US3505554A

US3505554A - Ionization pressure gauge

Info

Publication number: US3505554A
Application number: US696067A
Authority: US
Inventors: Sergei Arkadievich Vekshinsky; German Anatoliev Nichiporovich
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-01-05
Filing date: 1968-01-05
Publication date: 1970-04-07
Anticipated expiration: 1987-04-07

Description

April 7, 1970 s. A. vEKsHlNsKY ET AL 3,505,554

IONIZATION PRESSURE GAUGE Filed Jan. 5, 1968 FIG-.l

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United States Patent Office 3,505,554 Patented Apr. 7, 1970 U.S.S.R.

Filed Jan. 5, 1968, Ser. No. 696,067 Int. Cl. H01j 41 00 U.S. Cl. 313-157 4 Claims ABSTRACT OF THE DISCLOSURE An ionization pressure gage comprises an anode cylinder mounted inside a casing with a cathode extending along the axis of the anode cylinder. At one end of the anode cylinder is an ion collector electrode and at the other end of the anode cylinder is a shield, a magnetic lield being created to cause electrons emitted by the cathode to undergo spiral rotation as a cloud of electrons within the cathode-anode space. A control anode is disposed outside of the cathode-anode space in close proximity to the cathode at a spacing which is chosen so that all electrons emitted in the area of the control anode fall thereon. The control anode may be of cylindrical shape and receive the cathode therewithin.

The present invention relates to apparatus for measuring low gas pressures, and more particularly to magnetron ionization pressure gauges with thermionic cathodes.

Ionization pressure gauges are known in which the system of electrodes comprises an anode cylinder, a thermionic cathode extending along the axis of the anode cylinder, said cathode emitting electrons which form an electron cloud undergoing spiral rotary motion in the space between the cathode and the anode cylinder under the action of a magnetic iield, a collector electrode and a shield, which latter two are disposed at the respective ends of the anode cylinder. The ion current in such pressure gauges is proportional to the gas pressure, provided the electron emission current I- from the cathode is constant, said electron emission current being equal to the electron current in the circuit including the cathode and the anode (the cathode-anode current) with the value of the applied magnetic field H equalling zero. It is, therefore, necessary to maintain constancy of the emission current I0- from the cathode, when the measurements of the gas pressure are carried out.

A disadvantage of the ionization pressure gauges of the known kind lies in the impossibility of control over the value of this emission current I0- concurrently with the measurements of the gas pressure, since in the presence of the magnetic field during the operational duty of the gauge, the anode current sharply decreases and its value is dependent upon the pressure, thus rendering impossible the evaluation of the emission current by the anode current value.

In another known kind of ionization pressure gauge, still another constituent part is added to those mentioned above, this additional part being a control anode disposed adjacent to the cathode within the cathode-anode space, i.e. within the space occupied by the spirally rotating cloud of electrons. This additional control anode enables measuring and controlling the emission current, since the electron current I1- fed to the control anode is proportional to the electron emission current I0* and is independent of the gas pressure within a considerably broad range of the gas pressure values.

However, the positioning of the control anode within the rotating cloud of electrons itself introduces a number of disadvantages, namely:

(l) The control anode current in the absence of the magnetic Iield is not equal to the control anode current, when the magnetic field is applied. Subsequently, it is quite diflicult to evaluate the true relationship between the emission current IO- which is measured in the absence of the magnetic field and the control anode current I1* which is used to judge and control the operation of the gauge.

Thus, with the magnetic field strength equalling zero, the current arriving at the control anode is equal to If. When the value of the applied magnetic field is above critical, a rotating cloud of electrons is formed about the cathode, and some of the electrons impinge on the control anode, thus increasing the current applied to it, namely 11 I10.

(2) In case the potential at the control anode is varied by mere fractions of a volt, as well as in case the position of the control anode with respect to the rest of the electrodes is shifted but slightly, it immediately influences the operation of the whole ionization gauge, and, correspondingly, causes sharp variations in the control anode current, as well as in the ion current and the cathodeanode current.

(3) The control anode current Il* is independent of the gas pressure (which fact makes it possible to evaluate and control the operational duty of the ionization gauge), but this independence does not cover the whole range of pressures at which the gauge may operate. Thus, it has been found that with the emission current IU- equalling 1.1()9 A., the control anode current I1* starts being dependent on the gas pressure P, when P equals 108 mm. of mercury. With the emission current being 1.10-8 A., this dependence is detected at P=l07 mm. of mercury; and even with the emission current as high as 1.106 A., the control anode current I1- starts varying with P=1()-6 mm. of mercury.

A further disadvantage inherent in the both above described kinds of known ionization pressure gauges is their comparatively complicated structure owing to the necessity of providing an exterior source of the magnetic ield.

It is an object of the present invention to provide an ionization pressure gauge, in which the value of the electron current fed to the control anode is independent of the value of the magnetic lield applied.

It is another object of the present invention to provide an ionization pressure gauge in which the influence eX- erted by the control anode on the operational characteristics or duty of the gauge is eliminated.

It is still another object of the present invention to provide an ionization pressure gauge, in which the range of evaluated and control values of the emission current should be extended over the whole range of the operational gas pressures measured by the gauge.

It is a further object of the present invention to provide an ionization pressure gauge of simplified structure, owing to the elimination of the external source of magnetic field.

With these and other objects in View, the ionization pressure gauge embodying the present invention comprises a control anode positioned exteriorly of the cathode-anode space with its rotating cloud of electrons, said control anode being located at close proximity to the cathode, the spacing between said control anode and said cathode being so chosen that all electrons emitted by said cathode within the area thereof covered by said control anode fall onto the latter.

In a preferred embodiment of the present invention, the control anode is positioned outside the cathode-anode space where the rotating cloud of electrons is formed, on the metal shield side.

Also in a preferred embodiment of the present invention the control anode acquires the form of a cylinder spacingly receiving the cathode thereinside and having the radius which is less than the distance of the spreading of electrons from the cathode under the combined action of the electric and magnetic fields.

In order to create a spirally rotating cloud of electrons in the cathode-anode space of the guage, the anode cylinder may be made of a magnetic material.

According to these novel features of the present invention, the influence of the magnetic field strength H on the electron current I1- applied to the control anode is eliminated; also eliminated is the infiuence of the control anode itself on the operational duty of the gauge, the range of the evaluated and controlled values of the emission current is extended over the whole range of pressures measured by the gauge, and the structure of the gauge is simplified.

Other objects and advantages of the present invention will be better understood from the following detailed description of an embodiment thereof, with due reference to the accompanying drawing, in which:

FIG. 1 is a schematic sectional vie-w of the ionization pressure gauge emboding the present invention;

FIG. 2 shows the same pressure gauge, as in FIG. 1, but with the anode cylinder made of a magnetic material;

FIG. 3 is a graph showing the dependence between the control anode current Iland the emission current If;

FIG. 4 is a graph showing the relationship between the control anode current I1- and the magnetic field strength H with a constant value of the emission current If; and

FIG. 5 is a graph showing the dependence between the current If applied to the control anode and pressure with the value of the emission current I being constant.

In the drawing, the system of the electrodes of an ionization pressure gauge embodying the present invention comprises an anode cylinder 1 (FIG. l), an ion collector electrode 2, a shield 3, a control anode 4 and a cathode 5. The collector electrode 2 and the shield 3 are shaped as discs disposed at the opposite ends of the anode cylinder 1. The control anode is shaped as a cylinder arranged coaxially with the anode cylinder 1, -with the shield 3 located intermediate the anode cylinder 1 and the control anode 4. The cathode extends along the axis of the anode cylinder 1 and the control anode 4 through openings in the collector electrode 2 and the shield 3, with a spring 6 provided for tensioning the cathode. A holder 7 of the cathode S provided on the collector electrode 2 side of the gauge projects by several millimetres into the cathode-anode space, for the hot thermionic portion of the cathode 5 to lie in the area where a potential barrier exists, which prevents the travel of positive ions formed at the cathode 5 to the collector electrode 2.

In a modification of the ionization pressure gauge embodying the present invention, the shield 3 may have no opening. In this case the shield 3 separates the cathode 5 into two portions and is maintained under the potential of the cathode.

In order to be connected to a source of vacuum, the whole system of the electrodes is mounted inside a glass container 8. Alternatively, the system of the electrodes may be mounted inside a metal container or arranged in an exposed state on a suitable flange with the use of ceramic insulation members.

The magnetic field needed for the operation of the pressure gauge is created by a hollow cylinder-shaped permanent magnet 9. Alternatively, the magnetic field can bc created by an electromagnet coil or a solenoid.

Shown in FIG. 2 is an ionization pressure gauge in which the anode cylinder 1' itself is made of a material having magnetic properties and is a cylinder-shaped hollow .permanent magnet providing the magnetic field for the operation of the gauge. This feature makes it possible to do without a separate exterior magnet and thus to simplify the structure of the pressure gauge.

Below is an example of an operational characteristics of the pressure gauge shown in FIG. 1:

Potential difference between the anode cylinder and cathode 5=+400 v.;

Potential difference between the control anode 4 and cathode 524-400 v.

Potential difference between the cathode 5 and ground Potential difference between the collector electrode 2 and cathode 5:-200- v.;

Potential difference between the shield 3 and cathode Electron emission current I0*=l.l07 A.;

Magnetic field strength H=450 oersteds.

-For the electron current Ilthrough the control anode 4 to stay at a constant value with the magnetic field strength H lbeing increased from zero to an operational value, it is necessary that the minimal spacing between the cathode 5 and the control anode 4 be less than the distance of the spreading of electrons from the cathode 5 under the combined action of the electric and magnetic fields. For a cylinder-shaped control anode the above requirement may be exposed as follows:

waxy/if where r is the radius of the control anode 4 in mm.;

H is the strength of the magnetic field in oersteds;

V is the potential difference between the control anode 4 and the cathode S in volts.

Accordingly, the radius r of the control anode 4 should not exceed 3 mm. for the operational characteristics of the pressure gauge, as given above.

The shield 3 is located intermediate the anode cylinder 1 and the control anode 4 in order to eliminate the interaction and mutual influence of their respective electric fields. Due to negative potential of the shield 3 with respect to the cathode 5, migration of electrons from the area of the control anode 4 to that of the anode cylinder l is prevented and vice versa. In this manner the influence exerted by the control anode 4 on the operational characteristics of the pressure gauge is eliminated, and the electron current value I1- through the control anode 4 can ybe maintained constant.

With the voltage supplied to the electrodes being maintained at constant values, and the applied magnetic field strength equalling zero, the electron current in the anode cylinder 1, which is equal to the emission current If, and the electron current If in the control anode 4 are defined by the temperature of the cathode 5, and a given value of I0- brings about a corresponding value of I1- for any value of the pressure P below 1.10*4 mm. of mercury. This is illustrated in FIG. 3, where the abscissa axis corresponds to the values of the emission current I0- in amperes, and the ordinate axis shows the values of the control anode current Ilin ampers.

In the absence of the magnetic field, i.e. with the magnet 9 removed, the emission current IO- is adjusted to an operational value, and the corresponding control anode current I1- is measured. When the magnetic field is now applied, whose strength is above the critical point, electrons emitted by the cathode 5 start rotating thereabout, forming a spirally rotating cloud of electrons. Under these conditions only a small fraction of the total number of the electrons reach the anode .1, whereby the electron current fed to the anode 1 is sharply reduced. The molecules of a gas, present in the area of the rotating cloud of electrons are ionized, and the resulting ions migrate to the collector electrode 2. The value of the ionic current applied to the collector electrode 2 is a measure of Igas pressure. .The control anode current I1- is not changed by the application of the magnetic field, as is illustrated in the graph shown in FIG. 4, where the abscissa indicates the magnetic field strength H in oersteds, and the ordinate indicates the corresponding values of the current I1- in amperes in control anode 4.

Strict correspondence of the current I1- in control anode 4 to the emission current IO- is established over a wide range of the pressures measured, which is illustrated in FIG. 5 where the abscissa shows gas pressures P in mm. of mercury, while the ordinate indicates the emission current I0- and the control anode current Il in amperes.

By evaluating and stabilizing the current Ilin control anode 4 in the process of taking measurements, the operational characteristics of the pressure gauge may be thus evaluated and stabilized.

When operating an ionization pressure gauge shown in FIG. 2, in which the anode 1 acts at the same time as a permanent magnet, it is impossible to measure the emission current I0, and the operational characteristic of the pressure gauge is set according to the values of the current Il in control anode 4 which is evaluated and stabilized in the process of taking pressure measurements.

From the above description it has been made clear that in an ionization pressure gauge with a control anode, embodying the present invention, the electron current through the control anode is virtually unaiected by the strength of the magnetic iield applied, the influence of the control anode on the operational characteristics of the gauge is eliminated, and the range of controlled and sta-bilized values of the control anode current, and, subsequently, of the emission current is extended over the whole range of the operation of the gaufie, with the structure of the gauge itself considerably simplified.

Although the present invention has been described in connection with a preferred embodiment thereof, it should be understood that various changes may be introduced and various modifications may be made without departing from the spirit and scope of the invention, as those skilled in the art will be sure to appreciate.

What is claimed is:

1. An ionization pressure gauge comprising a casing, an anode cylinder mounted inside said casing, a cathode extending along the axis of said anode cylinder and adapted to emit electrons, an ion collector electrode located at one end of said anode cylinder, a shield located at the opposite end of said anode cylinder, means for creating a magnetic iield under the action of which the electrons emitted by said cathode form a spirally rotating cloud of electrons within the cathode-anode space dened by said anode cylinder, said cathode, said ion collector electrode and said shield; a control anode disposed exteriorly of said cathode-anode space with the rotating cloud of electrons, said control anode being arranged in close proximity to said cathode, the spacing between said controlanode and said cathode being so chosen that substantially all electrons emitted by said cathode in the area covered by said control anode fall onto the latter.

2.. An ionization pressure gauge, as set forth in claim 1, in which said control anode is disposed exteriorly of said cathode-anode space with the rotating cloud of electrons, on the same side of said anode cylinder, as said shield.

3. An ionization pressure gauge, as set forth in claim 1, in which said control anode is shaped as a cylinder receiving said cathode thereinside, said cylinder having a radius which is smaller than the distance of the spreading of the electrons from said cathode under the combined action of the electric and magnetic elds present.

4. An ionization pressure gauge, as set forth in claim 1, in which said anode cylinder is made of magnetic material adapted to create a magnetic field, under the action of which a rotating cloud of electrons can be formed within said cathode-anode space.

References Cited UNITED STATES PATENTS 3,239,715 3/1966 Laierty 313-7 X RAYMOND F. HOSSFELD, Primary Examiner U.S. Cl. X.R.