Classifications

• • 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
  • H01J23/06—Electron or ion guns
  • H01J23/065—Electron or ion guns producing a solid cylindrical beam
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2225/00—Transit-time tubes, e.g. Klystrons, travelling-wave tubes, magnetrons
  • H01J2225/02—Tubes with electron stream modulated in velocity or density in a modulator zone and thereafter giving up energy in an inducing zone, the zones being associated with one or more resonators
  • H01J2225/04—Tubes having one or more resonators, without reflection of the electron stream, and in which the modulation produced in the modulator zone is mainly density modulation, e.g. Heaff tube

Definitions

• the present invention relates to the field of electron tubes with axial beam with grid and in particular those with inductive output known under the abbreviation IOT (for the English name Inductive Output Tube). It relates more particularly to the grid of these tubes.
• An IOT comprises an electron gun which emits an electron beam directed along a longitudinal axis, this beam passing through a resonant cavity with which it interacts, before being collected in a collector which adjoins the resonant cavity.
• the barrel comprises a cathode generally with a concave emissive part, a heating device, a control grid and an anode, the grid being located between the cathode and the anode.
• the grid is used to modulate the emission of electrons so as to group them into packets as soon as they are emitted by the cathode.
• the beam thus modulated crosses the single cavity in which electromagnetic energy is extracted.
• FIG. 1 very schematically illustrates a known electron gun for an IOT type tube.
• the thermoemissive cathode bears the reference 1. It is solid with an emissive face 2 concave.
• a heating device 3 by conduction or radiation is located opposite the emissive face of the cathode 1.
• the control grid bears the reference 4. It is placed opposite the emissive face 2 of the cathode 1. It is very close to it, the interval which separates them can be of the order of a few tenths of a millimeter.
• the electrons form a beam (not shown) directed along the axis XX '.
• the electrons are grouped in bundles as soon as they pass through the central opening 6. Beyond the central opening 6, they enter the body of the tube (shown in dotted lines) from the resonant cavity to the collector.
• the grid 4 comprises an openwork part 7 with bars in a central area and a solid peripheral part 8, the assembly being in the form of a substantially flat or slightly concave disc to follow the emissive face 2 of the cathode 1.
• the grid 4 is fragile and its bars are thin.
• the grid 4 is intended to be connected to a grid connection part 10 situated at the base of the barrel, opposite the grid 4 relative to the heating device 3. It receives by this part 10 an electrical modulation signal .
• This connection is made by means of a support 9 electrically integral conductor on one side of the solid part 8 of the grid 4 and on the other of the grid connection part 10.
• This support 9 is formed by the assembly of several substantially cylindrical parts, one of which 91 surrounds the grid 4.
• a cathode connection part a connection part for the heater and an anode connection piece.
• the support 9 of the grid 4 is located near the cathode and surrounds it. It is generally made of metal because of its electrical properties because it helps to transmit the modulation signal to the gate 4.
• Grid 4 in the state of the art, and for reasons of thermoelectric properties, is made of pyrolytic graphite, a material known for its very low coefficient of expansion in the deposition plane.
• the grid 4 is subjected to significant thermal and electrical stresses but to play its role and modulate the beam effectively it must be able to accept them without deforming.
• the grid-cathode interval must remain substantially constant during the operation of the tube, this is an important parameter in the efficiency of the modulation and the stability of the signal.
• the grid 4 heats on the one hand because of its proximity to the thermoemissive cathode 1 and on the other hand because of the emitted electrons which inevitably strike it.
• the grid is generally made of pyrolitic graphite and the support 9 of metal.
• the present invention seeks to overcome these drawbacks and for this purpose proposes a grid for an electron beam tube with an axial beam with improved performance which is particularly simple to produce. It leads to an inexpensive cannon which allows, in operation, to maintain a precisely defined cathode-grid distance, independent of the temperature stabilization time of the different electrodes. It allows the removal of the metal grid support.
• the grid according to the invention has the shape of a bell and is mono-material, this bell having an openwork part at its top, this part being substantially transverse to the axis of the beam.
• the grid will preferably be made of pyrolitic graphite because of its thermal, electrical and mechanical properties suitable for this type of application.
• the grid is in one piece.
• the top of the hollow bell to place the openwork part at the bottom of the hollow and border the openwork part with a tubular wall integral with the skirt by an annular part which the space of the skirt.
• the grid is intended to be fixed at the base of the bell to a grid connection piece.
• This grid connection piece may include a sleeve around which the grid is fitted.
• the fixing between the grid and the grid connection part can be carried out for example by soldering, screwing.
• the present invention also relates to an electronic tube with an axial beam equipped with such a grid.
• FIG. 2 an axial beam electron tube according to the invention whose barrel comprises a grid according to the invention
• FIG. 3a a perspective view of a grid according to the invention with a series of slots and Figures 3b, 3c different variants for the slots.
• FIG. 4 an electronic tube with axial beam according to the invention with a grid whose top has a hollow.
• FIG. 2 schematically shows a grid 20 according to the invention mounted in an electronic tube with an axial beam 50 directed along the axis XX '. It is assumed that the tube has an inductive output (IOT). Only a part of the barrel of the tube is represented, the rest is shown diagrammatically by dotted lines.
• the grid 20 has the shape of a bell 22 and is made of a single material. This bell 22 has a top 21 and is extended by a substantially cylindrical skirt to a base 27.
• the perforated part 23 of the grid 20, substantially transverse to the axis XX 'of the beam is located at the top 21 of the bell.
• This perforated part 23 is intended to be placed opposite the active face 41 of the cathode 40 when it is mounted in the barrel of the electronic tube.
• the perforated part 23 follows the surface of the active part 41 of the cathode 40 and for this purpose it can be concave, in a bowl, for example substantially spherical.
• Other configurations are possible such as an openwork part
• the grid 20 is mono-material from the top 21 of the bell to its base 27. This characteristic contributes to solving the problem of deformation generated by the differential expansions encountered in the prior art. With such a mono-material bell structure, it is no longer necessary to provide a metal support near the cathode 40 between the perforated part 23 and the connecting part of the grid 24.
• the base 27 of the bell 22 is fixed to the grid connection part 24, this part 24 serving to supply the electrical modulation signal applied to the grid 20.
• the grid connection piece 24 is remote from the cathode 40 and is located near the cathode connection piece 42. In the region of the connection pieces, the temperature never becomes as intense as at the level of the perforated part. 23 facing the active face 41 of the cathode. The harmful effects of the differential expansion between the grid 20 and the connecting piece of the grid 24 are not significant on the perforated part 23.
• the grid connection piece 24, electrically conductive, may include a sleeve 25 around which the base 27 of the bell 22 fits.
• the grid 20 and the sleeve 25 can be joined together using screws 26 which pass through the sleeve 25 and the skirt of the bell 22.
• screws 26 which pass through the sleeve 25 and the skirt of the bell 22.
• holes 28 in the skirt of the bell 22 and threads in the sleeve 25 are provided to accommodate the screws 26.
• Figure 3a shows a perspective view of a grid 20 according to the invention with holes 28 in the skirt of the bell 22.
• the perforated part 23 is drawn hatched for clarity. This structure is not limiting.
• Another type of attachment can consist of a brazing of the base 27 of the bell 22 on the grid connection piece 24.
• a brazing of the base 27 of the bell 22 on the grid connection piece 24 it is possible to provide on the periphery of the base 27 of the bell a series of longitudinal slots 30, these slots 30 bringing a certain flexibility at the level of the inevitable deformations which occur during heating. These slots 30 provide elastic compensation for differential expansion and remove the mechanical stresses in the grid.
• slots 30 may not open onto the lower edge of the skirt of the bell 22 but stop before so as to delimit a wedge 31 between the base of the bell 22 and the end of the slots 30.
• the base of the bell is divided into a number of blades spaced the width of the slots.
• These slots 30 do not deteriorate the electrical contact with the grid connection part 24.
• the wedge 31 ensures rigidity of the base 27 of the bell before mounting on the sleeve 25 but after tightening it can break.
• the holes 28 are located between the slots 30 in the example shown.
• the slots 30 may be of constant width, but it can be envisaged that they have an upper part 30.1 and a lower part 30.2 of different widths, these two parts being connected to one another.
• Figures 3a, 3b, 3c show several slot configurations
• the slots 30 have a constant width.
• the upper part 30.1 is wider than the lower part 30.2 and in FIG. 3c, it is the reverse.
• These slots 30 and these holes 28 can be produced by any known means such as sawing or sandblasting machining for example.
• the grid 20 is advantageously made of pyrolitic graphite which has thermal, mechanical, electrical properties which are particularly well suited to this application.
• the techniques for making one-piece pyrolitic graphite grids are well mastered. Other materials can however be used.
• the grid connection piece 24 can be made of an electrically and thermally conductive material, typically copper, molybdenum, an iron-nickel-cobalt alloy or the like.
• the sleeve 25 can also be made of the same materials if it is not in one piece with the rest of the anode connection part 24 which is in the form of a collar.
• dielectric spacers 43 On either side of the grid connection piece 24 and the cathode connection piece 42 are shown dielectric spacers 43 which serve for electrical insulation and mechanical maintenance between the connection pieces and therefore the different electrodes concerned.
• the wall of the grid from the base 27 is a rising wall directed along the axis XX 'at the level of the skirt 53, then it returns towards the axis XX' at the level of the annular part 52, then it enters the bell at the level of the wall tubular 51 and ends with the perforated part 23 substantially transverse to the axis XX '.
• the skirt 53, the annular part 52 and the re-entrant tubular wall 51 have substantially the same thickness.
• the length of the tubular wall 51 is adjusted to obtain the focusing action.
• the tubular wall 51 and the skirt 53 are spaced from each other by the annular part 52.
• the tubular wall 51 reentrant with respect to the annular part is shown substantially vertical.
• the skirt 53 and the tubular wall 51 are two substantially coaxial hollow cylinders mounted one inside the other, the tubular wall 51 being inside the skirt 53.
• This substantially cylindrical tubular wall 51 plays the role of a wehneit; it pushes back towards the axis XX 'the electrons having crossed the grid to 8

Landscapes

• Microwave Tubes (AREA)
• Electrodes For Cathode-Ray Tubes (AREA)
• Cold Cathode And The Manufacture (AREA)
• Electron Sources, Ion Sources (AREA)
• Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)

Applications Claiming Priority (5)

Publications (2)

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ID=26234131

Family Applications (1)

Country Status (7)

Families Citing this family (4)

Family Cites Families (21)

• 1998
  • 1998-02-24 FR FR9802202A patent/FR2775118B1/fr not_active Expired - Fee Related
• 1999
  • 1999-02-12 US US09/622,165 patent/US6635978B1/en not_active Expired - Fee Related
  • 1999-02-12 EP EP99902588A patent/EP1055246B1/de not_active Expired - Lifetime
  • 1999-02-12 CA CA2319620A patent/CA2319620C/fr not_active Expired - Fee Related
  • 1999-02-12 CN CNB99802774XA patent/CN100346443C/zh not_active Expired - Fee Related
  • 1999-02-12 WO PCT/FR1999/000171 patent/WO1999041762A1/fr not_active Ceased
  • 1999-02-12 DE DE69930836T patent/DE69930836D1/de not_active Expired - Lifetime

Non-Patent Citations (1)

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