EP1328004A2 - Electron tube with a cooled tubular sheath - Google Patents

Abstract

The electron tube has a tubular sheath (10) in which the electron beam travels. An outer guard section (28) provides sheath mechanical maintenance. There is a resin (36) between the sheath and the guard providing thermal transfer.

Description

The invention relates to electronic amplifier tubes operating in microwave. It applies more particularly to traveling wave tubes (TOP) also called TWT (from English Traveling Wave Tube), and it is therefore about such a tube that it will be described. Such tubes are used, for example, for the transmission of telecommunication between earth and satellites. They also serve as power transmitters in radars.

We briefly recall that a TOP is a vacuum tube using the principle of the interaction between an electron beam and a wave electromagnetic microwave, to transmit to the wave microwave part of the energy contained in the beam of electrons, so as to obtain at the outlet of the tube a microwave wave energy greater than that of the wave injected at the inlet of the tube.

Figure 1 recalls the general principle of a TOP. The TOP depicted is a propeller TOP, but other types of TOP such as TOP with coupled cavities, TOP with guides folded in meanders, etc., are equally concerned with the invention.

TOPs have an elongated tubular sheath 10 in which vacuum is created, with at one end an electron gun 11 emitting an electron beam 12 and, at a second end, a collector 14; the collector collects the electrons that have given up part of their initial energy to the electromagnetic wave that we want to amplify. The electron beam 12 is substantially cylindrical over most of the length of the tube between the barrel 11 and the manifold 14 along an axis 15. This cylindrical beam shape is obtained on the one hand, thanks to the shape a cathode 16 of the electron gun 11 (convergent cathode in the form of bowl), and, on the other hand, by means of magnetic focusing provided over the entire length of the sheath 10 between the outlet of the barrel electron 11 and the collector input 14. In the electron gun 11, it's cathode 16 which emits the electron beam 12. These means of focusing are permanent annular magnets 18 axially magnetized and alternating magnetization from one magnet to the next; these magnets surround the sheath 10 and are separated from each other by pole pieces 20 to high magnetic permeability.

In the case of a helical TOP, the electron beam 12 changes to inside a helical conductive structure 22 along which flows the microwave electromagnetic wave to be amplified; amplification of microwave energy occurs by interaction between this wave and the electron beam 12 passing through the center thereof. The propeller is used to slow down the microwave, so that its speed, along axis 15 of the electron beam 12, ie substantially equal to that of the beam of electrons 12.

A signal to be amplified with power Pe is injected at one end of the helical conductive structure 22 through a plug and a window 24 inside the sheath 10. An amplified power signal Ps is extracted at another end of the helical conductive structure 22 at through a plug and a window 26.

Figures 2 and 3 show in more detail how the scabbard 10 is thus realized connecting the sheath 10 with a casing 28 enclosing the whole sleeve 10.

The sheath 10 proper is formed of the pole pieces 20 and spacers 30 separating the pole pieces 20. The spacers 30 are, for example, made from an alloy based on copper and nickel nonmagnetic. The outside diameter of the spacers 30 is smaller than that of the pole pieces 20, thus, the magnets 18 whose internal diameter is substantially equal to the outside diameter of the spacers 30 are held between the spacers, for example by means of resin. The thickness of the spacers 30 measured along the axis 15 is substantially equal to the thickness of the magnets 18. The propeller 22 is located inside the sheath 10 and dielectric rods 32 make it possible to support mechanically the propeller inside the sleeve 10. The rods 32 are elongated along axis 15 and are, for example, three in number arranged at 120 ° around the axis 15. This 120 ° arrangement of the sticks 32 is good visible in figure 3.

Fins 34 mechanically hold the sleeve 10 to inside the casing 28. The fins 34 also make it possible to evacuate towards the casing 28 of the heat produced inside the sheath. The fins 34 are made from metal sheets, for example copper alloy. The fins 34 are arranged perpendicular to the axis 15 and they are based on the one hand, at the end of the pole pieces 20 and, on the other hand, on the casing 28.

• maintenir l'étanchéité entre le vide régnant à l'intérieur du fourreau 10 et l'atmosphère extérieure ;
• maintenir et aligner de l'hélice 22 par l'intermédiaire des bâtonnets diélectriques 32 ;
• évacuer la chaleur produite dans le tube électronique vers l'extérieur.

Cette chaleur provient notamment de :

• l'hélice 22 qui chauffe à la fois sous l'effet du bombardement de certains électrons mal focalisés et par effet joule, en raison des courants hyperfréquences qu'elle transporte ;
• du collecteur 14 qui est relié mécaniquement et donc thermiquement au fourreau 10 ;
• du canon à électrons 11 et plus particulièrement d'une cathode et de son filament de chauffage.

In summary, the main functions of the sheath 10 are:

• maintain the seal between the vacuum inside the sheath 10 and the outside atmosphere;
• hold and align the propeller 22 through the dielectric rods 32;
• evacuate the heat produced in the electronic tube to the outside.

This heat comes in particular from:

• the propeller 22 which heats both under the effect of the bombardment of certain poorly focused electrons and by the Joule effect, because of the microwave currents it carries;
• the manifold 14 which is mechanically and therefore thermally connected to the sleeve 10;
• electron gun 11 and more particularly a cathode and its heating filament.

hélice : de 1 à 7 % ;

collecteur : de 78 à 84 % ;

canon à électrons : 15 %.

In an experimental implementation, it was found that the heat emitted by the three elements mentioned above is distributed as follows:

helix: from 1 to 7%;

collector: 78 to 84%;

electron gun: 15%.

Because of this distribution, there are more fins 34 in the vicinity of the manifold 14 than in the vicinity of the barrel electrons.

The production and assembly of the fins 34 are complicated to achieve. In particular, we are required to impose tight tolerances in dimensions of the pole pieces 20 and the fins 34 in order to ensure good mechanical and thermal contact between the pole pieces 20, the fins 34 and the casing 28.

The invention aims to simplify the mechanical maintenance of the sheath 10 relative to the casing 28 while ensuring good transfer thermal between the sleeve 10 and the casing 28.

To this end, the invention relates to an electronic tube comprising an elongated tubular sheath inside which develops a electron beam, a housing ensuring the mechanical maintenance of the sheath, and means for ensuring a thermal transfer from the sleeve to the casing in order to cool the sheath, characterized in that the means for ensuring the heat transfer include a resin filling a free volume located between the sleeve and the housing.

By removing the fins 34 described above, we can expand manufacturing tolerances for pole pieces 20. The use of resin also makes it possible to mechanically hold magnets 18 and, possibly, corrective magnetic shunts that can be attached to the outer walls of the sleeve 10. These shunts have the function of modify the magnetic field created by the magnets 18 inside the scabbard 10.

In addition, the resin increases the rigidity of the mounted electronic tube in its housing 28.

The removal of the fins improves the heat dissipation of the sheath 10 towards the casing 28. More specifically, the fins formed localized thermal bridges through which heat circulated. Replacing the fins by resin, the heat transfer is no longer localized, it is more homogeneous. This avoids possible hot spots between the fins 34.

• la figure 1 représente schématiquement le fonctionnement général d'un tube électronique ;
• la figure 2 représente, en coupe par un plan contenant l'axe du faisceau d'électrons, un tube électronique connu ;
• la figure 3 représente en coupe par un plan perpendiculaire à l'axe du faisceau d'électrons, un tube électronique connu ;
• - la figure 4 représente en coupe par un plan perpendiculaire à l'axe du faisceau d'électrons, un tube électronique selon l'invention ;

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, embodiment illustrated by the attached drawing in which:

• Figure 1 schematically shows the general operation of an electronic tube;
• FIG. 2 represents, in section through a plane containing the axis of the electron beam, a known electronic tube;
• Figure 3 shows in section through a plane perpendicular to the axis of the electron beam, a known electronic tube;
• - Figure 4 shows in section through a plane perpendicular to the axis of the electron beam, an electronic tube according to the invention;

To simplify the rest of the description, the same elements will bear the same references in the different figures.

Figures 1 to 3 have already been described above for introduce the invention.

In the electron tube shown in Figure 4, the fins 34 have been replaced by a resin 36 filling the free volume between the sheath 10 and the casing 28. This resin, once polymerized, ensures that the times the mechanical retention of the sheath 10 relative to the casing 28 as well as the thermal transfer of the heat emitted inside the electronic tube towards the casing 28. A radiator fixed to the casing 28 or similar means, not shown in Figure 4, will, for example, remove this heat by a heat transfer fluid circulating in the radiator. The resin can, for example, be formed by "Stycast 3050" supplied by Emerson and Cuming, resin to which an adequate catalyst is added.

Advantageously, granules 38 made are drowned in the resin. in a material whose thermal resistance is lower than that of resin. These granules improve the heat transfer of the sheath 10 towards the casing 28. One can choose metal granules by aluminum-based example.

Advantageously, the dimensions of the granules 38 are chosen so that a characteristic dimension of these granules 38, by example the diameter, if the granules 38 are substantially spherical, is substantially equal or similar while remaining less than the smallest of dimensions of the free volume left between the sheath 10 and the casing 28. This characteristic is visible on figure 4 on which one distinguishes granules which can slide between the lower part of the sheath 10 and the casing 28. In this zone, the larger the granules 38, the better the heat transfer between the sleeve 10 and the casing 28. In indeed, by increasing the dimensions of the granules 28, the number is reduced of contact zones between the sleeve 10 and the casing 28 passing through the granules. It is through these contact zones that the heat. The fewer these areas, the better the transfer thermal. We realized that by using smaller granules or even of the powder, the thermal conductivity is closer to that of the resin as the material constituting the powder or the granules. Thanks to this largest possible characteristic dimension of the granules 38, we is not obliged to choose a resin among that having a good conductivity thermal. This characteristic frees the choice of resin.

Claims (2)

Electronic tube comprising an elongated tubular sheath (10) inside which an electron beam (12) develops, a casing (28) ensuring the mechanical retention of the sheath (10), and means for ensuring a thermal transfer of the sheath (10) towards the casing (28) in order to cool the sheath (10), characterized in that the means for ensuring the thermal transfer comprise a resin (36) filling a free volume situated between the sheath (10) and the casing (28), in that the means for ensuring the thermal transfer comprise, embedded in the resin, granules (38) made of a material whose thermal resistance is lower than that of the resin and in that a dimension characteristic of granules (38) is substantially equal while remaining less than the smallest of the dimensions of the free volume. Electronic tube according to claim 1, characterized in that the material of the granules (38) comprises aluminum.

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