EP1095390A1

EP1095390A1 - Multibeam electronic tube with magnetic field for correcting beam trajectory

Info

Publication number: EP1095390A1
Application number: EP99929381A
Authority: EP
Inventors: A. Thomson-CSF Propr. Int. Dept. Brevets BEUNAS; G. Thomson-CSF Propr. Int. Dpt.Brevets FAILLON
Original assignee: Thomson Tubes Electroniques
Current assignee: Thales Electron Devices SA
Priority date: 1998-07-03
Filing date: 1999-07-02
Publication date: 2001-05-02
Anticipated expiration: 2019-07-02
Also published as: KR20010085278A; DE69925125D1; KR100593845B1; WO2000002226A1; CN1308769A; EP1095390B1; FR2780809B1; JP2002520772A; JP4405674B2; FR2780809A1; US6486605B1

Abstract

The invention concerns a multibeam electronic tube with several substantially parallel electron beams (1-7), passing through a body (10). Some (2-7) of the beams (1-7) at least define an interbeam volume (22), each beam (2-7) defining the interbeam volume (22) is subjected to a disturbing azimuthal magnetic field (B theta ) induced by all the others. The tube comprises means (M) allowing, in at least one conducting element (23) located in the interbeam volume (22), a counter current (l') to circulate in a direction opposite to that of the current (l) of the beams (1-7), said counter current (l') generating at the beams (2-7) defining the interbeam volume (22), a corrective magnetic field for countering the disturbing magnetic field (B theta ). The invention is applicable to travelling-wave tubes or multibeam klystrons.

Description

MULTI-BEAM ELECTRONIC TUBE WITH MAGNETIC FIELD OF CORRECTION OF BEAM TRAJECTORY

The present invention relates to multi-beam longitudinal interaction electronic tubes such as, for example, klystrons or traveling wave tubes. These tubes generally constructed around an axis have several longitudinal electron beams parallel to this axis. These beams are often produced by a common electron gun, equipped with several cathodes and are collected at the end of the race in one or more collectors. Between the barrel and the collector, they pass through a body which is a microwave structure at the exit of which is extracted microwave energy. This structure can be formed of a succession of resonant cavities and sliding tubes. The electron beams, to keep their long and fine shape, are focused by the magnetic field of a focusing centered on the main axis and which surrounds the microwave structure.

The advantages of multi-beam electronic tubes are as follows: the current produced is higher and / or the high voltage and the length are shorter.

At substantially equal performance, the size of the tube is generally reduced. The power supply and the modulator used are thus simplified and more compact. The interaction efficiency is better due to the generally lower perveance of each of the beams.

For klystrons, the bandwidth is widened due to the fact that the cavities are charged with a higher current.

One of the main drawbacks compared to single-beam tubes is that it is difficult to generate an optimum focusing magnetic field which allows the beams to circulate in the microwave structure without notable interception by the sliding tubes.

In multi-beam klystrons the intercepted current, called body current, is often of the order of 4 to 8% whereas it does not exceed 2 to 3% in conventional single-beam klystrons even when the beam is strongly modulated at high frequency such as this is the case with high yielding klystrons. Too much interception leads not only to a prohibitive heating requiring a complex and expensive cooling system but also to a malfunction of the tube because it can occur expansion, degassing, frequency changes, oscillations, excitations of parasitic modes, reflected electrons, ion bombardments and a disturbed interaction between the beam and the microwave structure.

This interception is due to the increase in space charge forces under the effect of the higher density modulation as one approaches the collector, which leads to an increase in the cross section of the beams which consequently approach the walls of the sliding tubes. It is also partly due to the focusing device which inevitably produces a radial magnetic field in areas where the axial magnetic field varies, that is to say near the barrel and the collector. In addition, the focalizer is never perfect, it produces parasitic defocusing magnetic components.

Another important cause of defocus specific to multibeam tubes is that each beam creates an azimuthal magnetic field which, depending on the configuration of the tube and its operating mode, may disturb the other beams. This azimuthal magnetic field is reflected, at the offset axes, by a centrifugal radial force which deflects them.

We know that it is possible, with particular care for the configuration of the focusing device and its winding, to reduce the defocusing magnetic components. Using intermediate pole pieces in the body of the tube can also help reduce the radial magnetic field.

Improvements can also be made at the level of the barrel so that the magnetic flux lines substantially follow the trajectory of the electrons as soon as they are emitted. One can also act on the inclination of the sliding tubes so that they follow the general movement of the beams.

On the other hand, all of these solutions do not combat the azimuthal magnetic field induced, at the level of an offset beam, by all the others. The present invention therefore aims to reduce or even cancel this induced azimuthal magnetic field without degrading the gain or yield characteristics.

To achieve this, the present invention provides a multibeam electronic tube comprising several substantially parallel electron beams passing through a body. Among these beams, at least some, delimit an inter-beam volume. Each of the beams delimiting the inter-beam volume is subjected to a disturbing azimuthal magnetic field induced by all the others. The tube comprises, at the level of the body, means allowing, in at least one conductive element located in the inter-beam volume, a circulation of a counter-current in a direction opposite to that of the current of the beams, this counter-current generating at level of the beams delimiting the inter-beam volume, a magnetic field of correction which opposes the disturbing magnetic field. The conductive element can be integrated into the body or, on the contrary, electrically isolated from the body.

The means allowing the circulation of the counter-current in the conductive element integrated into the body may include a ground connection, near the entry of the body, so that the counter-current comes from the current of the beams which closes by this ground, the collector being at an intermediate potential between that of cathodes producing the beams and ground.

Preferably, this ground connection will be connected to a high voltage power supply which delivers the potential to the cathodes. In this type of tubes, whether klystrons or traveling wave tubes, the body has a succession of cavities and at the input and output of the cavities, the beams are contained in sliding tubes. When the sliding tubes are hollowed out within the same conductive block, this conductive block serves as a conductive element in which the counter-current flows.

To force circulation in the inter-beam volume, the conductive block may have a resistance, in a central part including the inter-beam volume, smaller than that possessed by a peripheral part of the block, situated around the central part. To obtain these different resistances, the central part can be made of a first material and the peripheral part of a second material, the second material having the greatest resistance.

We can also recommend cutting baffles around the periphery of a block to increase resistance at this location.

When two successive cavities have a common wall integral with a conductive block, a resistive insert can be included in the conductive block and the common wall, this resistive insert forces the counter current to circulate in the conductive block in a loop around the insert and in the common wall on either side of the insert in opposite directions.

The means allowing the circulation of the counter-current may comprise a first connection means near the inlet of the body and a second connection means near the outlet of the body, these connection means being intended to be connected to a power supply. having to deliver the counter current.

In the configuration where the conductive element is integrated into the body, the latter and / or the collector must be electrically isolated from various members with which they are usually in electrical contact.

In configurations where the sliding tubes are not hollowed out within the same conductive block, the inter-beam volume is hollow at the level of the sliding tubes and it is possible to accommodate the conducting element therein substantially parallel to the sliding tubes and without electrical contact with the body.

This conductive element may comprise a rigid section at the inlet and at the outlet of a cavity and a flexible connection which spans a cavity by connecting two rigid sections situated on either side of the cavity.

Other characteristics and advantages of the invention will appear on reading the description of exemplary embodiments of multibeam tubes in accordance with the invention, this description being made in conjunction with the appended figures which represent:

FIG. 1 a, in cross section, the body of a multibeam tube according to the invention,

- Figure 1b, the magnetic field induced by an electron beam, FIG. 2, a longitudinal section of a multibeam klystron according to the invention,

FIGS. 3a, 3b, partial longitudinal and transverse sections of the body of a klystron according to the invention with a conductive element integrated into the body,

FIGS. 4a, 4b, partial longitudinal and transverse sections of another variant of another of a klystron according to the invention, with a conductive element integrated into the body,

FIGS. 5a, 5b, 5c of partial longitudinal and transverse sections of the klystron body according to the invention with conductive elements isolated from the body,

- Figure 6, a longitudinal section of a multi-beam traveling wave tube according to the invention.

Figure 1a shows in cross section, the electron beams 1-7 of a multibeam tube. These substantially parallel beams are each contained in a sliding tube 13 at the level of the section. These sliding tubes 13 are hollowed out in the same conductive block 15 which forms part of the body 10 of the tube. One of these beams 1 is centered on a central axis, perpendicular to the sheet, passing at point 0. The other beams 2 to 7, arranged on a circle centered at 0, are offset. They are conventionally substantially equidistant from each other.

We refer to Figure 1b. A beam i of current li creates at a point N distant from d of the axis of the beam, in a plane perpendicular to beam i, a magnetic field bei substantially equal to: bei = Mo ϋ / 2 π d

with μ ₀ magnetic permeability of the medium.

At least one offset beam 7 of the tube of FIG. 1a is therefore subjected on the one hand to its own field bg7 which generates a non-deviant centripetal focusing force and to the resultant BΘ of the fields bel, bθ2, bθ3, bθ4, bθ5, be6 induced by all the other beams 1 to 6.

B, b _û 1 + bn 2 + b ₀ 3 + bn 4 + α 5 + bo ⁶ This resulting BQ field generates a centrifugal radial force which deflects the beam 7 opposite the central axis. Regarding the central beam 1, if it exists, for reasons of symmetry it is not deflected.

Reference is made to FIG. 2 which shows a multibeam tube according to the invention. This tube is a multibeam klystron. It is built around an axis XX '.

It is assumed that the tube has several beams numbered from 1 to 7 arranged like those of FIG. 1a to which we also refer. Among these seven beams, six referenced from 2 to 7 delimit an inter-beam volume 22. In the example, they are placed on a circle of radius a and the inter-beam volume 22 is cylindrical. The last beam 1 is centered on the axis XX ', the others are offset. The beams 1 to 7 are produced by a barrel 17, they then enter a body 10 which they pass through and at its outlet S are collected in a collector 11. The barrel 17 has seven cathodes 18 which produce the beams 1 to 7 when '' they are brought to an appropriate VK potential delivered by a high voltage A1 supply. It also includes an anode 16 which accelerates the electrons towards the entry E of the body 10. It is brought to a less negative potential than that VK of the cathodes. In Figure 2, only three cathodes are visible.

The body 10 is formed by alternating cavities 20 and sliding tubes 13. The cavities 20 have side walls 27. The beams 1 to 7 are contained in the sliding tubes 13 before entering the first cavity 20, leaving the last cavity 20 and more generally between each cavity 20. The body 10 is placed in a tubular focusing device 12. The body 10 begins after an input pole piece 19.1 and ends before an output pole piece 19.2.

Each of the beams 2 to 7 delimiting the inter-beam volume 22 is subjected to a defocusing azimuthal magnetic field which deflects it. This azimuthal magnetic field is induced by all the others as we have just described in FIGS. 1. In an attempt to attenuate, or even eliminate the effects of this induced azimuthal magnetic field, the multibeam electronic tube according to the invention comprises, at level of the body 10, means M allowing, in at least one conductive element 23 located in the interbeam volume 22, a circulation of a counter-current I 'in the opposite direction from the current I carried by all the beams. This counter-current I 'generates at the level of the disturbed beams 2 to 7 an azimuthal magnetic field of correction B'Θ which tends to oppose the induced azimuthal magnetic field BQ.

In the example of FIG. 2, the conductive element 23 is integrated into the body 10 of the tube and the means M allowing the circulation of the counter current I 'comprise a ground connection P, near the entry E of the body 10, so that the counter current I 'comes from the current I carried by all the beams which closes with this mass. The collector 11 is naturally at a potential VQ intermediate between that V of the cathodes 18 and the ground.

At the inlet and outlet of the cavities 20 are placed conductive blocks 15 within which are hollowed out as many sliding tubes 13 as beams 1-7 as described in FIG. 1a.

These conductive blocks 15 form the conductive element 23 inside which the counter-current I ′ circulates. In FIG. 1a, the conducting block 15 shown is a cylinder of radius a + g + t with g radius of a sliding tube and t thickness of material located between the sliding tubes 13 and the edge of the block 15. This thickness t contributes to sealing inside the body 10. In the configuration shown in FIG. 2, the counter-current I 'circulates throughout the body 10 in the opposite direction to the current I of the beams 1-7 but only the part which circulates inside the inter-beam space 22 provides a correction. The part circulating outside the inter-beam volume 22, in particular in the side walls 27 of the cavities, does not participate in the correction but does not induce disturbance.

In the example in FIG. 2, the ground connection P is located at the level of the anode 16 of the barrel 17. It can be envisaged to bring it to the level of the input pole piece 19.1. This input pole piece 19.1 prevents the cathodes 18 from being disturbed by the magnetic field of the focusing device 12.

In this configuration, the potential VK of the cathodes 18 is delivered by the supply A1 which is connected between the cathodes 18 and the ground connection P.

Conventionally, in this type of tube, a ground connection was made at the collector 11 or if it was electrically isolated from the body 10 at the output pole 19.2 which prevents the electrons collected in the collector 11 from being disturbed by the magnetic field of the focusing device 12.

Circulating the counter current I 'in a conductive element 23 integrated into the body 10 of the tube now requires electrical insulation of this body 10 and / or of the collector 11 with respect to other organs of the tube with which they were in electrical contact in the conventional configurations of the prior art. These include the focusing device 12 which will be electrically isolated from the body 10 using dielectric material 24.1. In the example, the insulation is done by means of the pole pieces 19.1, 19.2 of entry and exit. These pole pieces 19.1, 19.2 are in conventional tubes in contact with the body at its inlet E and at its outlet S. For example, a sheet 24.1 of teflon inserted between the focusing device 12 and the pole pieces 19.1, 19.2 will be used. They are also transmission guides, located at the level of the extreme cavities. An input waveguide 25.1 is connected to the first cavity 20 and allows a signal to be amplified to be injected there. This waveguide 25 is electrically isolated from the body 10 using an insulating flange 24.2. The last cavity 20 communicates with an output waveguide 25.2, intended for the transmission of the microwave energy produced by the tube to a user member (not shown). This waveguide 25.2 is electrically isolated from the body 10 using an insulating flange 24.2.

Generally, a cooling device 26 is provided around the manifold 11 and even possibly of the body 10. This cooling device 26 will be electrically isolated from the manifold 11 and if necessary from the body 10. This insulation can be obtained by making the cooling device with dielectric materials, for example at least one conduit 28 made of plastic material in which a resistant cooling fluid circulates. As coolant deionized water can be used.

The calculations show that the counter-current I 'giving an exact compensation is such that I' = ^Λ AI, I corresponding to the total current of all the beams 1 to 7 of the tube.

The azimuthal magnetic field induced on one of the beams delimiting the inter-beam space 22, by the other beams is worth: 051

B _n = μn - ¹ - if the beams delimiting the inter-beam space are θ ^u 2πa arranged on a circle of radius a.

If the total current I of the beams 1 to 7 is circulated in the conductive block 15, having a section of radius a + g + t, the counter-current I 'is 2

and this counter current I 'allows an exact compensation if the

2 values of a, g and t are such that the value is 0.5. Quantities such as a = 21.8 mm, g = 6 mm and t = 3 mm allow the optimum result to be obtained. The dimensions a, g, t are illustrated in FIG. 1a but are not shown to scale.

One way of obtaining an optimum counter current I ′ from a current flow throughout the body 10 is to force the current to pass preferentially through the interbeam volume. Figures 3a, 3b, 4a, 4b show in longitudinal and transverse section a portion of the body 10 of a multibeam klystron according to the invention in which the circulation of current in the interbeam volume is promoted in two different ways.

Two successive cavities 20 are shown diagrammatically in FIG. 3a. They are not shown in Figure 4a for simplicity. The cross sections of Figures 3b, 4b are made along the cutting plane aa.

In FIGS. 3a, 3b, the conductive blocks 15 are formed by a central part 31 surrounded by a peripheral part 32. The sliding tubes 13 are located in the central part 31. The limit of the inter-beam volume 22 corresponds substantially to the circle , in dotted lines in FIG. 3b, passing through the center of the sliding tubes 13 and the central part 31 includes the inter-beam volume 22.

By making for at least one of the blocks, the central part 31 in a first material and the peripheral part 32 in a second material and choosing these materials so that the resistivity of the first material is lower than that of the second material, this preferential circulation in the interfaiseau volume 22. The central part 31 can for example be made based on copper and the peripheral part based on stainless steel. Other choices are possible. The choice of material of the peripheral part 32 must be compatible with the desired seal. Another solution for increasing the resistivity at the periphery of at least one block 15 relative to that in the interfaiseau volume is to cut baffles 33 at the periphery of the block 15. These baffles 33 are illustrated in FIGS. 4a, 4b. This configuration with baffles can be combined with that described in Figures 3a, 3b as Figures 4 show but it is not necessary.

Instead of the counter current I 'coming from the current I of the beams, it is possible that the means M allowing the circulation of the counter current I' comprise two connection means C1, C2, one near the entry E of the body 10 and the other near its output S, these connection means being intended to be connected to the terminals of a low voltage supply A2 having to deliver the counter current I '. Figure 6 (described later) shows this characteristic applied to a multibeam traveling wave tube. It is of course applicable to multibeam klystrons. In the multibeam klystrons described, there is a compensation for the trajectory of the beams where the counter-current circulates inside the inter-beam volume, that is to say at the level of the sliding tubes 13. However, these slip 13 occupy about 75% of the length of the body 10 which means that only 25% of the length of the beams does not receive correction but this is not a problem. A suitable correction at the input and output of the cavities 20 can be envisaged if necessary to reduce this harmful defocusing effect.

In the configurations where the sliding tubes 13 are not hollowed out within the same conductive block 15 and that they are produced by tubes 13 connected to the cavities 30 and separated from each other, the interbeam volume 22 is not not full of conductive material.

Figures 5a, 5b show in partial longitudinal and transverse sections, a multibeam klystron body with this characteristic. Now the conductive element 23 in which the counter current circulates I 'is electrically insulated and distinct from the body 10. It extends in the inter-beam volume 22, parallel to the sliding tubes 13, without electrical contact with them or with the cavities 20. It can be formed of rigid conductive sections 34 located at the inlet and outlet of the cavities, these sections being able to be rigid conductive rods sheathed with insulator 37 such as alumina.

Over the entire length of the body, there will be a succession of rigid conductive sections 34, two rigid conductive sections 34 located on either side of a cavity 20 being connected by a flexible connection 35 which spans the cavity 20. The flexible connections 35 may be metallic braid sheathed with insulation.

The means M allowing the circulation of the counter-current I 'comprise at the two ends of the conductive element 23 connection means C1, C2 intended to be connected to a supply A2 having to deliver the counter-current I'.

If the tube does not have a central beam as illustrated in FIG. 5c, a single conductive element 23 suffices in the center, if the tube has a central beam as illustrated in FIG. 5b, several are desirable, arranged between the central beam 1 and the beams 2-7 delimiting the inter-beam volume 22.

The harmful magnetic field induced at one of the beams by the others appears in the tube only when it operates in continuous mode or with relatively long pulse durations. This is the case for many tubes used in telecommunications, industrial, scientific, and even radar applications.

In fact, each time the beams are injected into the body 10, they induce, for a certain time, in the sliding tubes, eddy currents which oppose the disturbing induced magnetic field.

By calling F the repetition frequency of the tube, the thickness e of material which the disturbing induced magnetic field can pass through is given by:

with p resistivity of the material in Ω.cm and μ _r relative permeability of the material. For copper p is 1.72 10 ^" Ω. Cm and μ _r is 1.

If the tube comprises in a ring six beams separated by a thickness e of copper of 16 millimeters, the repetition frequency F is 17 Hz maximum, which amounts to saying that the pulses can only last 30 to 40 ms without defocusing effect.

Transmission problems in multibeam klystrons are all the more troublesome the longer the power and the pulse lengths. The tubes which have just been described are klystrons. A multibeam tube according to the invention could also be of the traveling wave tube type as illustrated in FIG. 6.

In this type of tube, the body 10 is formed by a succession of cavities 30 coupled to each other by irises 21 placed on a common wall 36. The beams 1 to 7 are contained in sliding tubes 13 before penetrating in the first cavity 30, leaving the last cavity 30 and more generally between the cavities 30. But now the sliding tubes 13 occupy less than 50% of the length of the body 10, which means that the correction obtained is less effective but still interesting. The conducting blocks in which the sliding tubes 13 are hollowed are marked with the reference 15 and the common walls 36 are integral with the conducting blocks 15.

To promote the circulation of the counter-current I ′ in the interbeam volume 22 over the greatest possible length, it is possible to include in the conductive blocks 15 and in the common walls 36, inserts

200 resistives that the counter current I 'will bypass. These inserts 200 are shown in FIG. 6 in two parts 201. 202 integral with one another.

The first part 201 placed in the conductive blocks 15 has the form of a tubular element, it surrounds the sliding tubes 13. The counter current I 'circulates in the conductive block 15 in a loop around the first part

201.

The second part 202 extends from the first part 201 in the thickness of the common wall 36 like a flange.

The counter current I 'circulates in the common wall 36 on either side of the second part 202 in opposite directions. By making a radial section of a block 15, an insert 200 has the shape of a T whose leg is the second part 202 and whose transverse bar is the first part 201. The circulation of the counter current I 'which bypasses the insert 200 is seen in detail on the circled zoom in FIG. 6. These inserts 200 can be made, for example from stainless steel, from alumina or even be recesses.

Now the means M allowing the circulation of the counter current I 'comprise two connection means C1, C2 one near the entry E of the body 10 and the other C2 near the exit S of the body, these means of connection C1, C2 being intended to be connected to the terminals e1, e2 of a low-voltage supply A2 having to deliver the counter current I '. In FIG. 6, the first connection means C1 is located at the input pole piece 19.1 and the second connection means C2 is located at the base of the manifold 11. The first connection means C1 could be on the anode 16 and the second on the output pole piece. In the example described, the second connection means C2 is brought to ground, but other potentials could be envisaged.

A resistor R suitably chosen in series with the low voltage supply A2 makes it possible to adjust the value of the counter current. In Figure 6 conventionally, another supply A1 is shown. It is connected between the cathodes 18 and the collector 11 and is used to create the beams 1 to 7. It is a high voltage supply.

The multibeam tubes according to the invention do not have a modified structure compared to existing tubes, it suffices to provide the connections described.

Claims

1. Multibeam electronic tube comprising several electron beams (1-7) substantially parallel, passing through a body (10), among the beams (1-7) at least some (2-7) delimit an inter-beam volume (22), each beam (2-7) delimiting the inter-beam volume (22) being subjected to a disturbing azimuthal magnetic field (BΘ) induced by all the others, characterized in that it comprises means (M) allowing, in at least one element conductor (23) located in the inter-beam volume (22), a circulation of a counter-current (I ') in a direction opposite to that of the current (I) of the beams (1-7), this counter-current (I ') generating at the level of the beams (2-7) delimiting the inter-beam space (22), a magnetic correction field aimed at opposing the disturbing magnetic field (BΘ).

2. Multibeam electronic tube according to claim 1, characterized in that the conductive element (23) is integrated into the body (10) of the tube.

3. Multibeam electronic tube according to one of claims 1 or 2, comprising a barrel (17) with one or more cathodes (18) which emit the electrons from the beams (1-7), these beams passing through the body (10) from an inlet (E) to an outlet (S) where they are collected by at least one collector (11), characterized in that the means (M) allowing the circulation of the counter-current (I ') comprise a connection (P) of mass near the entry (E) of the body (10), so that the counter-current (I ') comes from the current (I) of the beams (1-7) which is closed by this mass, the collector (11) having an intermediate potential (VQ) between the mass and that (VK) of the cathodes (18).

4. Electronic tube according to claim 3, characterized in that the connection (P) ground is located at an anode (16) which is provided with the barrel (17).

5. Electronic tube according to claim 3, characterized in that the ground connection (P) is at the level of a pole piece (19.1) located at the inlet (E) of the body (10).

6. Electronic tube according to one of claims 3 to 5, characterized in that the connection (P) ground is intended to be connected to a supply (A1) which delivers the potential (VK) to the cathodes (18).

7. Electronic tube according to one of claims 1 or 2, characterized in that the means (M) allowing the circulation of the counter current (I ') comprise a first connection means (C1) near the inlet ( E) of the body and a second connection means (C2) near the outlet (S) of the body, these connection means (C1, C2) being intended to be connected to a power supply (A2) intended to deliver the counter current (I ')

8. Electronic tube according to one of claims 1 to 7, characterized in that the body (10) comprises a succession of cavities (20, 30), the beams (1-7) being contained at the inlet and outlet of the cavities (20, 30) in sliding tubes (13) hollowed out within a conductive block (15), these conductive blocks (15) serving as a conductive element (23).

9. Electronic tube according to claim 8, characterized in that at least one block (15) conductor has a resistance, in a central part (31) encompassing the inter-beam volume, lower than that which it has in a peripheral part ( 32) surrounding the central part (31).

10. Electronic tube according to claim 9, characterized in that the central part (31) is made of a first material and the peripheral part (32) of a second material, the first material having a lower resistivity than that of the second material .

11. Electronic tube according to one of claims 8 to 10, characterized in that the periphery of at least one block (15) bears on its periphery baffles (33) in order to increase its peripheral resistivity.

12. Electronic tube according to claim 8, characterized in that two successive cavities (30) have a common wall (36) which bears on a conductive block (15), the conductive block (15) and the common wall (36) including a resistive insert (200) which forces the counter-current (I ') to circulate in the conductive block (15) in a loop around the insert and in the common wall (36), on either side of the 'insert (200) in opposite directions.

13. Electronic tube according to one of claims 2 to 12, in which the beams (1-7) are collected in a collector (11) and which comprises one or more members (26, 25, 12) which cooperate with the body (10) and / or the collector (11), characterized in that these members (26, 25, 12) are electrically isolated from the body (10) and / or from the collector (11).

14. Electronic tube according to claim 13, characterized in that it comprises, as the member electrically isolated from the body and / or the collector, a cooling device (26) surrounding the body and / or the collector, formed from at least a conduit (28) made of insulating material in which a resistant fluid circulates.

15. Electronic tube according to one of claims 13 or 14, characterized in that it comprises as a member electrically isolated from the body (10), a tubular focusing device (12) in which the body is placed, a dielectric element (24.1) being arranged at the inlet (E) and at the outlet (S) of the body (10) to isolate it from the focusing device. •

16. Electronic tube according to one of claims 13 to 15, characterized in that it comprises as organ electrically isolated from the body (10), at least one transmission guide (25.1, 25.2) isolated by a dielectric flange (24.2) of the body (10).

17. Electronic tube according to claim 1, the body (10) of which comprises a succession of cavities (20) and in which the beams (1-7) are contained, at the inlet and at the outlet of the cavities (30), in tubes sliding (13), separated from each other, characterized in that the conductive element (23) is longitudinal and extends in the inter-beam volume (22) parallel to the sliding tubes (13), without electrical contact either with the sliding tubes and with the cavities.

18. Electronic tube according to claim 17, characterized in that the conductive element comprises a rigid conductive section (33) at the inlet and at the outlet of a cavity (20), two successive sections (33) on either side of the cavity being connected by a flexible connection (35) spanning the cavity (20).

19. Electronic tube according to one of claims 17 or 18, characterized in that the conductive element (23) is sheathed with insulation.

20. Electronic tube according to one of claims 17 to 19, characterized in that the means (M) allowing the circulation of the counter-current

(I ') comprise, at each end of the conductive element (23), connection means (C1, C2) for connecting them to the terminals of a power supply (A2) intended to deliver the counter current (Y).