US3080104A - Ionic pump - Google Patents

Ionic pump Download PDF

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Publication number
US3080104A
US3080104A US763293A US76329358A US3080104A US 3080104 A US3080104 A US 3080104A US 763293 A US763293 A US 763293A US 76329358 A US76329358 A US 76329358A US 3080104 A US3080104 A US 3080104A
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cathode
members
anode
collector electrode
sputtered
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US763293A
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Thomas A Vanderslice
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General Electric Co
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General Electric Co
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Priority to NL243654D priority Critical patent/NL243654A/xx
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Priority to US763293A priority patent/US3080104A/en
Priority to FR805704A priority patent/FR1236351A/fr
Priority to GB3238959A priority patent/GB882781A/en
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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
    • H01J41/12—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 ionic pumps for lowering the pressure of evacuated systems to extremely low values.
  • ionic pumps such as is described and claimed in latent 2,755,014, Westendorp et al., are highly useful in removing gases from low pressure vacuum systems particularly those of limited volumes. These pumps are particularly useful for the removal of inert gases from vacuum systems, since these gases cannot be chemically getter-ed and thereby removed.
  • Such pumps operate by causing ionizing electrons to traverse elongated curvilinear paths through the pump volume to undergo a large number of ionizing collisions with gaseous molecules. The ions so formed, are then attracted to and embedded into one or more cathode electrodes and are thereby removed from the system.
  • ionic pumps as described above, are of great utility and function quite satisfactorily to obtain extremely low pressures, the pumping action is somewhat limited by the limited area of the cathode utilized.
  • a further object of the invention is to provide ionic pumps in which a collector electrode provides a surface for cleanup of inert gas particles.
  • an ionic pump including cathode and anode electrodes located in an area adapted to contain gaseous molecules. Electrons are emitted from the cathode and, under the influence of an impressed magnetic field and the coexistant electric field established between cathode and anode electrodes, describe greatly elongated curvilinear paths. This results in a large number of ionizing collisions with inert gas molecules. The inert gas ions so formed, are accelerated toward the cathode, but are collected by a collector electrode in close proximity thereto. Ions collected by the collector electrode are subsequently covered by deposited cathode material which has been sputtered by the cathode, thus continually presenting a clean absorbent surface for the reception of high energy inert gas ions.
  • FIG. 1 is a vertical cross-sectional view of an ion pump constructed in accord with one feature of the present invention
  • PK 2 is a partially-sectioned vertical view of an alternative embodiment of the device of FIG. 1,
  • FIG. 3 is a cross-sectional view of a detail of the device of H6. 2 and illustrates a protective means for the metallic leads thereof, and
  • FIG. 4- is a partially-sectioned vertical view of an ionic pump constructed in accord with another feature of the present invention.
  • an ionic pump of the disc-seal type constructed in accord with the present invention includes substantially hemispherical cathode members 2 and 3, an apertured anode member 4 and cylindrical collector elecice trodes 5 and 6 juxtaposed closely adjacent to respective cathode members 2 and 3.
  • Each of the cathode and anode members possesses an annular portion at the periphery thereof, which is of substantially the same diameter as the diameter of cylindrical electrodes 5 and 6.
  • Adjacent electrode members are separated by insulating ceramic annular members which are hermetically sealed to the adjacent members to cause the formation of an evacuable envelope.
  • cathode member 2 is electrically separated from and hermetically sealed to collector electrode 5 by an annular member 7
  • collector electrode 5 is electrically separated from and hermetically sealed to anode member 4 with annular insulating member 8.
  • Anode member 4 is likewise electrically separated from and hermetically sealed to collector electrode 6 by annular insulating member 9 and collector electrode 6 is electrically separated from and hermetically sealed to cathode member 3 by insulating member it
  • Each of insulating members '7, 8, 9 and lit have cross-sectional areas which define a re-entrant portion having a surface which is not in line-of-sight relationship with any active surface portion of cathodes 2 and 3. This is achieved in the device of FIG.
  • thermionic filaments 11 and 12 may, if desired, be located in close juxtaposition to the hemispherical surfaces of cath odes 2 and 3. If thermionic filaments Ill and 12 are included, the entrance of electrical connections 14 thereto is achieved by passing these leads through suitable insulated, hermetically sealed apertures 15 in the disc shaped portion of cathode members 2 and 3 respectively. Access to the ion pump, suitable for connecting the device to a vacuum system, the pressure of which is to be lowered to an extremely low value, is achieved by means of tubulation 16 which is connected with an orifice 17 in one of cathode members 3.
  • a magnetic field substantially normal to the plane of anode member 4 and indicated schematically by arrow H, is provided by electromagnetic coil 16a.
  • a cylindrical permanent magnet properly demensioned so as to slip over the cylindrical envelope formed by the metallic and ceramic members comprising ion pump 1 and properly insulated therefrom so as not to short circuit the electrodes thereof, may be utilized.
  • Operating potentials are supplied by a unidirectional voltage source as indicated generally by battery 17a and potentiometer i8.
  • Anode member at is biased positively with respect to cathode members 2 and 3 to a potential of several thousand volts.
  • Collector electrodes 5 and 6 are biased positively with respect to cathode members 2 and 3 but negative by a value of several hundred volts with respect to anode member t by connection to center tap 19 on potentiometer 13.
  • a suitable alternating current voltage source may be substituted for unidirectional voltage source 17a.
  • a suitable value for the magnetic field strength, H may be from several hundred to several thousand oersteds.
  • Electrode members 2 and 3 are constructed of an active metal which is a good getter for chemically active gases and which further possesses the characteristic of being readily sputtered under positive ion bombardment. Such materials include titanium, zirconium, hafnium, and like materials. Likewise anode 4 is preferably constructed of such material, although, since no sputtering occurs from the anode the anode may very well be constructed of other materials.
  • Anode electrode 4 may constitute an apertured disc as is illustrated in FIG. 1 or may, alternatively, comprise a honeycomb structure which contains a plurality of apertures. It is only necessary that anode 4 be o permeable to the majority ofi electrons attracted thereto from cathodes 2 and 3.
  • anode 4 and collector electrodes and 6, as well as cathodes 2 and 3 are composed of titanium metal so that annular insulating members 7, 8, 9, and may be composed of a suitable titanium-matching ceramic as, for example, a forsteritc disclosed and claimed in application SN. 546,215, Pincus, filed Nov. 10, 1955, now Patent No. 2,912,340, issued November 10, 1959 and assigned to the assignee of the present invention. Assembly may be as described in the copending Lafierty application 690,849, filed October 17, 1957, now Patent Number 2,957,751, issued October 25, 1960 and assigned to the present assignee.
  • the anode is apertured and prefierably comprises a ring, and since most of the electron flux is concentrated at the center of the device away from the periphery of the ring anode by the magnetic field, most of the electrons emitted from cathodes 2 and 3 will pass through the ring anodeelongated curvilinear path and may enter into an ioniz-- ing'collision.
  • the positive ions created by such collisions while likewise affected by the electric and magnetic fields, because of their great mass, are accelerated directly toward the nearest cathode and strike the cathode with a force of the order of 10 electron volts.
  • collector electrodes 5 and 6 are only several hundred volts, or thereabout, negative with respect to the electron-ion plasma, the positive ions attracted thereto do not impinge thereupon with extremely high energy so as tocause thematerial thereof to be sputtered.
  • the potential of the collector electrodes is deliberately chosen to be sufficiently negative with respect to the plasma to attract positive ions, but insufiiciently negative to cause these ions to impinge upon the collector with sufiicient fiorce to cause any substantial sputtering thereform.
  • devices c'onstruc-ted'in' accord with the present inven tion function by the concurrent and continued processes of attraction of positive ions to the collector electrodes and the coveringof these collected positive ions by metallic particles sputtered from the cathode.
  • Devices const'ructed in accord with the present invention are capable,
  • filaments 11 and 12' which may; for example, be composed of a highly electron emissive material such as tungsten wire, be-utilized.
  • a sufficient number of electrons are created by ionizing collisions of electrons with gas molecules and by the impingement of high energy ions upon the cathodes, causing the emission of secondary electrons, tosustain the discharge between cathodes 2 and 3 on one hand and anode 4 on the other hand.
  • pressures below 10- mm When, however, pressures below 10- mm.
  • an auxiliary source of electrons sufficient to causeionizing collisions be provided.
  • Such an auxiliary source of electrons may be provided by energizing either thermionic emitting-filaments 11 or 12 :by closing either of switches 20-to connect a suitable source of potential represented generally by batteries- 21 across theenergized filament. Either one or both filaments may be energized. Since the area of these filaments is relatively small with respect to the area of cathodes 2 and 3,.
  • the filaments have little effect upon the operation of the device' other than to provide an auxiliary source of electrons, when neded, to allow the attainment of extremely low pressures as, for example, l0 mm'. of mercury. It will be appreciated, however, that thermionic filaments are not necessary for'the operation of the devices.
  • FIG. 2 of the drawing there is illustrated an alternative'emb'od-imen't of the device of FIG. 1 wherein a conventional glass or other vitreous envelope structure is utilized rather than the metal and ceramic disc-seal type construction of the device of FIG. 1.
  • cathode electrodes 2 and 3- and anode electrode 4 have the same configuration and spatial arrangement as in the device of FIG. 1'.
  • Collector electrode 5 comprises a continuous cylindrical member which is in close juxtaposition to both of cathodes 2 and- 3, and is substituted for the two collector electrodes 5 and 6 of the device of FIG. 1.
  • Magnet 16b which may be either an electromagnet or a metallic permanent magnet which slips closely over the glass envelope 22 enclosing the elements, establishes a magnetic field which is substantially normal to the plane of anode 4 and performs the same function as-in the device of FIG. 1.
  • Lead and support members 23 pass through there-entrant portion 24 of envelope 22 as isconventionalin glass electron discharge devices.
  • a breakdown shield 25 is built up upon each of members 23 to prevent electrical breakdown occurring from the point at which these members enter into re-entrant glass portion 24 of envelope 22.
  • the device of FIG. 2 is connected in circuit identically as the device of FIG. 1 and functions substantially the same, the important difference being that the envelope is a vitreous material such as glass rather than ceramic and metal, and that the collector electrode is single unitary cylindrical member rather than the plurality of electrodes of the device of FIG. 1.
  • breakdown-preventing members 25 which are mounted upon lead and support members 23.
  • breakdown members 25 comprise a re-entrant glass member entirely surrounding the lead wire and connected with the re-entrant portion 24 of envelope 22.
  • FIG. 4 of the drawing there is rep-resented, in a partially sectioned vertical view, another alternative embodiment of the invention.
  • the device of FIG. 4 includes an evacuable glass or other vitreous envelope 26, having therein a cathode electrode 27, a cylindrical anode electrode 28, concentric with and surrounding cathode 27, and a pair of disc shaped collector electrodes 29 and 36 positioned at the ends of anode cylinder 23.
  • Cathode electrode 2'7 is, in this embodiment, a thermionic cathode and is heated to thermionic emission temperatures, either by the passage of a high current therethrough or by a heater filament enclosed in the center thereof.
  • cathode 27 is constructed of a material which is readily sputtered and is conveniently constructed of titanium, zirconium, hafnium and like materials as are the cathodes of the devices of FIGS. 1 and 2.
  • Anode and collector elec trodes need not be of any particular material and may conveniently comprise nickel, fernico, iron or any material suitably used for the electrodes of electron discharge devices.
  • Cathode, anode and collector electrodes of the device of FIG. 4 are biased similarly to the analogous electrodes of the device of PEG. 1, so that the anode is maintained several thousand volts positive with respect to the cathode and the collector electrode is several hundred volts negative with respect to the anode electrode.
  • the strength of the magnetic field maintained within the volume defined by the anode electrode may be several hundred oersteds and is adjusted so that the tube operates as a magnetron, biased to cutoff. That is to say, electrons thermionioally emitted from the cathode are subjected to crossed electric and magnetic fields and spiral around the cathode in circular paths so as to just miss impinging upon the anode cylinder.
  • This curvilinear path increases the probability of ionizing collisions of electrons with gas molecules between the time they are ejected from filament 27 and collooted by anode 28.
  • Collector electrodes 29 and 35 are positioned in close juxtaposition to the cathode and properly biased to collect positive ions of inert and other gases formed by electron-gas molecules collisions and to co1- lect metal sputered from cathode 27 as are the collector electrodes of the devices of FIGS. 1 and 2.
  • the main difference in the device of FIG. 4 as compared with the devices of FIGS. 1 and 2 is that this device uses crossed electric and magnetic fields and magnetron operation whereas the devices of FIGS. 1 and 2 utilize an oscillating plasma discharge.
  • ionic pumps capable of pumping evacuated systems down to extremely low pressures, even as low as 10* mm. of mercury pressure utilizing the concept of a cathod, an anode and negatively biassed third electrode positioned in close juxtaposition to a cathode which is composed of a readily sputterable material. Electric and magnetic fields are properly impressed thereupon so that electrons passing between cathode and anode electrodes describe greatly elongated curvilinear paths to cause a large number of ionizing collisions.
  • An ionic pump device adapted to remove gases from an enclosure by the mechanism of entrapment of positive ions by sputtered metallic particles and comprising: an apertured cylindrical anode member; a pair of apertured cylindrical collector electrode members disposed on opposite sides of said anode member and coaxial therewith, a pair of cathode members each having a discsha-ped peripheral portion disposed on opposite sides of said collector electrode members and forming end-wall members for said device; a plurality of annular insulating ceramic members interposed between said cathode members and said collector electrode members and between said collect-or electrode members and said anode member respectively and hermetically sealed thereto to form an hermetically sealed envelope; means for supplying operating potentials to each of said cathode, anode and collector electrode members to cause an oscillating electron discharge to exist between said cathodes and the subsequent creations of positive ions thereby by collision with gas molecules, which ions are attracted to said collector electrode members and covered by metallic particles sputtered from said cathode members
  • A11 ionic pump device adapted to remove gases from an enclosure by the mechanism of entrapment of positive ions by sputtered metallic particles and comprising: an evacuable envelope having means for con necting said device to a volume to be evacuated; a cathode member having a cylindrical surface of substantial area sufficient to serve as a source from which accelerated positive ions may eject metallic particles by sputtering upon collision therewith and extending along the longitudinal axis of said envelope; an anode member having a cylindrical surface within said envelope coaxial with and external of said cathode member; a pair of ion collector electrode members electrically insulated from said cathode and anode members substantially closing the ends of an annular space defined within said envelope by said cathode and anode member and serving as a repository for positive ions and metallic particles sputtered from said cathode; means for applying a magnetic field within said device longitudinally along said axis so that electrons emitted by said cathode member execute elong
  • An ionic pump device adapted to remove gases from an enclosure by the mechanism of entrapment of positive ions by sputtered metallic particles and comprising: an evacuable envelope defining a space adapted to contain gas molecules; means for connecting said envelope to an enclosure to be evacuated; mean-s providing ionized gaseous molecules Within said space, said means including cathode means adapted to sustain a cold electron discharge and to serve as a continuous source of sputtered particles when bombarded by high velocity positive ions, and anode means, each of said cathode and anode means including active surfaces located within said envelope between which.
  • electrons may pass to cause ionization of said gas molecules; means for establishing a magnetic field in said space to cause the path of electrons passing between said cathode means and anode means to be greatly elongated so as to permit a large number of ionizing collisions between electrons and gas molecules;-ion collector means electrically insulated from said cathode means andsaid anode means, located ad jacent to said cathode means, providing an electrode-free space therebetwecn, and including a substantial surface for the deposition of positive ions and metallic particles sputtered from said cathode means; said anode meansbeing located within said envelope at a position outside of said electrode-free space so as to sustain an oscillating discharge without electrically shielding said ion co llector means from said discharge and impeding the free flow of positive ions from said discharge to said ion collector means; and means for applying operating potentials to each of said cathode, anode and ion collector means to cause metallic particles
  • the ionic pump device of claim 3 wherein the meansfor applying operating potentials maintains said ion collector means at a potential which is sufiiciently negative with respect to said anode means as to attract positive ions thereto and sufiiciently positive with respect to said cathode means asto prevent positive ions being attracted thereto with a velocity sufficient to cause a substantial sputtering of metallic particles therefrom.
  • An ionic pump device adapted to'rernove gases from an enclosure by the mechanism of entrapment of positive ionsby sputtered metallic particles and comprising: an evacuable envelope defining a space adapted to contain gas molecules; means for providing ionized gas molecules within said space, said'means including a pair of oppositely disposedcathodemembers and an anode member located therebetween and apertured' to permit electrons to oscillate between said cathode members, eachof said cathode members' and said anode member having an active surface located within said envelope and defining therein, a discharge space, said cathode members being of substantial area and comprising an easily sputtered metal; means for establishing a magnetic field within said discharge space to causethe path of electrons passing between said cathodeand' said anode members to be greatly elongated so as to permit a large number of ionizing collisions between electrons and gas molecules; ion collector means located adjacent tosaid cathode'members
  • An ionic pump device adapted toremove gases from an enclosure by the mechanism of entrapment of positive ions by sputtered metallic particles and comprising: an evacuable envelope defining a space adapted to contain gas molecules; means for connecting said envelope to an enclosure to beevacuated; means for ionizing saidmolecules, said means including a pair of oppositely disposed cathode members both comprising an easily sputtered metal and adapted to sustain acold electron discharge and to serve as continuous sources of sputtered particles when bombarded by high velocity positive ions, and an anode member located therebetween and apertured to allow electrons to pass therethrough, said catode members and said anode member each having an ac-- tive surface within said envelope and defining therewith a discharge space; means for establishing a magnetic field within said discharge space substantially normal to the plane of said apertured anode member to cause electrons from said discharge space to said collector electrode;
  • An ionic pump device adapted to remove gases from an enclosure by the mechanism of entrapment of positive ions by sputtered metallic particles and comprising: an evacuable envelope having means for connecting said device to a volume to be evacuated; a pair of oppositely disposed cathode electrode members within said envelope adapted to sustain a cold electron discharge and serve as a continuous source of sputtered metallic particles when bombarded by positive ions; an apertured anode" electrode member spaced intermediate between said cathode electrode members to allow electrons to oscillate therebetween and defining with said cathode electrode members, a discharge space; means for establishing.
  • An ionic pump device adapted to remove gases from an enclosure by the mechanism of entrapment of positive ions by sputtered metallic particles and comprising: an evacuable envelope defining a space adapted to contain gas molecules; means for connecting said envelope to an enclosure to be evacuated; means for ionizing said molecules, said means including a pair of oppositely disposed cathode members comprising an easily sputtered metal and both adapted to sustain a cold electron discharge and to serve as continuous sources of sputtered particles when bombarded by high velocity positive ions, and an anode member located therebetween and apertured to allow electrons to pass therethrough, said cathode and said anode members each having an active surface located within said envelope and defining therein a discharge space; means for establishing a magnetic field in said discharge space substantially normal to the plane of said apertured anode member to cause electrons passing between anode and cathode members to follow greatly elongated curvilinear paths, thus facilitating a large number of ionizing collisions

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Application Number Priority Date Filing Date Title
NL243654D NL243654A (fr) 1958-09-25
US763293A US3080104A (en) 1958-09-25 1958-09-25 Ionic pump
FR805704A FR1236351A (fr) 1958-09-25 1959-09-22 Pompe ionique
GB3238959A GB882781A (en) 1958-09-25 1959-09-23 Improvements in ionic pump

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US1110812XA 1958-09-25 1958-09-25
US763293A US3080104A (en) 1958-09-25 1958-09-25 Ionic pump

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3228590A (en) * 1964-01-02 1966-01-11 Gen Electric Triode ionic pump
US3280365A (en) * 1963-04-15 1966-10-18 Gen Electric Penning-type discharge ionization gauge with discharge initiation electron source
US3307774A (en) * 1963-11-08 1967-03-07 Philips Corp Vacuum ion pump
US3324729A (en) * 1964-09-14 1967-06-13 Gen Electric Method and apparatus for detecting leaks

Citations (8)

* 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
US2131897A (en) * 1937-02-27 1938-10-04 Rca Corp Electronic vacuum pump
US2146025A (en) * 1935-12-28 1939-02-07 Philips Nv Coating by cathode disintegration
US2460175A (en) * 1945-07-31 1949-01-25 Hazeltine Research Inc Ionic vacuum pump
US2636664A (en) * 1949-01-28 1953-04-28 Hertzler Elmer Afton High vacuum pumping method, apparatus, and techniques
US2726805A (en) * 1953-01-29 1955-12-13 Ernest O Lawrence Ion pump
US2755014A (en) * 1953-04-24 1956-07-17 Gen Electric Ionic vacuum pump device
GB797232A (en) * 1955-07-11 1958-06-25 Manfred Von Ardenne Improvements in or relating to high vacuum ion pumps

Patent Citations (8)

* 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
US2131897A (en) * 1937-02-27 1938-10-04 Rca Corp Electronic vacuum pump
US2460175A (en) * 1945-07-31 1949-01-25 Hazeltine Research Inc Ionic vacuum pump
US2636664A (en) * 1949-01-28 1953-04-28 Hertzler Elmer Afton High vacuum pumping method, apparatus, and techniques
US2726805A (en) * 1953-01-29 1955-12-13 Ernest O Lawrence Ion pump
US2755014A (en) * 1953-04-24 1956-07-17 Gen Electric Ionic vacuum pump device
GB797232A (en) * 1955-07-11 1958-06-25 Manfred Von Ardenne Improvements in or relating to high vacuum ion pumps

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3280365A (en) * 1963-04-15 1966-10-18 Gen Electric Penning-type discharge ionization gauge with discharge initiation electron source
US3307774A (en) * 1963-11-08 1967-03-07 Philips Corp Vacuum ion pump
US3228590A (en) * 1964-01-02 1966-01-11 Gen Electric Triode ionic pump
US3324729A (en) * 1964-09-14 1967-06-13 Gen Electric Method and apparatus for detecting leaks

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