US2283041A - Electron focusing system - Google Patents

Electron focusing system Download PDF

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Publication number
US2283041A
US2283041A US354882A US35488240A US2283041A US 2283041 A US2283041 A US 2283041A US 354882 A US354882 A US 354882A US 35488240 A US35488240 A US 35488240A US 2283041 A US2283041 A US 2283041A
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US
United States
Prior art keywords
cathode
electron
cross
electrode
over
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
US354882A
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English (en)
Inventor
Broadway Leonard Francis
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.)
EMI Ltd
Electrical and Musical Industries Ltd
Original Assignee
EMI Ltd
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 EMI Ltd filed Critical EMI Ltd
Application granted granted Critical
Publication of US2283041A publication Critical patent/US2283041A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/48—Electron guns
    • H01J29/488—Schematic arrangements of the electrodes for beam forming; Place and form of the elecrodes

Definitions

  • This invention relates to electron focusing systems used in electron discharge tubes such as cathode ray tubes.
  • the electron gun in a cathode ray tube usually comprises a source of electrons such as a directly or indirectly heated cathode, a shield surrounding the cathode, which may also serve as a modulating electrode, and first and second anodes or accelerating electrodes between which an electron lens is formed which focuses the electrons upon a screen such as a fluorescent screen or a mosaic electrode.
  • Electro-magnetic focusing means such as a coil surrounding the electron beam may be employed instead of electrostatic means.
  • the electron beam is caused to cross over at the cathode by means of the converging lens formed by the penetration of the first anode field through the apertured electrode which serves to modulate the beam. After leaving the cross-over the beam is defined by a stopping diaphragm, and finally focused on the fluorescent or other screen by the electrostatic lens formed between the first and second anodes.
  • the object of the present invention is to provide an electron gun and a method of operation therefor, which substantially reduces, or elimito the cause mentioned, and an essential feature of the invention lies in designing an electron gun such that the image of a virtual cross-over'instead of a real cross-over is produced upon the screen.
  • the electron gun in a cathode ray tube comprises acathode, a modulating electrode and first and second anodes and saidcathode has a convex emitting surface, the portion of said modulating electrode adjacent the'emittingsurface of said cathode being composed of fine wire mesh shaped to conform substantially to the shape of said emitting surface, whereby penetration of the anode field within said modulatingelectrode is substantiallyprevented and said electron gun, in operation, produces an electron beam in which no cross-over occurs between said emitting surface and the point at which it is desired to focus said beam.
  • the electron gun includes a convex cathode C which is indirectly heated by a filament F, a modulating electrode M and the first and second anodes A1 and A2 respectively.
  • the modulator electrode M consists of a fine gauze mesh which is carefully formed so that it is always parallel to the convex emitting surface of the cathode, and the mesh of which is so fine that substantially no penetration of the anode field takes place in the region between the mesh and the cathode. It has been found that a gauze containing more than 100 meshes per inch is satisfactory for this purpose.
  • the potential of the modulator electrode at the point at which the electron beam current is cut off is only slightly negative with respect to the potential of the cathode, and in operation the modulation voltage is mainly applied in the positive sense with respect to the cathode potential. While 1 have shown the tube in the drawing in section, it will be appreciated that the anodes A1 and A2 are cylindrical and that the effective surfaces of the convex cathode C and control or modulator electrode M are substantially spherical in form and are concentric one with the other.
  • the electron beam diverges from the convex surface of the cathode, the outline of the beam nates, the limitations of the current density due being indicated at B, and is brought to focus on a fluorescent screen by means of the electrostatic lens formed between the first and second anodes A1 and A2.
  • the beam may be focussed by electro-magnetic means.
  • the potential of the anode A1 may be several hundred volts
  • the potential of the anode A2 may be several thousands of volts, but it will of course be understood that these voltages will be determined by the general design of the tube. It will be seen from the drawing that the electron beam has only one real cross-over point, namely, at its final focus upon the target such as the fluorescent screen S, the other cross-over being virtual and situated behind the cathode surface at the point P.
  • a cathode ray tube comprising an envelope, a target within said envelope, a convex cathode facing and exposed to said target, a controlelectrode adjacent said cathode having a portion effective on electrons emitted by said cathode which is concentric with said convex cathode 1 whereby electrons aredirected toward said target along diverging paths, said cathode and com trol electrode having centers of curvature more remote from said target than the convex surfaces thereof, and means to terminate said diverging paths and direct said electrons along converging paths to said target.
  • a cathode ray tube comprising an envelope, a target within said envelope, a cathode having a spherical surface whose center of curvature-is more remote from said target than said surface, a modulator electrode of fine wire mesh gauze adjacent and concentric with the spherical a fine wire mesh of at least one hundred mesh per inch interposed betweensaidcathode and anode the surface of said mesh wbeing convex toward said target to prevent substantial penetration of the field generated byv said anode within the space betweensaid cathode and electrode and to .cause electrons emitted bysaid cathode to diverge from an axis between said cathode and target and means to direct electrons following diverging paths along converging paths substantially intersecting at said target.

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  • Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
  • Cold Cathode And The Manufacture (AREA)
US354882A 1939-09-07 1940-08-30 Electron focusing system Expired - Lifetime US2283041A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB255241X 1939-09-07
GB250740X 1940-07-25

Publications (1)

Publication Number Publication Date
US2283041A true US2283041A (en) 1942-05-12

Family

ID=26257471

Family Applications (1)

Application Number Title Priority Date Filing Date
US354882A Expired - Lifetime US2283041A (en) 1939-09-07 1940-08-30 Electron focusing system

Country Status (5)

Country Link
US (1) US2283041A (de)
CH (1) CH255241A (de)
DE (1) DE839837C (de)
FR (1) FR939215A (de)
GB (1) GB534627A (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2462082A (en) * 1941-12-19 1949-02-22 Int Standard Electric Corp Thermionic valve
US2482151A (en) * 1944-08-18 1949-09-20 Philips Lab Inc Cathode-ray projection tube
US2672568A (en) * 1951-03-27 1954-03-16 Int Standard Electric Corp Electron gun for cathode-ray tubes
US3143685A (en) * 1961-07-24 1964-08-04 Multi Tron Lab Inc Character display cathode ray tube
US3377492A (en) * 1965-08-03 1968-04-09 Hughes Aircraft Co Flood gun for storage tubes having a dome-shaped cathode and dome-shaped grid electrodes
DE3137227A1 (de) * 1980-09-19 1982-07-22 Shinryo Air Conditioning Co., Ltd., Tokyo Verfahren und vorrichtung zum veraschen von klaerschlamm

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2462082A (en) * 1941-12-19 1949-02-22 Int Standard Electric Corp Thermionic valve
US2482151A (en) * 1944-08-18 1949-09-20 Philips Lab Inc Cathode-ray projection tube
US2672568A (en) * 1951-03-27 1954-03-16 Int Standard Electric Corp Electron gun for cathode-ray tubes
US3143685A (en) * 1961-07-24 1964-08-04 Multi Tron Lab Inc Character display cathode ray tube
US3377492A (en) * 1965-08-03 1968-04-09 Hughes Aircraft Co Flood gun for storage tubes having a dome-shaped cathode and dome-shaped grid electrodes
DE3137227A1 (de) * 1980-09-19 1982-07-22 Shinryo Air Conditioning Co., Ltd., Tokyo Verfahren und vorrichtung zum veraschen von klaerschlamm

Also Published As

Publication number Publication date
DE839837C (de) 1952-05-26
GB534627A (en) 1941-03-12
CH255241A (de) 1948-06-15
FR939215A (fr) 1948-11-08

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