FR2670321A1 - CAVITY HYPERFREQUENCY TUBE WITH DIELECTRIC STRUCTURE AND METHOD OF MAKING TUBE CAVITY. - Google Patents

Abstract

The present invention relates to a microwave tube with at least one electron beam (32) passing through at least one resonant cavity (34) forming an integral part of the tube. The cavity comprises at least one structure made of solid dielectric material with a dielectric constant greater than one. Application to klystrons of reduced bulk.

Description

-1 2670321

  HYPERFREQUENCY TUBE WITH CAVITY PROVIDED WITH

DIELECTRIC STRUCTURE AND METHOD

  REALIZATION OF A CAVITY OF THE TUBE.

  The present invention relates to microwave tubes with linear electron beams passing through the

  less a resonant cavity These tubes are called type "O".

  These tubes are particularly of the family of klystrons. The present invention aims at reducing the bulk, the weight and the

cost of such tubes.

  A classical klystron is a microwave tube modulated by an electron beam Its principle is based on the interaction between a linear electron beam directed along an axis, and an electromagnetic wave induced in resonant cavities. of the electromagnetic wave is parallel to the axis of the beam

  of electrons A focusing device surrounds the cavities.

  The cavities, generally four or five in number, are placed one after the other along the axis of the electron beam. They are separated by sliding tubes which are generally tubes of small diameter with respect to the length of the electromagnetic wave The electron beam formed in a barrel passes successively through cavities and sliding tubes It is collected in a collector The microwave cavity is introduced into the first cavity; the last cavity is connected to a user device. Generally the barrel, the periphery of the cavities, a part of the sliding tubes and the collector define an enclosure whose interior is subjected to vacuum All these parts comprise metal parts, they are connected together, at these metal parts, to ensure continuity and sealing of the vacuum chamber This connection is preferably a solder or any method known to those skilled in the art The cavities are an integral part of the vacuum chamber They usually have the shape of cylinders or parallelepipeds and are built with walls

  brazed together to hold the vacuum.

  In other configurations, the tube comprises a separate vacuum chamber. The cavities are disposed inside the vacuum chamber and the outside of the cavities are also subjected to vacuum. The sliding tubes are also placed inside the cavity. the vacuum chamber and these sliding tubes are bathed

  internally and externally by vacuum.

  The resonance frequency of a cavity is a function of its geometric dimensions and the relative dielectric constant of the internal medium to the cavity. The dielectric constant

relative of emptiness is equal to one.

  A klystron cavity is often used in its fundamental mode TM 01 By fundamental mode we mean the one that resonates the lowest in frequency The cavity can however resonate on many other modes The cavities of the classical klystrons are cumbersome In many applications, it would be desirable to reduce their footprint

  to reduce that of the klystrons.

  The present invention proposes a microwave tube with at least one electron beam passing through at least one resonant cavity forming part of the tube, this cavity having, for the same resonant frequency, reduced dimensions compared to those of the cavities of the art. Known reduction of dimensions can lead to significant weight reduction which is a significant advantage A cavity of a microwave tube according to the invention comprises a solid dielectric material structure This dielectric material has a

  relative dielectric constant higher than that of vacuum.

  For the same resonant frequency, the cavity has dimensions smaller than that of an equivalent cavity but

without dielectric structure.

  A tube according to the invention will preferably comprise at least one electron beam passing through at least one resonant cavity forming part of the tube, the cavity comprising a structure of solid dielectric material, of constant

  relative dielectric greater than one.

  Preferably, the dielectric structure comprises a

  recess for passing the electron beam.

  In certain configurations, the periphery of the cavity

  can be formed by a conductive envelope.

  In other configurations, the periphery of the cavity may

  be formed by at least a portion of the dielectric structure.

  At least one zone of the dielectric structure is connected to a conductive element This element may be external or may be embodied by at least one conductive deposition on at least the area of the dielectric structure. This connection may be sealed. An active metal may contribute to ensuring this. sealed connection The dielectric material is preferably chosen

  with dielectric losses as low as possible.

  The active metal may typically be either titanium, zirconium or manganese, or an alloy of at least two

of these metals.

  In some embodiments, the active metal may be included in a solder, the conductive member being brazed to the dielectric structure. In other embodiments, the active metal covers the area of the dielectric structure. The conductive member may be attached to the metal. directly or via one or more layers of an auxiliary metal. Preferably, the auxiliary metal is copper or

nickel.

  The element materialized by the conductive deposit may consist of active metal coated with a complementary metal

  the active metal being in contact with the dielectric material.

  The dielectric structure can be monoblock or be

consisting of several blocks.

  The invention also relates to a method for producing a

  cavity of a microwave tube according to the invention.

  It comprises at least the following steps coating a dielectric structure comprising a recess, with a curable resin and machinable filling the recess; machining the resin so as to expose at least a portion of the dielectric structure; depositing metal on the dielectric material and the remaining resin to materialize the conductive element; drilling two orifices, vis-a-vis, in the metal, at the hollow portion of the dielectric structure

removal of the resin.

  The deposition of metal can be done in several times depositing a thin layer of an active metal followed by the deposit of at least

  a thicker layer of a complementary metal.

  The invention will be better understood and other features and advantages will become apparent upon reading the

  following description, illustrated by the attached figures which

  represent: FIG. 1: a longitudinal section of a cavity of a microwave tube according to the invention; Figure 2 is a longitudinal section of a first variant of a cavity of a microwave tube according to the invention; Figure 3: a longitudinal section of a microwave tube according to the invention; Figure 4: a cross section of a second variant of a cavity of a microwave tube according to the invention; Figure 5 is a longitudinal section of a third variant of a cavity of a microwave tube according to the invention; FIGS. 6a to 6e are longitudinal sections of a cavity of a microwave tube according to the invention, during the

  different stages of its realization.

  FIG. 1 represents in longitudinal section a cavity of a microwave tube according to the invention. This tube is a klystron. It comprises a succession of cavities separated by sliding tubes. This succession can contribute to delimiting a vacuum chamber or be contained in a vacuum chamber An electron beam, directed along an axis XX ', passes through the succession of cavities The cavity shown is an intermediate cavity, it is between two other cavities It is bounded by a metal conductive envelope 3 It is closed and has two adjacent slip tubes 1 These slip tubes 1 are conductive and are traversed by the electron beam They penetrate into the cavity facing each other Inside the cavity, they are separated by an interaction space 2 It is assumed, in the example described, that the envelope of the cavity and the portions of sliding tubes outside the cavity contribute delimit the vacuum chamber The cavity comprises a solid dielectric material structure In the example described, it is a block which has a recess preferably central The cavity shown is a cylinder of revolution axis XX 'Block 4 of The dielectric material may have the shape of a tube coaxial with the axis XX 'Its central recess allows the electron beam to pass In FIG. 1, the block 4 of dielectric material does not occupy the entire volume of the envelope 3 It could occupy a larger part Inside the cavity and sliding tubes 1 reigns a high vacuum, outside there is an ambient atmosphere because the

  cavity helps to delimit the vacuum chamber.

  The block 4 of dielectric material is mechanically fixed to the casing 3 of the cavity It could have been mechanically fixed to the sliding tubes 1 The mechanical fixing can be done by staples, clips, springs or any other means

  known There is no sealing constraint to respect.

  The experiment and the cavity theory show that if the relative dielectric constant of the internal medium of a resonant cavity is increased, its dimensions can be reduced without changing its resonance frequency. It is thus possible to reduce its bulk. , the cavity is limited by the metal shell 3, the dielectric structure significantly reduces the dimensions of the cavity but

  finally the weight of the cavity changes little.

  A solid dielectric material whose relative dielectric constant is much greater than one is preferably chosen. A dielectric material may be, for example, a ceramic such as alumina, beryllium oxide, aluminum nitride or a material such as barium titanate whose dielectric constant is about 400 When the value of the dielectric constant of the dielectric material is high, it becomes even possible to remove the conductive envelope limiting the cavity Si further losses microwaves of the dielectric material are weak, the presence or absence of metal boundary dielectric material does not significantly change the energy level

present in the cavity.

  FIG. 2 represents a cavity formed of a dielectric structure 20 but without a conducting envelope.

  crossed by an electron beam directed along an axis XX '.

  The cavity shown is also an intermediate cavity The dielectric structure 20 comprises a block of dielectric material, in the form of a tube coaxial with the axis XX ', whose two ends are closed by a dielectric wall 21 substantially transverse to the axis XX' Each wall is pierced with an orifice 22 allowing the electron beam to pass. The electron beam is not shown. The orifices 22 are aligned before entering and leaving the cavity.

  electron beam is contained in a slip tube 23.

  The inside of the sliding tubes 23 and of the cavity is subjected to vacuum. It is supposed that the portions of sliding tubes outside the cavity and around the cavity contribute to delimit a vacuum chamber. In this configuration, the cavity and the slip tubes must be sealingly connected, to ensure the continuity and sealing of the vacuum chamber At least one zone of the dielectric structure 20 is sealingly connected to a sliding tube 23 The sliding tubes 23 are metal,

for example copper.

  To achieve the sealed connection between the dielectric structure 20 and the sliding tubes 23, it is possible to use an active metal. This active metal reduces the oxides of the dielectric material and carries out a chemical bonding.

  intimately on the dielectric material.

  Without limitation, the active metal may be titanium, zirconium, manganese or an alloy of at least two of these metals These metals provide continuity of

connection compatible with vacuum.

  In some embodiments, the sliding tube 23 can be brazed to the dielectric structure 20 with solder at

active metal.

  In other embodiments, the active metal is deposited on the dielectric structure. This deposition may be in the vapor phase or from a suspension containing the active metal. The sliding tube 23 can be attached by soldering or any other method. on the active metal It may be necessary to deposit on the active metal one or more superposed layers of an auxiliary metal such as copper or nickel. Preferably, the outer layer of auxiliary metal is deposited by electrolysis. several layers, the intermediate layer or layers can be deposited in the vapor phase The sliding tube is soldered on the outer layer of auxiliary metal The brazing is facilitated The tube can also

  to be fixed by any other known means.

  The dielectric structure 20 comprises at least one part which is in direct contact with the electron beam and which is

free of metallization.

  The presence of the dielectric structure reduces the size of the cavity By removing the envelope

  metallic one has considerably reduced its weight.

  FIG. 3 represents, in longitudinal section, a

  realization of a klystron according to the invention.

  This klystron has an electron gun 31 which produces

  a linear electron beam 32 directed along an axis XX '.

  The electron beam 32 is emitted towards a collector 33.

  Between the barrel 31 and the manifold 33 follow one another cavities 34,35,36 interconnected by sliding tubes 37 The electron beam 32 passes successively through the cavities 34,35,36 and the sliding tubes 37 In the figure 3, three cavities are shown; an inlet cavity 34 which is closest to the barrel 31, an outlet cavity 36 which is the closest to the collector 33 and an intermediate cavity 35 disposed between the inlet cavity 34 and the outlet cavity 36. , around the cavities 34,35,36, the portions of sliding tubes 37 located between the cavities and the collector 33 are connected together in a sealed manner and delimit a vacuum chamber 30 The cavities 34, 35, 36 each comprise a The reinforcements 39 are made of metal The dielectric material has a relative dielectric constant greater than

  one and has microwave losses as low as possible.

  The cavities are free of conductive casing.

  The dielectric structure 38 is a hollow block in order to let the electron beam 32 pass through. The block, in the example described, has the shape of a tube coaxial with the axis XX '.

  having both ends open.

  The dielectric structure 38 and the metal plates 39 make the periphery of the cavities To ensure the tightness and continuity of the vacuum enclosure, at least one zone of the dielectric structure 38 is sealingly connected to an armature 39 can be used an active metal as described previously This active metal is intimately fixed on the dielectric material. In FIG. 3, each metal armature 39 is sealed to one side on a base of one of the tubes of dielectric material. These armatures 39 are pierced with an orifice 40 so as to allow the beam to pass through. electrons 32. The other side of the frames 39 is fixed, tightly, either on one of the sliding tubes 37, or on the manifold 33, or on the barrel 31 This depends both on the position of the armature on the cavity and the position of the cavity in the tube The shapes of the reinforcements 39 are adjusted to give the cavities the desired resonant frequencies as well as to ensure a sufficient electric field level at the level of the electron beam 32 and the weight of the klystron were significantly reduced compared to conventional klystrons. A microwave wave to be amplified is introduced into the input cavity 34 via a transmission line 41 The transmission line 41 shown is a coaxial line This is only an example This coaxial line crosses in a sealed manner one of the armatures 37 of the cavity

34.

  The microwave wave is extracted from the output cavity 36. This cavity is connected to a transmission line. In FIG. 3, for the sake of clarity, it is not shown.

the transmission line at the exit.

  The dimensions of the zone of the dielectric structure connected to the conductive element can vary in large proportions. In FIG. 2, this zone is of little importance. It could be envisaged in FIG. 3 that the external lateral surfaces of the dielectric tubes are also

  connected to a metal element.

  Instead of being formed of a single block of dielectric material, the dielectric structure may comprise a plurality of blocks side by side This embodiment is shown in Figure 4 is a cross section of a cylindrical cavity The cavity is crossed by an electron beam 40 It is contained in a sliding tube 41 before entering the cavity The dielectric structure comprises four blocks 42 of cylinder sector dielectric which are side by side so as to form a tube It can be envisaged that the tube has its two bases each closed by

  an armature as previously described in FIG.

  These frames are not visible in FIG. 4 The periphery of the cavity contributes to defining a vacuum enclosure. To seal the cavity, the blocks 42 can be sealed in a crown

  metal 43, itself connected tightly to the frames.

  The frames can be connected tightly to the rest of

the enclosure.

  FIG. 5 represents, in longitudinal section, another variant of a cavity of a microwave tube according to the invention. This cavity 50 is contained inside a cylindrical vacuum chamber 51 made of metal. the chamber 51 has a high vacuum The outside and inside of the cavity are bathed by the vacuum The cavity shown is an intermediate cavity It comprises two adjacent sliding tubes 52 It is crossed by an electron beam directed according to a axis XX 'The beam is not shown The cavity comprises a dielectric structure 53 monobloc, tube-shaped coaxial with the axis XX' The dielectric block 53 is mechanically fixed to the vacuum chamber 51 and the sliding tubes 52 There is no sealing constraint to respect in this configuration We won

  on the volume and also on the weight of the microwave tube.

  FIGS. Ga to Ge represent, in longitudinal section, the various steps of a method of producing a cavity of a microwave tube according to the invention. This method is particularly applicable in the case where the dielectric structure comprises a recess which is important The dielectric structure is connected in a sealed manner to at least one conductive element Here one will partially cover the dielectric structure of metal and at the same time form reinforcements The process makes it possible to carry out the reinforcements directly without having to use external elements reported it on the dielectric material The periphery of the cavity obtained

  helps delimit the vacuum chamber of a klystron.

  Starting from a block 60 of a dielectric material having a recess 62 This material may be ceramic Here the block 60 has the shape of a ring, of radial square or rectangular section with two chamfered interior angles.

than a non-limiting example.

  The first step consists in coating the block 60 in a curable and machinable resin 61. The cavity 62 is filled completely with the block 60.

  Methylmethacrylate This step is shown in Figure 6a.

  After solidification of the resin 61, the second step consists in machining the latter and in exposing at least one zone of the dielectric structure. This step is shown in FIG. 6b. In the resin 61, two frustoconical truncated cavities 63 are made. at the central recess 62 and the dielectric is exposed on the two bases and on the outer lateral surface of the ring. The shape given to the resin in the central recess is a function of that it is desired to give the conductive element which will be integral with the dielectric structure This is metal reinforcements The volume of resin 61 remaining in the central recess 62 corresponds to the interior volume of the cavity which will be subjected to empty. The third step, represented in FIG. Gc, consists of depositing on the dielectric-resin assembly, metal to materialize the reinforcements. This step can be done in several stages. It can first be deposited, for example, in the vapor phase. thin layer 64 of an active metal can be

  use as active metal a previously mentioned metal.

  This thin layer 64 may then be covered with one or more thicker layers, a complementary metal such as copper or nickel. In FIGS.

  a layer 65 of complementary metal.

  The thickness of the layer 64 of active metal is typically of the order of a few tens of nanometers. The thickness of the outer layer 65 of complementary metal is typically between 0.5 and several millimeters. If there is one or more other layers of complementary metal, their thicknesses are of the order of a few micrometers. Preferably, the layer 64 of active metal can be

deposited in the vapor phase.

  The outer layer 65 of complementary metal is preferably deposited electrolytically. The other layers may be deposited in the vapor phase or electrolytically. The next step is to drill an orifice 66, in each armature so that the cavity can be traversed by an electron beam The orifices are placed vis-à-vis at the recess of the dielectric structure . The last step is to remove the resin inside the cavity This elimination can be done by heating or chemical dissolution Figure 6 e represents the cavity at the end of the last step It can then be connected sealed to two slip tubes or to a

collector or to a gun.

  The present invention is not limited to the examples described. The microwave tube according to the invention may be a multibeam klystron, a klystrode or a traveling wave tube. The embodiments described are only examples. The dielectric material will be chosen for its relative dielectric constant. greater than one, its low dielectric losses, its affordable cost In addition it will preferably be easy to solder

and / or metallize.

Claims (14)

  1 microwave tube with at least one electron beam (32) passing through at least one resonant cavity (34) forming an integral part of the tube, characterized in that the cavity comprises a structure (38) of solid dielectric material of relative dielectric constant greater than one. 2 microwave tube according to claim 1, characterized in that the dielectric structure (38) comprises a   recess for passing the electron beam (32).   Microwave tube according to one of claims 1   or 2, characterized in that the dielectric structure (38) comprises at least one part which is in direct contact with the   electron beam (32) and which is free of metallization.   4 microwave tube according to one of claims 1   at 3 characterized in that the periphery of the cavity is formed of a conductive envelope (3) surrounding the structure dielectric (4).   Microwave tube according to one of claims 1   at 3, characterized in that the periphery of the cavity is formed   by at least a part of the dielectric structure (20).   Microwave tube according to Claim 5, characterized in that the dielectric material has losses.   dielectrics as small as possible.   7 microwave tube according to one of claims 1 to G, characterized in that at least one zone of the dielectric structure (38) is integral with a conductive element (39), this element being either an external element or a element materialized by a conductive deposit on at least the area of the dielectric structure (38).   Microwave tube according to claim 7, characterized in that the connection between the dielectric structure (38) and the conductive element (39) is sealed. 9 microwave tube according to claim 8 characterized in that an active metal contributes to ensure the tight connection by being chemically fixed to the material dielectric.   Microwave tube according to Claim 9, characterized in that the active metal is either titanium, zirconium or manganese, or an alloy of at least two previous metals.   Microwave tube according to one of claims 9   or 10, characterized in that the active metal is included in a solder, the external conductive element being brazed to the structure dielectric.   Microwave tube according to one of claims 9   or 10, characterized in that the area of the dielectric structure is at least partially covered with the active metal and that the outer conductive element is attached to the active metal directly or via one or   several layers of an auxiliary metal.   Microwave tube according to claim 12, characterized in that the auxiliary metal is copper or nickel.   Microwave tube according to one of claims 9   at 10, characterized in that the element materialized by the conductive deposit comprises active metal (64) covered with a complementary metal (65), the active metal (64) being in contact with the dielectric material.   Microwave tube according to Claim 14, characterized in that the complementary metal is copper or nickel.   Microwave tube according to one of the claims -1   15, characterized in that the dielectric structure (38) is piece.   Microwave tube according to one of claims 1   at 15, characterized in that the dielectric structure is   consisting of several blocks (42).   18 Process for producing a cavity of a microwave tube according to claim 7, characterized in that it comprises at least the following steps: coating a dielectric structure comprising a recess, with a hardenable and machinable resin by filling the recess; machining the resin so as to expose a portion of the dielectric structure; depositing metal on the remaining resin and the dielectric structure to materialize the conductive element; drilling two orifices, vis-à-vis, in the metal at the hollow portion of the dielectric structure removal of the resin.   19. Production method according to claim 18, characterized in that the metal deposition consists of a deposition of a thin layer of an active metal, then a deposition of   less a thicker layer of a complementary metal.