JP2540073B2 - Vacuum gauge - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vacuum gauge utilizing the ionization phenomenon of gas, and more particularly, it produces a rotating electron current in a space where an electric field and a magnetic field intersect with each other, thereby generating a rotating electron current. The present invention relates to a vacuum gauge of a type that increases ionization (hereinafter referred to as a crossed electromagnetic field type).

[Prior Art] A large number of vacuum gauges are known. Among them, the hot cathode ionization vacuum gauge is the most reliable,
Most commonly used. However, the conventional hot cathode ionization vacuum gauge is disadvantageous in that "the ion current generated per unit volume of the vacuum gauge" (hereinafter referred to as sensitivity) is small,
When the pressure becomes extremely low, the ion current becomes extremely small, and the photocurrent due to the soft X-ray cannot be ignored. Therefore, the hot cathode ionization vacuum gauge becomes difficult to measure at a pressure of 10 ^-10 Torr or less due to the measurement limit by the soft X-ray.

On the other hand, a crossed electromagnetic field type cold cathode ionization vacuum gauge is known. For example, a Penning vacuum gauge and a magnetron vacuum gauge. This type of vacuum gauge can obtain a large ion current (high sensitivity), so that it is not necessary to measure a minute current, and a vacuum gauge power supply can be inexpensive. However, it has a drawback of low accuracy and is used only for rough measurements.

[Problems to be Solved by the Invention] In the above-mentioned crossed electromagnetic field type cold cathode ionization vacuum gauge, the relationship between pressure and ion current (also referred to as discharge current) is not completely proportional, and the theoretical aspect is The accuracy is low because it is not clear. According to the idea of the present inventors, the conventional cold cathode ionization vacuum gauge measures the ion current, but the rotating electron current (corresponding to the anode current of the hot cathode ionization vacuum gauge) is a source of the ion current. ) Is not measured, it is assumed that the accuracy is low. That is, since the pressure measurement is not performed based on the ratio of the rotating electron current to the ion current, the reliability is considered to be poor.

By the way, in the following documents, there is a description about the above-mentioned measurement of the rotating electron current.

Journal of Applied Physics, 33 [6] (1962) (USA), W. Knauer, "Mechanism of Penning discharge at low pressure" p.2093-2099 In this paper, Penning is used to measure the rotating electron current indirectly. A sensor coil is wound around the discharge tube. Then, the rotating electron current is intermittently turned on and off by intermittently turning on and off the Penning discharge, and the current induced in the sensor coil by this interruption is measured. The rotating electron current is obtained from the value of this induced current.

The inventors of the present invention tried to improve the crossed electromagnetic field type ionization vacuum gauge by taking this document as a hint, measure the rotating electron current constantly, and obtain the ratio between this and the ion current to measure the pressure. We have developed a vacuum gauge for performing.

Therefore, an object of the present invention is to improve the precision of this type vacuum gauge by measuring the rotating electron current while maintaining the high sensitivity (large ionic current) which is a characteristic of the crossed electromagnetic field type ionization vacuum gauge. It is to plan.

[Means and Actions for Solving the Problem] In order to achieve the above object, the vacuum gauge according to the first invention of the present application has the following features. First, this vacuum gauge forms a magnetic field that intersects with an electric field created by a cathode, an anode, and a cathode and an anode, as in the conventional case, as an element constituting a crossed electromagnetic field type ionization vacuum gauge. It is provided with a magnetic field forming means and an ion collector for collecting ions ionized by rotating electrons. Furthermore, the present invention includes, as a particularly adopted new element, means for measuring a rotating electron current generated by the action of an electric field and a magnetic field. Then, the pressure is measured by obtaining the ratio of the rotating electron current and the ion collector current obtained by the measuring means.

The reason for measuring the rotating electron current in addition to the ion collector current is as follows. The more gas molecules there are, the more ions that are ionized by them, which flow into the ion collector. The conventional cold cathode ionization vacuum gauge is
This ion collector current was measured to find the pressure.
However, the rotating electron current that causes ionization of gas molecules is not always constant, and if the rotating electron current fluctuates, the ion collector current will change even at the same pressure.
On the other hand, in the present invention, since the pressure is obtained from the ratio of the rotating electron current and the ion collector current, the accuracy of pressure measurement is significantly higher than that in the case where the pressure is obtained only based on the ion collector current. Improve. That is,
According to the present invention, the reliability of the crossed electromagnetic field type vacuum gauge can be improved to the same level as that of the BA gauge, and the sensitivity can be maintained to the same level as the conventional crossed electromagnetic field type.

In the present invention, "measuring the rotating electron current" means not only directly measuring the rotating electron current but also indirectly measuring the rotating electron current by measuring a physical quantity that depends on the rotating electron current. Including that.

In addition to the characteristics of the first invention described above, the vacuum gauge according to the second invention of this application determines the pressure by controlling the rotating electron current to a constant value and measuring the ion collector current at this time. For example, the measurement result of the rotating electron current is
The rotating electron current can be kept constant by feeding back to the anode voltage or feeding back to the current flowing in the electromagnet as the magnetic field setting means. If the rotating electron current is kept constant, more accurate pressure measurement can be expected.

In the vacuum gauge according to the third invention of this application, a voltage composed of a direct current component and an alternating current component is applied between the cathode and the anode.
In the conventional cold cathode ionization vacuum gauge, only a direct current of several thousand volts is applied, but in the third invention, an alternating current component is added to this. By applying the alternating current component, the voltage between the electrodes periodically fluctuates, and the magnitude of the rotating electron current also fluctuates accordingly. The fluctuating rotating electron current can be detected by electromagnetic induction. That is, by adding the AC component, the electromagnetic induction phenomenon can be used as "a means for measuring the rotating electron current".

[Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings.

 The embodiments will be described in the following order.

I. First embodiment (hot cathode magnetron type) b. Second embodiment (cold cathode magnetron type) c. Various examples of electrode changes d. Third embodiment (Penning type) e. Measurement of rotating electron current by microwave f. Measurement of rotating electron current by synchrotron radiation. Measurement of rotating electron current by probe a. First Embodiment (Hot Cathode Magnetron Type) FIG. 1 is a configuration diagram of the first embodiment of the present invention, in which a gauge ball portion is a longitudinal sectional view. FIG. 2 is a sectional view taken along line II-II in FIG.

The magnetron vacuum gauge is generally a cold cathode, but a hot cathode type is also known from the following documents.

"Vacuum", Vol. 9, No. 2 (Sho 41), Nakao, "Characteristics of magnetron gauge" p.49-59 In Fig. 1, a cathode 10 comprises a hot cathode filament 11 and lead wires 12 and 13. Most of the lead wire 13 is covered with an insulating film 14. The insulating film 14 prevents electrons from being emitted from the surface of the lead wire 13 and prevents the lead wire from coming into contact with other components, and prevents the generation of dark current based on these. . The anode 20 includes a cylindrical anode electrode 21 and a lead wire 22. In this embodiment, the anode electrode 21 has a diameter of 18 mm and a length of 24 mm. At the center of the anode electrode 21, the above-mentioned hot cathode filament 11 is arranged.

The ion collector 50 is a disk-shaped ion collector electrode 51.
And lead wire 52. The ion collector electrode 51 is arranged near one end of the anode electrode 21 in the axial direction and perpendicular to the axis of the anode electrode 21.

The hot cathode filament 11, the anode electrode 21, and the ion collector electrode 51 described above are housed inside a glass container 60. The container 60 includes a measuring pipe 61 and a connecting pipe 62. The connecting pipe 62 is attached to a vacuum chamber or the like where pressure should be measured. The shield 63 is a metal component having a large number of holes and is arranged so as to face the ion collector electrode 51. The shield 63 prevents dissipation of rotating electrons, which will be described later, and is applied with a negative potential. The large number of holes are provided to ensure the conductance.

The magnetic field setting means 30 is arranged around the container 60.
The magnetic field setting means 30 is composed of two cylindrical permanent magnets 31 and a yoke 32 between them. The magnetic field generated by the permanent magnet 31 is directed in the axial direction of the anode electrode 21 in the space 27 between the hot cathode filament 11 and the anode electrode 21. On the other hand, in the inter-electrode space 27, the electric field is directed in the radial direction of the anode electrode 21.
Therefore, the electric field and the magnetic field are orthogonal to each other in the inter-electrode space 27. In this embodiment, the strength of the magnetic field created by the permanent magnet 31 is
It is 2500 gauss at the hot cathode filament 11.

A recess 33 sandwiched between the inner surface of the yoke 32 and the two permanent magnets 33
The sensor coil 41 is housed in. Sensor coil
Reference numeral 41 is for measuring the intensity of a rotating electron current, which will be described later, and is wound 2000 turns.

 Next, the electrical configuration of this vacuum gauge will be described.

A DC power supply 23 and an AC power supply 24 are connected in series between the cathode 10 and the anode 20, and the cathode 10 side is grounded. DC power supply
The output voltage of 23 is about 2 to 2.5 kV, and the output voltage of AC power supply 24 is 1 to 2 k in amplitude (difference between the maximum peak and the minimum peak).
It is about V. And the total voltage is about 3kV maximum
Therefore, the minimum voltage is set to 0 V or higher (preferably 500 V or higher). The frequency of alternating current is not particularly limited, but is 10 to
1000Hz is available.

A changeover switch 25 is provided between the anode 20 and the power supplies 23 and 24 so that it can be switched to another power supply 26. For example, for high pressures of 10 ^-4 Torr or more, a low power, low voltage power supply can be used as the other power supply 26.

A filament heating power source 15 is provided between the two lead wires 12 and 13 of the cathode 10, and a DC voltage of several volts is applied to the hot cathode filament 11.

A DC power supply 54 applies a negative voltage of about 0 to −100 V to the ion collector 50.

The two lead wires of the sensor coil 41 are connected to each other after passing through the bandpass filter 42 to form a loop. An ammeter 42 is inserted in this loop. The bandpass filter 43 is for removing noise having a frequency different from the frequency of the alternating current applied to the anode in the output current of the sensor coil.

 Next, the operation of this vacuum gauge will be described.

Between the anode electrode 21 and the hot cathode filament 11, a fourth
An anode voltage as shown in the figure is applied. The maximum value of the anode voltage is 3 kV and the minimum value is 1 kV. The direct current component of the applied voltage is 2 kV, and the amplitude of the alternating current component is also 2 kV. Frequency of AC component is 300
Hz. Minus 100 V is applied to the ion collector electrode 51. 5V is applied to both ends of the hot cathode filament 11. Keep the shield 63 at -100V.

When this vacuum gauge is operated under the above conditions, first, thermoelectrons fly out from the hot cathode filament 11 and the anode electrode 21
Head to. However, the trajectory of the electrons is bent by the action of the magnetic field, resulting in the rotational movement 17 as shown in FIG. As a result, the electrons make a rotational movement over an extremely long distance before reaching the anode electrode 21, colliding with gas molecules in the middle thereof and ionizing them. Due to such a phenomenon, a discharge having a high electron density occurs in the inter-electrode space 27. It becomes difficult for the electrons to reach the anode electrode 21, and the anode current becomes extremely small as compared with a normal BA gauge. Therefore, the soft X-rays generated when the electrons collide with the anode electrode are reduced, and the measurement limit by the soft X-rays moves to a lower pressure region than that of the BA gauge. Most of the ions generated by the ionization of gas molecules are collected at the ion collector electrode 51, and this is detected by the ammeter 53 as the ion collector current Ic. The value of this ion collector current is 10 compared to the conventional BA gauge of the same size.
The size is about 00 times. Therefore, it is not necessary to measure a minute current, and a circuit for measuring the ion collector current becomes extremely inexpensive.

Since the anode voltage fluctuates as shown in FIG. 4, the intensity of the rotating electron current also fluctuates accordingly. When the rotating electron current fluctuates, the magnetic flux density penetrating the sensor coil 41 changes, and an alternating current is induced in the sensor coil 41. This induced current is detected by the ammeter 42. Since the variation rate of the rotating electron current is proportional to the intensity of the rotating electron current, the rotating electron current Ir can be obtained by obtaining the magnitude of the induced current.

When the pressure inside the gauge sphere is P and the sensitivity coefficient of the vacuum gauge is S, the pressure P can be obtained by the following equation.

P = (1 / S) (Ic / Ir) Here, as an example of measurement, in the case of nitrogen gas having a pressure of 1 to 10 ⁻⁶ Torr under the above operating conditions, the ion collector current Ic = 10 μA, rotation An electron current Ir = 460 mA was obtained.
By substituting this into the above equation, the sensitivity coefficient S = 24 is obtained.
Since it was experimentally confirmed that the pressure P and the current ratio (Ic / Ir) have a linear relationship, the pressure P can be obtained by obtaining Ic and Ir and substituting them in the above equation. it can. FIG. 3 shows the relationship between the pressure P and the ion collector current Ic at this time.

Next, another operation method of this vacuum gauge will be described. In the above operating method, only the rotating electron current is measured, but it is possible to further proceed to control the rotating electron current at a constant level. There are several ways to do this. The first method is to feed back the output of the ammeter 42 to the DC power supply 23 and change the anode voltage so that the output of the ammeter 42 becomes constant. The second method is to feed back the output of the ammeter 42 to the voltage of the hot cathode filament power supply 54. The third method is to use an electromagnet instead of the permanent magnet 31, and feed back the output of the ammeter 42 to the current flowing through the electromagnet to change the strength of the magnetic field.

In this way, not only the ratio of the ion collector current to the rotating electron current is measured but also the rotating electron current is controlled to be constant, so that more accurate pressure measurement becomes possible.

In any of the above operating methods, when trying to measure a pressure of 10 ^-4 Torr or more, the anode voltage source is switched to the low voltage power source 26 by the changeover switch 25, and the anode electrode
It is preferable to apply a voltage of about 100 V to 21.

In addition, in order to measure the rotating electron current, a loop including the hot cathode filament 11 may be used instead of the sensor coil 41 described above. That is, the ammeter 18 and the bandpass filter 19 are inserted in the loop composed of the lead wire 12, the filament 11, and the lead wire 13. Since an alternating current induced by a rotating electron current flows in this loop,
The rotating electron current can be obtained by measuring the induced current with the ammeter 18. Bandpass filter 19
Has the same role as the bandpass filter 43 described above.

The vacuum gauge of FIG. 1 can also be used as a nude gauge. In other words, the container 60 is not used, and only the pressure measuring portion is inserted into the container to be measured. In that case, the anode electrode 21 is a hollow container, and the permanent magnet 31 and the sensor coil 41 are attached to the outside or inside thereof.

B. Second Embodiment (Cold Cathode Magnetron Type) FIG. 5 is a longitudinal sectional view of a gauge sphere mainly showing only the electrode portion of the cold cathode magnetron type embodiment. In this embodiment, a cold cathode rod 16 is used instead of the above-mentioned hot cathode filament. The advantage of the cold cathode is that it does not disturb the system to be measured as compared with the hot cathode. That is, the temperature of the system to be measured does not rise, and the gas emission is small. However, generally speaking, the cold cathode is inferior in discharge stability to the hot cathode and the ion collector current is likely to be unstable.

When the present invention is applied to such a cold cathode magnetron type, lack of reliability due to instability of discharge can be solved. That is, in the present invention, in addition to the ion collector current, the rotating electron current that is the source of ionization is also measured. Therefore, even if the ion collector current fluctuates irregularly, If a ratio is obtained, such fluctuations can be offset. Therefore, by utilizing the present invention, the reliability can be improved while maintaining the advantages of the cold cathode.

The differences when the cold cathode magnetron type is adopted will be described below.

The electrical configuration is different from that of FIG. 1 in that the filament power supply 15 is not required, and the lead wire 13 at the other end is
Is also unnecessary, when measuring pressure of 10 ^-4 Torr or more,
Do not reduce the anode voltage to about 100 V, unlike the hot cathode type,
Set to 0 to 1000V.

In the case of the cold cathode, the discharge is likely to be unstable, and various noises are superimposed on the current induced in the sensor coil. Therefore, the bandpass filter 42 shown in FIG. 1 is indispensable.

Although FIG. 5 shows an example in which the sensor coil 411 is arranged next to the permanent magnet 311, the sensor coil 41 may be arranged as shown in FIG. Of course, even in the hot cathode type shown in FIG. 1, the arrangement of the sensor coil 411 as shown in FIG. 5 can be selected. After all, the sensor coil may be located anywhere that it can couple with the rotating electron current.

C. Various Modifications of Electrodes The cathode or anode shown in FIG. 1 can be modified as follows.

FIG. 6 shows a hairpin-shaped hot cathode filament 111. However, when this cathode is used, the ammeter of Fig. 1
The rotating electron current using 18 cannot be measured. This is because in the loop including the filament 111, the change rate of the magnetic flux passing through the loop is extremely small.

FIG. 7 shows a cylindrical anode electrode 21 having a slit 28 formed therein.
Indicates 1. This anode electrode can function as a one-turn coil by looping the lead wire as shown in FIG. That is, an alternating current is induced in the one-turn coil by the rotating electron current, and the rotating electron current is to be measured by measuring this with an ammeter 29.

FIG. 8 shows a square anode electrode 212, which can also be used as a one-turn coil.

FIG. 9 shows a cold cathode magnetron type cathode structure with an end plate. Disc-shaped end plates 161 and 162 are fixed to the cold cathode rod 16, and these are arranged near both ends of the anode electrode 21.

FIG. 10 shows an inverse magnetron type electrode structure. That is, the anode rod 213 is arranged at the center of the cylindrical cathode electrode 163. In the illustrated example, the end plates 164, 16 are provided at both ends of the cathode electrode 163 in order to prevent the diffusion of electrons outside the discharge space.
5 is provided.

D. Third Embodiment (Penning Type) FIG. 11 shows a Penning type vacuum gauge to which the present invention is applied. A pair of disk-shaped cathode electrodes 166 and 167 are arranged near both ends of the cylindrical anode electrode 21. The voltage applied between the anode and the cathode and the method of measuring the rotating electron current are basically the same as those in the embodiment of FIG.

E. Measurement of Rotating Electron Current by Microwave FIG. 12 and FIG. 13 show an example of detecting microwave as another means for measuring the rotating electron current. Although an example of a cold cathode type is shown in these drawings, the same can be applied to the case of a hot cathode.

In FIG. 12, a microwave extraction electrode 70 is arranged near one end of the anode electrode 21. Microwave extraction electrode 70
Is composed of a coupling group 71 and a transmission line 72. Since the intensity of the generated microwave depends on the rotating electron current, the rotating electron current can be measured by detecting the intensity of the microwave.

In FIG. 13, a cavity 214 is provided in the anode electrode 21, and a coupling group 71 is arranged inside it.

F. Measurement of Rotating Electron Current by Synchrotron Radiation FIGS. 14 and 15 show an example of detecting synchrotron radiation as another means for measuring the rotary electron current. 14 is a cross-sectional view of the gauge ball, and FIG. 15 is a cross-sectional view taken along the line XV-XV of FIG. Since the electrons emit light when the electrons rotate in the magnetic field, the rotating electron current can be measured by measuring the intensity of the emitted light by the emitted light detecting means 80.

An opening 215 is formed in the anode electrode 21, and the emitted light 81 generated in the discharge space passes through the opening 215. The emitted light 81 reaches the photosensitive section 82, is converted into an electron stream, and is detected. The photosensitive section 82 is composed of a secondary electron emission plate, a secondary electron multiplier tube, and the like.

In FIGS. 14 and 15, the magnetic field setting means outside the container is omitted.

G. Measurement of rotating electron current with a probe Fig. 16 shows another means for measuring rotating electron current.
An example of using the probe 90 will be shown. A small opening 216 is formed in the anode electrode 21, and the probe electrode 91 is inserted into the discharge space from there. The probe electrode 91 is covered with an insulating coating 93 except for the discharge space, and is connected to an external instrument by a lead wire 92. The rotating electron current can be measured by measuring the current and potential of the probe 90. The mounting position of the probe 90 can be set to a position other than that shown in the drawings as required.

When any one of the above three types of rotating electron current measuring means, that is, microwave, synchrotron radiation, or probe is used, the AC power supply 24 shown in FIG. 1 is not always necessary.
This is because it is not necessary to change the rotating electron current.

The respective embodiments, electrode structures, and rotating electron current measuring means shown in the respective drawings can be used in combination with each other unless there is a particular problem.

[Effects of the Invention] The vacuum gauge according to the first invention of the present application measures the pressure by measuring the rotating electron current in a crossed electromagnetic field type vacuum gauge and determining the ratio of this to the ion collector current. ing. Therefore, there are the following effects. Although the crossed electromagnetic field type conventional vacuum gauge has high sensitivity, it has a problem in measurement accuracy because it measures only the ion collector current.However, in the present invention, the ratio between the ion collector current and the rotating electron current is Since it is used, the measurement accuracy is significantly improved while maintaining high sensitivity.

In addition to the features of the first invention, the vacuum gauge according to the second invention of this application controls the rotating electron current to be constant, so that improvement in measurement accuracy can be expected more.

In addition to the features of the first invention, the vacuum gauge according to the third invention of this application applies a voltage composed of a DC component and an AC component between the cathode and the anode. Therefore, the rotating electron current fluctuates periodically, and this rotating electron current can be measured by utilizing the electromagnetic dielectric phenomenon.

[Brief description of drawings]

1 is a configuration diagram of the first embodiment, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, FIG. 3 is a graph showing a pressure-ion collector current curve of the first embodiment, and FIG. FIG. 5 is a graph showing the anode voltage of the first embodiment, FIG. 5 is a sectional view of the essential parts of the second embodiment, and FIGS. 6 to 10 are explanatory views showing various modifications of the cathode or the anode. Is a sectional view of an essential part of the third embodiment, FIGS. 12 and 13 are illustrations of microwave detection means, FIGS. 14 and 15 are illustrations of radiation detection means, and FIG. 16 is description of probe. It is a figure. 10 …… Cathode 20 …… Anode 23 …… DC power supply 24 …… AC power supply 30 …… Magnetic field setting means 40 …… Rotating electron current measuring means 50 …… Ion collector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Kobayashi 5-8-1, Yotsuya, Fuchu-shi, Tokyo NIDEC ANELVA CORPORATION (56) References JP 55-156825 (JP, A) JP 40 -1436 (JP, B1)

Claims (3)

(57) [Claims] 1. A cathode, an anode, a magnetic field setting means for forming a magnetic field that intersects an electric field formed by the cathode and the anode, and means for measuring a rotating electron current generated by the action of the electric field and the magnetic field. And an ion collector that collects ions ionized by rotating electrons, and the pressure is measured by determining the ratio of the rotating electron current to the ion collector current. 2. The vacuum gauge according to claim 1, wherein the rotating electron current is controlled to be constant, and the pressure is measured by measuring the ion collector current. 3. The vacuum gauge according to claim 1, wherein a voltage composed of a direct current component and an alternating current component is applied between the cathode and the anode.