JPH0349023B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a superfluid helium generator,
In particular, the present invention relates to improvements in a superfluid helium generator that supplies liquid helium from a normal fluid helium tank to a superfluid helium tank.

[Technical background of the invention and its problems]

As is well known, liquid helium transitions to a superfluid state at temperatures below its lambda point (2.17K).
Such superfluid helium is used as a refrigerant for cooling superconducting coils and in various experiments.

By the way, to generate superfluid helium,
Generally, a method is used in which the inside of a container containing liquid helium is evacuated using a vacuum pump, and the liquid helium inside the container is cooled by the latent heat of vaporization at that time. Since the amount of liquid helium stored inside the container is limited, it cannot be operated for a long time, and liquid helium must be replenished at regular intervals. In this case, it is complicated to frequently replenish liquid helium from the outside to the superfluid helium tank. In particular, if a 4.2K constant-flow helium tank is added to the superfluid helium generator to cool the superconducting magnet device, it is more efficient to supply liquid helium from this constant-flow helium tank. be.

As a superfluid helium generator that satisfies such requirements, there is one shown in FIG. 8, for example.

That is, in FIG. 8, reference numeral 1 denotes a normal flow helium tank whose outer surface is covered with a heat shield member 3 via a vacuum insulation tank 2, and which contains normal flow helium P of 4.2K inside. Inside this normal-flow helium bath 1, there is a superconducting coil 4 to be cooled near the bottom surface, and a vacuum vessel 5 is placed above this superconducting coil 4, respectively.
It is housed in a relationship that is immersed in. Vacuum container 5
a bottomed cylindrical portion 6 that protrudes downward from its bottom surface so as to fit into the center hole of the superconducting coil 4;
A cylindrical upper projecting peripheral wall 7 extending from the upper surface above the liquid level of the normally flowing helium P is integrally formed. A superfluid helium tank 8 is housed inside the vacuum container 5, and a vacuum insulation tank 9 is formed between the superfluid helium tank 8 and the vacuum container 5. The superfluid helium tank 8 is
It has a bottomed cylindrical part 10 that fits into the bottomed cylindrical part 6 of the vacuum insulation tank 5 from below the bottom surface, and superfluid helium Q is accommodated inside.

In addition, reference numeral 11 in the figure denotes a helium gas exhaust pipe which is provided from the upper wall of the superfluid helium tank 8 to the inside of the upper circumferential wall 7 of the vacuum vessel 5 and through the upper wall of the normal flow helium tank 1 in an airtight manner. It is. The upper end of this exhaust pipe 11 is connected to the vacuum pump 1 via piping 12.
Connected to 3.

Therefore, a communication pipe 16 is provided inside the vacuum insulation tank 9 to connect the normal flow helium tank 1 and the superfluid helium tank 8. The communication pipe 16 includes a valve 17 for selectively opening and closing the communication pipe 16.
is inserted. This valve 17 can be opened and closed by an operating rod 18 guided to the upper wall of the normal flow helium tank 1.

The superfluid helium generator configured in this manner is used as a testing device for the superconducting coil 4 by installing a measuring probe in the bottomed cylindrical portion 10 of the superfluid helium tank 8. When the amount of superfluid helium Q stored becomes small, the valve 17 is opened by operating the operating rod 18, and the normal fluid helium P stored in the normal fluid helium tank 1 is transferred to the superfluid helium tank 8. supply After introducing normal flow helium at 4.2K into the superfluid helium tank 8, the valve 17 is closed and the vacuum pump 13 is operated to reduce the pressure inside the superfluid helium tank 8. As the pressure decreases, liquid helium cools to a temperature corresponding to its saturated vapor pressure, and when it reaches the lambda point, it transitions to a superfluid state. This device generates superfluid helium in this way.

However, the conventional superfluid helium generator has the following problems.

That is, when the temperature Ts of the liquid helium contained in the superfluid helium tank 8 becomes below the lambda point, the thermal conductivity of the superfluid helium becomes extremely large. Therefore, since the temperature gradient inside the connecting pipe 16 from the superfluid helium tank 8 to the valve 17 becomes approximately zero, the temperature on the superfluid helium tank side of the valve 17 also decreases.
It becomes Ts. Since the distance between the shut-off portion of the valve 17 is also extremely short, the temperature difference δT occurring between both ends of the shut-off portion is also extremely small. Therefore, the temperature Ts of the liquid helium contained in the superfluid helium tank 8 is (2.18−δT)
When the temperature drops below K, the temperature on the constant flow helium tank 1 side of the valve 17 also crosses the lambda point. As mentioned above, the thermal conductivity of liquid helium below the lambda point is very high, so when the temperature on the normal flow helium tank 1 side of the valve 17 drops below the lambda point, the temperature inside the connecting pipe 16 will decrease. The gradient disappears, and eventually even the temperature at the helium supply port of the constant-flow helium tank 1 falls below the lambda point.

Normally, the specific gravity of liquid helium is maximum at the lambda point, so the superfluid helium at the lambda point generated at the helium supply port of the constant flow helium tank 1 will fall to the bottom of the constant flow helium tank 1 one after another. . Therefore, the steady state does not occur until all of the helium located below the upper surface of the helium supply port in the normal flow helium tank 1 becomes superfluid helium. In other words, it is the liquid helium in the superfluid helium tank 8 that is desired to be cooled to below the lambda point, but in conventional equipment, the liquid helium in the superfluid helium tank 1 is cooled to below the lambda point.
Even the liquid helium inside had to be brought into a superfluid state, which not only increased cooling costs but also required a long time for initial cooling.

[Purpose of the invention]

The present invention was made in view of these problems, and its purpose is to suppress the heat flow between the normal flow helium tank and the superfluid helium tank, and thereby to reduce the initial cooling of the superfluid helium. An object of the present invention is to provide a superfluid helium generator that can efficiently perform the following steps in a short period of time.

[Summary of the invention]

In the present invention, a first valve is inserted on the superfluid helium tank side of a communication pipe connecting a superfluid helium tank and a normal flow helium tank, and a second valve is inserted on the normal flow helium tank side of the communication pipe. exists inside the communicating pipe and between the two valves with the first and second valves closed when the liquid helium inside the superfluid helium tank is cooled to below the lambda point. The invention is characterized in that it is equipped with means for vaporizing or discharging liquid helium.

〔Effect of the invention〕

By employing the above configuration, a helium gas having low thermal conductivity or a vacuum layer can be interposed inside the communication pipe that connects the superfluid helium tank and the normal flow helium tank. Therefore, when cooling the liquid helium inside the superfluid helium tank, it is possible to create a temperature gradient between the superfluid helium tank and the normal flow helium tank using the helium gas or vacuum layer. , heat flow between the normal flow helium tank and the superfluid helium tank can be significantly reduced. Therefore, in this case, there is no need to cool the liquid helium inside the constant flow helium tank below the lambda point.
Liquid helium inside a superfluid helium tank can be efficiently cooled.

[Embodiments of the invention]

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

FIGS. 1 and 2 show an example in which the present invention is applied to the above-mentioned test apparatus, and the same parts as in FIG. 8 are given the same reference numerals. Therefore, the explanation of the overlapping parts will be omitted.

This embodiment differs from the conventional example in the following points.
That is, the connecting pipe 21 provided inside the vacuum insulation tank 9 and connecting the normal-flow helium tank 1 and the superfluid helium tank 8 has two valves, that is, a first valve on the superfluid helium tank 8 side. 22, and a second valve 23 is inserted on the side of the normal flow helium tank 1. Both valves 22 and 23 can be opened and closed by operating rods 24 and 25 extending to the upper wall of the normal flow helium tank 1, respectively. Between the valves 22 and 23 of the communication pipe 21, one end side of a pipe 26 extends to the upper part of the normal flow helium tank 1, passing through the upper wall of the vacuum container 5 and the upper wall of the normal flow helium tank 1, respectively, in an airtight manner. It is connected. The other end of the pipe 26 is connected to the upper end of the helium gas exhaust pipe 11 via an exhaust valve 27 and a pipe 28 . The exhaust valve 27 is connected to the operating rod 29
The structure allows for opening and closing operations. Note that at the upper end of the exhaust pipe 11 and the pipe 2
A butterfly valve 30 that selectively opens and closes the exhaust pipe 11 is provided between the part where 8 is connected and the part leading to the superfluid helium tank 8 .

The operation of the apparatus according to this embodiment configured as described above will be explained with reference to FIG. 1 and FIG. 2, which shows section A in the figure in detail.

First, when supplying liquid helium into the superfluid helium tank 8, the operating rods 24 and 25 are operated to open the first and second valves 22 and 23.
As a result, liquid helium is supplied from the normal flow helium tank 1 to the superfluid helium tank 8. Once the liquid helium has been transferred, the first and second valves 2
2 and 23, the butterfly valve 30 is closed and the exhaust valve 27 is opened. At this time, the inside of the communication pipe 21 is filled with liquid helium. When the vacuum pump 13 is operated in this state, the liquid helium inside the communication pipe 21 is vaporized, and the helium gas generated thereby is transferred from the pipe 26 to the exhaust valve 27 to the pipe 2.
8 - exhaust pipe 11 - piping 12 - vacuum pump 13 for evacuation. When the helium gas inside the connecting pipe 21 is exhausted and the degree of vacuum has improved, the exhaust valve 2
Close 7.

Next, the superfluid helium tank 8 contained
When cooling liquid helium at 4.2K to 2.18K, the exhaust valve 27 is closed, the butterfly valve 30 is opened, and the vacuum pump 13 is operated to reduce the pressure inside the superfluid helium tank 8. By this,
The liquid helium contained in the superfluid helium tank 8 is cooled to a temperature corresponding to the saturated vapor pressure, and finally becomes a superfluid state.

In this case, the superfluid helium tank 8
and a communication pipe 21 connecting the constant flow helium tank 1.
Since the inside of the tube is in a vacuum state, heat conduction by superfluid helium is blocked in this vacuum section. In other words, it is possible to create a temperature gradient in this vacuum portion.

As shown in FIG. 3, a heater 36 is provided in the connecting pipe 21, and a power source 38 is connected to the heater 36 via a switch 37, so that the switch 37 is turned on when the helium inside the connecting pipe 21 is exhausted. By doing so, the evaporation of helium is promoted by the heater 36, and the exhaust speed inside the communication pipe 21 can be increased.

FIGS. 4 and 5 show an example of the configuration of an apparatus that achieves the effects of the present invention without evacuating the inside of the connecting pipe 22.

That is, in this case, the first valve 22 is
It is arranged below the valve 23 of.
Therefore, the communication pipe 21 has a portion 21a that extends relatively long in the vertical direction. As shown in FIG. 5, a protruding peripheral wall 41 that protrudes inward is provided inside this portion 21a.

The operation of this embodiment configured in this way will be explained.

First, when supplying liquid helium to the superfluid helium tank 8, the first and second valves 22, 23
is opened, and the liquid helium contained inside the normal-flow helium tank 1 is transferred to the inside of the superfluid helium tank 8. When the supply of liquid helium to the superfluid helium tank 8 is completed, the first and second valves 22, 2
3 is closed, and the butterfly valve 30 is further opened to operate the vacuum pump 13. In this state, the inside of the communication tube 21 is filled with liquid helium. As the pressure inside the superfluid helium tank 8 is reduced, the liquid helium inside the superfluid helium tank 8 is cooled to a temperature corresponding to the saturated vapor pressure. Along with this, the liquid helium P inside the communication pipe 21 is also cooled, and its density gradually increases. Therefore, a gas phase is generated in the portion between the valves 22 and 23 inside the communication pipe 21. Since the first valve 22 is located below the second valve 23, the liquid helium P accumulates on the first valve 22 side, and the gas phase accumulates on the second valve 23 side. As the cooling progresses further and the liquid helium inside the superfluid helium tank 8 becomes below the lambda point, the gas phase portion increases further and the inside of the communication tube 21 is almost filled with helium gas.

If the inside of the communication tube is filled with helium gas in this manner, a temperature gradient can be imparted to the helium gas, so that the above-described effects can be obtained.

Note that superfluid helium has the property of creeping up the inner surface of the pipe. For this reason, in this embodiment, a projecting peripheral wall 41 is provided in the gas phase forming portion of the communication pipe 21, and this projecting peripheral wall 41 prevents the superfluid helium from rising. Such a projecting peripheral wall 41 is
By providing multiple stages, the effect can be further enhanced. As a result, heat inflow through the superfluid helium liquid film formed on the inner surface of the tube wall can also be reduced.

Further, instead of such a projecting circumferential wall 41, for example, as shown in FIG. When the free liquid level of the liquid helium P drops to between the intermediate valve 42 and the first valve 22, the intermediate valve 42 is closed by the operating rod 43 to prevent the superfluid helium from rising up. You can do it like this.

FIG. 7 is a diagram showing an example in which the present invention is applied to a pressurized superfluid helium generator.

That is, in the figure, 51 is a normal flow helium tank containing 4.2K normal flow liquid helium P, and 52 is an unsaturated superfluid helium tank containing unsaturated superfluid helium. A saturated superfluid helium tank 53 for cooling the inside of the unsaturated superfluid helium tank 52 is housed inside the unsaturated superfluid helium tank 52 . One end side of this saturated superfluid helium tank 53 is
Julia Thomson (hereinafter referred to as "JT") valve 5
4. Connected to the normal flow helium tank 51 via the primary side of the JT heat exchanger 55. The other end of the saturated superfluid helium tank 53 is connected to the suction port of a vacuum pump 56 via the secondary side of the JT heat exchanger 55. A discharge port of the vacuum pump 56 is connected to a refrigerator 58 via a compressor 57. The refrigerator 58 cools the inside of the constant flow helium tank 51.

The normal flow helium tank 51 and the unsaturated superfluid helium tank 52 are connected by a connecting pipe 61. The unsaturated superfluid helium tank 5 of this connecting pipe 61
A first valve 62 is inserted in the portion located on the second side. Further, a second valve 63 is inserted into a portion of the communication pipe 61 located on the normally flowing helium tank 51 side. Both valves 6 of the connecting pipe 61
A pipe 64 is connected between 2 and 63, and this pipe 64 is connected to a vacuum pump 6 through an exhaust valve 65.
6. A heater 6 is installed in the communication pipe 61.
7 is installed.

On the other hand, the refrigerator 58 and the unsaturated superfluid helium tank 5
2 is connected by a communication pipe 71. A third valve 72 is inserted into a portion of the connecting pipe 71 located on the unsaturated superfluid helium tank 52 side. Further, a fourth valve 73 is inserted into a portion of the communication pipe 71 located on the refrigerator 58 side.
A pipe 74 is connected between the valves 72 and 73 of the communication pipe 71, and the pipe 74 is connected to the vacuum pump 66 via an exhaust valve 75. A heater 76 is installed in the communication pipe 71. Note that a safety valve 77 is connected to the pipe 64, which opens when there is overpressure inside the pipe 64. And both helium tanks 51, 52, JT heat exchanger 55,
JT valve 54, each valve 62, 63, 65, 72, 73
The tubes 61, 64, 71, 74, etc. are covered with a heat shield member 78 to prevent heat from entering from the outside.

Next, the operation of the device configured in this way will be explained.

First, when initially injecting liquid into the unsaturated superfluid helium tank 52, the exhaust valves 65 and 75 are both closed, and the valves 62, 63, 72, and 73 are opened to inject liquid helium. 4.2K liquid helium
When sufficient liquid helium is accumulated inside the normal flow liquid helium tank 51 and the unsaturated superfluid helium tank 52, the valve 72,
73, open the valve 75, and operate the vacuum pump 66 to evacuate the inside of the communication pipe 71. At this time, the heater 76 may be energized to increase the exhaust speed.

Next, the valves 62 and 63 are closed loosely enough to allow some liquid helium to leak, and cooling is started. Cooling is carried out by maintaining the inside of the unsaturated superfluid helium tank 52 at one pressure, and by using a vacuum pump 56, a compressor 57,
This is done by operating the refrigerator 58.
In other words, due to the operation of the vacuum pump 56, a portion of the 4.2K helium in the constant flow helium tank 51 is
It flows through a path from the primary side of the heat exchanger 55 to the JT valve 54 to the saturated superfluid helium tank 53 to the secondary side of the JT heat exchanger 55. The inside of the saturated superfluid helium tank 53 is turned into the unsaturated superfluid helium tank 5 by the vacuum pump 56.
Assuming that the helium is evacuated to a saturated vapor pressure corresponding to a temperature lower than the temperature inside the tank 2, the helium leaving the normal flow helium tank 51 will be heated to a temperature of, for example, 2.2K while passing through the primary side of the JT heat exchanger 55. pre-cooled to
Next, JT expands with the JT valve and becomes gas and liquid.
This liquid evaporates while passing through the saturated superfluid helium tank 53, thereby cooling the helium in the unsaturated superfluid helium tank 52.

The density of liquid helium in the unsaturated superfluid helium tank 52 changes until it is cooled to the lambda point, but since the valves 62 and 63 are slightly open,
The pressure within the unsaturated superfluid helium tank 52 is maintained at one atmosphere.

When the liquid helium inside the unsaturated helium tank 52 reaches the lambda point, the valves 62 and 63 are closed, and the valve 65 is closed.
Open it and drive the vacuum pump 66. As a result, the inside of the communication pipe 61 is exhausted. At this time, the heater 67 may be energized to increase the exhaust speed. As a result, the heat flow between the normal flow helium tank 51 and the unsaturated superfluid helium tank 52 through the inside of the communication pipe 61 is significantly reduced, so that the liquid helium contained in the unsaturated superfluid helium tank 52 is cooled. can be done efficiently.

By the way, such a pressurized superfluid helium generator is usually used for cooling a superconducting magnet device, etc. Therefore, in this case, it is necessary to fully consider countermeasures against superconductor breakdown. In this device, the valves 62 and 65 are composed of electromagnetic valves.
2 and 65 are fully opened when pressure vibration within the unsaturated superfluid helium tank 52 at the time of superconductor breakdown is detected. When the valves 62 and 65 are opened, the helium gas in the unsaturated helium tank 52 flows through the safety valve 77.
It is now being released into the atmosphere through

As described above in each embodiment, according to the present invention, the aforementioned effects can be fully achieved. Furthermore, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view showing a schematic configuration of a superfluid helium generator according to a first embodiment of the present invention, and FIG.
The figure is a partially cutaway enlarged side view showing in detail the A part in the same figure, FIG. 3 is a partially cutaway enlarged side view showing the main part of a modification of the same device, and FIG. 4 is a second embodiment of the present invention. FIG. 5 is a longitudinal cross-sectional view showing a schematic configuration of the superfluid helium generator according to the example, FIG. 5 is a partially cutaway enlarged side view showing section B in the same figure in detail, and FIG. FIG. 7 is a flow diagram showing a schematic configuration of a superfluid helium generator according to a third embodiment of the present invention, and FIG. 8 is a schematic diagram showing a schematic configuration of a conventional superfluid helium generator. FIG. 1,51...Normal flow helium tank, 4...Superconducting coil, 8...Superfluid helium tank, 11...Exhaust pipe, 13,56,66...Vacuum pump, 16,2
1, 61, 71... connecting pipe, 17, 22, 23,
62, 63, 72, 73... Valve, 18, 24, 2
5, 43... Operating rod, 27, 65, 75... Exhaust valve, 36, 67, 76... Heater, 41... Projection wall, 42... Intermediate valve, 52... Unsaturated superfluid helium tank, 53 ...Saturated superfluid helium bath, 54...
...JT valve, 55...JT heat exchanger, 57...compressor, 58...refrigerator, 77...safety valve, P...
...normal fluid helium, Q... superfluid helium.

Claims (1)

[Scope of Claims] 1. A normal flow helium tank containing normal flow liquid helium, a superfluid helium tank containing superfluid liquid helium, a communication pipe connecting these helium tanks, and a communication pipe connecting these helium tanks. In the superfluid helium generator, the superfluid helium generator is equipped with a cooling means for cooling the normal flow liquid helium supplied from the normal flow helium tank to the superfluid helium tank via a pipe to a temperature below the lambda point. first and second valves that are respectively inserted in the superfluid helium tank side and the normal flow helium tank side and are closed before operating the cooling means, and the communication when these valves are closed; A superfluid helium generator comprising a discharge means for discharging liquid helium present in a portion of the pipe located between the two valves. 2. The superfluid helium generator according to claim 1, wherein the evacuation means includes a vacuum pump that evacuates a portion of the communication pipe located between the two valves. 3. The superfluid helium generator according to claim 2, wherein the discharge means includes a heater that heats a portion of the communication pipe located between the two valves. 4. A normal-flow helium tank that contains normal-flow liquid helium, a superfluid helium tank that contains superfluid liquid helium, and a connecting pipe that connects both helium tanks, and the normal-flow helium tank that contains normal-flow liquid helium. In the superfluid helium generator, the superfluid helium generator is equipped with a cooling means for cooling the normal flow liquid helium supplied from the fluid helium tank to the superfluid helium tank to a temperature below the lambda point, in which the connecting pipe is connected to the superfluid helium tank side. first and second valves, each of which is interposed in such a manner that one of the valves is located below the one located on the side of the normally flowing helium bath, and which are closed prior to operating the cooling means; is closed, the liquid helium existing between the two valves in the communication pipe is cooled with liquid helium in the superfluid helium tank through a component of the valve located below to generate a gas phase. A superfluid helium generator characterized by: 5. The communication pipe according to claim 4, wherein the communication pipe is provided with a projecting peripheral wall inside a portion extending in the vertical direction between the first valve and the second valve. Superfluid helium generator. 6. The superfluid helium generator according to claim 4, wherein the communication pipe is provided with an intermediate valve between the first valve and the second valve.