US3868541A - Filament-current control unit in electron-beam apparatus - Google Patents

Filament-current control unit in electron-beam apparatus Download PDF

Info

Publication number
US3868541A
US3868541A US258549A US25854972A US3868541A US 3868541 A US3868541 A US 3868541A US 258549 A US258549 A US 258549A US 25854972 A US25854972 A US 25854972A US 3868541 A US3868541 A US 3868541A
Authority
US
United States
Prior art keywords
electron
cathode
filament
wehnelt
control unit
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US258549A
Other languages
English (en)
Inventor
Zuijlen Peter Van
Leendert Antonius Fontijn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
US Philips Corp
Original Assignee
US Philips Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by US Philips Corp filed Critical US Philips Corp
Application granted granted Critical
Publication of US3868541A publication Critical patent/US3868541A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/24—Circuit arrangements not adapted to a particular application of the tube and not otherwise provided for
    • H01J37/242—Filament heating power supply or regulation circuits
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/63—Generation or supply of power specially adapted for television receivers

Definitions

  • An electron-beam apparatus is provided with an electrode for intercepting a portion of the electron beam so as to achieve automatio cathode temperature control.
  • the filament current is controlled by means of a signal derived from this interception electrode.
  • the invention relates to an electron-beam apparatus comprising a cathode for thermal emission of an electron beam, a Wehnelt electrode, and a filament-current control unit.
  • an operating temperature which is lower than the optimum temperature results in a comparatively small emissive power of the cathode.
  • an electron beam to be emitted by the cathode has, at least on the cathode surface, a comparatively small current density. This has an adverse effect on the optical properties of the apparatus. Too high an operating temperature of the cathode reduces the service life of the cathode, particularly in the case of directly-heated filament cathodes.
  • a known method of adjusting the cathode temperature is based on the visual evaluation of an image of the emissive cathode to be formed on a phosphor screen. The temperature is then adjusted such that a reasonably uniform image is formed on the phosphor screen.
  • This adjusting method has the drawback that the adjustment criterion is formed by subjective observations and that a cathode image must be formed for any readjustment. It was found that the use of this criterion usually gives rise to an excessively high cathode temperature.
  • an electron-beam apparatus of the kind set forth according to the invention is characterized in that the electron-beam apparatus is provided with an interception electrode for local interception of part of the electron beam, said interception electrode forming part of the filament-current control unit.
  • the subjective criterion is replaced by an objective measuring value which is to be generated in the electron-beam apparatus, it no longer being necessary to use a reference value.
  • a periodic variation is associated with the Wehnelt resistance or the Wehnelt voltage, a resultant signal from the interception screen being used for adjusting the optimum cathode temperature.
  • FIG. 1 is a diagrammatic view of an electron microscope provided with a filament-current control unit according to the invention
  • FIG. 2 shows a cathode Wehnelt circuit for using a filament-current control unit with a varying Wehnelt resistance
  • FIG. 3 shows a cathode Wehnelt circuit for using a filament-current control unit with a varying Wehnelt voltage.
  • An electron microscope l as shown in FIG. 1 comprises, moving against the direction of movement of an electron beam 2 to be generated therein, a phosphor screen 3 for intercepting the electron beam, a projection lens 4, an intermediate lens 5, a diffraction lens 6, an objective lens 7, a second condensor lens 8, a first condensor lens 9, an acceleration anode 10, a Wehnelt electrode 11, and a cathode 12.
  • the cathode is formed by two interconnected filaments 13.
  • the filaments are connected, via filament-supply conductors 14, to a current-control unit 15 which is connected to an interception electrode 17 via a coupling 16.
  • the interception electrode 17 intercepts, for example, at least 5% of the electron beam 2.
  • the interception electrode preferably consists of a plate having a round aperture with a diameter of approximately 300 microns.
  • the interception electrode can also be arranged elsewhere in the electron microscope, the diameter of the aperture being adaptable to the location.
  • the interception electrode is preferably made of an electrically conductive material, in which case it must be electrically insulated from the electron microscope so as to be capable of supplying an electrical output signal.
  • the coupling 16 is then formed by an electrical conductor.
  • the interception electrode in another embodiment comprises a phosphor which is to be activated by the electron beam.
  • a signal is obtained which is dependent of the beam-current intensity, it being possible for said signal to be intercepted, for example, by a light-sensitive element of the filament-current control unit 15.
  • the device can also be constructed such that the display screen 3 or if the entire emitted electron beam impinges upon the display screen, a portion of the display screen, acts as the interception electrode.
  • An electrical or optical signal which is dependent of the beam-current density is then derived from the display screen.
  • the detected signal is applied to the currentcontrol unit 15 which controls the filament current in accordance with the received signal.
  • the cathode Wehnelt circuit 15' forming a part of the current control unit 15, comprises a series of resistors 20 and a selector switch 21 for adjusting an operating value for the Wehnelt resistance.
  • a switch 22 a variation of, for example, lO to 20% of the operating value of the Wehnelt resistance is effected by inserting or not inserting resistors of a series of resistors 23 in the circuit arrangement.
  • FIG. 2 also shows the two interconnected filaments 13, provided with two equal resistors 24 and 25, the Wehnelt electrode 11 and a switching point 26 which is to be connected to cathode potential.
  • the signal intensity will decreaseif the cathode temperature is adjusted too low, and will increase if the cathode temperature is adjusted too high.
  • the filament current can be readjusted such that the signal again obtains the initial intensity, i.e. the intensity associated with the operating value of the Wehnelt resistance. This process can subsequently be repeated until a Wehnelt resistance variation no longer influences the signal. The optimum cathode temperature is thus reached.
  • the readjustment of the filament current can be readily effected automatically by providing the filament-current control unit with a circuit for generating a difference signal between the signal at the operating value of the Wehnelt resistance and the signal at the decreased Wehnelt resistance.
  • the filament current is then controlled by this difference signal, for example, via a servomechanism (not shown).
  • FIG. 3 A cathode Wehnelt circuit for more practical filament-current control according to the invention is shown in FIG. 3.
  • This Figure shows the Wehnelt elec trode 11, the cathode 13 with the cathode resistors 24 and 25, a Wehnelt circuit 27 and a voltage source 28.
  • the Wehnelt circuit 27 generates the Wehnelt voltage, the value of which is dependent of the geometry of the electron-beam apparatus.
  • a periodic, preferably sinusoidal, voltage variation is superimposed by the voltage source 28. For example, an alternating voltage having a peak-to-peak value of V can be superimposed on a nominal cathode Wehnelt voltage of 200 V.
  • a phase sensitive element can be advantageously used for controlling the filament current. This is because in these cases the measuring on the edge of the electron beam produces an insufficiently accurate impression of the brightness variations at the centre of the electron beam.
  • An electron-beam apparatus comprising a cathode for the thermal emission of an electron beam, A Wehnelt electrode in proximity to said cathode for controlling said electron beam, a filament current control unit including a variable resistance coupled between said Wehnelt electrode and said cathode for maintaining a desired emission of said electron beam, and an interception electrode for intercepting a portion of the electron beam said filament-current control unit being operable for adjusting the temperature of said cathode to a value at which minimum signals resulting from variation of said variable resistance are generated at said interception electrode.
  • variable resistance is a Wehnelt resistance and means for varying the Wehnelt resistance.
  • filament-current control unit comprises a voltage generator for superimposing a voltage variation on a cathode-grid voltage.
  • the filament-current control unit further comprises a phase-sensitive detector for controlling the filament-current and thereby maintaining the temperature of said cathode, a preset phase shift with respect to the applied signal establishing the criterion for adjustment.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Sources, Ion Sources (AREA)
US258549A 1971-06-05 1972-06-01 Filament-current control unit in electron-beam apparatus Expired - Lifetime US3868541A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL7107749A NL7107749A (enrdf_load_stackoverflow) 1971-06-05 1971-06-05

Publications (1)

Publication Number Publication Date
US3868541A true US3868541A (en) 1975-02-25

Family

ID=19813316

Family Applications (1)

Application Number Title Priority Date Filing Date
US258549A Expired - Lifetime US3868541A (en) 1971-06-05 1972-06-01 Filament-current control unit in electron-beam apparatus

Country Status (9)

Country Link
US (1) US3868541A (enrdf_load_stackoverflow)
AU (1) AU469599B2 (enrdf_load_stackoverflow)
CA (1) CA966228A (enrdf_load_stackoverflow)
CH (1) CH543176A (enrdf_load_stackoverflow)
DE (1) DE2225864A1 (enrdf_load_stackoverflow)
FR (1) FR2140427B3 (enrdf_load_stackoverflow)
GB (1) GB1390425A (enrdf_load_stackoverflow)
IT (1) IT961307B (enrdf_load_stackoverflow)
NL (1) NL7107749A (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0040117A1 (fr) * 1980-05-08 1981-11-18 Thomson-Csf Tube cathodique polychrome et dispositif de visualisation équipé d'un tel tube
EP0031579A3 (en) * 1979-12-26 1982-05-12 Tokyo Shibaura Denki Kabushiki Kaisha Electron beam apparatus
US5118991A (en) * 1989-09-09 1992-06-02 Ptr Prazisionstechnik Gmbh Electron beam generator for an electron gun
US20050134297A1 (en) * 2003-12-02 2005-06-23 Kentaro Tezuka Electron beam generating apparatus and optical sampling apparatus using the same

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2313703B (en) 1996-06-01 2001-03-21 Ibm Current sensing in vacuum electron devices

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2987610A (en) * 1959-02-20 1961-06-06 Zeiss Carl Method and means for welding using a controlled beam of charged particles
US3223885A (en) * 1963-04-29 1965-12-14 Gen Electric Stabilization circuit for electron beam apparatus
US3229157A (en) * 1963-09-30 1966-01-11 Charles M Stevens Crucible surface ionization source
US3689798A (en) * 1968-07-17 1972-09-05 Mo Energeticheskij Institut Device for automatically controlling electrical conditions of an electron beam unit
US3691377A (en) * 1970-01-16 1972-09-12 Isao Matsui Automatic control system for varying a d.c. high voltage for accelerating tube of electron microscope and the like

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2987610A (en) * 1959-02-20 1961-06-06 Zeiss Carl Method and means for welding using a controlled beam of charged particles
US3223885A (en) * 1963-04-29 1965-12-14 Gen Electric Stabilization circuit for electron beam apparatus
US3229157A (en) * 1963-09-30 1966-01-11 Charles M Stevens Crucible surface ionization source
US3689798A (en) * 1968-07-17 1972-09-05 Mo Energeticheskij Institut Device for automatically controlling electrical conditions of an electron beam unit
US3691377A (en) * 1970-01-16 1972-09-12 Isao Matsui Automatic control system for varying a d.c. high voltage for accelerating tube of electron microscope and the like

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0031579A3 (en) * 1979-12-26 1982-05-12 Tokyo Shibaura Denki Kabushiki Kaisha Electron beam apparatus
EP0168064A1 (en) * 1979-12-26 1986-01-15 Kabushiki Kaisha Toshiba A method for determining the optimum operative conditions of an electron gun
EP0040117A1 (fr) * 1980-05-08 1981-11-18 Thomson-Csf Tube cathodique polychrome et dispositif de visualisation équipé d'un tel tube
US5118991A (en) * 1989-09-09 1992-06-02 Ptr Prazisionstechnik Gmbh Electron beam generator for an electron gun
US20050134297A1 (en) * 2003-12-02 2005-06-23 Kentaro Tezuka Electron beam generating apparatus and optical sampling apparatus using the same
US7307432B2 (en) * 2003-12-02 2007-12-11 Yokogawa Electric Corporation Electron beam generating apparatus and optical sampling apparatus using the same

Also Published As

Publication number Publication date
CH543176A (de) 1973-10-15
AU4294172A (en) 1974-02-07
AU469599B2 (en) 1976-02-19
FR2140427B3 (enrdf_load_stackoverflow) 1975-08-08
GB1390425A (en) 1975-04-09
CA966228A (en) 1975-04-15
NL7107749A (enrdf_load_stackoverflow) 1972-12-07
IT961307B (it) 1973-12-10
DE2225864A1 (de) 1973-02-15
FR2140427A1 (enrdf_load_stackoverflow) 1973-01-19

Similar Documents

Publication Publication Date Title
US2453118A (en) Concentrated arc discharge device
US3866077A (en) Electron emitters
US3962583A (en) X-ray tube focusing means
US2075140A (en) Tilting oscillator and modulator
US3374386A (en) Field emission cathode having tungsten miller indices 100 plane coated with zirconium, hafnium or magnesium on oxygen binder
US3196246A (en) Means for observing a workpiece in electron beam machining apparatus
US3751701A (en) Convergent flow hollow beam x-ray gun with high average power
US3691377A (en) Automatic control system for varying a d.c. high voltage for accelerating tube of electron microscope and the like
GB2183904A (en) Cathode focusing arrangement
US3868541A (en) Filament-current control unit in electron-beam apparatus
US2852716A (en) Cathode ray tube and electron gun therefor
US4247801A (en) Cathode current control system
US2509053A (en) Space current device employing mutually bombarded electrodes
US2227484A (en) Incandescent screen tube
US4890031A (en) Semiconductor cathode with increased stability
US3213311A (en) Electron discharge device
JPS58147947A (ja) 粒子線発生装置とその運転方法
Young A technique for studying the multiple emission sites on broad area electrodes in a vacuum
US4506191A (en) Light source cathode ray tube
US4020387A (en) Field emission electron gun
US3745342A (en) Electron beam apparatus comprising a cathode to be heated by an energy beam
US3303345A (en) Image amplifier with magnification grid
US3363961A (en) Cathode arrangement of an electron microscope for reducing the occurrence of virtualcathodes
US2593261A (en) Cathode-ray tube
US2185283A (en) Cathode ray discharge device