EP0488852A1 - Kathode für Ultrahochfrequenzröhren - Google Patents

Kathode für Ultrahochfrequenzröhren Download PDF

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Publication number
EP0488852A1
EP0488852A1 EP91403105A EP91403105A EP0488852A1 EP 0488852 A1 EP0488852 A1 EP 0488852A1 EP 91403105 A EP91403105 A EP 91403105A EP 91403105 A EP91403105 A EP 91403105A EP 0488852 A1 EP0488852 A1 EP 0488852A1
Authority
EP
European Patent Office
Prior art keywords
emissive
cathode
cathode according
edges
electrons
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Withdrawn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
EP91403105A
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English (en)
French (fr)
Inventor
Georges Mourier
Arvind Shroff
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.)
Thales Electron Devices SA
Original Assignee
Thomson Tubes Electroniques
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 Thomson Tubes Electroniques filed Critical Thomson Tubes Electroniques
Publication of EP0488852A1 publication Critical patent/EP0488852A1/de
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/02—Electrodes; Magnetic control means; Screens
    • H01J23/04—Cathodes
    • 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
    • H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/02—Electrodes; Magnetic control means; Screens
    • H01J23/09—Electric systems for directing or deflecting the discharge along a desired path, e.g. E-type

Definitions

  • the present invention relates to electronic tubes, and more particularly to microwave electronic tubes; precisely the invention relates to a construction of the cathode which supplies the electrons in these tubes.
  • An electronic tube generally, comprises an electron source, the cathode, and one or more electrodes brought to different voltages from the cathode, thus creating electrostatic fields inside the tube.
  • the tube is evacuated to allow the electrons to evolve under the sole influence of the electromagnetic fields which reign inside the tube, without collisions with particles of gas being in their trajectories.
  • the energy acquired by the electron is substantially equal to the voltage between the cathode and the anode.
  • the homogeneity of the speed imparted to the electrons during their acceleration, the homogeneity of the spatial distribution of the electrons and their final speed in the beam, the stability of the beam ... are all parameters (this list is not exhaustive) that must be mastered to extract the highest performance from the electron gun and the tube which use it.
  • the fields vary rapidly in space, because the discontinuities or small radii of curvature at the ends of the different electrodes make concentrations of field lines, or, on the contrary, regions where the lines of fields are more sparse or spaced.
  • the electrodes are of finite dimensions and therefore have at least one edge. In the region of the edges of the electrodes, the fields vary more quickly.
  • the Wehnelt is consequently thermally insulated from the cathode, which makes it possible to maintain it at a lower temperature and avoid parasitic emission from this electrode. This thermal insulation is obtained by a small spacing between the cathode and the Wehnelt.
  • the object of the invention is to provide a simple shape of the electric field lines at the edge (s) of the emissive region of the cathode, while keeping sufficient thermal insulation between the cathode and the Wehnelt.
  • the invention provides a cathode construction for microwave electronic tube, said cathode having a shape and a surface, said surface having an electron emissive part, this emissive part having edges and being located inside these edges; characterized in that: outside and in the immediate vicinity of said edges, the surface of the cathode is non-emissive of electrons and conductive of electricity.
  • this non-emissive and conductive refractory material is disposed in the immediate vicinity of the emissive part of the cathode, it will be brought to the same temperature.
  • the thermal insulation of the Wehnelt beam forming electrode will be ensured as in the prior art, with a spacing between the Wehnelt and the neighboring refractory and non-emissive part.
  • the invention does not relate to the configuration of the cathode and the training electrode or Wehnelt; nevertheless, a characteristic of the invention would make it possible to eliminate the Wehnelt without losing the advantages associated with its use.
  • FIG. 6 schematically shows in axial section another embodiment of a cathode for a gyrotron according to the invention, in which the beam-forming electrode has been omitted.
  • a conventional cathode which consists of a conductive and porous body 1 impregnated with an electron emissive material.
  • the cathode is generally brought to a negative high voltage and heated to high temperature; it releases electrons from the surface, which are accelerated by the surrounding electrostatic fields.
  • the cathode has a particular shape depending on the application; in the case of Figure 1 it has the shape of a pellet with a concave surface; it also has an axis of symmetry of revolution which is indicated in the figure.
  • a cathode can have several different shapes well known to those skilled in the art: flat or gutter ribbon, braided wires, forms of revolution, spherical cap, frustoconical sector of revolution, etc.
  • the electrostatic field on the surface of a conductor is always zero in the direction parallel to the surface, so the field electric is necessarily perpendicular to the surface of the cathode, and the electrons begin their trajectory along the field lines perpendicular to the surface which are shown in the figure.
  • the electrons which are emitted towards the edges of the cathode are therefore accelerated in very different directions along these field lines, and are difficult to use in an electron tube of linear geometry.
  • Figures 2a and 2b show an improvement well known in the prior art, which consists in placing, around the cathode 1, a beam forming electrode or "Wehnelt" 2, brought to the same high voltage as the cathode.
  • a beam forming electrode or "Wehnelt” 2 brought to the same high voltage as the cathode.
  • this is arranged a short distance from the cathode to provide thermal insulation.
  • these elements are vacuum in operation, so even a small space is thermally insulating; nevertheless, a short distance from the emissive surface of the cathode, the Wehnelt is shaped so as to move it further away from the cathode to minimize heat transfer.
  • Wehnelt 2 near the cathode 1 has the effect of smoothing the electric field in the region of the edges of the emissive cathode, and it can be seen in FIG. 2a that the field lines are much more regular at the edges of the cathode 1 as in the previous figure.
  • Figures 3a and 3b show two embodiments of a cathode according to the invention.
  • a ring 3 of refractory, conductive and non-emissive material is placed in direct contact with the edges of the cathode.
  • the Wehnelt 2 beam-forming electrode 2 is placed around this ring 3 as in the prior art it was placed around the cathode.
  • the ring 3 can be made for example of carbon, or of a refractory carbide such as tungsten carbide or tantalum; or pyrolytic graphite, or pyrolytic graphite covered with a refractory carbide formed locally or deposited by a process known to those skilled in the art.
  • Figures 3a and 3b differ only in the geometry of this non-emissive refractory ring: in Figure 3a the ring is arranged around the emissive body of cylindrical shape; and in FIG. 3b the non-emissive ring is of the same external diameter as the body of the cathode, projecting from the emissive face of the latter.
  • This latter arrangement can be carried out in several ways, either by placing an annular part in a projection designed for this purpose; or by locally creating a carbide of this geometry on the surface of the porous tungsten cathode.
  • Those skilled in the art will easily imagine other embodiments capable of obtaining the advantages of the invention according to the description given here.
  • Figure 4 shows another example of a particular embodiment according to the invention; it is a cathode intended to operate under a current regime limited by the space charge. Indeed, in the case of cathode operating with strong pervéances or strong emission currents, the presence of a large quantity of electrons in the space around the emissive surface of the cathode, the charge of space, modifies the electrostatic fields present in the absence of electrons.
  • FIG. 4 therefore, it can be seen that the geometry of the non-emissive part 3 has been slightly modified, since the equipotential surface of the non-emissive ring is brought to an angle A relative to the normal to the emissive surface of the cathode 1. According to theory, the optimal value of this angle A is 67.5 °.
  • the beam-forming electrode 2 is, as in the previous cases, separated by a small space from the heated parts to ensure thermal insulation.
  • FIGS. 5a and 5b an exemplary embodiment of a cathode according to the invention is seen for application in an electronic tube of the gyrotron type.
  • a gyrotron one seeks to manufacture a hollow electron beam, with a very high transverse speed and having a very precise energy. This is why we seek to avoid any anomaly of trajectory or energy of electrons coming from the edges of the emissive region. of the cathode.
  • the cathode of a gyrotron has a shape of convex revolution having the shape of a spherical cap extended by a frustoconical sector of revolution. Since we are looking for a hollow beam, when viewed from a point on the axis of revolution, the emissive part 1 of the cathode in the form of an emissive tape having the shape of a ring as shown in the figure 5b.
  • This emissive tape of constant width and of circular and parallel edges is a part of the surface defined between two planes perpendicular to the axis of revolution, these two planes cutting the surface at the circular edges thus defining said emissive tape, with two non-emissive parts 3 respectively inside and outside of, and in electrical and thermal contact with this tape.
  • the Wehnelt 2 beam-forming electrode has the same functions as in the previous figures, and is kept spaced from the heated part for thermal insulation.
  • the emissive and non-emissive parts of the cathode are produced either in separate pieces assembled subsequently; either by treatment of a tungsten body, part of which is carburetted locally, and the other part is impregnated, the two operations carried out according to methods known to those skilled in the art.
  • FIG. 6 shows another embodiment of a cathode according to the invention for application in an electronic tube of the gyrotron type, with elimination of the beam-forming electrode. Similar to the cathode shown in Figure 5, this cathode is designed to minimize the mass that must be brought to high temperature, to minimize the electrical heating power required.
  • the cathode is of a form of revolution as in figure 5, but hollow.
  • the non-emissive parts 3 are arranged on either side of the emissive part 1, which has a recess 5 for the location of a filament of heater.
  • the non-emissive parts 3 refractory and electrically conductive are connected by thin parts 4, also refractory and electrically conductive. These thin parts reduce the thermal conduction from the heated emissive part 1 to the unheated non-emissive parts 3, thereby reducing the heating power required to maintain the operating temperature of the emissive part 1.
  • This construction could be carried out advantageously by soldering, for example, elements 4 of thin non-emissive sheet between the more solid parts of the non-emissive parts 3 and the emissive part 1.
  • the presence of a non-emissive and conductive part adjacent to the edges of the emissive part makes it possible to obtain trajectories of electrons coming from the emissive part which are not at all disturbed by the edges of the latter.
  • the advantage thus obtained is particularly appreciated in tubes of very high power, very high efficiency, very high frequency, or any combination of high performance required.
  • the regularity and predictability of the trajectories allow easy calculation, and therefore computer-aided design can be used with good results. This is particularly important for obtaining performances which are at the limit, or beyond the state of the art.

Landscapes

  • Microwave Tubes (AREA)
  • Solid Thermionic Cathode (AREA)
EP91403105A 1990-11-27 1991-11-19 Kathode für Ultrahochfrequenzröhren Withdrawn EP0488852A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9014786A FR2669771A1 (fr) 1990-11-27 1990-11-27 Cathode amelioree pour tubes hyperfrequence.
FR9014786 1990-11-27

Publications (1)

Publication Number Publication Date
EP0488852A1 true EP0488852A1 (de) 1992-06-03

Family

ID=9402617

Family Applications (1)

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EP91403105A Withdrawn EP0488852A1 (de) 1990-11-27 1991-11-19 Kathode für Ultrahochfrequenzröhren

Country Status (3)

Country Link
EP (1) EP0488852A1 (de)
JP (1) JPH04286837A (de)
FR (1) FR2669771A1 (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2726121A1 (fr) * 1994-10-21 1996-04-26 Thomson Tubes Electroniques Dispositif de chauffage par rayonnement pour cathode a chauffage indirect
DE10013634A1 (de) * 2000-03-18 2001-09-27 Thomson Tubes Electroniques Gm Kathodenstrahlröhre
FR3007192A1 (fr) * 2013-06-14 2014-12-19 Thales Sa Canon electronique a optique amelioree

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1392755A (en) * 1972-04-24 1975-04-30 Air Liquide Cathodes for electron guns
EP0122182A1 (de) * 1983-04-07 1984-10-17 Commissariat à l'Energie Atomique Kathode für Elektronenkanone
US4495442A (en) * 1981-09-17 1985-01-22 Tokyo Institute Of Technology Cold-cathode magnetron injection gun
EP0363055A2 (de) * 1988-10-05 1990-04-11 Fujitsu Limited Elekronenkanone und deren Herstellungsverfahren

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU786677A1 (ru) * 1979-07-25 1989-02-23 Институт прикладной физики АН СССР Мазер на циклотронном резонансе
SU897039A1 (ru) * 1980-07-28 1989-09-30 Институт прикладной физики АН СССР Двухлучева электронна пушка мазера на циклотронном резонансе (ее варианты)
JPH081786B2 (ja) * 1984-10-01 1996-01-10 日本電気株式会社 電子管用電子銃
JPS61138430A (ja) * 1984-12-10 1986-06-25 Toshiba Corp ジヤイロトロン用電子銃
JPH0221540A (ja) * 1988-07-11 1990-01-24 Nec Corp マイクロ波管用電子銃

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1392755A (en) * 1972-04-24 1975-04-30 Air Liquide Cathodes for electron guns
US4495442A (en) * 1981-09-17 1985-01-22 Tokyo Institute Of Technology Cold-cathode magnetron injection gun
EP0122182A1 (de) * 1983-04-07 1984-10-17 Commissariat à l'Energie Atomique Kathode für Elektronenkanone
EP0363055A2 (de) * 1988-10-05 1990-04-11 Fujitsu Limited Elekronenkanone und deren Herstellungsverfahren

Non-Patent Citations (6)

* Cited by examiner, † Cited by third party
Title
JAPANESE JOURNAL OF APPLIED PHYSICS vol. 20, no. 11, Novembre 1990, TOKYO pages 789 - 792; K.MINAMI ET AL.: 'Cold cathode magnetron injection gun for relativistic electron beams with a long pulse width' *
PATENT ABSTRACTS OF JAPAN vol. 10, no. 259 (E-434)(2315) 4 Septembre 1986 & JP-A-61 085 754 ( NEC CORPORATION ) 1 Mai 1986 *
PATENT ABSTRACTS OF JAPAN vol. 10, no. 332 (E-453)(2388) 12 Novembre 1986 & JP-A-61 138 430 ( TOSHIBA CORPORATION ) 25 Juin 1986 *
PATENT ABSTRACTS OF JAPAN vol. 14, no. 163 (E-910)(4106) 29 Mars 1990 & JP-A-2 021 540 ( NEC CORPORATION ) 24 Janvier 1990 *
SOVIET INVENTIONS ILLUSTRATED Week 9004, 7 Mars 1990 Derwent Publications Ltd., London, GB; AN 90-028499/04 & SU-A-786 677 (V.E.ZAPELOV) 23 Février 1989 *
SOVIET INVENTIONS ILLUSTRATED Week 9004, 8 Août 1990 Derwent Publications Ltd., London, GB; AN 90-199237/26 & SU-A-897 039 (AS USSR APPLIED PHYSICS, GORKY UNIVERSITY) 30 Septembre 1989 *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2726121A1 (fr) * 1994-10-21 1996-04-26 Thomson Tubes Electroniques Dispositif de chauffage par rayonnement pour cathode a chauffage indirect
DE10013634A1 (de) * 2000-03-18 2001-09-27 Thomson Tubes Electroniques Gm Kathodenstrahlröhre
FR3007192A1 (fr) * 2013-06-14 2014-12-19 Thales Sa Canon electronique a optique amelioree

Also Published As

Publication number Publication date
JPH04286837A (ja) 1992-10-12
FR2669771A1 (fr) 1992-05-29

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