JP2002039902A - Ionization vacuum gauge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance measuring sensitivity and accuracy in a BA-type ionization vacuum gauge. SOLUTION: In the BA-type ionization vacuum gauge 10, an ion collector electrode 16 in an open grid 12 is formed into a loop shape, and the loop surface thereof is arranged directed toward a filament 14. Electrons, discharged from the filament 14 fly so as to be focused inside the loop of the ion collector electrode 16 and collides with gas molecules herein to form ions. By causing electrons to fly to focus them into the loop of the ion collector electrode 16, ions can be formed in the vicinity of the ion collector electrode 16, and an electron moving path is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum gauge, and more particularly to an ionization gauge capable of measuring a pressure from a high vacuum to an ultra-high vacuum.

[0002]

2. Description of the Related Art An ionization gauge is known as a device capable of measuring pressure from a high vacuum to an ultra-high vacuum. The ionization gauge accelerates thermoelectrons emitted from the heated filament and collects ions generated when the thermoelectrons collide with gas molecules. Since the amount of ions to be collected is proportional to the density of gas molecules, the pressure can be measured based on the amount of ions generated.

A known triode ionization vacuum gauge has a problem of an X-ray effect that limits the measurement pressure. When a hot electron collides with a grid for accelerating the same, soft X-rays are emitted, but the residual current generated by the soft X-rays cannot be distinguished from the ion current generated by trapping ions. In the case of measuring an ultra-high vacuum with a small number of ions, the effect of the residual current on the ion current becomes large, making accurate measurement difficult.

[0004] From such a background, BA (Bayard-Alper
The t) ionization gauge was invented and used for measuring ultra-high vacuum. In a BA ionization gauge, the ion collector electrode is formed in a linear shape and is arranged in a grid. Due to this linear ion collector electrode, the area irradiated with soft X-rays is extremely small, and the effect of the residual current due to the X-ray effect is small, so that pressure measurement in an ultra-high vacuum up to 10 ^-8 Pa is possible. .

[0005]

On the other hand, in the BA type ionization gauge, the ion collector electrode is at a negative potential with respect to the potential of the filament, so that the electrons emitted from the filament repel the ion collector electrode. , Its trajectory is modified. As a result, the following problem occurs.

(1) In the BA type ionization vacuum gauge, a spiral grid which is opened up and down is generally used, but due to the repulsion of electrons to the ion collector electrode, some of the electrons are corrected in the vertical direction of the grid. And spread out of the grid. For this reason, the amount of ions generated is smaller than the number of electrons emitted from the filament, and the measurement sensitivity is not always good. In this case, there is a method in which the upper and lower sides of the grid are closed to restrict the diffusion of electrons. However, it is difficult to design and manufacture the grid, resulting in an increase in cost.

(2) Due to the repulsion of electrons to the ion collector electrode, the efficiency of ion generation in the vicinity of the ion collector electrode is low, so that ions are difficult to be collected.

On the other hand, Japanese Patent Application Laid-Open No. 11-72406 discloses a BA-type ionization gauge in which two ion collector electrodes are arranged separately in a grid. In this type of BA-type ionization gauge, although the problem described in (2) above can be solved, the problem of the diffusion of electrons out of the grid described in (1) cannot be avoided.

In the BA type ionization vacuum gauge,
If each ion collector electrode is formed too thin, the stability of the shape is lost and the reliability of the measurement is reduced, so that these cannot be made too thin. As a result, the probability of electron collision with the ion collector electrode increases, and the effect of the X-ray effect cannot be ignored.

[0010] Accordingly, an object of the present invention is to reduce the amount of electrons emitted from a filament out of an open grid by devising the shape of an ion collector electrode, thereby improving the sensitivity of pressure measurement. It is to provide a vacuum gauge.

It is another object of the present invention to provide an ionization vacuum gauge having an ion collector electrode having a stable shape, thereby improving the reliability of measurement.

Still another object of the present invention is to provide an ionization gauge capable of extending the electron orbit in an open grid by devising the shape of the ion collector electrode.

Yet another object of the present invention is to provide a conventional B
A By providing an ionization gauge that achieves each of the above objects without drastically changing the design of the ionization gauge, the cost can be reduced and the controller used in the conventional BA ionization gauge can be used. enable.

[0014]

SUMMARY OF THE INVENTION An ionization gauge according to the present invention comprises an open grid forming an anode volume, an electron source located outside the anode volume, and an ion collector located within the anode volume. Is provided. In the present invention, the ion collector is formed in a loop shape, and a surface formed by the loop faces the electron source.

[0015] Electrons emitted from the filament are drawn to the grid which is made to have a positive potential, and from the gap into the anode volume. Here, within the anode volume, the electrons repel the ion collector and their trajectories are modified,
Since the ion collector has a loop shape, many electrons are orbitally corrected by the repulsive force so as to be focused in the loop. Many electrons passing through the loop reach the opposite side of the grid and once exit the anode volume, but are again drawn back into the anode volume, this time on the opposite side of the ion collector loop. From here. In the process of repeating this flight, the electrons collide with gas molecules in the anode volume and generate ions. Here, since many ions are generated in the space within the loop of the ion collector, the efficiency of trapping ions by the loop-shaped ion collector disposed around the ion collector is extremely high. Also,
The effect of focusing of electrons by the loop of the ion collector electrode increases its flight path length and increases the electron density within the anode volume and thus the generated ion density.

In this case, the open grid is
Preferably, the ion collector is formed in a cylindrical shape, more preferably in an elliptical cylindrical shape, and the ion collector is arranged in a plane including a major axis of the ellipse.

Also, in the present invention, the electron source is:
The elliptic cylindrical open grid is preferably arranged in a circle whose diameter is the major axis.

It is preferable that the open grid is formed in a spiral coil shape. In the present invention, it is preferable that the ion collector has a vertically long loop shape in the axial direction of the open grid.

Further, it is preferable that an end of the ion collector in an axial direction of the open grid is accommodated in an anode volume formed by the open grid.

The ion collector is preferably formed in a square loop, but may be circular or elliptical.

The ion collector has a shaft diameter of 0.1 mm.
It is preferably 20 mm or less.

In a preferred embodiment of the present invention, the electron source is formed in a linear shape along the axial direction of the open grid, and is disposed substantially at the center in the width direction of the loop-shaped ion collector.

[0023] The ionization gauge of the present invention can also be configured to contain the open grid, the electron source and the ion collector, and to have an enclosure for supporting them.

In this case, the envelope may be an ionization vacuum gauge made of glass, and may further include a ground electrode covering the outside of the open grid and the electron source.

Further, the ion collector may be supported by the outer enclosure.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are views showing a glass-enclosed ionization vacuum gauge according to an embodiment of the present invention, and show a perspective view in which a part thereof is cut away, a plan sectional view thereof, and a side sectional view thereof, respectively. ing. In these figures, the ionization gauge 10 includes a grid 12, a filament 14, an ion collector electrode 16, and a ground electrode 18, and its periphery is covered by a glass envelope 20.

The grid 12 is an open grid in which a thin metal wire made of a material such as tungsten or molybdenum is formed in a spiral cylindrical shape, and the upper and lower sides thereof are open. The grid 12 is maintained at a higher potential (for example, 180 V) than the electrons emitted from the filament 14 by the voltage applied from the electrode terminals 22. The potential forms an anode volume inside the grid 12 where electrons from the filament 14 are accelerated. The electrons accelerated in the grid 12 collide with gas molecules existing in the space and generate ions. In a preferred embodiment, the grid 12 has an elliptical cylindrical shape, as seen in FIG. As will be described later, by making the grid 12 elliptical, the distance between the filament 14 and the ion collector electrode 16 can be reduced.

The filament 14 is located outside the anode volume formed by the grid 12. The filament 14 is formed by processing a thin metal wire made of a material such as tungsten or iridium into a hairpin shape, and its upper and lower ends are connected to and supported by the electrode terminals 24. By applying a predetermined voltage (for example, 45 V) to the filament 14 from the electrode terminal 24, electrons are emitted along the axis of the filament 14 and are drawn into the grid 12. As shown in FIG. 2, in a preferred embodiment, the filaments 14 are located on an extension of the minor axis of the ellipse of the grid 12 and are located within a circle whose major axis is the diameter. By arranging the grid 12 in an elliptical shape and arranging the filament 14 in the circle, the distance between the filament 14 and the ion collector electrode 16 can be shortened, and the external dimensions of the ionization gauge can be reduced. is there. In one embodiment,
The filament 14 is a tricoat iridium having a diameter of about 0.125 mm.

The ion collector electrode 16 is connected to the grid 12
Are disposed in the anode volume formed by the above, and have a loop shape. In the embodiment shown in the drawings, the ion collector electrode 16 has a vertically long rectangular shape composed of upper, lower, left and right sides. However, the ion collector electrode 16 may be formed by a circular or elliptical loop. The loop-shaped ion collector electrode 16 has a measuring terminal 26 joined to the upper side thereof by spot welding or other methods, and is suspended from the envelope 20 via this. The measuring terminal 26 is drawn out from above the envelope 20 to the outside,
Connected to an ammeter not shown. Ion collector electrode 1
6 is set to the same ground potential as the envelope 20. As a result, the ammeter connected to the ion collector electrode 16 measures the ion current flowing through the ions collected by the electrode. A general measuring unit measures the pressure in the anode volume based on the current value.

The loop-shaped ion collector electrode 16 is shown in FIG.
As shown in FIG. 2 and FIG. 2, the surface formed by the loop is arranged so as to lie within a plane including the major axis of the elliptical grid 12. That is, the surface of the loop-shaped ion collector electrode 16 formed by the loop is the filament 1
It is aimed at 4. In the embodiment, the filament 14 is located substantially at the center of the loop-shaped ion collector electrode 16 in the width direction. In such an arrangement,
Many of the electrons emitted from the filament 14 and drawn into the grid 12 are supplied to the loop-shaped ion collector electrode 1.
6 inside the loop. The operational aspects of the loop ion collector electrode 16 will be described later. The loop-shaped ion collector electrode 16 has, for example, a diameter of 0.18 mm.
The wire can be formed by looping a wire material such as molybdenum coated with platinum into a loop shape having a vertical diameter of about 20 mm and a horizontal diameter of 1 mm.
It is about 2 mm. The loop-shaped ion collector electrode is less likely to lose its shape, and can be stably held in the envelope 20 by suspending it.
The stable shape of the ion collector electrode guarantees its high measurement reliability.

The earth electrode 18 has a cylindrical shape.
Within 0, the periphery of the grid 12, the filament 14, and the ion collector electrode 16 is covered. The ground electrode 18 is maintained at a predetermined potential (for example, a ground potential) via the electrode terminal 28, and suppresses the influence of the ions attached to the envelope 20 on the measurement.

The envelope 20 is preferably formed in a cylindrical shape from Kovar glass or the like. The ionization vacuum gauge 10 is connected to a vacuum chamber via a pipe 30 provided in the envelope 20, maintains the same degree of vacuum, and enables pressure measurement in the vacuum chamber. .

Next, the functional aspects of the ionization gauge provided with the loop-shaped ion collector electrode according to the present invention will be described. FIG. 4 shows electrons of a conventional ionization gauge having a linear ion collector electrode (FIG. 4A) and an ionization gauge of the present invention having a loop ion collector electrode (FIG. 4B). FIG. 3 is a conceptual diagram for explaining the difference in the trajectory of the trajectory.

A conventional ionization gauge 40 shown in FIG.
, A linear ion collector electrode 42 is provided at the center of a spiral grid 41. Filament 4
The electrons emitted from 3 are drawn to the grid 41 which is set to a positive potential, and fly through the gap inside and outside the anode volume 44. However, in the anode volume 44, electrons repel the ion collector electrode 42 which is set to a negative potential with respect to the filament 43, so that its trajectory is corrected.
As a result, the electron density in the vicinity of the ion collector electrode 42 decreases, the probability of collision with gas molecules in the vicinity decreases, and the flight distance of the electrons decreases. Also,
Due to the repulsive force of the ion collector electrode 42, some of the electrons exit the anode 41 out of the open upper and lower regions of the grid 41 and do not contribute to ion generation. For these reasons, the ion collection efficiency of the ion collector electrode 42 is deteriorated, and the measurement sensitivity is limited.

On the other hand, in an ionization vacuum gauge 45 according to the present invention shown in FIG. 2B, a loop-shaped ion collector electrode 47 is disposed in a spiral grid 46 with its loop surface facing the filament 48. ing. Filament 4
Electrons emitted from 8 are drawn by a grid 46 which is made to have a positive potential, and reaches the anode volume 49 from the gap. Here, in the anode volume 49, the electrons repel the ion collector electrode 47, and their trajectories are corrected. However, since the ion collector electrode 47 has a loop shape, many electrons are generated by the repulsive force. The trajectory is corrected to focus in the loop. Many electrons passing through the loop
It reaches the opposite side of the grid 46 and once exits the anode volume 49, but is again drawn back into the anode volume, this time passing from the opposite side of the loop of the ion collector electrode 47. In the process of repeating this flight, the electrons collide with gas molecules in the anode volume 49 to generate ions. Here, since many ions are generated in the space in the loop of the ion collector electrode 47, the ion collection efficiency of the loop-shaped ion collector electrode 47 disposed around the ion collector becomes extremely high. Also, the effect of focusing of electrons by the loop of the ion collector electrode 47 increases the flight path length, and increases the electron density in the anode volume 49, and thus the generated ion density. As a result, the measurement sensitivity of the ionization gauge is improved, and a higher degree of vacuum can be measured.

FIGS. 5 to 7 show a metal-enclosed ionization gauge according to another embodiment of the present invention. FIG. 5 is a perspective view showing the inside of the gauge and FIG.
And a side sectional view thereof. In these figures, the ionization gauge 50 includes a grid 52, a filament 54, and an ion collector electrode 56, and its periphery is covered with a metal envelope 58.

The grid 52 is basically the same as that in the previous embodiment, and is an elliptic cylindrical open grid in which fine metal wires are spirally formed. The filaments 54 are arranged outside the anode volume formed by the grid 52. In the present embodiment, two filaments are provided (one is reserved for the case where the other is disconnected). As in the previous embodiment, as apparent from FIG.
Are located in a circle whose diameter is the major axis of the ellipse of the grid 52.

The ion collector electrode 56 is connected to the grid 52
Are arranged in a volume of the anode formed by a rectangular loop. In the present embodiment, the loop-shaped ion collector electrode 56 has a measurement terminal 60 joined to the lower side thereof, and is supported by the envelope 58 via the measurement terminal 60. As in the previous embodiment, the loop-shaped ion collector electrode 56
Indicates that the surface formed by the loop is an elliptical grid 5
It is arranged to lie in a plane containing the two major axes and is directed to the filament 54. Also in the ionization gauge 50 according to the present embodiment, many of the electrons emitted from the filament 54 and drawn into the grid 52 are focused so that they are collected at the center, and the inside of the loop of the loop-shaped ion collector electrode 56 is formed. pass. By the action, the electron trajectory is extended and ions are generated in the loop-shaped ion collector electrode 56, which contributes to the measurement.

The embodiment of the present invention has been described with reference to the drawings. The application range of the present invention is not limited to the matters described in the above embodiment, and various changes or improvements can be made based on the description in the claims. In each of the above embodiments, the ionization gauge provided with the envelope made of glass or metal has been described. However, the present invention can be applied to an ionization gauge having no envelope. Further, in the above-described embodiment, the grid is formed to have an elliptical cylindrical shape, thereby shortening the distance between the filament and the loop-shaped ion collector electrode, so that electrons from the filament are easily guided into the loop. It is apparent that the advantages of the present invention can be enjoyed even in an ionization gauge having a perfect circular grid configuration.

[0040]

As described above, according to the present invention, since the ion collector electrode is formed in a loop shape and the electrons from the electron source are focused in the loop, the generation of ions near the ion collector electrode is achieved. Efficiency is increased, and the flight path of the electrons is lengthened, so that the electron density in the region is improved. This enables higher vacuum pressure measurement.

Further, according to the present invention, since the ion collector electrode has a loop shape, it is stable in shape, which improves the reliability of measurement. Further, since the shape is stable, the ion collector electrode can be formed from a wire having a relatively small diameter.
Similar to the type ionization gauge, the problem of the X-ray effect can be minimized.

Further, according to the present invention, the ionization gauge according to the present invention can be manufactured without largely changing the design of the conventional BA ionization gauge, thereby reducing the manufacturing cost. In addition, a controller used in a conventional BA ionization gauge can be used.

[Brief description of the drawings]

FIG. 1 is a partially broken perspective view showing a glass-enclosed ionization gauge according to an embodiment of the present invention.

FIG. 2 is a plan sectional view of the ionization gauge of FIG. 1;

FIG. 3 is a side sectional view of the ionization gauge of FIG. 1;

FIG. 4 is a concept for explaining a difference in electron trajectory between a conventional ionization gauge having a linear ion collector electrode and an ionization gauge according to the present invention having a loop ion collector electrode. FIG.

FIG. 5 is a perspective view showing the inside of a metal-enclosed ionization gauge according to another embodiment of the present invention.

FIG. 6 is a plan sectional view of the ionization gauge of FIG. 5;

FIG. 7 is a side sectional view of the ionization gauge of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ionization gauge 12 Grid 14 Filament 16 Ion collector electrode 18 Earth electrode 20 Enclosure 22, 24, 28 Electrode terminal 26 Measurement terminal 30 Piping 50 Ionization gauge 52 Grid 54 Filament 56 Ion collector electrode 58 Enclosure 60 Measurement terminal

Claims (14)

[Claims] 1. An open grid forming an anode volume, an electron source disposed outside the anode volume, and a loop-shaped ion collector disposed within the anode volume, wherein the ion collector is formed by the loop. A surface directed toward the electron source. 2. The ionization gauge according to claim 1, wherein the open grid is formed in a cylindrical shape. 3. The ionization gauge according to claim 2, wherein the open grid is formed in an elliptical cylindrical shape, and the ion collector is arranged in a plane including a major axis of the ellipse. 4. The electron source is arranged in a circle whose diameter is the major axis of the elliptic cylindrical open grid.
The ionization gauge described in 1. 5. The ionization gauge according to claim 2, wherein the open grid is formed in a spiral coil shape. 6. The ionization gauge according to claim 1, wherein the ion collector has a vertically long loop shape in an axial direction of the open grid. 7. An ionization gauge according to claim 1, wherein an end of said ion collector in an axial direction of said open grid is contained within an anode volume formed by said open grid. 8. The ionization gauge according to claim 1, wherein the ion collector is formed in a rectangular loop. 9. An ion collector having a shaft diameter of 0.20
The ionization gauge according to any one of claims 1 to 8, which is not more than mm. 10. The ionization vacuum gauge according to claim 1, wherein the electron source is formed in a linear shape along the axial direction of the open grid. 11. The ionization vacuum gauge according to claim 10, wherein the electron source is disposed substantially at the center in the width direction of the loop-shaped ion collector. 12. The ionization vacuum gauge according to claim 1, further comprising an envelope that houses the open grid, the electron source, and the ion collector, and that supports them. 13. The ionization gauge according to claim 12, wherein the envelope is a glass ionization gauge, and further comprising a ground electrode covering the outside of the open grid and the electron source. 14. The ionization gauge according to claim 12, wherein the ion collector is suspended from the outer enclosure.