JPH08320271A - Gas leak detecting device - Google Patents

Abstract

PURPOSE: To quickly find the gas leaked position of a heat insulated vacuum vessel and specify the generating position by setting two neodymium(Nd) flat permanent magnets with a fixed space so that S-pole and N-pole are mutually opposed, and arranging a positive electrode and a negative electrode between the flat permanent magnets so as to be right-angled to each other. CONSTITUTION: Two neodymium(Nd) flat permanent magnets 3 are set with fixed space so that S-pole and N-pole are mutually opposed, and a positive electrode 1 and a negative electrode 2 are arranged between the flat permanent magnets 3 so as to be right-angled to each other. The positive electrode 1, the negative electrode 2 and the permanent magnets 3 are closely adhered together through a high insulator 4. The high insulator 4 is formed of ceramics containing mica crystal excellent in free-cutting, whereby the device is downsized. A pressure detector 13 carries a current proportional to the vacuum pressure in the space between the negative electrode 2 and the positive electrode 1 by applying a high voltage between the positive electrode 1 and the negative electrode 2. The pressure detector 13 detects an abnormal pressure rise at leak. A plurality of pressure detectors 13 are installed into the vacuum vessel, whereby the pressure detectors 13 detect the gas in the order closer to the leak position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas leak detecting device for detecting a gas leak from a vacuum container, and more particularly to a gas leak detecting device suitable for finding a leak occurrence place of a vacuum container cooled to an extremely low temperature.

[0002]

2. Description of the Related Art When a minute crack is generated in the wall of a liquid helium container cooled to an extremely low temperature, helium leaks into the adiabatic vacuum container and the heat insulation performance is significantly deteriorated. Therefore, a large amount of liquid helium evaporates and the liquid helium container must be repaired. Conventionally, as a means for confirming this leak, a method of detecting with a detector attached outside a vacuum container accommodating a liquid helium container has been widely used. As a device for detecting this gas leak, a method is known in which the residual gas in the liquid helium container kept at the liquid nitrogen temperature is analyzed using a mass spectrometer. An example thereof is described in JP-A-58-97637.

[0003]

SUMMARY OF THE INVENTION In the above conventional technique,
Although the presence or absence of helium gas leaking into the liquid helium container can be detected, it was not possible to determine where the leak occurred in the liquid helium container, and the location of the leak could not be specified. In particular, in the case of a cold leak phenomenon that occurs only in the extremely low temperature range, this leak phenomenon does not occur even after the temperature is raised to room temperature, so the leak location cannot be identified by a general detector operating at room temperature. was there. For this reason, there has been a problem that the entire cryogenic portion forming the vacuum heat insulating container of liquid helium has to be recreated.
Further, in a magnetic levitation superconducting magnet for which a lightweight and small-sized superconducting magnet is desired, there is a demand for downsizing of a leak detector so as to cope with the case where the installation space is small. further,
It was necessary that the leak detector be a cattle that does not break even when the vibration of a magnetic levitation train runs.

The object of the present invention is to satisfy the above conditions, and
It is to find the leak occurrence place of the heat insulation vacuum container as soon as possible.

[0005]

In order to achieve the above object, the present invention provides a gas leak detector comprising neodymium (Nd).
Two flat plate permanent magnets of the system are installed with a certain gap so that the S pole and the N pole face each other, and the anode and the cathode are arranged at right angles between the flat plate permanent magnets. Further, the anode, the cathode and the permanent magnet are in close contact with each other via a high insulator. This high insulator is miniaturized by using ceramics containing mica crystals that are excellent in free cutting. In the gas leak detector, by applying a high voltage between the anode and the cathode, a current proportional to the vacuum pressure in the cathode and the anode space flows between the anode and the cathode. This gas leak detector detects a pressure increase more than when the gas leaks. In other words, the gas leak detector can be said to be a pressure detector. By mounting a plurality of pressure detectors in the vacuum container, the pressure detectors detect the gas in the order closer to the leaked position in the vacuum container, so that the leak occurrence location can be specified.

[0006]

For example, when helium gas leaks from a liquid helium container to an adiabatic vacuum container, gas molecules or electrons move to the anode and cathode while spirally moving due to the magnetic flux density of the permanent magnet and the high voltage orthogonal thereto. collide. The number of collisions per unit time depends on the pressure of the vacuum, the magnetic flux density, the space volume of both electrodes and the voltage between the anode and the cathode, and the output signal of the leak detector increases as these values increase. However, superconducting devices, especially superconducting magnets for magnetic levitation trains, are being made lighter and more compact in order to increase the number of passengers. Therefore, the volume of the conventional Penning vacuum gauge is too large, and it is impossible to mount the Penning vacuum gauge in the vacuum container. Further, a Pirani vacuum gauge smaller than this cannot detect a pressure of 10 to ³ Torr or less. The pressure detector of the present invention can be processed with high accuracy by adopting ceramics containing mica crystal as an electric insulator, and other main constituent parts are made of metal and can be easily processed with high accuracy. Therefore, miniaturization was achieved.

A feature of the present invention is that the transient pressure increase immediately after the leak is measured by a plurality of pressure detectors. The point to be noted in this case is to eliminate variations in the output signal of the pressure detector for a certain pressure value in the vacuum container.
Therefore, the material of the electrodes and other parts is non-magnetic material in order to avoid magnetic influence. Moreover, the variation in the output signal could be eliminated by adjusting the voltage between the anode and the cathode. Therefore, when the gas leaks, it is possible to identify the leaked position by utilizing the property that the output signal from the pressure detector near the leak position increases. In addition to the direct output signal of the pressure detector, a signal processing circuit for integrating this signal is provided in case the gas leak flow rate is small and the difference between the signals of each pressure detector is small.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. First, the structure of the pressure detector of the present invention will be described. FIG. 1 shows the pressure detector when there is one. Reference numeral 1 is a ring-shaped anode, and 2 is a circular flat plate cathode. The respective materials are austenitic stainless steel whose anode 1 is a non-magnetic material, and titanium whose cathode is a non-magnetic material. Other materials may be used for the anode and the cathode as long as they are nonmagnetic metals. Reference numeral 3 is a neodymium circular flat plate permanent magnet capable of obtaining high magnetic flux density, and the residual magnetic flux density is about 1 tesla (T). Reference numeral 4 is an electrical insulator, and 5 is a guide for holding the anode 1 and the permanent magnet 3. The material of this guide is the same as the electrical insulator, and is ceramics containing mica crystals. This ceramic has high electrical insulation and
Since the amount of outgas from the material and the amount of helium permeation are small, it is also suitable as a material for vacuum parts. Reference numeral 6 is a supporter for supporting and fixing the cathode 2, the electric insulator 4 and the permanent magnet 3 inside the guide 5. Reference numeral 8 is a cathode lead wire outlet provided in the guide 5. Reference numeral 9 is a stand for fixing the pressure detector main body to the flange 10. Reference numeral 11 denotes a rubber packing for airtightly joining the vacuum container (not shown) and the flange 10. Reference numeral 12 is a gas intake port for introducing the gas in the vacuum container into the pressure detector. Anode 1
Are sandwiched between two cathodes 2 via two guides 5. The permanent magnet 3 has a structure in which two cathodes 2 are sandwiched by an electric insulator 4. Thirteen
Will be called a pressure detector.

Next, the operation will be described with reference to FIGS. FIG. 2 shows a cross section of a superconducting magnet for a magnetic levitation train. FIG. 3 is a sectional view taken along line AA of FIG. 21 is a superconducting coil. The superconducting wire material of this superconducting coil is niobium titanium (NbTi) or niobium santin (N
b ₃ Su) and copper. 22 is liquid helium that cools the superconducting coil. Reference numeral 23 is a superconducting coil container that houses the superconducting coil 1 and liquid helium. Reference numeral 24 is a vacuum container for making a vacuum and insulating. Reference numeral 25 is a radiation shield for shielding the radiation heat from the room temperature vacuum container 23. Reference numeral 26 is a laminated heat insulating material in which dozens of aluminum vapor-deposited reflective tapes are stacked. The liquid helium 22 is a liquid helium container 2 provided above the superconducting coil container 23.
It is stored in 7. 28 is a liquid helium container 27
And a liquid helium introducing pipe for communicating with the superconducting coil container. Liquid helium 22 in liquid helium container 27
Flows into the lower superconducting coil container by the liquid helium introducing pipe 28. The gas evaporated by the heat received by the superconducting coil container 21 is guided from the returning liquid helium conduit 28 to the gas layer of the liquid helium container 27 above the superconducting coil 21. In this way, the liquid helium 22 around the superconducting coil 21 is naturally circulated until the liquid helium 22 in the liquid helium container 27 is exhausted. Liquid nitrogen 29
Flows from the liquid nitrogen container 30 into a nitrogen pipe (not shown) attached to the radiation shield 25. The radiation shield 25 is cooled to the liquid nitrogen temperature (77K).

In order to find the location where the helium gas leaks from the superconducting coil container 23, the superconducting coil container 23
4 on the outer wall of the superconducting coil container 23 between the radiation shield 25 and the radiation shield 25.
Each pressure detector 13 is attached. Pressure detector 13-
1, 13-2 and 13-3 normally detect the pressure in the vacuum container 24. The output signal from the pressure detector is transmitted from the connector 31 with good vacuum insulation through the control circuit 32,
It is inputted to the high speed recorder 33 and the data recorder 34. When the pressure in the vacuum container 24 is 10 to ⁶ Torr to 10 to ⁵ Torr and a voltage of DC 1000 V is applied between the anode 1 and the cathode 2 in FIG. 1, the anode 1 and the cathode 2 in FIG. μ
A current of several tens μA flows from A.

Here, FIG. 4 shows a display of the high-speed recorder when the helium gas leaks in the superconducting coil container 23. Pressure detectors 13-1 to 13-3
The signal decreases in the order of. It is also possible to read the delay of the time when the output signal of each pressure detector is increased. From these data, the leak location is closest to the pressure detector 13-1, then to the pressure detector 13-2,
It can be read that they are moving away in the order of 13-3. It can be estimated that the leaked position is near the point P in FIG. The accuracy of the leak occurrence location can be increased by increasing the number of pressure detectors. When the gas leak flow rate is small with respect to the volume of the vacuum container, the amount of increase in the output signal of the pressure detector is small. As a means for improving this, an electric circuit for integrating the output signal of the pressure detector 13 is provided. FIG. 5 shows an electric circuit when three pressure detectors 13 are used. Switch S
When W1 is connected to the upper side, the output signal of the pressure detector can be directly read, and when connected to the lower side, the direct output signal is integrated or differentiated and output. The switch SW2 is for switching between integration and differentiation, and the switch SW2
The signal is integrated when is connected above. FIG. 4 also shows the result of integrating the output signals of the pressure detectors 13-1, 13-2 and 13-3. As described above, the signal integrated as compared with the direct output signal has an effect of magnifying a change amount of the signal, and thus it is suitable to see which signal of the pressure sensor changes rapidly. The integration time is the resistance R of FIG.
And the content of the content C. In addition to this, an electronic circuit such as a filter circuit for removing noise added to the output signal should be installed if it does not hinder the responsiveness of the pressure detector.

The output signals of the plurality of pressure detectors show variations among the pressure detectors even under the same pressure. This is due to the finished dimensions of the pressure sensor, the assembly accuracy,
And it depends on the respective design errors such as the residual density of the permanent magnet. In order to eliminate this design error, two methods are conceivable: a method of increasing the processing accuracy of the pressure detector component and a method of varying the voltage between the anode 1 and the cathode 2 of the pressure detector 13. The former has a problem of high processing cost of parts. The latter will be described in detail with reference to FIG.

FIG. 6 shows the pressure and the output signal of the pressure detector 13 in a logarithmic graph in the horizontal and vertical directions, and shows the output signal characteristic of the pressure detector 13 with the voltage applied to the pressure detector 13 as a parameter. From FIG. 6, at the same voltage, the output signal of the pressure detector 13 is proportional to the pressure to the 1st power. Also,
It can be seen that at the same pressure, the output signal increases almost proportionally to the voltage applied to the pressure detector 13. Based on the above results, by adjusting the voltage applied to the pressure detector 13, the variation of the pressure detector 13 caused by the same pressure is eliminated. The variable resistance 10 MΩ in FIG. 5 functions to adjust this voltage.

FIG. 7 shows another embodiment of the present invention. This is a cross-sectional view of a cylindrical space chamber, and the same state as when placed in outer space with the artificial satellite model 35 installed in the space chamber can be simulated. The xenon lamp 36 uses the reflector 37 to reflect the emitted light to the artificial satellite model 3
The sunlight is simulated by focusing on 5. The vacuum pressure in outer space is the roughing pump 38 and the cryopanel 39.
In less than or equal to 1 × 10 ~ ⁶ Torr. The space chamber is a full-scale test, so the diameter is 10 m and the length is 15 m.
It is as large as m. Even in this case, the leak test is performed. As the pressure detector used here, a pressure detector group in which two or more pressure detectors are arranged is properly mounted in a space chamber for use. Reference numeral 40 indicates the pressure detector group. This is because the data amount of a plurality of pressure detectors is larger than that of a single pressure detector, so that the leak location can be easily estimated. A detailed view of the pressure detector group 40 is shown in FIGS. 8 and 9.
Each of the pressure detector groups 40 has the same configuration as in FIG. The pressure detector group of FIG. 8 requires eight permanent magnets to make four pressure detectors 13, and is satisfied with five permanent magnets. Thus, there is an advantage that the number of permanent magnets can be reduced. In FIG. 9, two pressure detectors 13 are mounted in pairs in the space chamber of FIG. After the pressure detector group 40 is installed in the large space chamber, the air in the space chamber is exhausted by the roughing pump 38, and the cryopanel is cooled by liquid cryogen to the liquid helium temperature (4.2).
By cooling to K), a high vacuum state is obtained in the space chamber. Even if a gas leak occurs in such a large vacuum container, each pressure detector group 40 or pressure detector 1
By monitoring the pressure in the space chamber, the leaked position can be easily found by the method described in (3). At the same time, the pressure distribution in the space chamber can be measured by the pressure detector group 40.

Up to now, the gas has been specified as helium, but this gas leak detector can be used for other gases such as air. Also, instead of the permanent magnet 3, an electromagnet or a superconducting magnet can sufficiently satisfy the function. Furthermore, by using a plurality of pressure detectors such as small and swallowing, it is possible to easily set up if there is a relatively narrow space, so it is possible to find a leak location of a small superconducting device such as a transfer tube.

[0016]

According to the present invention, by mounting a plurality of pressure detectors such as small and slender cows in a vacuum container, it is possible to easily find the location of gas leak due to the time delay of the output signal of each pressure detector. .

[Brief description of drawings]

FIG. 1 is a sectional view of a pressure detector.

FIG. 2 is a sectional view of a superconducting magnet for a magnetic levitation train.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is an explanatory diagram of a monitor.

FIG. 5 is an electric circuit diagram.

FIG. 6 is an explanatory diagram of a relationship between pressure and an output signal of a pressure detector.

FIG. 7 is a sectional view of the space chamber.

FIG. 8 is a sectional view of a pressure detector group.

FIG. 9 is a sectional view of another pressure detector group.

[Explanation of symbols]

1 ... Anode, 2 ... Cathode, 3 ... Permanent magnet, 4 ... Electrical insulator,
5 ... Guide, 12 ... Gas inlet, 21 ... Superconducting coil, 22 ... Liquid helium.

Claims (11)

[Claims] 1. A gas leak detection device comprising a pressure detector capable of measuring a vacuum pressure inside a vacuum container. 2. The pressure detector according to claim 1, wherein the pressure detector comprises a cylindrical anode and a disk-shaped cathode arranged at both ends of the anode in the axial direction, and further sandwiches the two cathodes. Similarly, the respective disk-shaped permanent magnets are installed, and the surfaces of the respective permanent magnets facing the anode are arranged so that the S pole and the N pole face each other, and the anode and the cathode, and the cathode and the A gas leak detection device in which permanent magnets are closely attached with an electrical insulator. 3. The gas leak detection device according to claim 2, wherein the electrical insulator is a ceramic containing a mica crystal. 4. The gas leak detection device according to claim 2, wherein the permanent magnet is a ceramic containing neodymium (Nd). 5. The anode and the cathode according to claim 2,
Gas leak detector that is a non-magnetic metal. 6. The gas leak detection device according to claim 2, wherein a hole is provided in the center of the anode of the pressure detector. 7. The gas leak detection device according to claim 2, further comprising a voltage adjustment circuit capable of adjusting a voltage between an anode and a cathode of each of the pressure detectors. 8. A gas leak detection device capable of performing data processing of an output signal by providing a differentiation or integration circuit for the output signal of the pressure detector according to claim 7. 9. A gas leak detection device according to claim 2, wherein all parts of the pressure detector except the permanent magnet are made of a non-magnetic material. 10. The gas leak detection device according to claim 2, wherein the pressure detector is mountable in a space having a gap of 15 mm or less. 11. Claims 1, 2, 3, 4, 5, 6, 7,
A plurality of the pressure detectors according to 8, 9 or 10 are mounted inside the vacuum container, and a transient pressure rise in the vacuum container immediately after gas leak is measured by the pressure detector, and A gas leak detection device that identifies the location of a gas leak based on data.