EP0326273A2 - Cathodes à chauffage direct - Google Patents

Cathodes à chauffage direct Download PDF

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Publication number
EP0326273A2
EP0326273A2 EP89300425A EP89300425A EP0326273A2 EP 0326273 A2 EP0326273 A2 EP 0326273A2 EP 89300425 A EP89300425 A EP 89300425A EP 89300425 A EP89300425 A EP 89300425A EP 0326273 A2 EP0326273 A2 EP 0326273A2
Authority
EP
European Patent Office
Prior art keywords
conductors
axis
cathode
cathode according
conductor
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.)
Withdrawn
Application number
EP89300425A
Other languages
German (de)
English (en)
Other versions
EP0326273A3 (fr
Inventor
Alan Hugh Pickering
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.)
Teledyne UK Ltd
Original Assignee
EEV 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 EEV Ltd filed Critical EEV Ltd
Publication of EP0326273A2 publication Critical patent/EP0326273A2/fr
Publication of EP0326273A3 publication Critical patent/EP0326273A3/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/15—Cathodes heated directly by an electric current

Definitions

  • This invention relates to a directly heated cathode which may, for example, be used to generate the electron beam in a travelling wave tube, magnetron or cathode ray tube.
  • Directly heated cathodes are those which are heated by a current flowing in the electron-emissive component itself, rather than in a separate heater circuit.
  • the present invention seeks to overcome both these problems by providing a directly heated cathode comprising two thin, thermally deformable conductors which are both rotationally symmetric about a common axis and are connected electrically and mechanically in the region of their common axis, and means for supplying a heater current to flow between their respective peripheral regions by way of their said connection.
  • the rotational symmetry of the conductors is maintained in spite of thermal expansion and contraction, thus avoiding deflection of an electron beam emitting surface on one of the conductors.
  • the conductors are thin and thermally deformable, so that cooling, although possible, is not necessary. Further, the symmetry of the conductors and the axial position of their connection ensure that the heater current is also distributed symmetrically about the axis and does not give rise to any magnetic field which would deflect the electron beam from the common axis.
  • the conductors are nested, dish-shaped conductors whose peripheral regions are their rims. Thermal strain in these conductors is accommodated by relative axial movement of the rim and the base, and by a symmetrical deformation of the base.
  • each dish-shaped conductor has a substantially square section, the rim extending substantially parallel to the axis of the conductor.
  • the current supplying means preferably comprises two cylinders, each of whose end edge is connected to the peripheral region of a respective one of the conductors for mechanical support.
  • a directly heated cathode comprises inner 4 and outer 5 nested, dish-shaped conductors which are rotationally symmetric about a common axis A.
  • the conductors 4, 5 each have a substantially square section, as shown in Figure 1, so that the rim extends parallel to the axis A.
  • the base of each conductor 4, 5, is concave to produce the desired focussing of the emitted electron beam. Allowance is made for deformation to a different curvature when hot.
  • the dish-shaped configuration also allows for relative axial movement of the rim relative to the base as a result of thermal expansion.
  • the conductors 4, 5 are thin sheet pressings of a tungsten-nickel alloy with a high tungsten content, preferably about 25 microns thick.
  • the outer surface of the base of the outer conductor 5 supports an electron-emissive surface, which may be a thin layer of barium, strontium or calcium oxide formed in a well-known manner.
  • the surface may, for example, be a porous mush of sintered nickel powder impregnated with barium oxide.
  • a mesh 8 close to, but spaced (by about 1mm) from, the outer conductor 5 acts as a grid to control the electron current emitted from the cathode.
  • the mesh 8 forms part of a dish-shaped conductor 6 similar to, but larger than, the inner and outer conductors 4,5, supported by a further coaxial support cylinder 3.
  • This mesh 8 may be of nickel, molybdenum or suitable alloys, and is treated to reduce thermionic emission.
  • a further grid (not shown), known as a shadow grid, is interposed between the mesh 8 and the outer conductor 5, and is connected electrically to the outer conductor 5, its wires being aligned with those of the mesh 8 to protect them from molecules or ions which are inevitably emitted from the volatile electron-emissive surface.
  • the inner surfaces of the two conductors 4, 5 are connected mechanically and electrically on the axis A, over a region which is small in comparison with the size of the conductors, by a weld 7 which may be made by spot welding or arc or laser welding.
  • the rims of the conductors 4, 5 are brazed or welded to the outer end surfaces of respective support cylinders 1, 2 which are co-axial with the conductors 4, 5.
  • the support cylinders provide mechanical support and also provide a means for supplying a heater current to the respective conductors 4, 5.
  • the support cylinders 1, 2 have electrical terminals (not shown) for connection to a variable heater current supply unit (not shown).
  • the heater current flows from the rim of one of the conductors radially through that conductor, through the weld 7, and radially through the other conductor to the rim of that other conductor. Due to the rotational symmetry of the conductors and support cylinders and to the axial position of the weld 7, the distribution of heater current is also rotationally symmetric, and will not give rise to any magnetic field which would tend to deflect an electron beam on the axis A from that axis. Thus the electron beam emitted along the axis A by the outer conductor 5 remains undeflected by the heater current.
  • the heating of the cathode by the passage of the heater current is ohmic, and the distribution of the heat generated is therefore a function of the current density.
  • the distribution of cathode temperature may be adjusted by appropriate choice of the lengths of the rims of the conductors 4, 5, and of the diameter of the central weld 7. Further, if necessary, holes could be laser cut in the rim of the outer conductor 5 so as locally to increase the current density and hence the ohmic heating.
  • thermal deformation of the cathode is accommodated so that the electron-emissive surface is maintained normal to the axis A, so that the electron beam is not deflected off the axis.
  • the composition and thickness of the conductors 4,5,6 is such as to give sufficient flexibility for such thermal expansion, leading to a satisfactory working life: no provisions for cooling are required.
  • the whole assembly has the advantage of being simply-constructed, rigid and robust, and no special provisions need to be taken to allow for expansion during warm up. It is anticipated that warm-up times as low as 2 seconds could be attained with such a cathode.
  • the inductance of the heater is very low, enabling it to be used with a switched-mode power supply.

Landscapes

  • Microwave Tubes (AREA)
  • Electrodes For Cathode-Ray Tubes (AREA)
  • Solid Thermionic Cathode (AREA)
  • Electron Sources, Ion Sources (AREA)
EP89300425A 1988-01-26 1989-01-18 Cathodes à chauffage direct Withdrawn EP0326273A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8801633A GB2214705A (en) 1988-01-26 1988-01-26 Directly heated cathode
GB8801633 1988-01-26

Publications (2)

Publication Number Publication Date
EP0326273A2 true EP0326273A2 (fr) 1989-08-02
EP0326273A3 EP0326273A3 (fr) 1990-07-11

Family

ID=10630502

Family Applications (1)

Application Number Title Priority Date Filing Date
EP89300425A Withdrawn EP0326273A3 (fr) 1988-01-26 1989-01-18 Cathodes à chauffage direct

Country Status (3)

Country Link
EP (1) EP0326273A3 (fr)
JP (1) JPH01281635A (fr)
GB (1) GB2214705A (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014041639A1 (fr) * 2012-09-12 2014-03-20 株式会社島津製作所 Dispositif à tube à rayons x et procédé d'utilisation d'un dispositif à tube à rayons x

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL14962C (fr) * 1923-10-17
FR692167A (fr) * 1930-01-28 1930-10-31 Cathode à protection thermique
BE514838A (fr) * 1951-10-15
US3461338A (en) * 1967-01-16 1969-08-12 Ibm Non-inductive filament configuration
FR1599106A (fr) * 1968-11-29 1970-07-15
EP0101108B1 (fr) * 1982-07-27 1987-01-21 BBC Aktiengesellschaft Brown, Boveri & Cie. Tube électronique, en particulier tube émetteur
US4473777A (en) * 1982-09-29 1984-09-25 The Perkin-Elmer Corporation Electron emitter assembly

Also Published As

Publication number Publication date
EP0326273A3 (fr) 1990-07-11
GB8801633D0 (en) 1988-02-24
GB2214705A (en) 1989-09-06
JPH01281635A (ja) 1989-11-13

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