US3860848A - High pressure ion source for ion optical analytical equipment and for particle accelerators - Google Patents

High pressure ion source for ion optical analytical equipment and for particle accelerators Download PDF

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Publication number
US3860848A
US3860848A US277310A US27731072A US3860848A US 3860848 A US3860848 A US 3860848A US 277310 A US277310 A US 277310A US 27731072 A US27731072 A US 27731072A US 3860848 A US3860848 A US 3860848A
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Prior art keywords
ion
ion source
ionization chamber
chamber
source
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US277310A
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English (en)
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Hans Kurt Knof
Hermann Dietrich Krafft
Volker Wilhelm Hausen
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KNOF DR HANS
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KNOF DR HANS
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/02—Details
    • H01J49/10—Ion sources; Ion guns
    • H01J49/14—Ion sources; Ion guns using particle bombardment, e.g. ionisation chambers
    • H01J49/147—Ion sources; Ion guns using particle bombardment, e.g. ionisation chambers with electrons, e.g. electron impact ionisation, electron attachment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J27/00—Ion beam tubes
    • H01J27/02—Ion sources; Ion guns
    • H01J27/20—Ion sources; Ion guns using particle beam bombardment, e.g. ionisers

Definitions

  • ABSTRACT A high pressure ion source having a metal gas inlet tube connected electrically at one end to the ion source and at the other end to a pressure reducing valve.
  • the electron gun has its cathode separated from the ionization chamber by a beam transmitting system that includes a metallic screened hole near the cathode. The screened hole communicates with a vacuum exit tube.
  • the ionization chamber includes a plurality of electrodes in the ion exit path. The space between the last electrode and the focusing electrodes is screened electrically from the chamber walls by a metallic grid.
  • the gas inlet tube, pressure reducing valve, ionization chamber and the grid are maintained at the same potential.
  • This invention is concerned with the construction of an ion source, in which a metal gas inlet tube is fitted at one end with the ionization chamber and at the other end with a pressure reducing valve.
  • the cathode of the electron gun is separated from the ion chamber by a beam transmitting system, which has at the cathode a vacuum exit tube.
  • a metal grid for electrostatic screening is fixed around the acceleration path of the ions, which leave the ion chamber.
  • the gas inlet tube, the pressure reducing valve and the screening grid are maintained at about the same potential as the ionization chamber.
  • This ion source can be operated at gas pressures of about 1 Torr in the gas inlet tube without gas discharges or sparking. Therefore, this high pressure ion source is especially useful as an electron attachment ion source for mass spectrometry.
  • atoms or molecules of a gas or a solid sample are ionized in an ion source and then accelerated and focused in one direction to produce an ion beam which can be directed into a mass spectrometer or a particle accelerator.
  • a mass spectrometer or a particle accelerator.
  • a frequently used ion source is the electron impact ion source for production of positive or negative ions which is run at electron energies between 7 and 200 eV. Sample molecules are thereby fragmented making it difficult to analyze mixtures.
  • An ion source which avoids fragmentation is the field ion source or field desorption ion source. This ion source is not stable in service and it can hardly be used for quantitative measurements. In addition, the sensitivity is rather poor compared with an electron impact ion source. Both these ion sources can be operated for gas pressures up to 10 Torr only. For a better detection limit higher gas pressures in the ion source are necessary.
  • An ion source which can be operated at higher gas pressures up to several Torr is for example the chemical ionization ion chamber.
  • a gas e.g., methane
  • methane is ionized by electron impact and the added sample gas becomes ionized by charge transfer from the methane.
  • charge transfer there may occur ion molecule reactions which result in ions differing from molecular ions.
  • Another ion source which can be operated at gas pressures of several Torr is the electron attachment ion source described by von Ardene (Zeitschrift fur angewandte Physik, Volume 11, 1959, page 121; Tabellen zur angewandten Physik, Volume 1, Berlin 1962).
  • This ion source is either a gas discharge ion source with a permanent gas discharge in a neutral gas, e.g., argon, or a modified electron impact ion source whereby the impact of the neutral gas with electrons at energies slightly above the ionization energy, secondary electrons are produced. In both cases low energy electrons are produced which can attach to molecules and atoms of the sample gas in the gas mixture to give negative ions.
  • the partial pressure of the sample is difficult to determine and, therefore, this ion source is used for qualitative measurements only.
  • the electrons are slowed down to an energy which still permits multiple ionization, e.g., 200 eV.
  • this one can be run with the sample gas alone and does not demand a neutral carrier gas.
  • this ion source was still unstable and only occasionally permitted quantitative measurements at pressures above 10 Torr in the region around the ion source. At these pressures stray currents occurred by gas discharge or sparking; these changed potentials and gave rise to strong fluctuations of the ion current.
  • This reconstructed ion source is characterized by the fact that with special potential screening and potential voltages it can be stably operated at high pressures.
  • FIG. 1 is a schematic diagram of a mass spectrometer employing the high pressure ion source of the present invention.
  • FIG. 2 is an enlarged view of the ion source, including the gas inlet system.
  • the ion path which is very sensitive to gas discharge and sparking, is screened against the surroundings at ground potential by a metallic grid 1 connected electrically with the ionization chamber 21. This grid 1 prevents the migration of charge carriers into the vicinity of the ion source 14, where they could produce gas discharge. v
  • the gas flow goes through a metallic tube 2 which is electrically connected with the ionization chamber 21 includes the metallic pressure reducing valve 9.
  • This metallic tube 2 is electrically isolated from the metallic vacuum wall 12 through which it passes.
  • a metallic pressure reducing valve 9 a non-metallic one can be used.
  • the other side 8 of the pressure reducing valve 9 is connected with a vessel containing gases, liquids, or solids under their vapor pressures.
  • the entrance of the electron path into the ionization chamber 21 is supplied with an electrode 3, which extends into the wall of the ionization chamber 21.
  • the evacuation of the liquid nitrogen cooled tube, the anode tube 16, is done by a diffusion pump 30 through a metallic screen 4 close to the cathode 15.
  • the bore of the vacuum line is larger than the diameter of the metallic screen 4 in the anode tube 16. Therefore, the space between the anode tube 16 (which has a potential of, e.g., 2.2 keV) and the outer vacuum wall (which has ground potential) can be kept under high vacuum to prevent gas discharge and sparking.
  • the stable performance of the invented ion source 14 is obtained by prevention of gas discharge and sparking in those parts of the ion source 14 which must be kept at stable potentials in order to have a constant ion current.
  • this is possible by screening the accelerating electrodes 24 and 25 and the focusing electrodes 26 with a metallic grid 1 (which has a potential of, e.g., 2.9 kV positive or negative) from the vacuum walls 18 (which have ground potential).
  • gas discharges at high gas pressures can be prevented by using a metal tube 2 and a metal pressure reducing valve 9, both of which have a potential of, e.g., 2.9 kV positive or negative.
  • the gas is contained in a Faraday cage and no gas discharge is possible.
  • Gas discharges in the electron path are suppressed at one end by an electrode 3 which extends into the wall of the ionization chamber 21 so that the gap is too narrow to allow build-up of a sufficient cathode fall for the ignition of a gas discharge.
  • a large vacuum pump 30 evacuates the gas in the anode tube 16. Therefore, it is possible to' maintain such a good vacuum between the anode tube 16 (with a potential of, e.g., 2.2 kV positive or negative) and the vacuum wall (with ground potential) that the ignition of a gas discharge is prevented.
  • the grid 1 of the ion path is maintained at the negative potential of the ionization chamber 21 and the three other electrodes 24 in the same ion path only a few volts different from this potential.
  • This fact differs from known constructions of electron impact ion sources, which use relative potentials of up to several hundred volts for these electrodes. Low voltage differences are especially important for electron attachment mass spectrometry since the negative ions can only be produced by electron attachment at low electron energies and it is important to prevent even minor stray fields which may come into the ionization chamber 21 from the electrodes 24 and may influence negatively the performance of the ion source 14. This effect is prevented by the above-mentioned electrode potentials.
  • the equipment shown in FIG. 2 could be stably operated with a sample vapour pressure in the reservoir of l80 Torr acetone, with a gas pressure in the gas inlet tube 8 of 1 Torr, and with a gas pressure in the space between the ion source 14 and the vacuum walls 12 and 18 of 1.5Xl0' Torr.
  • the potential of the gas inlet tube 2 and of the ion path were as follows: 2.9 kV for the ionization chamber 21, the gas inlet tube 2, the pressure reducing valve 9 and the first electrode 24A; 2.895 kV for the second electrode 24B; 2.830 kV for the third electrode 24C and again 2.900 kV for the grid 1.
  • the potentials of the electron path were: 2.1 kV for the electrode 3 extending into the ionization chamber 21, 2.2 kV for the anode tube 16 and --3.l kV for the cathode 15. Under these conditions it was possible to obtain mass spectra of negative ions in which the fragment ions showed much less intensity than the molecular ions. In addition it was possible to get ions of dimer molecules. Furthermore, the pressure dependencies of the ion intensities could be measured in the pressure region between 5X10- and 10' Torr. These pressures were measured in the space between the ion source 14 and the vacuum walls 12 and 18.
  • An ion source having an ionization chamber coupled to a gas inlet tube and surrounded by a source chamber having an ion exit port, a plurality of horizontally extending accelerating electrodes positioned adjacent the ionization chamber, between the ionization chamber and the ion exit port in the source chamber, and an electron gun communicating with the ionization chamber, wherein the improvement comprises:
  • a grid positioned within the source chamber and extending vertically from said accelerating electrodes toward the ion exit port in the source chamber to define an ion exit path for screening the ions from the source chamber, said grid being maintained at about the same potential as the ionization chamher.
  • said gas inlet tube is metallic and is maintained at about the same potential as the ionization chamher.
  • said ionization chamber is maintained at a pressure of between about 10 and about 1 Torr.
  • the space between the ionization chamber and the source chamber is maintained at a pressure of about 5X10 to about 10 Torr.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Plasma & Fusion (AREA)
  • Analytical Chemistry (AREA)
  • Combustion & Propulsion (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Electron Tubes For Measurement (AREA)
  • Electron Sources, Ion Sources (AREA)
US277310A 1971-08-31 1972-08-02 High pressure ion source for ion optical analytical equipment and for particle accelerators Expired - Lifetime US3860848A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE2143460A DE2143460C3 (de) 1971-08-31 1971-08-31 Ionenquelle

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US3860848A true US3860848A (en) 1975-01-14

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US (1) US3860848A (ref)
DE (1) DE2143460C3 (ref)
FR (1) FR2153239B1 (ref)
GB (1) GB1398167A (ref)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4638209A (en) * 1983-09-08 1987-01-20 Anelva Corporation Ion beam generating apparatus
US12282031B2 (en) * 2010-06-09 2025-04-22 Quest Diagnostics Investments, LLC Mass spectrometric determination of tert-butyldimethylsilyl derivatized methylmalonic acid

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4240007A (en) * 1979-06-29 1980-12-16 International Business Machines Corporation Microchannel ion gun
JPH07118295B2 (ja) * 1985-10-30 1995-12-18 株式会社日立製作所 質量分析計
IL81375A (en) * 1987-01-23 1990-11-05 Univ Ramot Method and apparatus for producing ions by surface ionization of energy-rich molecules and atoms
EP3688789A4 (en) * 2017-09-29 2021-09-29 Perkinelmer Health Sciences Canada, Inc OFF-AXIS IONIZATION DEVICES AND SYSTEMS

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2601097A (en) * 1949-07-20 1952-06-17 Arthur R Crawford Mass spectrometer for simultaneous multiple gas determinations

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2601097A (en) * 1949-07-20 1952-06-17 Arthur R Crawford Mass spectrometer for simultaneous multiple gas determinations

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4638209A (en) * 1983-09-08 1987-01-20 Anelva Corporation Ion beam generating apparatus
US12282031B2 (en) * 2010-06-09 2025-04-22 Quest Diagnostics Investments, LLC Mass spectrometric determination of tert-butyldimethylsilyl derivatized methylmalonic acid

Also Published As

Publication number Publication date
FR2153239B1 (ref) 1976-10-29
DE2143460A1 (de) 1973-03-15
GB1398167A (en) 1975-06-18
DE2143460C3 (de) 1974-05-16
FR2153239A1 (ref) 1973-05-04
DE2143460B2 (de) 1973-10-18

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