US3280365A - Penning-type discharge ionization gauge with discharge initiation electron source - Google Patents

Penning-type discharge ionization gauge with discharge initiation electron source Download PDF

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Publication number
US3280365A
US3280365A US272984A US27298463A US3280365A US 3280365 A US3280365 A US 3280365A US 272984 A US272984 A US 272984A US 27298463 A US27298463 A US 27298463A US 3280365 A US3280365 A US 3280365A
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Prior art keywords
discharge
anode
penning
cathode
filament
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US272984A
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English (en)
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James R Young
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General Electric Co
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General Electric Co
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Priority to DEG40302A priority patent/DE1265338B/de
Priority to FR970976A priority patent/FR1389330A/fr
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J41/00—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas; Discharge tubes for evacuation by diffusion of ions
    • H01J41/02—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas
    • H01J41/04—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas with ionisation by means of thermionic cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J41/00—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas; Discharge tubes for evacuation by diffusion of ions
    • H01J41/02—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas
    • H01J41/06—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas with ionisation by means of cold cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J41/00—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas; Discharge tubes for evacuation by diffusion of ions
    • H01J41/12—Discharge tubes for evacuating by diffusion of ions, e.g. ion pumps, getter ion pumps
    • H01J41/14—Discharge tubes for evacuating by diffusion of ions, e.g. ion pumps, getter ion pumps with ionisation by means of thermionic cathodes
    • H01J41/16—Discharge tubes for evacuating by diffusion of ions, e.g. ion pumps, getter ion pumps with ionisation by means of thermionic cathodes using gettering substances
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J41/00—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas; Discharge tubes for evacuation by diffusion of ions
    • H01J41/12—Discharge tubes for evacuating by diffusion of ions, e.g. ion pumps, getter ion pumps
    • H01J41/18—Discharge tubes for evacuating by diffusion of ions, e.g. ion pumps, getter ion pumps with ionisation by means of cold cathodes
    • H01J41/20—Discharge tubes for evacuating by diffusion of ions, e.g. ion pumps, getter ion pumps with ionisation by means of cold cathodes using gettering substances

Definitions

  • the present invention relates to ionization gauges and ionic pumps and more particularly to such devices as use a Penning-type discharge to cause ionization of gas molecules so that their presence may be measured and pressure of the gas determined and, in the pump use, that the ions be removed from an enclosure. More specifically, this invention relates to improved Penning type discharge initiating means for the mentioned devices.
  • One parameter which serves as a limiting factor in ionization gauges and ionic pumps is the low limit of measunable or operating pressure. In some such devices this pressure is set by the X-ray photo emission within the device causing a background of X-ray originated electron current. Another limitation is caused by the difficulty of starting ionization gauges and ionic pumps at very low pressures due -to the small number of ionizable particles present at very low pressures.
  • I provide an ionic gage device utilizing a Penning type electric discharge and including an apertured anode member having a planar cathode member coaxially positioned transversely at either longitudinal end thereof.
  • One cathode is provided with a de-centered, i.e., off center, aperture therein behind which I provide a thermionic cathode member which is adapted to be momentarily energized to thermionic emission.
  • Emitted electrons are drawn through the apertured cathode into the interaction space between the anode and cathodes to ionize gas particles therein to cause the establishment of an electric discharge of the Penning-type.
  • the filament is then de-energized while the discharge continues.
  • Decentering the aperture and filament prevents excessive deterioration by positive ion bombardment. Its location outside the interaction or discharge space minimizes positive ion bombardment during starting and prevents the filament being coated with contaminating particles. Additionally, since the filament is cold and inactivated during all times other than starting, it does not deteriorate to any appreciable extent.
  • FIGURE 1 is a schematic sketch of an ionization gauge constructed in accord with one embodiment of the present invention together with circuit means for operation thereof.
  • FIGURE 2 is a perspective view, with parts broken away, of another embodiment of the invention.
  • FIGURE 3 is a vertical cross-sectional view of an ionization gauge representing still another embodiment of the invention.
  • an ionization gauge represented generally as 1 includes a hollow cylindrical anode member 2 and a pair of transverse plan ar cathode members 3 and 4 adjacent the open ends of cylinder 2.
  • Anode 2 and cathodes 3 and 4 define an or ionization space 5 within which ionization of gaseous particles takes place. This ionization is accomplished by use of a Penning-type discharge.
  • a Penning-type discharge is an oscillating electron discharge in which an electron is repelled from one cathode, attracted by the positive potential of the anode, and accelerated toward the other cathode until it is repelled by the negative potential thereon, whereby it reciprocates back and forth between the two cathodes, making innumerable of reciprocating passes before it is finally laterally attracted to the anode.
  • a longitudinal magnetic field parallel with the anode axis, is utilized to impart a helical motion to the electrons.
  • Means for providing a starting burst of electrons to cause the ionization gauge to become operative at extremely low pressures, as for example, below about 10* mm. of mercury, are provided by a de-centered aperture 6 in cathode 3, and electron emissive means such as thermionic filament 7 located immediately behind aperture 3.
  • filament 7 may be activated by transformer 8, comprising a primary coil 9 and a secondary coil 10, which causes alternating voltage to be impressed across filament 7, upon the closing of switch 11 which connects conductor 12 through filament 7 and cathode 3 across the secondary It or" transformer 8.
  • filament 7 may be connected to a separate supply of undirectional voltage through switch 11.
  • a unidirectional voltage source represented generally by battery 13 through a current measuring device represented generally by ammeter 14.
  • a magnetic field having a flux density of, for example, 750 to 2000 gauss may be provided by a permanent magnet represented schematically by magnetic poles 15 and 16.
  • the device of FIGURE 2 is illustrative of actual ionization gauges which have been constructed in accord with the present invention.
  • the ionization gauge of FIGURE 2 includes a cylindrical apertured anode 2 and a pair of disc-shaped cathode members 3 and 4 concentric thereto which define an interaction space therebetween.
  • Cathode 3 includes an off center hole 6 behind which there is located thermionic filament 7.
  • Hole or aperture 6 is minute in size, being sufiiciently large to admit a burst of electrons to interaction space 5, but yet not being excessively large to expose filament 7 to substantial positive ion bombardment from the interaction space.
  • 'I'hermionic filament 7 is connected between two terminal members 17 and 18 rather than being connected at one end thereof to cathode 3. This connection arrangement provides greater flexibility in arranging power supplies for the filament and for the ionization gauge anode and cathode.
  • Thermionic filament 7 may conveniently be made of 0.003" tungsten wire or may be the same wire wound into a loose helix; Alternatively, thoria coated irridium wire may be used. During energization the filaments operate at approximate temperatures of from 1000 C. to 3000 C. and are extremely efiicient thermionic emitters.
  • a magnetic field sufficient to cause the establishment of a Penningtype electric discharge within intenaction space 6 is provided by magnetic poles 15 and 16 which are juxtaposed longitudinally along the line normal to cathodes 3 and 4.
  • transverse apertures 19 in anode 2 may be in many shapes, sizes and forms and the anode may even constitute a partial -for.aminate article or mesh. It is required, however, that the apertures be such as not to allow material sputtered within interaction chamber from cathodes 3 and 4 to deposit upon the electrode leads or upon the insulating envelope wall so as to electrically short circuit the electrodes. In the embodiment of FIG- URE 2, three A" diameter apertures, all located in the upper arc of horizontal cylinder 2 are quite satisfactory.
  • envelope 19 which preferably has at least a central region 21 wherein the external configuration of envelope 20, which may be a non-conducting, non-magnetic, vitreous or refractory materials as for example, hard glass or quartz, is shaped with a pair of planar surfaces. These planar surfaces are substantially parallel with the plane of the cathode discs to facilitate bringing the poles and 16 of the magnetic means as close thereto as is possible.
  • Operating potentials are supplied to the ionization gauge by bringing leads through a conventional pine 22 or equivalent means to lead pins 23 and 24 which connect the anode and cathodes respectively to high voltage, and leads 25 and 26 which connect filament terminals 17 and 18 to an appropriate source.
  • Envelope 20 containing the ionization gauge is also provided with tubulation means 27 for connecting the gauge to a suitable enclosure, the pressure of which is to be measured thereby.
  • an ionization gauge of the present invention In order that an ionization gauge of the present invention be utilized, it must first be connected through tubulation 27 to a device, the pressure of which is to be measured.
  • the ionization gauges of the pres ent invention are so simple, inexpensive and easily manufactured, they are generally, but not necessarily, incorporated with a vacuum system upon the construction thereof.
  • switch 11 When it is desired to start the ionization gauge to cause a measurement of the pressure of the system to stable Penning-type discharge is initiated with switch 11 closed for a period of approximately only 5 seconds.
  • Other more conventional gauges without the starting means utilized in the present invention may, at these pressures require days before a random event causes the starting thereof, or may never start at all.
  • ion pumping by trapping or removal of ions it is desirable that ion pumping by trapping or removal of ions be maintained at a minimum.
  • inactive materials which do not actively pump, as for example, platinum, copper, tungsten and stainless steel.
  • Ionic pumps utilizing the Penning-type discharge are generally similar in structural configuration to ionization gauges utilizing the Penning-type discharge, with the more notable exception that, rather than using inactive metals as the cathodes, the cathodes are constructed of good gas gettering and sputtering active materials, as for example titanium, to cause sputtered material to fill getter the gas in the interaction space.
  • the cathodes are constructed of good gas gettering and sputtering active materials, as for example titanium, to cause sputtered material to fill getter the gas in the interaction space.
  • collector electrodes are provided in the interaction space and preferably biased .at a suitable potential to attract positive ions which are later covered by this sputtered material.
  • collector electrodes are provided in the interaction space and preferably biased .at a suitable potential to attract positive ions which are later covered by this sputtered material.
  • ionic pumps and gases utilizing the Penning-type discharge may be improved so as to make it possible for, such devices to be started initially at extremely low pre'ssures or to resume pumping at such pressures if for one reason or another pumping is discontinued.
  • ends are achieved in accord with my invention by the inclusion therein of an aperture within the body of one of the cathodes thereof which is de-centered from the longitudinal axis of the anode and particularly from the longitudinal axis of the Penning discharge between the cathodes so as to avoid the highly concentrate area of erosion on the cathode thereof.
  • This aperture is backed by a thermionic filament which is suitable to provide, upon the instantaneous excitation thereof, thermionically emitted electrons which are drawn into the discharge and interaction space by the positive potential of the anode and are sufficient to cause sufiicient ionization within the interaction space so that a Penning-type discharge may be initiated.
  • FIGURE 3 of the drawing illustrates a vertical crosssectional view of another embodiment of the invention wherein an ionization gauge utilizing a Penning-type discharge and the inventive concept of this invention is further made more sensitive by the incorporation therein of an electron focusing means and an electron multiplier device which make possible the attainment of measurements at pressures at low as mm. of mercury.
  • the ionization gauge of FIGURE 3 includes an ion source means 30 for producing a measurable ion current, an ion focusing means 31 and an electron multiplier means 32..
  • the ion source means, represented generally by 30, in FIGURE 3 includes a cylindrical anode member 33 with the ends thereof closed by disc-shaped cathode members 34 and 35.
  • Cathode member 35 is centrally apertured coaxial with anode 33 by the inclusion of a grid 36 in the central portion thereof so as to allow the free passage of electrons therefrom. Operating potentials and circuit connections for this device are similar to those used for the device of FIGURE 2 and illustrated in FIG- URE 1.
  • Cathode 34 is apertured off-center with respect to anode 33 to provide aperture 37 having thermionic filament 38 therebehind, as provided in the embodiments of FIGURES 1 and 2.
  • a longitudinal magnetic field of such strength sufficient to sustain a Penning-type discharge, as disclosed hereinbefore, is conveniently established by cylindrical magnet 39.
  • An electron focusing cylinder is provided collinear with, and longitudinally spaced from, the grid opening 36 in cathode 35.
  • Electron muitiplier, means represented generally by 32 is also located longitudinally aligned with and spaced from electron focusing means 31.
  • Evacuable envelope 40 which is similar in nature to envelope 19 of FIGURE 2, may be connected to a system through tubulation 41.
  • the Penning-type discharge is initiated within the interaction space by pulsing of a voltage to filament 38 to cause a pulse of electrons to be drawn through aperture 37 into the interaction space by the attraction of the kilovolt potential upon anode 33 and a Penning-type discharge is initiated between cathodes 34 and 35.
  • Electron multiplying means 32 may comprise a conventional electronic multiplier, as for example, that disclosed in Rev. Sci. Instr., vol. 18, p. 739 (1947).
  • the electrical output of this gauge is taken from leads 42. Since the ion-electron charge multiplying means is capable of providing a gain between 10 and 10" with a background as low as 1 pulse every 10 to 100 seconds, this embodiment of the invention should therefore be capable of measuring ion currents near one ion every 100 seconds or ion currents of 10 amperes. Since the gauge has a sensitivity of approximately 1 ampere per millimeter of mercury and since the characteristic of the gauge is substantially linear, this embodiment of the invention should be capable of measuring pressures as low as 10* mm. of mercury.
  • Ionization gauges constructed in accord with the invention are extremely sensitive, and may be readily started as very low pressures without including continuously operating hot filaments that are subject to destruction by positive ion bombardment. Additionally, the low pressure limit of these gauges is below the X-ray limit of most prior art gauges.
  • An ionization device for measuring and attaining low pressures and starting means therefor comprising in combination,
  • (c) means to cause a Penning type discharge between said cathodes and said anode in said interaction space
  • said source and injection means being positioned and arranged to minimize the concentrated erosive effects of said Penning discharge.
  • said electron injection means comprises electron emission means positioned adjacent one of said cathodes.
  • said electron injection means comprises the combination of one of said cathodes defining an aperture therethrough and a thermionic emissive emitter adjacent said aperture to :inject electrons therethrough into said interaction space.
  • An ionization gage for use in measuring very low pressures and starting means therefor comprising in com bination
  • said initiating means comprising a thermionic emissive filament outside of said interaction space and adjacent one of said cathodes,
  • An ionization gage and starting means comprising in combination,
  • said opening being further characterized in proportion, with an anode of about 1.25 cm. diameter, said cathode opening having a diameter of about .5 to 1.5 mm., and spaced radially from about 3 mm. to about 5 mm. from the longitudinal axis of said anode and Penning discharge,
  • (j) means to energize said thermionic emissive filament to inject and direct electrons through said electron opening axially into said interaction space to initiate said Penning discharge.
  • An ionic device useful in attaining and measuring low vacua comprising: an evacuable envelope having means for attaching the same to a vacuum system; an apertured anode member supported therein; a pair of oppositely disposed substantially parallel cathode members disposed adjacent opposite ends of said anode memher and defining therewith an interaction space, one of said cathode members having therein a minute aperture decentered so as to avoid the central portion thereof which is subject to deep ion erosion; means for supplying a burst of electrons Within said interaction space to initiate therein a Penning type electric discharge at very low pressures and including a thermionic filament located adjacent the aperture in said one cathode and outside of said interaction space, means for supplying electric current to said filament, and means to temporarily energize said filament only until said discharge is initiated; means for impressing a magnetic field in said interaction space which is substantially normal to the planes of said cathodes, and means for applying a positive potential to said anode relative to said cathodes suf
  • An ionization gauge comprising: an evacuable envelope having means for attaching the same to a system the pressure of which is to be measured; a hollow cylindrical anode member supported therein; a pair of oppositely disposed cathode members, one disposed adjacent each of the ends of said anode member to define therewith an interaction space, one of said cathode members having a minute aperture the-rein decentered sufiicient-ly to avoid the central portion thereof which is subject 8.
  • anode member and said cathode members are composed of a relatively inert poorly sputtered material selected from the group consisting of stainless steel, tungsten, platinum, molybdenum and copper.
  • An ionization gauge comprising: an evacuable envelope having means for attaching the same to a system the pressure of which is to be measured; an apertured anode member supported therein and having oppositely disposed ends and longitudinal side walls; a pair of oppositely disposed cathode members, one disposed adjacent each of the ends of said anode member to define therewith an interaction space, one of said cathode members having a minute aperture therein decentered sufficiently to avoid the central portion thereof which is subject to deep erosion by positive ion bombardment during operation; means for supplying a burst of electrons within said interaction space to initiate therein a Penning-type electric discharge at very low pressures and including a thermionic filament located adjacent the aperture in said one cathode member and outside of said interaction space, means for supplying electric current to said filament, and means to temporarily energize said filament only until said discharge is initiated; means for impressing a magnetic field substantially parallel with the longitudinal axis of said anode, and means for applying a positive potential to said anode
  • An ionization gauge comprising: an evacuable envelope having means for attaching the same to a system the pressure of which is to be measured; an apertured anode member supported therein and having oppositely disposed ends and longitudinal side walls; a pair of 0ppositely disposed cathode members, one dis-posed adjacent each of the ends of said anode member to define therewith an interact-ion space, one of said cathode members having a minute aperture therein decentered sufficicn-tly to avoid the central portion thereof which is subject to deep erosion by positive ion bombardment during operation, the other of said cathodes having a substantially permeable gridded central portion to allow ions to escape theret-hrough; means for supplying a burst of electrons within said interaction space to initiate therein a Penning-type electric discharge at very low pressures and including a thermionic filament located adjacent the aperture in said one cathode and outside of said interaction space, means for supplying electric current to said filament, and means :to temporarily
  • an ionic device of the type including an evacuable envelope attachable to a vacuum system and including therein a pair of oppositely disposed cathode members and an interposed anode member defining with said cathode members an interaction space within which a Penningtype discharge may be maintained, one of said cathode members having an aperture therein and a thermionic filament adjacent said aperture and external to said interaction space; a method of starting Which comprises energizing said thermionic cathode to cause the emission of electrons therefrom; applying a highly positive potential to said anode relative to said cathodes and to said filament to attract said electrons through said aperture into said interaction space so as to establish a Penning-type discharge therein; and deenergizing said filament as soon as said discharge is established.

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US272984A 1963-04-15 1963-04-15 Penning-type discharge ionization gauge with discharge initiation electron source Expired - Lifetime US3280365A (en)

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GB1053215D GB1053215A (US20110009641A1-20110113-C00185.png) 1963-04-15
US272984A US3280365A (en) 1963-04-15 1963-04-15 Penning-type discharge ionization gauge with discharge initiation electron source
DEG40302A DE1265338B (de) 1963-04-15 1964-04-08 Gasentladungseinrichtung mit Penning-Entladung zur Erzeugung und Messung von Hochvakuum
FR970976A FR1389330A (fr) 1963-04-15 1964-04-15 Perfectionnements à des dispositifs ioniques

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3378712A (en) * 1966-11-18 1968-04-16 Gen Electric Field emission ionization gauge with restricted line of sight between field emissionanode and ion collector
US4270091A (en) * 1978-01-25 1981-05-26 Varian Associates, Inc. Apparatus and method for measuring pressures and indicating leaks with optical analysis
US4380720A (en) * 1979-11-20 1983-04-19 Fleck Carl M Apparatus for producing a directed flow of a gaseous medium utilizing the electric wind principle
US5157333A (en) * 1991-03-12 1992-10-20 Mks Instruments, Inc. Discharge initiating means for cold cathode discharge ionization gauge
US5198772A (en) * 1991-03-12 1993-03-30 Mks Instruments, Inc. Removable discharge initiating means for cold cathode discharge ionization gauge
US20140070701A1 (en) * 2012-09-10 2014-03-13 The Regents Of The University Of California Advanced penning ion source

Citations (9)

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Publication number Priority date Publication date Assignee Title
US2081429A (en) * 1933-06-03 1937-05-25 Gaede Wolfgang Electron tube and method of operating the same
US2146025A (en) * 1935-12-28 1939-02-07 Philips Nv Coating by cathode disintegration
US2755014A (en) * 1953-04-24 1956-07-17 Gen Electric Ionic vacuum pump device
US2757306A (en) * 1955-02-23 1956-07-31 Nat Res Dev Ionisation gauge
US2988657A (en) * 1958-08-02 1961-06-13 Philips Corp Ion pump
US3080104A (en) * 1958-09-25 1963-03-05 Gen Electric Ionic pump
US3152280A (en) * 1960-06-07 1964-10-06 Ici Ltd Omegatron electrode assembly
US3193724A (en) * 1961-04-17 1965-07-06 Philips Corp Ionization manometer
US3204860A (en) * 1958-04-16 1965-09-07 Csf High-vacuum pump

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Publication number Priority date Publication date Assignee Title
DE1089112B (de) * 1958-02-13 1960-09-15 Thomson Houston Comp Francaise Vakuumpumpe

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2081429A (en) * 1933-06-03 1937-05-25 Gaede Wolfgang Electron tube and method of operating the same
US2146025A (en) * 1935-12-28 1939-02-07 Philips Nv Coating by cathode disintegration
US2755014A (en) * 1953-04-24 1956-07-17 Gen Electric Ionic vacuum pump device
US2757306A (en) * 1955-02-23 1956-07-31 Nat Res Dev Ionisation gauge
US3204860A (en) * 1958-04-16 1965-09-07 Csf High-vacuum pump
US2988657A (en) * 1958-08-02 1961-06-13 Philips Corp Ion pump
US3080104A (en) * 1958-09-25 1963-03-05 Gen Electric Ionic pump
US3152280A (en) * 1960-06-07 1964-10-06 Ici Ltd Omegatron electrode assembly
US3193724A (en) * 1961-04-17 1965-07-06 Philips Corp Ionization manometer

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3378712A (en) * 1966-11-18 1968-04-16 Gen Electric Field emission ionization gauge with restricted line of sight between field emissionanode and ion collector
US4270091A (en) * 1978-01-25 1981-05-26 Varian Associates, Inc. Apparatus and method for measuring pressures and indicating leaks with optical analysis
US4380720A (en) * 1979-11-20 1983-04-19 Fleck Carl M Apparatus for producing a directed flow of a gaseous medium utilizing the electric wind principle
US5157333A (en) * 1991-03-12 1992-10-20 Mks Instruments, Inc. Discharge initiating means for cold cathode discharge ionization gauge
US5198772A (en) * 1991-03-12 1993-03-30 Mks Instruments, Inc. Removable discharge initiating means for cold cathode discharge ionization gauge
US20140070701A1 (en) * 2012-09-10 2014-03-13 The Regents Of The University Of California Advanced penning ion source
US9484176B2 (en) * 2012-09-10 2016-11-01 Thomas Schenkel Advanced penning ion source

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DE1265338B (de) 1968-04-04
GB1053215A (US20110009641A1-20110113-C00185.png)

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