogen are not used, so in the event of an accident, there is almost no possibility of pressure rising due to evaporation of the refrigerant or cold helium gas or nitrogen gas blowing out, and the safety is as high as described above. This is a huge improvement compared to the conventional method.

However, this indirect cooling method also has major problems. In other words, the object to be cooled is super'l! The problem is that the initial cooling time of the four coils or the heat shield plate is too long. According to this method, if you install a helium refrigerator that has enough cooling capacity to accommodate the steady amount of heat input, the system will not cool down forever, which is the opposite.

If you try to cool it down quickly, you end up with a helium refrigerator that has too much room in its refrigerating capacity on a regular basis.

This will be explained using FIG. 12.

As shown in the diagram, the cryostat consists of a super IIL4 coil 16, a heat shield plate 17 that heat shields the surrounding area, and an insulated vacuum vessel 3 that maintains a vacuum to reduce the amount of heat intrusion from external machining. , a two-stage helium refrigerator 7 is installed. helium refrigerator 7
is a first stage that produces a refrigerant of 77 (K), and 4.51:
A cooling pipe 18 protruding from the second stage L which generates the refrigerant of 5g] surrounds the heat shield plate 17 and the outer periphery of the superconducting coil 16,
The cooling pipe 19 coming out from the second stage is made of Ni
The cooling pipes 18 and 19 surrounding the outer periphery of the conductive coil 16 and the object to be cooled are sufficiently thermally coupled.

The initial cooling of the object to be cooled in this L-shaped configuration is as follows.

First, only the first stage of the helium refrigerator 7 is operated, and the heat shield plate 17 and the superconducting coil 16t-77 (K
Cool to ``l. At this time, open the valve 20t, and !1
The refrigerant discharged from stage L is made to flow simultaneously through heat shield plate 17 and superconducting coil 16. After cooling both the heat shield plate 17 and the superconducting coil 16 at 77 CK)t, the valve 20 is closed, the second stage of the helium refrigerator 7 is activated, and the refrigerant sent out from the second stage is
It is passed through the superconducting coil 16 and cooled to 77 (K) and 14.5 (K).

After initial cooling, if the helium refrigerator 7 continues to operate steadily, the superconducting coil 16 can be maintained at a constant temperature of 4.5CK) and the heat shield plate 171-77(K)K, and the liquid helium ,Liquid nitrogen? It becomes possible to achieve a superconducting state without using it.

Next, let's calculate the initial cooling time 7, Figure 5, and Figure 6
In the nine superconducting device shown in the figure, the superconducting coil part is mO, 5C'm:l, s u s zo (m)
It is assumed that the heat shield part is ktl, Oc"lL]L.

The amount of heat input into the cryostat is 3 (W) at45 (
K], 50 (What 77 (K)), and the capacity of the helium refrigerator to cool this is set to 5 (W) at 4.5 CK: 1.70 CW, with a slight margin for the amount of heat input.
) at 77 (K).

A graph of the refrigerating capacity from 300 CK) to 4.5 (K) is shown in Figure 13.

In the diagram, solid lines 21 and 23 represent the refrigerating capacity of the helium refrigerator, and broken lines 22 and 24 represent the amount of heat entering the cryostat, and the L retaryostat is initially cooled to the amount of cooling that is the difference between the two. The entire temperature change of the cryostat during initial cooling is shown in FIG.

Is the solid line 25 super? The temperature change of the IL4 coil, and the broken line 26 shows the temperature change of the heat shield plate.

As is clear from Figure 14, a helium refrigerator with a cooling capacity almost equal to the amount of steady heat infiltration was used in the 5th ward.
When a cryostat with the dimensions shown in Fig. 6 is cooled, the temperature decreases from about 300 (K) to 77 (K).
It takes an enormous number of cooling days, about 5 [days], from 77 (K) to 4.5 (K).

In the above example, in order to keep the cooling port a for about - weeks, a helium cooler with about 10 times the refrigeration capacity is required, and the steady heat input amount is 3 [W] at 4.5 (K),
Although it is 50CW"1at77(K), the refrigeration capacity is 50CW" at 4.5(K).

It is necessary to install a huge refrigerator with a capacity of 700 (W) at 77CK), resulting in a large refrigerator that is not economical.

As mentioned above, in the conventional closed type Nori2 Iostat, which stores liquid helium and liquid nitrogen and condenses the evaporated gas in a refrigerator, the pressure inside the container increases and the refrigerant blows out in the event of an accident. There is a safety problem, and if an indirect cooling method that improves this point uses a small helium refrigerator that is highly economical in proportion to the amount of steady heat infiltration, it will take an enormous number of days for initial cooling. The problem arises that it is necessary.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned points, and its purpose is to provide a superconducting device that eliminates safety problems such as pressure increase within a container and refrigerant blow-out, and that can quickly perform initial cooling. , and a cooling method thereof.

[Summary of the invention]

The present invention cools the helium container, the liquid helium in the liquid nitrogen container, and the liquid nitrogen before steady cooling is performed using a refrigerator that cools the helium container, the liquid helium in the liquid nitrogen container, and the liquid nitrogen. A superconducting device equipped with an initial cooling means to pre-cool to around the cooling temperature, and before cooling with a refrigerator.

The desired purpose is achieved by using a cooling method for super-heavy 4 equipment in which liquid helium and liquid nitrogen are pre-cooled to around their cooling temperature in a separate system from the refrigerator, and then steadily cooled by the refrigerator. It is made from sea urchin residue.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail based on embodiments of the drawings. The same reference numerals will be used for the same parts as in the past.

An embodiment of the superconducting device of the present invention is shown in Fig. 41, Fig. JX2, and Fig. iii.

The superconducting device of this embodiment shown in the diagram also includes a helium container 1 in which a superconducting coil 29t'' is housed and immersed in liquid helium gum, and a helium container 1 provided around the helium container 1 to reduce heat intrusion into the helium container 1. It is generally composed of a liquid nitrogen container 2, and an insulated vacuum container 3 that stores the liquid nitrogen container 2 and the helium container 1 while keeping the surroundings in a vacuum,
A helium refrigerator 7 is installed in the outer cylinder of the insulated vacuum container 3. Furthermore, in this embodiment, the helium container 1,
and the liquid building block container 2 are each equipped with an initial cooling refrigerant injection port 27, 28 and its exhaust port (not shown), and the helium refrigerant 4, 5 (
Cooling pipes 18 and 19 for passing frozen gas He of 77 (K) and 77 (K) are installed in the inner and outer cylinders of the helium container 1 and the liquid nitrogen container 2, respectively. 2 and the cooling pipes 18, 19 are thermally well coupled.

Next, the cooling method of this embodiment in the L-shaped configuration will be described.

At the time of initial cooling, first, liquid nitrogen is injected into the helium container 1 and the liquid nitrogen container 2 through the injection port 27.28t, and precooled to the liquid nitrogen temperature. After that, helium container 1
The inside of the chamber is replaced with a helium gas atmosphere using gas He, and liquid helium is injected to cool the chamber to the liquid helium temperature. By initial cooling using the above method, the cooling time is usually
It can be done in several days.

Next, the helium container 1 and the liquid nitrogen container 2 are respectively filled with liquid helium 6'? After reaching L degree and liquid nitrogen temperature, the helium refrigerator 7 is operated.
It becomes possible to constantly maintain the helium container 1 and the liquid nitrogen container 2 at the liquid helium temperature and the liquid nitrogen temperature. In this case, the amount of heat intrusion into the helium volume a1 and the liquid nitrogen container 2 are respectively 3 (WE
at 4.2 (K).

5O(W) at 77(K), the helium refrigerator 7 has 3(W″l at 4.2(K), 50(W)a
The refrigeration capacity of t77(K) is sufficient, and it is possible to downsize the helium refrigerator 7 and improve economical efficiency.

- After reaching a steady state, the refrigerants in the helium container 1 and the liquid nitrogen container 2 can be discharged to the outside within each container 1, 2, and in a steady state, indirect cooling method is used. Similarly, it is possible to obtain a safe superconducting device in which there is no need to consider pressure rise due to evaporation of liquid helium or the like and refrigerant blowout in the event of an accident.

In the above example, the helium container 1t-g was cooled with helium, but it is also possible to pre-cool it to the liquid nitrogen temperature with liquid nitrogen and then cool it down to liquid helium once with the helium refrigerator 7. It is.

Normally, the refrigerating capacity of the helium refrigerator 7 has a slight margin with respect to the amount of heat input, so if the cooling is from the elementary temperature of liquid -111, the helium refrigerator 7 is used as shown in Figure 14. Even if it is, it can be cooled for about - weeks.

In this way, it is also possible to perform initial cooling without using expensive liquid helium.

Furthermore, in the above embodiment, when the superconducting coil 29 is energized, the temperature of the superconducting coil 29 increases when the amount of heat entering from the power lead increases, or when there is internal heat generation due to the persistent current switch. When there is a danger, it is necessary to immerse the superconducting coil 29 in liquid helium. Similarly, during maintenance of the helium refrigerator 7, if there is a risk of temperature rise in the superconducting coil 7, it is necessary to immerse the superconducting coil 7 in liquid helium.

By then expelling this liquid helium to the outside, it is possible to safely operate the cryostat without liquid helium on a regular basis.

In addition, the superconducting coil 29 or the helium container should have a sufficient heat capacity, so that even when the amount of heat entering temporarily increases, such as when electricity is applied or during maintenance of the helium refrigerator 7, the temperature of the superconducting coil 29 will not rise excessively. [It is possible to operate stably without immersing liquid helium by keeping the temperature margin at which the four states are destroyed.

In addition, in the above embodiment, during initial cooling, LN2
r It is also possible to use another refrigerator with a large refrigerating capacity without using LHe. The refrigerating route is to flow the frozen GHet directly into a helium container or liquid nitrogen container, or to flow it into the G)le pipe used for steady cooling.Also, another GHe pipe can be installed. You can also stream it there.

FIG. 4 shows another implementation flJ of the invention. The embodiment shown in the diagram adopts an indirect cooling system similar to that shown in Fig. 12, and cools the superconducting coil 16 and heat shield plate 17. It has a cooling system. The cooling systems 30 and 31 for initial cooling may be cooled with a separate helium refrigerator 32, or LNi
, LHet - initial cooling may be performed by direct flow.

Further, in the above embodiments, the helium refrigerator used regularly was housed inside the cryostat, but it may be installed outside.

〔Effect of the invention〕

According to the superconducting device and the cooling method thereof of the present invention described above, the helium container, the liquid helium in the liquid nitrogen container, and the liquid window; , liquid helium in a liquid nitrogen container, and a superconducting device equipped with an initial cooling means for pre-cooling the liquid nitrogen to around its cooling temperature; The super! Since this is a cooling method for 4 devices, a refrigerator is used for steady cooling, and a separate cooling system is used for initial cooling, so there is no pressure increase due to evaporation of liquid helium, liquid nitrogen, etc. during steady cooling. Since there is no risk of refrigerant blowing out, and the initial cooling can be performed quickly, the number of days required for cooling can be significantly reduced, making it very effective when used in this type of equipment.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing one embodiment of the superconducting device of the present invention, FIG. 2 is a perspective view of a helium container adopted therein, FIG. 3 is a cross-sectional view of FIG. 2, and FIG. Superelectric 4 of the present invention
A schematic sectional view showing another embodiment of the apparatus, FIG.
- A partially sectional front view of a CT superelectrometry device, Figure 6 is a side view of Figure 5, Figure 7 is a schematic cross-sectional view of a cryostat showing an example of open type cooling, and Figure 8 is a semi-sectional view. FIG. 9 is a diagram corresponding to FIG. 7 showing a closed cooling system example, FIG. 9 is a diagram corresponding to FIG. 7 showing a closed cooling train, and FIG. 10 is a conventional superconducting device that uses a closed cooling system. ] The schematic sectional view showing i, FIG. 11 is an example of cooling the object to be cooled by indirect cooling method? Figure 12 is a schematic cross-sectional view of a conventional superconducting device that uses an indirect cooling method, Figure 13 is a characteristic diagram showing the relationship between cooling capacity at Fi operating temperature, and Figure 14 is a graph showing the relationship between cooling days and temperature. This is a characteristic diagram showing the relationship. 1... Helium container, 2... Liquid nitrogen container, 3...
・Insulated vacuum container, 4...Service port, 5.7...
・Helium refrigerator, 16...Superconducting coil, 17...
・Heat shield plate, 18.19...Cooling pipe, 27
...Liquid helium inlet, 28...Liquid nitrogen inlet.

Claims (1)

[Claims] 1. A helium container housing a superconducting coil and immersed in liquid helium, and a liquid nitrogen container provided around the helium container to reduce heat intrusion into the helium container;
an insulated vacuum container that stores the liquid nitrogen container and the helium container while keeping the periphery thereof in vacuum; the helium container;
and a superconducting device comprising liquid helium in a liquid nitrogen container, and a refrigerator that cools the liquid nitrogen, in which the helium container and the liquid helium in the liquid nitrogen container are A superconducting device characterized by comprising an initial cooling means for pre-cooling liquid nitrogen to around its cooling temperature. 2. A pressure inlet for injecting an initial cooling refrigerant is provided in each of the helium container and the liquid nitrogen container, and the initial cooling refrigerant is injected into each container through the injection port to adjust the temperature of the liquid helium and the liquid nitrogen. The superconducting device according to claim 1, characterized in that the superconducting device is precooled to a nitrogen temperature. 3. Cooling pipes are provided in the inner and outer cylinders of the helium container and the liquid nitrogen container, and a refrigerant from the refrigerator is introduced through the cooling pipes to steadily cool each of the containers. The superconducting device according to item 1. 4. Liquid helium in a helium container in which the superconducting coil housed inside is immersed, and liquid nitrogen in a liquid nitrogen container provided around the helium container to reduce heat intrusion into the helium container. In a cooling method for a superconducting device in which liquid helium and liquid nitrogen are cooled by a refrigerator, before cooling in the refrigerator, the liquid helium and liquid nitrogen are precooled to around their cooling temperature in a system separate from the refrigerator, and then, A method for cooling a superconducting device, characterized in that steady cooling is performed using the refrigerator. 5. At the time of pre-cooling, first, liquid nitrogen is pressurized into the helium container and the liquid nitrogen container to pre-cool it to the liquid nitrogen temperature, and then the inside of the helium container is replaced with a helium gas atmosphere with gas helium. 5. A method for cooling a superconducting device according to claim 4, wherein liquid helium is injected to cool the superconducting device to a liquid helium temperature. 6. At the time of pre-cooling, an initial cooling refrigerant is injected into each container through injection ports provided in each of the helium container and liquid nitrogen container to pre-cool to the liquid helium temperature and the liquid nitrogen temperature, After that, the refrigerant from the refrigerator is introduced through cooling pipes provided in the inner and outer cylinders of the helium container and the liquid nitrogen container to steadily cool each of the containers. A method for cooling a superconducting device as described in .