JPH02218933A - Vacuum gage - Google Patents

Abstract

PURPOSE:To improve measurement accuracy by a method wherein rotating electron current is measured by a cross electromagnetic field type vacuum gage and the ratio of this to ion collector current is calculated. CONSTITUTION:When anode voltage is applied between an anode electrode 21 and a hot cathode filament 11, thermions emit from the filament 11 toward the electrode 21 while electric discharge having high electron density occurs in a space 27 between the electrodes. These electrons are hard to reach the electrode 21 reducing soft X-rays generated when the electrons collide with the electrode 21, while most of ions generated by ionization of gas molecules gather on an ion collector electrode 51 which are detected as ion collector current IC by an ampere meter 53. Since the anode voltage fluctuates, rotating electron current also fluctuates accordingly so that flux density through a sensor coil 41 varies inducing AC current at the coil 41. This induced current is detected by an ampere meter 42. By calculating this induced current, rotating electron current Ir can be calculated. When the pressure inside a gage sphere is assumed to P and the sensitivity coefficient of a vacuum gage is S, pressure P can be expressed by equation P=(1/S)(IC/Ir).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a vacuum gauge that utilizes the ionization phenomenon of gas.
In particular, it relates to a type of vacuum gauge (hereinafter referred to as crossed electromagnetic field type) that generates a rotating electron current in a space where an electric field and a magnetic field intersect, thereby increasing the ionization of gas.

[Prior Art] Many types of vacuum gauges are known. Among them, hot cathode ionization vacuum gauges are considered the most reliable and are the most commonly used. However, the drawback of normal hot cathode ionization vacuum gauges is 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 soft X-rays cannot be ignored.

Therefore, the hot cathode ionization vacuum gauge becomes difficult to measure at pressures below 10-1° Torr due to the measurement limit due to soft X-rays.

On the other hand, a crossed electromagnetic field type cold cathode ionization vacuum gauge is known. For example, Penning vacuum gauge, magnetron vacuum gauge, etc. This type of vacuum gauge can handle a large ion current (high sensitivity), so there is no need to measure minute currents, and the vacuum gauge power supply is inexpensive. However, it has the disadvantage of low accuracy and is only used for rough measurements.

[Problems to be solved by the invention] In the crossed electromagnetic field type cold cathode ionization vacuum gauge described above, the relationship between pressure and ion current (also referred to as discharge current) is not completely proportional, and the theoretical aspect is It is said that the accuracy is low because it is not clear. The inventors believe that conventional cold cathode ionization vacuum gauges measure ion current, but the rotating electron current that creates this ion current (equivalent to the anode current of hot cathode ionization vacuum gauges) ) was not measured, so it is assumed that the accuracy is low. In other words, the pressure is not measured based on the ratio of the rotating electron current to the ion current, so it seems that the reliability is poor.

By the way, the following literature describes the measurement of the above-mentioned rotating electron current.

Journal ol' Applied Physl
cs, 33 [(f] (1962) (USA),
W, Knauer.

“Mechanism of Penning discharge at low pressure” 9, 209
3-2099 In this document, a sensor coil is wound around the Penning discharge tube so that the rotating electron current can be measured indirectly. Then, by intermittently turning on and off the Penning discharge, the rotating electron current is intermittent, and the current induced in the sensor coil due to this intermittent interruption is measured. The rotating electron current is determined from the value of this induced current.

Taking this literature as a hint, the present inventors attempted to improve a crossed electromagnetic field type ionization vacuum gauge, and measured pressure by constantly measuring the rotating electron current and finding the ratio of this to the ion current. We have developed a vacuum gauge that performs this.

Therefore, the purpose of this invention is to improve the accuracy of this type of vacuum gauge by measuring rotating electron current while maintaining the high sensitivity (large ion current) that is characteristic of crossed electromagnetic field type ionization vacuum gauges. It's about trying.

[Means and operations for solving the problem] In order to achieve the above-mentioned object, the vacuum gauge according to the first invention of this application has the following features. First of all, this vacuum gauge is an element that constitutes a crossed electromagnetic field type ionization vacuum gauge.
As in the past, it is equipped with a cathode, an anode, a magnetic field forming means that forms a magnetic field that intersects the electric field created by the cathode and anode, and an ion collector that collects ions ionized by rotating electrons. . Furthermore, as a new element particularly adopted in this invention, a means for measuring rotating electron current generated by the action of an electric field and a magnetic field is provided. The pressure is then measured by determining the ratio between the rotating electron current and the ion collector current obtained by this 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
This ionizes and produces more ions, which flow into the ion collector. Conventional cold cathode ionization vacuum gauges measure this ion collector current to determine pressure. However, the rotating electron current that causes gas molecules to ionize is not always constant, and if the rotating electron current changes, the ion collector current will change even at the same pressure.

On the other hand, in this invention, the pressure is determined from the ratio of the rotating electron current and the ion collector current, so the accuracy of pressure measurement is dramatically improved compared to the case where the pressure is determined based only on the ion collector current. to improve. That is, the present invention can improve the reliability of a crossed electromagnetic field type vacuum gauge to the same degree as that of a B-A gauge, and furthermore,
Sensitivity can be maintained at the same level as the conventional crossed electromagnetic field type.

In addition, in this invention, "measuring rotating electron current"
This includes not only the direct measurement of the rotating electron current, but also the indirect measurement of the rotating electron current by measuring the physical properties dependent on the rotating electron current.

In addition to the features 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 rotating electron current can be kept constant by feeding back the measurement result of the rotating electron current to the anode voltage or to the current flowing through the electromagnet serving as the magnetic field setting means. If the rotating electron current is kept constant, more accurate pressure measurements can be expected.

In the vacuum gauge according to the third invention of this application, a voltage consisting of a DC component and an AC component is applied between the cathode and the anode. Conventional cold cathode ionization vacuum gauges apply only a direct current of several thousand volts, but the third invention adds an alternating current to this. By adding the alternating current, the voltage between the electrodes changes periodically, and the magnitude of the rotating electron current also changes accordingly.

The fluctuating rotating electron current can be detected by electromagnetic induction effects. That is, by adding an alternating current component, it becomes possible to utilize the electromagnetic induction phenomenon as a "means for measuring rotating electron current."

[Example] Next, embodiments of the invention will be described with reference to the drawings.

Examples will be described in the following order.

1st example (hot cathode magnetron type) 2nd example (cold cathode magnetron type) Examples of various changes to electrodes 3rd example (Penning type) Measurement of rotating electron current using microwaves Measurement of rotating electron current using synchrotron radiation Measuring Rotating Electron Current with a Probe, First Embodiment (Hot Cathode Magnetron Type) FIG. 1 is a block diagram of the first embodiment of the present invention, and the gauge sphere portion shows a longitudinal cross-sectional view. FIG. 2 is a sectional view taken along the line ■--■ in FIG.

Furthermore, magnetron vacuum gauges generally use a cold cathode.
Hot cathode types are also known from the following documents:

"Vacuum", Vol. 9, No. 2 (Sho 41), "Characteristics of Magnetron Gauges", p. 49-59, in Figure 1,
The cathode 10 includes a hot cathode filament 11 and a lead wire 12.
Most of the lead wires 13 are 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 parts, thereby preventing the generation of dark current based on these. . The anode 20 includes a cylindrical anode electrode 21 and a lead wire 22. In this example, 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 hot cathode filament 11 described above is arranged.

The ion collector 50 includes a disk-shaped ion collector electrode 5
1 and a lead wire 52. Ion collector electrode 51
The anode electrode 2 is placed near one end of the anode electrode 21 in the axial direction.
It is arranged perpendicular to the axis of 1.

The hot cathode filament 11, anode electrode 21, and ion collector electrode 51 described above are housed inside a glass container 60. The container 60 consists of a measurement tube 61 and a connection tube 62. The connecting pipe 62 is attached to a vacuum chamber or the like where the pressure is to be measured.

The shield 63 is a metal component with many holes, and is placed opposite the ion collector electrode 51 . This shield 63 prevents the dissipation of rotating electrons, which will be described later, and is applied with a negative potential. The reason for making a large number of holes is to ensure conductance.

A magnetic field setting means 30 is arranged around the container 60. The magnetic field setting means 30 consists of two cylindrical permanent magnets 31 and a yoke 32 between them.

The magnetic field created 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 this interelectrode space 27,
The electric field is oriented in the radial direction of the anode electrode 21. Therefore, the electric field and the magnetic field are orthogonal to each other in the interelectrode space 27. In this embodiment, the strength of the magnetic field created by the permanent magnet 31 is 2500 Gauss at the hot cathode filament 11.

Recess 3 sandwiched between the inner surface of yoke 32 and two permanent magnets
3 houses a sensor coil 41. The sensor coil 41 is for measuring the intensity of a rotating electron current, which will be described later, and is wound with 2000 turns.

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

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.

The output voltage of the DC power supply 23 is about 2 to 2.5 kV,
The output voltage of the AC power supply 24 has an amplitude (difference between maximum peak and minimum peak) of about 1 to 2 kV. The total voltage is such that the maximum voltage is approximately 3 kV and the minimum voltage is 07 or higher (preferably 500 V or higher). The frequency of the alternating current is not particularly limited, but 10 to 1000 Hz can be used.

A changeover switch 25 is provided between the anode 20 and the power sources 23 and 24, so that it is possible to switch to another power source 26. For example, for high pressures of 10-'Torr or more, a low power, low voltage power supply may be utilized as the other power supply 26.

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

The ion collector 50 is powered by a DC power supply 54.
A negative voltage of about -100V is applied.

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

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

An anode voltage as shown in FIG. 4 is applied to the surfaces of the anode electrode 21 and the hot cathode filament 11.

The maximum value of the anode voltage is 3 kV, and the minimum value is 1 kV. The DC component of the applied voltage is 2kV, and the amplitude of the AC component is also 2kV.
It is. The frequency of the alternating current component is 300 Hz. A voltage of minus 100 V is applied to the ion collector electrode 51. 5V is applied to both ends of the hot cathode filament 11. The shield 63 is set to -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 2
Head to 1. However, the trajectory of the electrons is bent by the action of the magnetic field, resulting in a rotational motion 17 as shown in FIG.

As a result, the electrons rotate over an extremely long distance before reaching the anode electrode 21, colliding with gas molecules on the way and ionizing them. Due to this phenomenon, a discharge with high electron density occurs in the interelectrode space 27. It becomes difficult for electrons to reach the anode electrode 21, and the anode current becomes extremely small compared to a normal BA gauge.

Therefore, the soft X generated when electrons collide with the anode electrode
The number of rays also decreases, and the measurement limit using soft X-rays moves to a lower pressure region than the B-A gauge. Many of the ions generated by ionization of gas molecules gather on 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 about 1000 times larger than that of a conventional BA gauge of similar size. Therefore, it is not necessary to measure minute currents, and the circuit for measuring ion collector currents becomes extremely inexpensive.

Since the anode voltage varies as shown in FIG. 4, the intensity of the rotating electron current also varies accordingly.

When the rotating electron current changes, the magnetic flux density passing through the sensor coil 41 changes, and an alternating current is induced in the sensor coil 41. This induced current is detected by an ammeter 42. Since the rate of change in the rotating electron current is proportional to the intensity of the rotating electron current, the rotating electron current 1r can be determined by determining the thickness of the induced current.

When the pressure inside the gauge bulb is P1 and the sensitivity coefficient of the vacuum gauge is S, the pressure P can be determined by the following equation.

P= (1/S) (I c/I r) where,
To give a measurement example, under the above operating conditions, the pressure is I
For the case of nitrogen gas at 10-' Torr, ion collector current 1 cm 10 μA 1 rotating electron current 1 r = 46
Obtained 0mA. Substituting this into the above equation, the sensitivity coefficient 5-
24 is obtained. Since it was experimentally confirmed that there is a linear relationship between pressure P and current ratio (Ic/Ir), from now on,
By finding Ic and Ir and substituting them into the above equation, the pressure P
can be found. FIG. 3 shows the relationship between the pressure P and the ion collector current 1c at this time.

Next, another method of operating this vacuum gauge will be explained.

In the above operating method, only the rotating electron current is measured, but it is also possible to go further and control the rotating electron current to be constant. 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 is 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. A 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, by not only measuring the ratio of the ion collector current to the rotating electron current but also controlling the rotating electron current to a constant value, it becomes possible to measure pressure with higher precision.

In any of the above operating methods, 1O-4T or
When measuring a pressure higher than r, it is preferable to switch the anode voltage source to the low voltage power supply 26 using the changeover switch 25 and apply a voltage of about 100 V to the anode electrode 21.

Note that 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, an ammeter 18 and a bandpass filter 19 are inserted into a loop made up of the lead wire 12, the filament 11, and the lead wire 13. Since an alternating current induced by the rotating electron current flows through this loop, the rotating electron current can be determined by measuring this induced current with the ammeter 18.

The role of the bandpass filter 19 is the same as that of the bandpass filter 43 described above.

The vacuum gauge of FIG. 1 can also be used as a nude gauge. That is, this is a type in which only the pressure measurement portion is inserted into the container to be measured without using the container 60. In that case, the anode electrode 21 is made into a hollow container, and the permanent magnet 31 and the sensor coil 41 are attached to the outside or inside of the container.

Second Embodiment (Cold Cathode Magnetron Type) FIG. 5 is a longitudinal cross-sectional view of a gauge bulb 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 hot cathode filament described above. The advantage of a cold cathode is that it does not disturb the system under test compared to a hot cathode. In other words, the temperature of the system to be measured does not rise, and less gas is released.

However, cold cathodes generally have poorer discharge stability than hot cathodes, and the ion collector current tends to become unstable.

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

The differences when a cold cathode magnetron type is adopted will be explained below.

The electrical configuration differs from FIG. 1 in that the filament power supply 15 is not required, and the lead wire 1 at the other end
3 becomes unnecessary. When measuring a pressure of 10-'Torr or more, the anode voltage is not lowered to about 100v as in the hot cathode type, but is set to 300 to 1000v.

In the case of a cold cathode, discharge tends to become unstable, and various noises are superimposed on the current induced in the sensor coil. Therefore, the bandpass filter 42 shown in FIG. 1 is particularly essential.

In FIG. 5, a sensor coil 41 is placed next to the permanent magnet 311.
Although the example in which the sensor coils 41 are arranged is shown, the sensor coils 41 may be arranged as shown in FIG. Of course, even with 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 can be placed anywhere as long as it can be coupled to 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 hot cathode filament 111 in the form of a hairpin. However, when this cathode is used, it is not possible to measure the rotating electron current using the ammeter 18 shown in FIG. This is because the rate of change in the magnetic flux passing through the loop including the filament 111 is extremely small.

FIG. 7 shows a cylindrical anode electrode 2 with a slit 28 formed therein.
11 is shown. This anode electrode can be made to function as a one-turn coil by looping the lead wire as shown in FIG. That is, an alternating current is induced in this one-turn coil by the rotating electron current, and the rotating electron current is measured by measuring this with an ammeter 29.

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

FIG. 9 shows a cold cathode magnetron type cathode structure with end plates. 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 inverted 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, end plates 164 and 165 are provided at both ends of the cathode electrode 163 in order to prevent electrons from diffusing outside the discharge space.

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

E. Measurement of rotating electron current using microwaves FIGS. 12 and 13 show an example of detecting microwaves as another means for measuring rotating electron current. Although these figures show examples of a cold cathode type, a hot cathode type can also be used.

In FIG. 12, a microwave extraction electrode 70 is placed near one end of the anode electrode 21. In FIG. The microwave extraction electrode 70 consists of a coupling loop 71 and a transmission line 72. Since the intensity of the generated microwaves depends on the rotating electron current, the rotating electron current can be measured by detecting the intensity of the microwaves.

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

Measurement of rotating electron current using synchrotron radiation FIGS. 14 and 15 show an example of detecting synchrotron radiation as another means for measuring rotary electron current.

Figure 14 is a cross-sectional view of the gauge sphere, and Figure 15 is the first
FIG. 4 is a sectional view taken along the line xv-xv in FIG. 4; When electrons rotate in a magnetic field, they emit light, so if the intensity of the synchrotron radiation is measured by the synchrotron radiation detection means 80, the rotating electron current can be measured.

An aperture 215 is formed in the anode electrode 21, and the emitted light 81 generated in the discharge space passes through the aperture 215. This 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 emitting plate, a secondary electron multiplier tube, and the like.

In addition, in FIG. 14 and FIG. 15, the magnetic field setting means outside the container is omitted.

Measurement of Rotating Electron Current Using a Probe FIG. 16 shows an example in which a probe 90 is used as another means for measuring the rotating electron current. There is a small opening 216 in the anode electrode 21.
is formed, from which a probe electrode 91 is inserted into the discharge space. The probe electrode 91 is covered with an insulating liquid 8193 except in the discharge space, and is connected to an external meter by a lead wire 92. By measuring the current, potential, etc. of this probe 90, the rotating electron current can be measured. The probe 90 may be attached to a position other than that shown in the drawings, if necessary.

Note that when using any of the above three types of rotating electron current measuring means, that is, microwave, synchrotron radiation, and probe, the AC power supply 24 shown in FIG. 1 is not necessarily required.

This is because there is no need to vary the rotating electron current.

The respective embodiments, electrode structures, and rotating electron current measuring means shown in each figure can be used in combination with each other unless there is any particular disadvantage.

[Effects of the Invention] The vacuum gauge according to the first invention of this application measures the pressure by measuring the rotating electron current in a crossed electromagnetic field type vacuum gauge and finding the ratio between this and the ion collector current. ing. Therefore, the following effects are achieved. Conventional crossed electromagnetic field type vacuum gauges have high sensitivity, but have a drawback in measurement accuracy because they measure only the ion collector current.However, in this invention, the ratio of the ion collector current to the rotating electron current has been improved. As a result, 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 a constant value, so it can be expected to further improve measurement accuracy.

In addition to the features of the first invention, the vacuum gauge according to the third invention of this application applies a voltage consisting 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 using the electromagnetic induction phenomenon.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of the first embodiment, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, Fig. 3 is a graph showing the pressure/ion collector current curve of the first embodiment, and Fig. 4 is a graph showing the pressure/ion collector current curve of the first embodiment. A graph showing the anode voltage of the first embodiment, FIG. 5 is a sectional view of the main part of the second embodiment, FIGS. 6 to 10 are explanatory diagrams showing various examples of changes to the cathode or anode, and FIG. 11 12 and 13 are explanatory diagrams of the microwave detection means. FIGS. 14 and 15 are explanatory diagrams of the synchrotron radiation detection means.
The figure is an explanatory diagram of the probe. 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

Claims (3)

[Claims] (1) a cathode, an anode, a magnetic field setting means for forming a magnetic field that intersects the electric field created 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; 1. A vacuum gauge, comprising: an ion collector that collects ions ionized by rotating electrons, and measures pressure by determining a ratio between the rotating electron current and the ion collector current. (2) The vacuum gauge according to claim 1, wherein the pressure is measured by controlling the rotating electron current to a constant value and measuring the ion collector current. (3) The vacuum gauge according to claim 1, wherein a voltage consisting of a DC component and an AC component is applied between the cathode and the anode.