GB2214705A - Directly heated cathode - Google Patents
Directly heated cathode Download PDFInfo
- Publication number
- GB2214705A GB2214705A GB8801633A GB8801633A GB2214705A GB 2214705 A GB2214705 A GB 2214705A GB 8801633 A GB8801633 A GB 8801633A GB 8801633 A GB8801633 A GB 8801633A GB 2214705 A GB2214705 A GB 2214705A
- Authority
- GB
- United Kingdom
- Prior art keywords
- conductors
- cathode
- cathode according
- directly heated
- axis
- 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- Withdrawn
Links
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
Landscapes
- Microwave Tubes (AREA)
- Electrodes For Cathode-Ray Tubes (AREA)
- Solid Thermionic Cathode (AREA)
- Electron Sources, Ion Sources (AREA)
Description
- 1 Directly Heated Cathode rd _ 2 14 '10 5 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.
Many conventional directly heated cathodes are complex and cumbersome due to the need for cooling mechanisms, to avoid mechanical deformation which would otherwise arise from thermal stress in the cathode and its support. This deformation would adversely affect the life of the cathode and would deflect the electron beam from its intended axis. The influence on the electron beam of magnetic fields generated by the heating current passing through the cathode has also been difficult to minimise.
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.
2 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 aire 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.
Preferably, the conauctors 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. Preferably, 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.
one way in which the invention-may be performed will now be described, by way of example only, with reference to the accompanying drawings, in which:
:i - 3 11 Figure 1 is a longitudinal section taken on the axis of the electron- emissive end region of a directly heated cathode embodying the invention, and Figure 2 is a transverse section taken on the line XX of Figure 1.
A directly heated cathode comprises inner 4 and outer 5 nested, dishshaped 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 emittedelectron 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 lmm) 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. In common with well-known practice, 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 mechapical support and also provide a means for supplying a heater current to the respective conductors 4, 5. To this end, the support cylinders 1, 2 have electrical terminals (not shown) for connection to a variable heater current supply unit (not v 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.
As described above, 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 6 - 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.
Further, the inductance of the heater is very low, enabling it to be used with a switched-mode power supply.
1 z 1
Claims (1)
1. 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. 2. A cathode according to claim 1, in which the conductors are nested, dishshaped conductors, whose peripheral regions are their rims.
1 3. A cathode according to claim 2, in which the dish shaped conductors each have a substantially square section, the rim extending substantially parallel to the axis of the conductor. 4. A cathode according to claim 1, 2 or 3, in which the supplying means comprise two cylinders, each of whose end edge is connected to the peripheral region of a respective one of the conductors for mechanical support.
A cathode according to any preceding claim, in which the outer surface of the outer conductor is coated with an oxide to enhance its electron emissivity. 6. A cathode according to any preceding claim, whose peripheral region has a plurality of apertures for determining the heater current density over the conductors.
7. A directly heated cathode substantially as described herein with reference to the accompanying drawings. 8. Electron beam generating apparatus comprising a cathode according to any preceding claim.
Pubbabed 1989 at The Patent Mee, State House, 8671 High Holborn, London WCIR 4TP. Further coplesmay be obtainedfrom The Patentomee.
S:aza St W-,rr rj-i,. 0,,oinjion. Man'. DII-I MY). 'Tinted by UuItiplex tachriquea Itd, St Mary Cray, Kent, Con. 1/87 0 t
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8801633A GB2214705A (en) | 1988-01-26 | 1988-01-26 | Directly heated cathode |
EP89300425A EP0326273A3 (en) | 1988-01-26 | 1989-01-18 | Directly heated cathodes |
JP1017389A JPH01281635A (en) | 1988-01-26 | 1989-01-26 | Directly heated cathode |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8801633A GB2214705A (en) | 1988-01-26 | 1988-01-26 | Directly heated cathode |
Publications (2)
Publication Number | Publication Date |
---|---|
GB8801633D0 GB8801633D0 (en) | 1988-02-24 |
GB2214705A true GB2214705A (en) | 1989-09-06 |
Family
ID=10630502
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB8801633A Withdrawn GB2214705A (en) | 1988-01-26 | 1988-01-26 | Directly heated cathode |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0326273A3 (en) |
JP (1) | JPH01281635A (en) |
GB (1) | GB2214705A (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US9887061B2 (en) * | 2012-09-12 | 2018-02-06 | Shimadzu Corporation | X-ray tube device and method for using X-ray tube device |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB707096A (en) * | 1951-10-15 | 1954-04-14 | Vickers Electrical Co Ltd | Improvements in heaters for electron emitters |
GB1256379A (en) * | 1968-11-29 | 1971-12-08 | Jean-Pierre Peyrot | Improvements in or relating to electron beam welding guns and cathode emitter structures therefor |
EP0101108A1 (en) * | 1982-07-27 | 1984-02-22 | BBC Aktiengesellschaft Brown, Boveri & Cie. | Electronic tube, particularly an emitter tube |
EP0104496A2 (en) * | 1982-09-29 | 1984-04-04 | The Perkin-Elmer Corporation | Electron emitter assembly |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
NL14962C (en) * | 1923-10-17 | |||
FR692167A (en) * | 1930-01-28 | 1930-10-31 | Thermally protected cathode | |
US3461338A (en) * | 1967-01-16 | 1969-08-12 | Ibm | Non-inductive filament configuration |
-
1988
- 1988-01-26 GB GB8801633A patent/GB2214705A/en not_active Withdrawn
-
1989
- 1989-01-18 EP EP89300425A patent/EP0326273A3/en not_active Withdrawn
- 1989-01-26 JP JP1017389A patent/JPH01281635A/en active Pending
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB707096A (en) * | 1951-10-15 | 1954-04-14 | Vickers Electrical Co Ltd | Improvements in heaters for electron emitters |
GB1256379A (en) * | 1968-11-29 | 1971-12-08 | Jean-Pierre Peyrot | Improvements in or relating to electron beam welding guns and cathode emitter structures therefor |
EP0101108A1 (en) * | 1982-07-27 | 1984-02-22 | BBC Aktiengesellschaft Brown, Boveri & Cie. | Electronic tube, particularly an emitter tube |
EP0104496A2 (en) * | 1982-09-29 | 1984-04-04 | The Perkin-Elmer Corporation | Electron emitter assembly |
Also Published As
Publication number | Publication date |
---|---|
EP0326273A3 (en) | 1990-07-11 |
EP0326273A2 (en) | 1989-08-02 |
GB8801633D0 (en) | 1988-02-24 |
JPH01281635A (en) | 1989-11-13 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US6646366B2 (en) | Directly heated thermionic flat emitter | |
US8254526B2 (en) | Thermionic electron emitter and X-ray source including same | |
US3882339A (en) | Gridded X-ray tube gun | |
EP0168641B1 (en) | X-ray tube | |
EP0553912B1 (en) | X-ray tube with improved temperature control | |
US4764947A (en) | Cathode focusing arrangement | |
US6115453A (en) | Direct-Heated flats emitter for emitting an electron beam | |
US4297612A (en) | Electron gun structure | |
US3983446A (en) | Gridded convergent flow electron gun for linear beam tubes | |
JP4230565B2 (en) | X-ray tube | |
US3983443A (en) | Vacuum electron device having directly-heated matrix-cathode-heater assembly | |
GB2214705A (en) | Directly heated cathode | |
EP0439852B1 (en) | X-ray tube comprising an exit window | |
US4631744A (en) | X-ray tube | |
US3450927A (en) | Thermionic cathode with heat shield having a heating current by-pass | |
GB2296371A (en) | Cathode arrangements utilizing diamond as an insulator | |
US4082938A (en) | Thermionic heater cathode assembly of electron-beam gun | |
JPS6079644A (en) | Electron gun for high power klystron | |
JPH0567442A (en) | X-ray tube | |
KR100195679B1 (en) | An electron-gun assembly with improved heat resistance | |
JPH0211713Y2 (en) | ||
KR200146154Y1 (en) | Multi-beam cathode | |
WO1988004468A1 (en) | Fast warm-up cathode arrangement | |
JPH0766747B2 (en) | Impregnated cathode | |
KR100244310B1 (en) | Magnetron |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |