EP0124396B1 - Electron beam injection device for a microwave generator - Google Patents

Description

The present invention relates to a device for injecting an electron beam for generators of radio waves for microwave frequencies. It relates more particularly to a device for injecting an electron beam propagating along an axis along a cycloidal trajectory under the action of a uniform electric field and subjected to a static magnetic field perpendicular to the axis and to the field electric.

This type of injection device can be used, in particular, in the new cyclotronic resonance masers proposed by the applicant in the new patent application filed on the same day as the present one and having for title "wave generator" microwave radio frequencies ”. In these generators based on a cyclotronic type interaction between an electron beam propagating between an electron gun and a collector and a high frequency electromagnetic field in a resonant structure, generators in which the electron beam travels along a trajectory cycloidal in a transverse magnetic field under the effect of a drift speed created by a uniform electric field, the injection device consists only of an electron gun subjected to a high magnetic field, identical to that prevailing in the structure resonant.

The electron gun used in this generator consists of two facing electrodes, one of which, the anode, is brought to a positive potential and the other, the sole, of which is brought to a negative or zero potential and by a cathode positioned in the plane of the hearth and brought to the same potential as the latter, at least one of the electrodes having a divergent profile such that the distance between electrodes is increasing from the cathode to the outside. However, with this type of electron gun, in order to obtain an electron beam propagating along a cycloidal trajectory with a substantially constant radius of rotation r _L , the voltage to be applied to the anode must be substantially higher than the voltage of power supply giving the energy of the electron beam.

The object of the present invention is to remedy this drawback by proposing a new type of injection device.

It also allows the use of a smaller magnetic field in the barrel than in the resonant structure.

The injection device according to the present invention is a device for injecting an electron beam along a cycloidal path for microwave radio wave generators using an electron beam propagating along an axis under the action of a uniform electric field and subjected to a static magnetic field perpendicular to the axis of propagation and to the electric field, as well as to the electromagnetic field of at least one resonant structure arranged along the axis. This device is characterized in that it includes an electron gun placed in an area where the magnetic field has an intensity lower than that of the field necessary to obtain a cyclotronic type interaction and electrodes positioned between the gun and the area of interaction in an area where the magnetic field has an increasing intensity in the direction of propagation of the beam to create in this area, a static electric field having two components in the plane perpendicular to the magnetic field, namely an Ex component in the direction of l the axis and a component Ey perpendicular to the component Ex and to the magnetic field so as to compensate for the movement perpendicular to the axis due to the increase in the magnetic field, in said zone.

Other characteristics and advantages of the present invention will appear on reading the description of two embodiments of radio wave generators for microwaves provided with an injection device according to the present invention.

This description is made with reference to

• - la figure 1 a est une vue en coupe schématique, dans un plan perpendiculaire au champ magnétique, d'un générateur d'ondes radioélectriques pour hyperfréquences comportant un dispositif d'injection conforme à la présente invention et la figure 1 b est une courbe représentant la variation du champ magnétique appliqué, selon l'axe de propagation;
• - la figure 2a est une vue semblable à celle de figure 1a d'un autre mode de réalisation du générateur et la figure 2b est une courbe semblable à celle de figure 1 b.

attached drawings in which:

• - Figure 1a is a schematic sectional view, in a plane perpendicular to the magnetic field, of a generator of radio waves for microwaves comprising an injection device according to the present invention and Figure 1b is a curve representing the variation of the applied magnetic field, along the propagation axis;
• - Figure 2a is a view similar to that of Figure 1a of another embodiment of the generator and Figure 2b is a curve similar to that of Figure 1b.

In the drawings, the same elements have the same references.

The generator represented in FIG. 1a essentially comprises three parts, namely an injection device 1, a resonant structure 2 and a collector 3, the assembly being placed inside a vacuum enclosure 4 brought to a potential no. According to the present invention, the injection device 1 is constituted by an electron gun 5 producing an electron beam in the direction x followed by means 6 to create an electric field E without component in the direction z but having two components E _x and Ey in the plane of the figure. The injection device 1 is placed in a static magnetic field perpendicular to the plane of the figure, that is to say in the z direction. The magnetic field applied in the present invention is such that the electron gun 5 is subjected to a magnetic field 8 ₁ of low value and the means 6 to a magnetic field B ₂ progressively increasing from the value 8 ₁ to a value B ₃ representing the magnetic field prevailing at the level of the resonant structure 2, as represented respectively by the parts 1, II, III in FIG. 1 b. More precisely, the electron gun 5 consists of two planar electrodes 7, 8 facing each other, one of which 7, called the anode, is brought to a positive potential V and the other, called sole, is formed of two parts 8, 8 ′ and is brought to a negative potential V _c and of a cathode 9 heated by a filament 10 and brought to the same potential V _c as the sole 8. This type of electron gun provides in known manner a beam following, in the direction x, a cycloidal path. In the embodiment shown, the means 6 are produced by four electrodes 11, 12, 13, 14 brought to continuous potentials such as, for example,

In this part, as explained in more detail below, the electrons being in an electric field having two components Ex and Ey and being subjected to a uniformly increasing static magnetic field of direction x, are brought to follow a cycloidal trajectory whose the radius of rotation gradually decreases as shown in Figure 1a.

avec n un entier et À la longueur d'onde de fonctionnement.The electron beam is then injected into the resonant structure 2 in which it interacts with a high frequency electromagnetic field. At the level of the resonant structure 2, the enclosure 4 has the shape of a cylinder of axis z inside which the static magnetic field B ₃ is almost uniform. The resonant structure 2 is constituted, in a known manner, by two spherical mirrors 15, 16 facing each other and positioned so that the distance H verifies the relationship

with n an integer and At the operating wavelength.

D'autre part, les deux miroirs 15 et 16 sont portés respectivement à la masse et à un potentiel négatif de manière à créer entre eux un champ électrique continu Ec de direction y qui assure la dérive du faisceau d'électrons suivant la direction x.In this case, the two mirrors 15, 16 constitute a "quasi-optical" resonator. One of the mirrors, namely the mirror 15, is provided with an orifice 17 connected to a waveguide 18. This waveguide 18 is used to send out, the electromagnetic energy given off by the electron beam to the electromagnetic beam which appears as a standing wave in the y direction with a high frequency electric field polarized in the x direction. To ensure the propagation of the electron beam in the direction x in the cylindrical part of the envelope 4, the two mirrors 15, 16 are preceded and followed by grids 19, 20 which are non-reflective at the operating frequency of the resonator and separated from a distance h such that

On the other hand, the two mirrors 15 and 16 are brought respectively to ground and to a negative potential so as to create between them a continuous electric field Ec of direction y which ensures the drift of the electron beam in the direction x.

The cylindrical part of the envelope 4 is preferably covered with absorbent substances 21 at the operating frequency to avoid parasitic resonances. These substances are, for example, in "carberlox" (brand).

The electrons having given up energy are then evacuated towards a collector 3 constituted by a part of the envelope 4 having a section in section in the plane x y in the shape of U.

Figure 2a shows an alternative embodiment of the generator of Figure la which then constitutes an amplifier. In this embodiment, only the resonant structure has been modified, the other parts remaining identical.

de manière à guider dans la direction x une onde progressive haute fréquence ayant au moins une composante de champ électrique haute fréquence dans le plan x y. L'onde progressive est injectée dans la structure par l'intermédiaire du guide d'one d'entrée 24 et elle est évacuée, après avoir reçu l'énergie cédée par le faisceau d'électrons, par l'intermédiaire du guide d'onde de sortie 25. D'autre part, pour obtenir la dérive du faisceau d'électrons suivant la direction x, les deux plaques sont polarisées de manière à créer entre elles un champ électrique continu de direction y.The new structure is formed by two flat parallel plates 22, 23 spaced from each other by a distance H 'such that

so as to guide in the x direction a high frequency traveling wave having at least one high frequency electric field component in the x y plane. The traveling wave is injected into the structure via the input one guide 24 and it is discharged, after having received the energy given up by the electron beam, via the wave guide. output 25. On the other hand, to obtain the drift of the electron beam in the direction x, the two plates are polarized so as to create between them a continuous electric field of direction y.

It will also be mentioned that all the elements shown in section in the x y plane are very elongated in the z direction. This characteristic of generators of this type constitutes an advantage over axial structures of the gyrotron type. Indeed, the dimension of the various elements in the z direction can correspond to a large number of wavelengths, which makes it possible to obtain, for a given cathode voltage, a very large current with a current density and a density of limited collector power.

As regards FIG. 2b, it is identical to FIG. 1b and gives the variation of the static magnetic field B in the direction x. The magnetic field is created in known manner using superconductive coils, for example.

We will now explain the operation of the two embodiments of Figures 1a and 2a, in particular the operation of the injection device object of the present invention.

The operation of the injection device is based on known principles which we will briefly recall below.

r_L ² étant le rayon de gyration du faisceau.Thus when an electron is subjected to a slowly variable axial magnetic field, we show that the trajectory is wound on force tubes and that we are in a regime called "adiabatic" for which

r _L ² being the beam gyration radius.

We also show that there is an analogous property in the case of a transverse injection in a non-uniform magnetic field.

Toutefois, on démontre que pour un système de grandes dimensions devant le rayon d'orbite des électrons, l'équation (1) reste valable.Thus, in the xy plane, the component B _z is a function of x and y, in principle only of R =

However, we show that for a large system in front of the electron orbit radius, equation (1) remains valid.

On the other hand, in the xy plane, the center of the electron orbit, with coordinates X (t), Y (t), moves according to the equations.

In the injection device 1 of the present invention, the electron gun 5 placed in a region of weak magnetic field B ₁ produces a beam of electrons progressing towards the central region of said field, where it is maximum, by moving perpendicular to its direction. The progression along a cycloidal trajectory is ensured by the electrodes placed in the vicinity of its trajectory and brought to appropriate potentials, which creates between the electrodes a uniform continuous electric field giving the electrons a speed of drift.

avec

pour que le faisceau d'électrons se propage dans la direction x.The electron beam is then subjected in the region of the means 6 to a magnetic field of direction B _z progressively increasing. In addition, the different potentials of the electrodes 11, 12, 13, 14 have been chosen so as to create an electric field having components in the directions x and y and to satisfy the equations below.

with

so that the electron beam propagates in the x direction.

In this case, the electron beam will be brought into the region of the increasing magnetic field to follow a cycloidal trajectory whose radius decreases progressively due to equation (1) in the direction x with a constant drift speed if the component Ey believes as B _z whose variation along x is given in Figures 1b and 2b. Indeed, the condition given by equation (5) avoids transverse drift and allows electrons to enter the increasing magnetic field which normally tends to repel electrons endowed with a speed of rotation towards the regions where B is more small, namely towards the barrel.

• avec e = charge de l'électron
• m = masse de l'électron

pour pouvoir obtenir l'interaction souhaitée dans la structure résonnante 2.With the above injection device, there is therefore obtained at the input of the resonant structure, an electron beam moving along a helical trajectory in the direction x in a strong transverse magnetic field so that the speed of rotation of the electrons be equal to

• with e = electron charge
• m = mass of the electron

to be able to obtain the desired interaction in the resonant structure 2.

• - possibilité de produire un faisceau d'électrons de grande section selon z donnant un courant et une puissance plus élevés;
• - absence d'électrons réfléchis vers le canon;
• - vitesse de dérive des électrons réglée uniquement par la tension appliquée sur les différentes plaques.

With this injection device, the following advantages are obtained:

• - possibility of producing a beam of electrons with a large section along z giving a higher current and power;
• - absence of electrons reflected towards the barrel;
• - electron drift speed set only by the voltage applied to the different plates.

Claims (3)

1. Device for injecting into a cyclotronic interaction zone an electron ray beam which is propagated along a cycloid path in the direction of an axis (x) under the action of a uniform electrical field and a static magnetic field (B) which extends perpendicularly to the propagation axis and to the electrical field, characterized by an electron gun (5) located in a zone (I) in which the magnetic field has an intensity (B₁) which is smaller than the intensity (B₃) of the field necessary to obtain a cyclotronic interaction, and electrodes (11-14) arranged between the electron gun and the interaction zone in a zone (II) in which the magnetic field has an intensity (B₂) increasing in the propagation direction of the electron ray beam so that in said zone a static electrical field is created having two components (E_x, Ey) in the plane perpendicular to the magnetic field, i.e. a component E_x in the direction of the axis and a component Ey perpendicular to the component E_x and to the magnetic field, so as to compensate the movement perpendicular to the axis due to the increase in the magnetic field in the zone (II).

2. Device according to claim 1, characterized in that four electrodes (11-14) are provided opposite each other in pairs and that between said electrodes different increase in potentials (V₁₁ < V₁₂ < V₁₃ < V₁₄) are applied such that an electrical field is created which has components in the directions x and y and is so selected that the following equations are fulfilled:

with

3. Device according to claim 2, characterized in that the variation of the component E_y is selected such that in the zone with the increasing mag- neticfield:

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