JPH0255101B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention is directed to the use of liquid helium to conduct various cryogenic tests using liquid helium as a cooling medium. This invention relates to a device that automatically supplies liquid helium.

BACKGROUND ART Recent developments in cryogenic engineering have been remarkable, and opportunities to conduct various cryogenic tests have recently increased significantly. Cryogenic tests often use liquid helium as a cooling medium. In this case, liquid helium is injected into a cooling container called a cryostat, and the test object or test equipment is heated directly or indirectly with liquid helium. It is usual to perform a low-temperature test by cooling the material to a certain temperature. Therefore, in cryogenic tests, it is necessary to supply liquid helium into the cryostat from a liquid helium storage container (referred to as a dewar).

Generally, to supply such liquid helium, a transfer pipe with an insulated double pipe structure called a transfer tube is usually used.
As shown in the figure, one end of the transfer tube 1 is immersed in liquid helium 3 in a liquid helium storage container 2, and the other end of the transfer tube 1 is immersed in a cryostat 4.
Normally, the inside of the liquid helium storage container 2 is pressurized, and the liquid helium in the storage container 2 is pumped into the cryostat 4 through the transfer pipe 1. Here, pressurization for pumping liquid helium is performed by supplying helium gas under pressure to the upper space in the liquid helium storage container 2, or by installing a heater into the liquid helium in the liquid helium storage container. This is done by immersing it in water and heating it with a heater to increase the pressure.

Note that the tip of the transfer tube 1 inside the cryostat 4 is normally left open close to the bottom surface inside the cryostat 4. That is, when liquid helium is first started to be supplied into the cryostat 4, the liquid helium usually vaporizes at the open end of the transfer tube 1; If the open end is close to the bottom surface inside the cryostat 4, the bottom surface will quickly drop in temperature due to the sensible heat of the vaporized helium gas, and this will eventually prevent the liquid helium from vaporizing. The liquid helium is then injected into the cryostat in the form of liquid helium. However, if the tip of the transfer tube 1 is far from the bottom of the cryostat, the vaporization of liquid helium at the tip of the transfer tube will not be prevented forever, and the liquid helium will This is because it is often impossible to inject the cryostat into the cryostat.

By the way, during a cryogenic test, the liquid helium in the cryostat gradually decreases due to gasification, so in order to continue the cryogenic test, it is necessary to replenish the liquid helium once it has decreased to a certain extent. be. Therefore, conventionally, as shown in Fig. 2, a level sensor 5 for detecting the level of liquid helium is provided in the cryostat, and the level sensor 5 is monitored to determine the level of liquid helium in advance. Once it has descended to near the determined position, the replenishment operation is carried out in the same manner as the initial supply operation. Note that the transfer tube may remain inserted into the cryostat even after the first supply operation, or may be removed from the cryostat after the first supply operation and reinserted in the next replenishment operation.

However, during actual cryogenic tests,
Monitoring the level of liquid helium, the cooling medium, and replenishing liquid helium are secondary tasks for test personnel, who are busy operating the main unit and monitoring the original experimental data. As a result, the cryogenic test may be interrupted without noticing the decrease in liquid helium until it runs out.
In addition, liquid helium was often wasted due to poor replenishment operations. Therefore, it is desired to develop a device that can automatically replenish liquid helium. If such a device were developed, it would not only eliminate the above-mentioned inconveniences, but also reduce the burden on test personnel who were required to monitor liquid levels and replenish the liquid, allowing them to focus on their primary focus on cryogenic testing. , the benefits are considered to be large.

As mentioned above, in order to automate the replenishment of liquid helium during cryogenic tests, the tip of the transfer tube mentioned above is kept immersed in the cryostat at all times during cryogenic tests, and the liquid helium in the cryostat is kept immersed. Automatically detects the liquid level, automatically starts pressurizing the liquid helium storage container in response to the detection signal (for example, heating and pressurizing with a heater as described above or pressurizing with helium gas), and transfers the liquid helium. It is conceivable to automatically supply liquid helium from the storage container via the transfer pipe into the cryostat by automatically opening the valve 6 of the pipe. However, this type of replenishment system actually has problems as described in the next section, making it difficult to put it into practical use.

Problems to be Solved by the Invention In actual cryogenic experiments, the length of the transfer tube for transferring liquid helium from the liquid helium storage container to the cryostat is usually several meters, and the initial Usually, a considerable amount of time has elapsed between one liquid helium supply operation and the next replenishment operation, or between the previous replenishment operation and the next replenishment operation. On the other hand, although the transfer pipe has an insulated double pipe structure, complete insulation is not possible, so as mentioned above, if time has passed since the first liquid helium supply operation or the previous liquid helium supply operation, In the intermediate portion of the transfer tube, liquid helium is gasified, and the temperature of the gasified helium and the inner wall of the transfer tube rises to near room temperature. If replenishment work is started in such a state, helium gas inside the transfer tube, which is close to room temperature, and gas warmed by the inner wall of the transfer tube will be pumped into the cryostat, and the amount will be greater than the amount described above. Since the length of the transfer tube is quite long, the amount is quite large.

If a considerable amount of helium gas close to room temperature is pumped into the cryostat in this way, the gas will raise the temperature of the liquid helium remaining in the cryostat and turn it into gas, causing the liquid helium to be wasted. It will end up being put away. In other words, in a cryostat, as mentioned above, the open end of the transfer tube is usually kept close to the internal bottom surface of the cryostat, and in this state there is a distance close to room temperature from the tip of the transfer tube. If a certain amount of helium gas is blown into the cryostat, a considerable amount of the previous residual liquid helium in the cryostat will quickly vaporize. Therefore, with this method, there is a problem that the loss of liquid helium is extremely large, the amount of expensive liquid helium consumed increases, and the cost of cryogenic testing becomes extremely high, making it difficult to put it into practical use. .

This invention was made against the background of the above circumstances, and is an apparatus that can automatically replenish liquid helium to a cryostat without causing loss due to vaporization of residual liquid helium in the cryostat during the replenishment operation. The purpose is to provide the following.

Means for Solving the Problems The present invention provides an apparatus for supplying liquid helium from a liquid helium storage container into a cryostat, in which one end is immersed in liquid helium in the liquid helium storage container and the other end is immersed in liquid helium in the liquid helium storage container. a heat-insulating transfer pipe inserted into the cryostat;
a pressure increasing means for increasing the pressure within the liquid helium storage container; a liquid level detector for detecting the liquid helium level within the cryostat; a discharge pipe that communicates with the cryostat, a discharge valve that opens and closes the discharge pipe, a temperature detector that detects the temperature within the discharge pipe, and a transfer pipe that is located closer to the cryostat than the branch position of the discharge pipe. It is characterized by comprising an on-off valve that opens and closes, and a control section that controls the release valve, the on-off valve, and the pressure increase means in accordance with signals from the liquid level detector and the temperature sensor. be.

Function In the apparatus of the present invention, when liquid helium is initially supplied into the cryostat, one end of the transfer tube is inserted into the liquid helium in the liquid helium storage container, and the other end is inserted into the cryostat. The pressure increase means is operated to increase the pressure inside the storage container and at the same time open the on-off valve. However, the discharge valve should be kept closed. In this way, the liquid helium in the liquid helium storage container is transferred and supplied into the cryostat via the transfer pipe by the pressure. When the level of liquid helium in the cryostat reaches a predetermined level, the liquid level detector detects this, and in response to the detection signal, the on-off valve is closed by a control signal from the control unit.
The pressure increase means are deactivated, thereby stopping the supply of liquid helium to the cryostat.

After a predetermined amount of liquid helium is stored in the cryostat in this way, various cryogenic tests are usually started, but during this time the liquid helium in the cryostat gradually evaporates and gradually The amount will decrease. During this time, the liquid helium in the transfer tube exposed to the atmosphere vaporizes, and the temperature of the vaporized helium gas and the inner wall of the transfer tube rises to near room temperature.

As mentioned above, when the amount of liquid helium in the cryostat decreases and its level reaches a certain predetermined level, the liquid level detector detects this, and in response to the detection signal, a control signal is sent from the control unit. This starts the operation of the pressure increasing means and opens the release valve. However, in this state, the on-off valve is closed. Therefore, the helium gas that has been vaporized in the transfer pipe and whose temperature has risen to near room temperature after the previous supply is discharged to the outside via the discharge pipe and the discharge valve by the pressure applied by the pressure increasing means.
When the temperature detector detects that the temperature of the released gas has dropped to a predetermined temperature,
In other words, when it is confirmed that the helium gas near room temperature that was present in the transfer tube has been almost completely exhausted and the inner wall of the transfer tube has been completely cooled, the control section responds to the signal from the temperature sensor. The release valve is closed and the on-off valve is opened by a control signal from the control signal. Note that the pressure increasing means continues to operate as is. Therefore, as in the first supply, the liquid helium in the storage container is supplied into the cryostat via the transfer pipe. When the level of liquid helium in the cryostat reaches a certain level, the on-off valve is closed by a command from the control unit in response to a signal from the liquid level detector, and the operation of the pressure increasing means is stopped. Helium supply is suspended.

Thereafter, when the liquid helium in the cryostat decreases to a certain level again, liquid helium is replenished in the same manner as described above.

As mentioned above, during replenishment, the helium gas near room temperature that initially existed in the transfer pipe is released to the outside via the release pipe and the release valve, and then
Supply of liquid helium gas into the cryostat is started only when the temperature detector detects that the temperature of the gas to be released has dropped to a certain temperature. Therefore, the helium gas vaporized in the transfer pipe and heated to near room temperature and the helium gas heated to near room temperature on the inner wall of the transfer pipe will not be blown into the cryostat. Therefore, by blowing helium gas near room temperature into the cryostat, liquid helium remaining in the cryostat is effectively prevented from being vaporized and lost.

In this manner, the apparatus of the present invention can automatically replenish liquid helium without losing the liquid helium remaining in the cryostat at the time of replenishment.

Example FIG. 1 shows an example of the apparatus of the present invention.

In FIG. 1, liquid helium 3 is stored in a liquid helium storage container 2, and one end 1A of a transfer tube 1 is immersed in this liquid helium 3. The transfer pipe 1 is generally referred to as a transfer tube, and usually has a heat-insulated double pipe structure. The other end 1B of the transfer tube 1 is inserted into the cooling chamber 4A of the cryostat 4, and its tip is close to the bottom surface of the cooling chamber 4A.

An on-off valve 10 for opening and closing the pipeline of the transfer pipe 1 is provided at a position as close as possible to the cryostat 4 in the transfer pipe 1, and this on-off valve 10 is composed of a microprocessor or the like. It is designed to be controlled by a control section 11. Further, a discharge pipe 12 that communicates with the outside is branched from a position in the transfer pipe 1 that is close to the on-off valve 10 (however, a position closer to the liquid helium storage container 2 than this on-off valve 10). The line 12 is provided with a discharge valve 13 and a temperature detector 14 for opening and closing the line. The discharge valve 13 is controlled by the control section 11, and the temperature sensor 14 is arranged so that its detection signal is given to the control section 11.

Furthermore, a liquid level detector 15 for detecting the liquid level of the liquid helium 3 is disposed inside the liquid helium storage container 2, and a heater is provided as a pressure increasing means for increasing the pressure inside the storage container 2. 1
6 are arranged. This heater 16 is controlled by the control section 11, and a detection signal from the liquid level detector 15 is supplied to the control section 11. The liquid helium storage container 2 also includes a pressure detector 17 and a gas release valve 1 for detecting the internal pressure of the storage container 2 (pressure of vaporized helium gas).
8 are connected. On the other hand, a liquid level detector 19 for detecting the level of the supplied liquid helium is disposed inside the cryostat 4, and a detection signal of this liquid level detector 19 is sent to the control unit 11. It's summery.

The operation of the above embodiment will be explained next.

First, when liquid helium is supplied to the empty cryostat 4, the heater 16 is activated to heat the liquid helium 3 in the liquid helium storage container 2 and increase the vapor pressure in the storage container 2. Further, while the discharge valve 13 remains closed, the on-off valve 10 is opened. In this way, the pressure increase in the storage container 2 causes the liquid helium 3 in the storage container 2 to be sent into the transfer pipe 1, and further as shown by the solid line arrow A in FIG.
As shown in the figure, the liquid passes through the on-off valve 10 and flows into the cryostat 4. At this time, the pressure inside the storage container 2 is detected by the pressure detector 17 connected to the storage container 2, and the signal is given to the control section 11 to feedback control the heat generation of the heater 16, Keep the internal pressure of 2 constant. In this way, when liquid helium is supplied into the cryostat 4 and its level reaches a predetermined level, it is detected by the liquid level detector 19, and the detection signal is given to the control section 11. , the operation of the heater 16 is stopped by a control signal from the control unit 11, the on-off valve 10 is closed, and the discharge valve 18 is opened. This completes the first liquid helium supply operation.

After that, when the liquid helium in the cryostat 4 decreases to a certain level, the liquid level detector 19 detects it, and the detection signal is given to the control section 11. Therefore, the operation of the heater 16 is started, and
The discharge valve 13 is opened and opened. The operation of the heater 16 increases the pressure in the liquid helium storage container 2 as described above, and the pressure in the liquid helium storage container 2 between the position of the storage container 2 in the transfer pipe 1 and the branch position of the discharge pipe 12 is close to room temperature. Helium gas flows through the discharge pipe 12 and the discharge valve 13 as shown by the broken line arrow B in FIG.
It is then released to the outside. The temperature of this released helium gas is detected by a temperature detector 14. This detected temperature means that the helium gas near room temperature that had accumulated in the transfer tube 1 has been almost completely exhausted.
Moreover, when the inner wall of the transfer pipe 1 is sufficiently cooled, the temperature decreases rapidly. Therefore, when the temperature drops to a predetermined liquid helium temperature or a temperature close to it, the control unit 11 generates a control signal to close the discharge valve 13 based on the signal from the temperature detector 14, and at the same time or subsequently, the control unit 11 generates a control signal to close the discharge valve 13. A control signal is generated to open the valve 10. This allows release valve 1
3 is closed, while the on-off valve 10 is opened, so that the liquid helium sent from the liquid helium storage container 2 into the transfer pipe 1 by the pressure is transferred to the first
As shown by the solid arrow A in the figure, it flows into the cryostat 4 through the on-off valve 10. When liquid helium is replenished into the cryostat 4 in this way and reaches a certain level, the opening/closing valve 10 is closed by a detection signal from the liquid level detector 19 in the same way as in the first supply described above. The operation of the heater 16 is stopped and the discharge valve 18 is opened.

In the above embodiment, a heater is used as a pressure increasing means, but in some cases, the pressure may be increased by supplying helium gas under pressure from the outside into the storage container 2 without using a heater. It may be configured as follows.

Effects of the Invention As is clear from the above explanation, according to the apparatus of the present invention, when replenishing liquid helium from the liquid helium storage container to the cryostat through the transfer pipe, it is possible to Helium gas that has vaporized in the transfer pipe and has risen in temperature to near room temperature between the previous replenishment and the next replenishment, and helium gas that has been warmed by the inner wall of the transfer pipe whose temperature has risen to near room temperature. This effectively prevents the residual liquid helium from being blown into the cryostat, and the remaining liquid helium in the cryostat is prevented from being lost due to the injection, without unnecessarily increasing liquid helium consumption. Liquid helium can be refilled automatically. As a result, it becomes possible to automatically replenish liquid helium to a cryostat at low cost.
Various effects can be achieved, such as preventing forgetting to replenish liquid helium during cryogenic tests and hindering the execution of the tests, and reducing the burden on test personnel.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an automatic liquid helium supply system of the present invention, and FIG. 2 is a schematic diagram showing an example of a conventional liquid helium supply system. 1...Transfer pipe, 2...Liquid helium storage container, 3...
Liquid helium, 4...Cryostat, 10...Opening/closing valve, 11...Control unit, 12...Discharge pipe line, 13...Discharge valve, 14...Temperature detector, 16...Heater as pressure increasing means, 19...Liquid level detector .

Claims (1)

[Claims] 1. A device for supplying liquid helium from a liquid helium storage container into a cryostat, one end of which is immersed in liquid helium in the liquid helium storage container, and the other end of which is immersed in the cryostat. A transfer pipe having an adiabatic structure to be inserted, a pressure increasing means for increasing the pressure in the liquid helium storage container, a liquid level detector for detecting the liquid helium level in the cryostat, and a cryostat in the transfer pipe. A discharge pipe branching from the transfer pipe at a nearby location and communicating with the outside, a discharge valve opening and closing the discharge pipe, a temperature detector detecting the temperature within the discharge pipe, and a branch position of the discharge pipe. The cryostat has an on-off valve that opens and closes the transfer pipe at a position closer to the cryostat, and a control section that controls the release valve, the on-off valve, and the pressure increasing means in response to signals from the liquid level detector and the temperature sensor. An automatic liquid helium supply device characterized by: