JP3580967B2 - Vacuum gauge - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hot cathode magnetron type vacuum gauge.
[0002]
[Prior art]
Conventionally, as this kind of vacuum gauge, a ruffy type vacuum gauge as shown in FIG. 1 is known. This ruffy-type vacuum gauge is provided with a magnet c surrounding the outer circumference of a cylindrical vacuum gauge container b having one end closed by an electrode terminal a and the other end being open, and the magnet c is provided inside the vacuum gauge container b. A configuration in which a cylindrical anode d, a filament e, a disk-shaped ion collector f, and a disk-shaped shield g for shielding the electrode terminal a from a discharge space are provided by supporting the electrode terminal a on a pin h inserted inside and outside. Having. The magnet c is magnetized in the cylindrical axis direction of the vacuum gauge container b, that is, magnetized so that both ends of the cylindrical axis have opposite polarities. The direction of the magnetic force lines is the axial direction of the vacuum gauge container b.
[0003]
The potentials of the anode d, the ion collector f and the shield g are 300, 45 and -10 V, respectively, for the filament e in the Rafferty embodiment, and the magnetic field strength is 250 Gauss.
[0004]
When the vacuum pressure is measured by the vacuum gauge, the filament e is energized to generate thermoelectrons therefrom. The thermoelectrons are accelerated by receiving a force in the direction of the anode d, but undergo a Lorentz force in the presence of the axial magnetic field of the magnet c to make a motion similar to a spiral motion in the space inside the anode d. In the absence of the magnet c, thermoelectrons immediately reach the inner wall of the anode d, but the orbit becomes very long due to the spiral motion of the thermoelectrons in the presence of the magnetic field, and during the flight of the thermoelectrons, Accordingly, the probability of ionizing gas molecules in the anode d is increased. Thermal electrons and ionized electrons make a spiral motion and finally reach the anode d. The ions ionized from the gas molecules are collected in the ion collector f. Since the ion current flowing through the ion collector f is proportional to the amount of gas in the space, by measuring the ion current, the pressure in the vacuum gauge container b and, consequently, the pressure in the vacuum space such as the pressure container to which the vacuum gauge is attached can be reduced. Can be measured. The characteristic of this Rafferty vacuum gauge is that the ion current is increased, that is, the sensitivity is increased by increasing the electron orbit by the magnetic field and increasing the probability of collision between the electrons and the gas in the space.
[0005]
[Problems to be solved by the invention]
In the conventional Rafferty vacuum gauge, electrons move spirally in the space inside the anode d in FIG. 1 and eventually strike the inner wall of the anode d. At the time of collision, soft X-rays are generated from the inner wall of the anode d Sometimes. Also, gas molecules adhering to the inner wall of the anode may be bombarded as ions by the colliding electrons. Some of the soft X-rays bombard the ion collector f and cause electrons to be emitted from the collector f by the photoelectric effect, and the electrons flow to the anode d. Thus, the current flowing through the ion collector f is the sum of the ion current and the photoelectron current due to the ionization of the gas in the space. Photoelectron current is independent of gas pressure, which is a factor that makes pressure measurements inaccurate. In addition, the ion current caused by the ions struck out of the inner wall of the anode also causes inaccuracy in measuring the pressure in the space. These factors are significant in pressure measurement in an ultra-high vacuum region where the number of gas molecules in the space is small, making the pressure measurement inaccurate.
[0006]
An object of the present invention is to improve pressure measurement accuracy of a hot cathode magnetron type vacuum gauge, which is a ruffy type vacuum gauge, in which gas molecules adhering to an inner wall of an anode are reduced by photoelectron current and are ejected as ions by electrons. The purpose of the present invention is to reduce the current caused by the above.
[0007]
[Means for Solving the Problems]
In the present invention, a filament that emits thermoelectrons, an anode that attracts the thermoelectrons emitted from the filaments along the lines of magnetic force of the magnet, and a filament are disposed in a vacuum gauge container provided with a magnet on the outer periphery. In a vacuum gauge in which a plate-shaped shield that repels the thermoelectrons at a negative potential and an ion collector into which ions generated by collision of the thermoelectrons with a gas in the vacuum gauge container are incident are provided. An anode is formed in a shell shape and provided so as to face the shield, an opening for conducting thermoelectrons is formed at a position of the anode facing the shield, and the ion collector is moved to the outer surface of the anode by the collision of the thermoelectrons. The above-mentioned object is achieved by arranging at a position not irradiated with X-rays generated from. The anode has a cylindrical body extending in the direction of the line of magnetic force and an end plate closing both ends thereof, and an opening is formed in the center of both end plates, and the cylindrical body is positioned at the middle of its length direction. The above-mentioned ion collector formed in a ring shape is provided between the divided portions, and a plate-shaped shield is provided at a position facing each opening outside the anode. It is convenient to adopt a configuration in which a filament is provided between the shield and the shield, the cross section of the ring of the ion collector is circular or rectangular, or by forming a projection at a position facing the opening of the shield, The above object can be achieved accurately.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The embodiment will be described with reference to FIGS. 2 and 3. In these figures, reference numeral 1 denotes a cylindrical non-magnetic metal vacuum gauge container having one end closed by an electrode terminal 2 and the other end opened. Reference numeral 3 denotes a magnet such as a permanent magnet provided around the outer circumference of the vacuum gauge container 1. The electrode terminal 2 is composed of an insulator 2a and a plurality of metal pins 2b inserted therethrough. The magnet 3 has a line of magnetic force directed to the other end of the vacuum gauge container 1 that is opened in the cylindrical axis direction. Magnetized to produce. Inside the vacuum gauge container 1, a filament 4 for emitting thermoelectrons, an anode 5 for attracting the thermoelectrons along the lines of magnetic force, a plate-like shield 6 for repelling the thermoelectrons at a negative potential from the filament 4, Further, an ion collector 7 into which ions generated by collision of the thermoelectrons with the gas in the vacuum gauge container 1 are provided while being held by the pin 2b.
[0009]
The above configuration is also provided with a conventional vacuum gauge, but in the present invention, the anode 5 is formed in a shell shape such as a container type having a small opening area, and the ion collector 7 is formed on the outer peripheral surface of the anode 5. It is arranged at a position that is invisible from the shield 6 and hard to see from the shield 6 to prevent the generation of photoelectron current due to soft X-rays and the generation of ion current due to ions struck out of the outer wall of the anode 5 so that accurate pressure measurement can be performed.
[0010]
More specifically, the anode 5 is provided on an end plate 5b having a shell shape such as a cylindrical container having an axis in the direction of the magnetic field lines and having both ends formed with openings 5a for conducting thermoelectrons in the center. And a ring-shaped ion collector with a diameter substantially equal to the average diameter of the container 5c between the divided portions. 7, a disk-shaped shield 6 is provided outside the container 5c at a position facing each of the conduction openings 5a. Then, the filament 4 was disposed between the shield 6 and the anode 5 on the electrode terminal 2 side. With this configuration, the probability that the thermoelectrons from the filament 4 collide with the outer wall rather than the inner wall of the anode 5 after passing through and reversing the anode 5 is increased, and the ion collector 7 is disposed between the divided portions of the anode 5. The presence of the end plate 5b on the anode 5 makes it difficult for soft X-rays and ions generated by collision of electrons to the outer peripheral surface of the anode 5 to collect on the ion collector 7.
[0011]
For example, a potential of +300 V with respect to the potential of the filament 4 is applied to the anode 5, a potential of +45 V is applied to the ion collector 7, and a potential of −10 V is applied to the shield 6. When measured, the thermoelectrons generated by energizing the filament 4 move spirally within the range limited by the shield 6 under the influence of the magnetic field lines of the magnet 3, and follow a very long orbit to the anode 5. In the meantime, gas molecules in the space of the anode 5 collide with and ionize them, and ions generated by the ionization are collected in the ion collector 7. Since the ion current of the ion collector 7 is proportional to the amount of gas in the space, the pressure can be measured by measuring the ion current.
[0012]
Such a principle operation is the same as that of a conventional vacuum gauge of this type, but thermionic electrons from the filament 4 and the electrons generated by the ionization of the gas move in a spiral motion along the lines of magnetic force, and the anode 5 The electrons are directed to the upper shield 6 through the conduction opening 5a of the upper end plate 5b, and these electrons are decelerated and inverted by the attractive force of the anode 5 and the repulsive force of the shield 6 which is negative with respect to the filament 4, As shown in locus A in FIG. Alternatively, it collides with the outer wall of the anode 5 as shown by a locus B. The radius of gyration of the spiral motion of the electrons is about 0.005 mm when the strength of the magnetic field is 250 Gauss and the electron energy is 300 eV, which is not shown. The electrons that have reentered the anode 5 collide with the inner wall of the anode or fly through the conduction opening 5a of the end plate 5b on the opposite side to the shield 6 on the opposite side, and are decelerated and inverted by the repulsive force. Collides with the inner or outer wall of the anode and disappears. In the anode 5, electrons are likely to move in the axial direction while making a spiral movement, so that the probability of collision with the outer wall of the anode 5 is higher than that of the inner wall.
[0013]
As described above, when an electron collides with the anode 5, soft X-rays may be generated, and gas molecules attached to the anode 5 may be ejected as ions. Only the conduction opening 5a of the end plate 5b is opened in the direction, and the ion collector 7 is installed in a place difficult to see from the shield 6 deep between the divided portions of the anode 5, so that electrons are transmitted from the inner wall of the anode 5 Also collide with the outer wall, in other words, many soft X-rays and ions are ejected on the outer surface of the anode 5, and the generated soft X-rays are not irradiated to the ion collector 7 and are ejected from the outer wall. It is difficult to collect the collected ions in the recessed ion collector 7. Therefore, the amount of ion current, that is, the amount of noise caused by the soft X-rays and the ions struck out of the anode 5 is reduced in the ion collector 7, and accurate pressure measurement in an ultra-high vacuum region can be performed.
[0014]
In the above embodiment, the ion collector 7 is formed by a ring having a circular cross section, but may be formed by a ring having a rectangular cross section as shown in FIG. If at least one of the two shields 6 for shielding the electrode is provided with a projection 6a facing the opening 5a of the anode 5 as shown in FIG. 5, the electron trajectory becomes large as shown in FIG. The pressure measurement in the ultra-high vacuum region can be more accurately measured by reducing the probability that electrons are bent and re-enter the inside of the anode container 5c and collide with the inner wall. Even if the potential of one shield 6 is made higher than the potential of the filament 4 and electrons collide with the shield 6, the probability that the electrons re-enter the anode vessel 5c and collide with the inner wall can be reduced, and accurate measurement can be performed. I can do it.
[0015]
【The invention's effect】
As described above, according to the present invention, the anode of the hot cathode magnetron type vacuum gauge is formed in a shell shape with a small opening, and the ion collector is not irradiated from the outer peripheral surface of the anode with X-rays generated by the collision of thermoelectrons. Since it is located at a position, the photoelectron current due to soft X-rays in the ion collector and the current due to ions struck out of the anode can be reduced, and the effect of accurate pressure measurement in the ultra-high vacuum region can be obtained. The anode is constituted by a two-part container having openings at both ends, a ring-shaped ion collector is provided between the divided parts, and a plate-shaped shield is provided respectively in opposition to each opening. By providing a filament between the opening and the shield, and further by adopting the configuration of claims 3 and 4, the above-mentioned effect can be obtained with a simple configuration. Obtained.
[Brief description of the drawings]
FIG. 1 is a cut-away side view of a conventional example. FIG. 2 is a perspective view in which a part of an embodiment of the present invention is cut away. FIG. 3 is a cut-away side view of FIG. 2 FIG. 5 is a cutaway side view of another embodiment of the present invention.
1 vacuum gauge container, 3 magnets, 4 filaments, 5 anodes, 5a conduction opening, 5b end plate, 5c container, 6 shield, 6a protrusion, 7 ion collector,

Claims (4)

A filament that emits thermoelectrons, an anode that attracts the thermoelectrons emitted from the filaments along the lines of magnetic force of the magnet, and a negative electrode that is more negative than the filaments are placed in a vacuum gauge container provided with a magnet on the outer periphery. In a vacuum gauge in which a plate-shaped shield that repels thermoelectrons and an ion collector into which ions generated by collision of the thermoelectrons with gas in the vacuum gauge container are incident, the anode is formed in a shell shape. And the anode is provided so as to face the shield. An opening for thermionic conduction is formed at a position of the anode facing the shield, and the ion collector is formed by X generated from the outer surface of the anode by the collision of the thermoelectrons. A vacuum gauge, wherein the vacuum gauge is arranged at a position not irradiated with a line. The anode has a cylindrical body extending in the direction of the line of magnetic force and an end plate closing both ends thereof, and an opening is formed in the center of both end plates, and the cylindrical body is divided at the middle in the longitudinal direction. And a ring-shaped ion collector is provided between the divided portions, and a plate-shaped shield is provided at a position facing each of the openings outside the anode. The vacuum gauge according to claim 1, wherein a filament is provided between the shields. The vacuum gauge according to claim 2, wherein a cross section of the ring of the ion collector is circular or rectangular. The vacuum gauge according to any one of claims 1 to 3, wherein a protrusion is formed at a position facing the opening of the shield.

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