JP5273034B2 - Helium leak detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid shortening of a lifetime of a microchannel plate caused by entrance of an excessive ion current into the microchannel plate used for a helium leak detector. <P>SOLUTION: This helium leak detector including a microchannel plate for detecting helium ion also includes a sector electrode for deflecting a helium ion beam to enter the microchannel plate. In the case of gross leak, the helium ion beam is not deflected so as not to enter the microchannel plate, but is allowed to enter a sector electrode, and an ion beam current is detected by the sector electrode. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a leak detector used for airtightness inspection of a vacuum vessel.

  In an analysis tube of a helium leak detector, an ion collector that detects helium ions as an ion current has been conventionally used to detect helium ions (for example, Patent Document 1). Further, in order to improve the sensitivity of the ion current, it is known to amplify the ion current by providing a microchannel plate immediately before the ion collector (see Patent Documents 2 and 3).

JP 2009-180633 A JP-A-8-35904 JP 2000-121484 A

  In the microchannel plate, the charge of ions incident on the microchannel plate, that is, the ion current is amplified by the microchannel plate and output. The lifetime of the microchannel plate depends on the total output current, that is, the total output charge amount, and the lifetime is shortened when the microchannel plate is used in a state where the output current is large. The output current is proportional to the amount of incident ions, that is, the incident ion current. In addition, the lifetime of the microchannel plate is shortened when used in a situation where the degree of vacuum is poor. In the case of a large leak, the degree of vacuum deteriorates and the amount of incident ions increases, so the life of the microchannel plate is shortened.

(1) The invention of claim 1 is a helium leak detector for detecting helium gas leaked from a subject by introducing it into an analysis tube, the analysis tube comprising a secondary electron multiplier for amplifying a helium ion current; A sector electrode composed of a ground side electrode and a positive potential side electrode for deflecting the helium ion beam in the direction of the secondary electron multiplier; a voltage source for supplying a voltage to be applied to the positive potential side electrode; An electron collector to which a secondary electron current emitted from the secondary electron multiplier is incident, an ammeter for measuring the secondary electron current incident on the electron collector, and a positive electrode connected to the voltage source or ammeter 1 switch SW1 and 2nd switch SW2 which connects an ammeter to an electronic collector or a positive potential side electrode, It is characterized by the above-mentioned.
(2) The invention according to claim 2 is the helium leak detector according to claim 1, wherein the ground side electrode of the sector electrode is at the ground potential, and the positive potential side electrode has the first switching in the case of fine leak. The switch SW1 is switched to apply a positive voltage so that the helium ion beam is incident on the secondary electron multiplier. In the case of gross leak, the first switch SW1 is switched so that the helium ion beam The positive potential side electrode is connected to an ammeter so as to be detected by the positive potential side electrode.
(3) According to the invention of claim 3, in the helium leak detector according to claim 2, in the case of fine leak, the second change-over switch SW2 connects an ammeter and an electron collector to provide a secondary electron multiplier. The secondary electron current emitted from the battery is measured.
(4) According to a fourth aspect of the present invention, in the helium leak detector according to the second aspect, in the case of a gross leak, the second change-over switch SW2 connects the ammeter and the positive potential side electrode, and the positive potential side electrode And measuring a helium ion current incident on the.
(5) A fifth aspect of the present invention is the helium leak detector according to any one of the first to fourth aspects, wherein the ground-side electrode and the positive-potential-side electrode of the sector electrode are formed and arranged in an arc shape. It is characterized by that.

  In the present invention, when the leak is large, a large ion current corresponding to the leak is detected by another ion collector so as not to enter the microchannel plate. This avoids an excessive ion current from entering the microchannel plate, thereby avoiding shortening the life of the microchannel plate.

It is a whole lineblock diagram showing the outline of the helium leak detector by an embodiment of the invention. It is a figure which shows the outline of a structure of the analysis tube of the helium leak detector by this invention, and the operation | movement outline of an analysis tube in case the amount of leaks is small (fine leak). In FIG. 2, it is the schematic which shows the method of detection of the ion current in case the amount of leaks is large (gloss leak). It is the schematic which shows the structure of the analysis tube of the conventional helium leak detector.

The operation of the helium leak detector according to the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an outline of a helium leak detector according to an embodiment of the present invention. The helium leak detector 1 is connected via a test port 2 to a vacuum vessel 10 which is a subject for leak inspection.

  The helium leak detector 1 includes four vacuum pumps of oil rotary pumps 3 and 4, a drag pump 5 and a turbo molecular pump 6, six valves V1 to V6 for opening and closing an exhaust path and a helium introduction path, an exhaust path and a vacuum. Three leak valves V7 to V9 for releasing the pump to the atmosphere, a leak calibration unit 7, an analysis tube 8, two Pirani type vacuum gauges P1 and P2 for detecting the degree of vacuum in the exhaust path, and a control device 9 And have. The valves V1 to V9 are opened and closed by actuators A1 to A9, respectively, and these actuators are controlled from the control device 9 based on instructions from the operator of the leak detector. Wiring to each actuator A1 to A9 is omitted. Further, on / off of each vacuum pump and vacuum gauge, and monitoring of the output value (vacuum degree) of the vacuum gauge are performed by each controller (not shown) and the control device 9, but these wirings are also omitted.

The analysis tube 8 is connected to the oil rotary pump 4 through a turbo molecular pump 6, a drag pump 5, and a valve V6. A vacuum vessel 10 which is a subject to be subjected to a leak test is connected to an oil rotary pump 3 through a test port 2 and a valve V1. The vacuum vessel 10 is connected to the exhaust port 6a of the turbo molecular pump 6 through a test port 2 and a valve V5. The leak calibration unit 7 is connected to the turbo molecular pump 6 through a valve V3 and a valve V4 or V5.
The valve V4 is connected in the middle of the exhaust stage of the turbo molecular pump 6, and is opened in the case of the intermediate exhaust mode of the helium leak detector. The valve V5 is connected by piping to the exhaust port 6a of the turbo molecular pump, and is opened in the case of the reverse diffusion exhaust mode of the helium leak detector.

The leak test of the vacuum container 10 as the subject is performed according to the following procedure. For simplicity, only the case of the reverse diffusion exhaust mode will be described.
(1) The valves V1 to V5 and the leak valves V7 to V9 are closed and the valve V6 is opened, and the analysis tube 8 has a predetermined degree of vacuum (in a series configuration of the turbo molecular pump 6, the drag pump 5, and the oil rotary pump 4). Evacuate until helium background value is below. The valve V3 remains closed except when the leak amount calibration is performed.
(2) A vacuum vessel 10 for performing a leak test is attached to the test port 2.
(3) After the inside of the analysis tube 8 falls below a predetermined background value, the valve V1 is opened, and the inside of the vacuum vessel 10 is evacuated (roughly evacuated) by the oil rotary pump 3.
(4) The valve V1 is closed and the valve V5 is opened, and leak detection by the analysis tube 8 is started. That is, helium (He) gas is sprayed from the outside (atmosphere side) to the leak test location of the vacuum vessel 10.
(5) When there is a leak at the leak test location of the vacuum vessel 10, He gas enters the vacuum vessel 10 together with air. The He gas and air reach the analysis tube 8 through the open valve V5 and the turbo molecular pump 6 together with the vacuum container and the residual gas in the pipe. When the analysis tube 8 detects the He gas, the leak amount of the vacuum vessel 10 is measured.
(6) When the above leak test is completed, the valve V5 is closed, the leak valve V7 is opened, and the vacuum vessel 10 is opened to the atmosphere.

  When calibrating the leak amount, the test port 2 is closed, the valves V3 and V5 are opened, and He gas is guided from the leak calibration unit 7 to the analysis tube 8 via the turbo molecular pump. He gas flows out from the leak calibration unit 7 at a prescribed flow rate. The detected value at this time becomes a reference value for the leak amount.

Next, the configuration and operation of the analysis tube 8 according to the present invention will be described with reference to FIGS.
FIG. 2 is a diagram showing an outline of the configuration of the analysis tube of the helium leak detector according to the present invention and an outline of the operation of the analysis tube when the amount of leak is small (fine leak). The analysis tube 8 includes an ion source 11, an acceleration slit 12, an intermediate partition wall 13, an acceleration slit facing wall 14, a first earth slit 15, a sector electrode 16, a second earth slit 17, a microchannel plate (MCP) 18, and an electron collector. 19, an ammeter 20, a change-over switch SW1, and a change-over switch SW2. A filament 11a is incorporated in the ion source 11, and this filament 11a is heated by a power source for heating the filament and emits thermoelectrons by applying a voltage of another power source for extracting thermoelectrons. Is well known, and illustration and description are omitted. The analysis tube 8 further includes an ion acceleration power source 21 for accelerating ions and a power source for applying a voltage for electron amplification in the MCP outside the analysis tube. Although description of the power source for electron amplification in the MCP is omitted, a negative voltage of several hundred volts is applied to the ion incident surface side of the MCP, and the surface on the electron collector side is configured to be grounded. Although these various power sources are also controlled by the control device 9, the wiring to these power sources is not shown and description is omitted.

  The sector electrode 16 is composed of two arc-shaped positive potential side electrodes 16a and ground side electrodes 16b having different lengths. The sector electrode 16 is formed and arranged to have an arc shape of about 90 °. A parallel plate electrode is formed in an arc shape. A positive deflection voltage is applied to the longer positive potential side electrode 16a in accordance with a switching position of a first switch SW1, which will be described later, or by being connected to the ammeter 20, the ground potential is substantially reduced. It is said. As shown in the figure, the positive deflection voltage may be obtained by dividing the voltage of the ion acceleration power source 21 or may be supplied from another independent power source. The shorter ground side electrode 16b is grounded.

  A region M indicated by a two-dot chain line in the figure is a magnetic field region sandwiched between horseshoe-shaped permanent magnets, and a magnetic field is generated in the magnetic field region M in the direction from the front of the paper. Illustration is omitted.

The He gas introduced into the analysis tube 8 is ionized by the action of the flow of thermal electrons (emission current) emitted from the filament 11a of the ion source 11, and becomes He ⁺ ions. He ⁺ ions are accelerated by a voltage applied from the ion acceleration power source 21 to the acceleration slit 12. He ⁺ ions are emitted as an ion beam from the opening 12a of the acceleration slit 12 to the region M where the permanent magnet forms a magnetic field. The voltage value of the acceleration voltage applied to the acceleration slit 12 is 240-300V. This ion beam includes not only He ⁺ ions but also ions derived from air components such as hydrogen, oxygen, nitrogen, water, and the vacuum side wall surface of the components constituting the helium leak detector such as the vacuum vessel 10, vacuum pump, and piping. There may be cases where ions or the like derived from hydrocarbons (C _m H _n ) generated from adhering water or dirt adhering to the vacuum side wall surface may be included.

As shown in FIG. 2, the He ⁺ ions are bent by the magnetic field in the region M, pass through the deflection trajectory R, pass through the opening 13 a of the intermediate partition wall 13, and then enter the opening 15 a of the first earth slit 15. . On the other hand, H ⁺ ions that are lighter than He ⁺ ions are largely deflected by a magnetic field and do not pass through the opening 13 a of the intermediate partition wall 13. O ⁺ , N ⁺ , (C _m H _n ) ^{+ and the} like heavier than He ⁺ ions are less deflected by the magnetic field in the region M, and do not pass through the opening 13a. In addition, since divalent ions other than He are less deflected than He ⁺ , they also do not pass through the opening 13a.
In this way, an ion beam containing only He ⁺ ions is generated and enters the opening 15 a of the first earth slit 15.

The above description is common to a case where the leak amount is small (fine leak) and a case where the leak amount is large (gross leak). Here, the operation of the analysis tube when the leak amount is small (fine leak) will be described.
As described above, the beam of only He ⁺ ions passes through the intermediate partition wall 13 and the first earth slit 15 and further enters the sector electrode 16. A deflection voltage obtained by dividing the voltage of the ion acceleration power supply 21 is applied to the positive potential side electrode 16 a of the sector electrode 16. As a result, He ⁺ ions passing through the sector electrode 16 are deflected in the MCP direction. At this time, the first changeover switch SW1 is in a state in which a voltage obtained by dividing the voltage of the ion acceleration power source 21 is applied to the positive potential side electrode 16a. The He ⁺ ions that have passed through the sector electrode 16 pass through the second earth slit 17 and enter the MCP 18. The He ⁺ ions incident on the MCP 18 generate secondary electrons in the MCP 18, and the secondary electrons are amplified in the MCP 18 and emitted from the MCP 18 toward the electron collector 19 as a secondary electron current. The secondary electron current incident on the electron collector 19 is measured by an ammeter 20. At this time, the second changeover switch SW2 is in a state of connecting the electron collector 19 and the ammeter 20. Since the current measured as described above is proportional to the amount of He ⁺ ions incident on the MCP 18, that is, the helium ion current, the amount of detected He ⁺ ions can be obtained.

Next, the operation when the leak amount is large (gross leak) will be described. FIG. 3 is a schematic diagram showing a method of detecting an ionic current when the leak amount is large (gross leak) in FIG.
As in the case of fine leak, He ⁺ ions enter the sector electrode 16, but in the case of gross leak, the first changeover switch SW1 is switched to connect the positive potential side electrode 16a to the ammeter 20 and positive No deflection voltage is applied to the potential side electrode 16a. In this case, the positive potential side electrode is almost at ground potential. As a result, the He ⁺ ions incident on the sector electrode 16 travel straight and enter the positive potential side electrode 16a without bending the trajectory. Thus, the positive potential side electrode 16a operates as an ion collector, and the helium ion current is measured by switching the second changeover switch SW2 and connecting the ammeter 20 to the positive potential side electrode 16a. This helium ion current corresponds to the amount of detected He ⁺ ions.

Further, the features of the present invention will be described in comparison with the prior art. FIG. 4 is a schematic diagram showing a configuration of an analysis tube of a conventional helium leak detector based on Patent Document 2. Until He ⁺ ions are incident on the first earth slit 15, it is the same as the embodiment of the present invention shown in FIG. 2 and FIG.
In the prior art (see Patent Document 2), the sector electrode 16 of the present invention is not provided, the first earth slit 15 is provided in front of the MCP 18, and the He ⁺ ions that have passed through the first earth slit 15 are MCP 18. Is incident on.

  In this prior art, when a gross leak occurs, a large ionic current is incident on the MCP 18. Patent Document 1 describes a method of changing the amplification factor of the MCP 18 by changing the voltage applied to the MCP 18. Thereby, in the case of gross leak, the amplification factor of the MCP 18 is reduced, and the output from the MCP 18, that is, the amount of amplified secondary electrons can be suppressed, whereby the total output current of the MCP 18 can be suppressed. It is possible to avoid shortening the lifetime to some extent. However, in the case of gross leak, the degree of vacuum also deteriorates, so that deterioration of the MCP 18 due to this is unavoidable.

In the present invention, in the case of gross leak, as shown in FIG. 3, the application of the deflection voltage to the positive potential side electrode 16a of the sector electrode 16 is stopped, and the He ⁺ ions are detected by the positive potential side electrode 16a. Helium ion current can be measured without using. This can prevent the life of the MCP 18 from being shortened.

  In general, in a helium leak detector, various low energy ions are actually generated. In order to prevent these undesired various low energy ions from passing through the first earth slit 15, a suppressor slit (for example, Patent Document 1) is further provided after the first earth slit 15, and positive ions are added thereto. It has been common practice to eliminate these ions from entering the ion collector by applying a voltage. In the present invention, the sector electrode 16 has the effect of this suppressor slit and eliminates the detection of unwanted ions.

  Patent Document 3 discloses a combination of an electrode and an MCP having functions equivalent to those of the sector electrode 16 as shown in FIG. However, even in the case of gross leak, the MCP is used to measure the ionic current. In the present invention, as described above, in the case of gross leak, the ion current is measured without using the MCP, so the lifetime of the MCP is not impaired.

  Whether the leak is a gross leak or a fine leak is determined based on the evacuation time after the vacuum vessel 10 is attached, the output values of the two Pirani type vacuum gauges P1, P2, the load (consumption current) of each vacuum pump, and the detected ion current. Although the size and the like and combinations thereof are determined, this description is omitted. From the viewpoint of protecting the MCP, it is desirable to measure the first ion current as described above, assuming a gross leak.

  In the above description, the sector electrode 16 in the embodiment of the present invention shown in FIGS. 1 and 2 is composed of the arc-shaped positive potential side electrode 16a and the ground side electrode 16b. The electrode 16a and the ground-side electrode 16b do not have an arc shape as described above, but the helium ion beam may be deflected in the direction of the microchannel plate 18 by the electric field formed by these electrodes. For example, a simple configuration in which two parallel plate electrodes having different lengths are installed obliquely with respect to the helium ion beam incident thereon may be employed.

  Furthermore, a helium ion beam may be deflected by using a permanent magnet or an electromagnet that generates a magnetic field so as to overlap the area of the sector electrode 16. In this case, the positive potential side electrode 16a and the ground side electrode 16b of the sector electrode 16 are often set to the same potential, but may not be the same potential. The intensity of the magnetic field and the potential of the sector electrode are adjusted by the energy of the helium ion beam incident on the sector electrode, pass through the second earth slit, and enter the MCP.

  In the above description, an example in which a voltage obtained by dividing the voltage of the ion acceleration power source 21 is used as a power source for applying a change voltage to the positive potential side electrode 16a of the sector electrode 16 is described. You may supply from the power supply.

  1 and 2 show examples using the MCP for the embodiment of the present invention, but various secondary electron multipliers other than the MCP, such as a channeltron, can also be used. .

  In the above description, the helium ion beam is selected by passing the deflection trajectory R1 of the helium ion beam through the opening 13a of the intermediate partition wall 13. It may be performed by passing through the opening 15 a of the earth slit 15.

  The above description is an example of an embodiment of the present invention, and the present invention is not limited to this example, and various embodiments are possible within the scope of the present invention.

1. Helium leak detector
2. Test port 3. Oil rotary pump 4. Oil rotary pump
5. Drug pump
6 ... Turbo molecular pump
6a ... Exhaust port 7 ... Leak calibration part 8 ... Analytical tube 9 ... Control device 10 ... Vacuum vessel 11 ... Ion source
11a Filament 12 Acceleration slit
12a Opening 13 Intermediate partition
13a ... Opening 14 ... Acceleration slit facing wall
15. First earth slit
15a ... Opening 16 ... Sector electrode
16a ... Positive potential side electrode 16b ... Ground side electrode 17 ... Second earth slit
18. Microchannel plate (MCP)
19. Electron collector
20 ... Ammeter
21. Ion acceleration power supply
M ... Magnetic field region R ... Helium ion deflection trajectory SW1 ... First selector switch
SW2 Second switch
P1 Pirani vacuum gauge P2 Pirani vacuum gauge V1 to V6 Valve V7 to V9 Leak valve A1 to A9 Actuator

Claims (5)

In the helium leak detector that detects helium gas leaked from the analyte by guiding it to the analysis tube.
The analysis tube is
A secondary electron multiplier that amplifies the helium ion current;
A sector electrode composed of a ground side electrode and a positive potential side electrode for deflecting a helium ion beam in the direction of the secondary electron multiplier;
A voltage source for supplying a voltage to be applied to the positive potential side electrode;
An electron collector on which a secondary electron current emitted from the secondary electron multiplier is incident;
An ammeter for measuring a secondary electron current incident on the electron collector;
A first changeover switch SW1 for connecting the positive potential side electrode to the voltage source or the ammeter;
A helium leak detector comprising: a second changeover switch SW2 for connecting the ammeter to the electron collector or the positive potential side electrode. The helium leak detector according to claim 1,
The ground side electrode of the sector electrode is at ground potential,
In the case of fine leak, a positive voltage is applied to the positive potential side electrode so that the helium ion beam is incident on the secondary electron multiplier by switching the first changeover switch SW1. In the case of a gross leak, the first selector switch SW1 is switched to connect the positive potential side electrode to the ammeter so that the helium ion beam is detected by the positive potential side electrode. Helium leak detector. The helium leak detector according to claim 2,
In the case of the fine leak, the second changeover switch SW2 connects the ammeter and the electron collector, and measures the secondary electron current emitted from the secondary electron multiplier. Helium leak detector. The helium leak detector according to claim 2,
In the case of the gross leak, the second changeover switch SW2 connects the ammeter and the positive potential side electrode, and measures the helium ion current incident on the positive potential side electrode. Detector. The helium leak detector according to any one of claims 1 to 4,
The helium leak detector according to claim 1, wherein the ground side electrode and the positive potential side electrode of the sector electrode are formed in an arc shape.

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