RU2649066C1 - Ion gauge of orbitron type - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: use: for measuring high and ultrahigh vacuum. Essence of the invention lies in the fact that the ionization manometer of the orbitron type contains a cylindrical anode placed in a cylindrical body at one end thereof, having a positive potential of about several hundred volts, a cylindrical collector of ions with zero potential, in which said cylindrical anode is placed coaxially, and having a length several times greater than its diameter, a thermionic cathode having a positive potential which is lower than the anode potential and is about several tens of volts, made in the form of a piece of wire and placed parallel to the axis of the anode at a distance from the surface of the anode in the radial direction equal to the length of the thermionic cathode and an electric shield, having a cathode potential located between the anode and the cathode, the electric shield is made in the form of a metal jar surrounding the thermionic cathode and located coaxially with it, so that the bottom of the cup faces the housing tube, and a slit opening is formed on the side surface of the jar for electron liberation, preferably in azimuth direction with respect to the anode axis, wherein one end of the cathode is electrically connected to the bottom of the metal jar and, on the opposite side, the jar is closed by a dielectric disc with an opening through which the traverse is electrically connected to the other end of the cathode.

EFFECT: technical effect: providing the possibility of extending the measurement limits towards low pressures, as well as reducing the measurement error.

1 cl, 3 dwg

Description

Technical field

The present invention relates to techniques for measuring high and ultrahigh vacuum and can be used to create ionization vacuum gauges with measurement limits from 1 Pa to 10 ^-11 Pa.

State of the art

Orbitron-type ionization gauges (Mourad W. G., Pauly T., Herb R. G. Orbitron Ionization Gauge, Scientific Instruments Review, 1964. Volume 35, No. 6, pp. 661-665; or Vostrov G.A., Rozanov L.N. Vacuum gauges, Leningrad, ed. Engineering, 1967, 236 p.). The electrode system of such manometric transducers contains two long concentric cylinders - the inner one, which is the anode, and the outer one, which is the ion collector, the thermionic cathode, located near one of the cylinder ends, and the rod, located between the cathode and the anode and providing local screening of the cathode from the anode potential. In the operating range of the measured pressures, the ion collector current is proportional to the gas pressure. Using this transducer, a pressure measurement in the range of 10^-3to 10^-9 Pa

The measurement of gas pressure below 10 ^-9 Pa is limited by soft X-ray emission of electrons when they are braked at the anode and emission of positive ions from the cathode. These factors create an ion collector current component that is independent of pressure. When it becomes comparable with the ion current as the pressure decreases, an unacceptable error in the measurement of pressure occurs, which determines the lower limit of measurement.

Closest to the claimed technical solution is a manometric orbitron type transducer Mourad W. G., Pauly T., Herb R. G. Orbitron Ionization Gauge, Scientific Instruments Review, 1964, Volume 35, No. 6, pp. 661-665, or Meyer E. A., Herb R. G. Performance Study of the Orbitron Ionization Gauge, Vacuum Science & Technology, 1967, Volume 4, No. 2, pp. 63-70). A diagram of a known gauge transmitter is shown in FIG. one.

The pressure gauge contains a straight filament cathode 1 (Fig. 1) in the form of a thin filament, a rod screen 2, which simultaneously feeds the filament current of the cathode, a cylindrical anode 3, a cylindrical ion collector 4 having zero potential, and a cylindrical reflector 5 shielding the space 6 near the cathode from high about 500V anode potential 3.

The electrons from the cathode 1 are accelerated by the electric field in the direction perpendicular to the plane of the drawing, since their movement to the anode 3 is prevented by the screen 2. At the same time, they receive a slight acceleration along the axis of the anode 3. As a result, spiral-shaped electron trajectories are formed, directed to the loose end of the anode 3, near which the axial component of the electric field at the end of the anode changes the direction of the spiral to the opposite. Near the fixed end of the anode 3, the change in direction of the spiral is repeated.

After many reciprocating movements of the electrons along the axis of the anode 3 up to hundreds of times with simultaneous rotation around it up to thousands of revolutions, the electrons enter the anode 3 due to the gradual curvature of the trajectories by the local electric field of the cathode 1. The path of the electrons to go to the anode 3 by several orders more than in conventional ionization manometers and amounts to about 100 m, and, accordingly, there is a greater number of ionizing electron impacts with residual gas molecules. The reflector 5, having a small negative potential, helps to lengthen the trajectories of the electrons before it hits the anode 3.

Ions under the influence of an electric field go to a collector 4, the current of which is a measure of gas pressure at a constant controlled value of the electron current between the cathode 1 and anode 3. The sensitivity of orbitron type pressure gauges is several orders of magnitude higher than conventional pressure gauges.

A large electron path length is provided at a certain value of the cathode potential, about 10% of the anode potential, on which the azimuthal and axial components of the electron velocity depend, and, consequently, the spiral phase corresponding to the interaction of the electron with the local cathode field. When the potential of the cathode 1 deviates from the optimal value, the interaction becomes "unsuccessful" and after a small number of turns of the spiral, the electron goes to anode 3 and its path turns out to be small.

A similar effect occurs if the electrons start from sections of the cathode 1, remote from its center, or at an angle to the normal to the plane of the drawing. This is the cause of one of the disadvantages of the orbitron gauge type, since the intensity of soft x-ray radiation, which limits the lower measurement limit, is proportional to the total number of electrons entering the anode, and the useful signal, i.e. the ion current is proportional only to the part of the anode current associated with electrons moving in a spiral and having a long path. Another disadvantage of this orbitron type gauge converter is the lack of protection of the 4 ion collector from the current of positive ions emitted from the surface of the cathode 1. At first glance, this protection is available, since the potentials of the cathode region of the space are several tens of volts higher than the cathode. However, it turns out that the ions can move along the traverse of the cathode 1 to the region with lower potential and go to the collector 4.

SUMMARY OF THE INVENTION

The technical problem to which the invention is directed is the creation of an orbitron type gauge converter, in which the expansion of the measurement limits towards low pressures, as well as the reduction of the pressure measurement error, is provided.

The problem is solved by creating an ionization gauge of the orbitron type, which contains placed in a cylindrical body at one of its ends

a cylindrical anode having a positive potential of about several hundred volts,

a cylindrical ion collector with zero potential, in which said cylindrical anode is coaxially placed and having a length several times its diameter,

thermionic cathode having a positive potential that is lower than the potential of the anode and is about several tens of volts, made in the form of a piece of wire and placed parallel to the axis of the anode at a distance from the anode surface in the radial direction equal to the length of the thermionic cathode,

a cylindrical reflector concentric with the anode and placed opposite the cathode,

the end of the cathode is placed at a distance from the end of the reflector in the axial direction equal to the length of the cathode,

an electric screen having a cathode potential located between the anode and cathode and preventing the movement of electrons to the anode along a rectilinear path,

wherein the thermionic cathode and the electric screen form a cathode assembly, and

the housing contains a pipe for connecting to a vacuum system,

characterized in that

the electric screen of the cathode assembly is made in the form of a metal cup surrounding the thermionic cathode and arranged coaxially with it, so that the bottom of the cup faces the nozzle of the housing, and a slot hole is made on the side surface of the cup for electrons to exit, mainly in the azimuthal direction with respect to the anode axis, with one end the cathode is electrically connected to the bottom of the metal cup, and on the opposite side the cup is closed by a dielectric disk with an opening through which the traverse passes, eski connected to the other end of the cathode.

Preferably, the length of wire from which the thermionic cathode is made has a length of about 5 mm and a diameter of about 50 microns.

The proposed design of the cathode assembly provides a decrease in the number of electrons entering the anode “along a short path”, i.e. without a large number of revolutions around the anode, and protects the ion collector from contact with positive ions emitted by the cathode, which in turn provides.

The orbitron type pressure gauge according to the invention comprises expanding the measurement limits towards low pressures, as well as reducing the pressure measurement error.

Brief Description of the Drawings

The invention is further explained in the description of the preferred embodiment with reference to the accompanying drawings, in which:

FIG. 1 depicts a known orbitron type gauge transducer;

FIG. 2 schematically shows a cathode assembly of an ionization gauge transducer according to the invention;

FIG. 3 depicts schematically an orbitron type gauge converter according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The orbitron type ionization manometer 7 (Fig. 2), according to the invention, comprises a cylindrical anode 10, which has a positive potential of about several hundred volts, a cylindrical ion collector 11 with zero potential, which is coaxially located, located in a cylindrical housing 8 at one end thereof 9 cylindrical anode 10. The collector 11 has a length that is several times its diameter

In the housing 8 is also placed a thermionic cathode 12 having a positive potential, which is lower than the potential of the anode 10 and is about several tens of volts. The cathode 12 is made in the form of a piece of wire and placed parallel to the axis of the anode 10 at a distance from the surface of the anode in a radial direction equal to the length of the thermionic cathode 12.

In the described embodiment, the tungsten wire segment from which the thermionic cathode is made has a length of about 3-5 mm and a diameter of about 50-100 μm.

A cylindrical reflector 13, concentric with the anode 10 opposite the cathode 12, is also located in the housing 8, while the end of the cathode 14 is placed at an axial direction equal to the length of the cathode 12 from the end face 15 of the cylindrical reflector 13.

An electric shield 16 is placed in the housing 8, having the potential of the cathode 12 located between the anode 10 and the cathode 12 and preventing the movement of electrons to the anode along a straight path.

The housing 8 is made of glass and contains a pipe 17 for connection with a vacuum system (not shown).

The thermionic cathode 12 and the electric screen 16 form a cathode assembly 18.

The collector 11 is fixed in the housing 8 on two inputs 19 and 20, which are welded to the beam 21, 22. The reflector 13 is mounted on the input welded to the beam 24. The anode 10 is connected to the input 25, which is supplied with a voltage of 300-500 V. Cathode 12 mounted on the input 26, mounted on the beam 27, which is supplied with a voltage of 30 V, while the electric screen 16, mounted on the beam 28, is supplied with a voltage of 32 V. The tavern 27 has the form of a wire or strip.

The electric screen 16 (Fig. 3) of the cathode assembly 18 according to the invention is made in the form of a metal cup made of foil surrounding the thermionic cathode 12 and arranged coaxially with it, so that the bottom 29 of the cup faces the nozzle 17 of the housing 8, and a slotted hole is made on the side surface of the cup hole 30 for the exit of electrons mainly in the azimuthal direction relative to the axis of the anode 10, i.e. perpendicular to the X-Y plane of the drawing. In this case, one end of the cathode 12 is electrically connected to the bottom 29 of the metal cup, and on the opposite side the cup is closed by a dielectric disk 31 with an opening 32 through which a traverse 27 passes, electrically connected to the end 33 of the cathode 12.

The other end of the cathode 12 passes through an opening 34 in the bottom of the glass and is electrically connected to a second beam 28, which is electrically connected to the screen 16

The work of the gauge orbitron type converter is as follows.

The glow voltage of the cathode 12 is applied between the traverses 27 and 28 (Fig. 3). At the same time, a positive potential of the order of 10% of the potential of the anode 10 is supplied to the traverse 28 and the screen 16. The ion collector 11 has zero potential. The given potentials form an electric field that penetrates through the slit 30 of the screen 16, accelerates the electrons emitted from the central part of the cathode 12 and forms from them a beam of a certain configuration, propagating in a given direction. The electron paths in accordance with the principle of operation of the orbitron type gauge converter have a spiral shape, as described above.

The presence of a screen with an exit slit 30, in comparison with the known construction, significantly reduces the number of electrons passing an insufficiently long path before leaving the anode, and provides a higher ratio of the useful signal (ion current) to the background current due to x-ray radiation.

At the same time, the influence of the background current associated with the emission of positive ions from the cathode 12 is eliminated; they do not exit through the slit 30, since the points of space in it have positive potentials, and the insulator 31 impedes the movement of ions along the traverse 27.

Thus, the use of the proposed design of the cathode assembly 18 with a glass-shaped electric screen 16 having a small hole 30 for electron exit and an insulator 31 preventing the positive ions emitted by the cathode 12 from leaving the screen 16 allows us to expand the lower measurement limit of the orbitron type gauge converter to 10 ^-11 Pa and at the same time reduce the pressure measurement error.

Claims (12)

1. An orbitron type ionization pressure gauge comprising those placed in a cylindrical body at one end thereof a cylindrical anode having a positive potential of about several hundred volts, a cylindrical ion collector with zero potential, in which said cylindrical anode is coaxially placed and having a length several times its diameter, thermionic cathode having a positive potential that is lower than the potential of the anode and is about several tens of volts, made in the form of a piece of wire and placed parallel to the axis of the anode at a distance from the anode surface in the radial direction equal to the length of the thermionic cathode, a cylindrical reflector concentric with the anode and placed opposite the cathode, the end of the cathode is placed at a distance from the end of the reflector in the axial direction equal to the length of the cathode, an electric screen having a cathode potential located between the anode and cathode and preventing the movement of electrons to the anode along a rectilinear path, wherein the thermionic cathode and the electric screen form a cathode assembly, and the housing contains a pipe for connecting to a vacuum system, characterized in that the electric screen of the cathode assembly is made in the form of a metal cup surrounding the thermionic cathode and arranged coaxially with it, so that the bottom of the cup faces the nozzle of the housing, and a slot hole is made on the side surface of the cup for electrons to exit, mainly in the azimuthal direction with respect to the anode axis, with one end the cathode is electrically connected to the bottom of the metal cup, and on the opposite side the cup is closed by a dielectric disk with an opening through which the traverse passes, eski connected to the other end of the cathode. 2. The ionization manometer according to claim 1, characterized in that the length of wire from which the thermionic cathode is made has a length of about 5 mm and a diameter of about 50 microns.

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