FR2648272A1 - Microwave tube with exit coaxial with the collector - Google Patents

Abstract

The invention relates to a microwave tube with longitudinal electron beam 4 passing through at least one exit cavity 30 and received in a collector 32 aligned with the axis of the tube. The exit cavity 30 is coupled to an end-use element by way of a transmission line 35. Instead of being transverse to the axis of the tube, the transmission line is kept coaxial with the collector 32. This transmission line can be a coaxial waveguide which surrounds the collector 32. This construction makes it possible to obtain an axisymmetric microwave tube.

Description

HYPERE TUBE; EQUITY WITH COAXIAL OUTPUT
WITH THE COLLECTOR.

 The present invention relates to microwave tubes with longitudinal electron beams passing through at least one outlet cavity. It relates more particularly to conventional klystrons and all derived tubes, in particular multi-skin klystrons, single-beam, multi-beam, hollow beam klystrodes, klystrons with overmoded cavities, etc.

 A classic single-beam klystron is a tube with speed modulation of an electron beam. Its principle is based on the interaction between a longitudinal electron beam and induced electromagnetic fields in resonant cavities.

A focusing device surrounds the cavities. This device prevents the electron beam from diverging. The cavities four in number or clnq are placed one after the other, along the axis of the electron beam. They are separated by sliding tubes. The electron beam formed by a cannon passes successively through the resonant cavities and the sliding tubes. It is collected by a generally cylindrical collector, coaxial with the electron beam and placed downstream of the last cavity.

 The focusing device often consists of an electro-calming agent. It has the shape of a hollow cylinder, it can serve as an envelope for the tube. During assembly, the assembly of cavities integral at one end of the barrel and at the other end of the manifold is immersed in the focusing device.

 The collector collecting the electron beam heats up and is cooled by causing circulating, around its outer wall, a refrigerant, water for example.

 A microwave wave to be amplified is introduced into the first cavity located near the barrel; the last cavity or output cavity is connected to an external use member via a short transmission line. This line is generally a rectangular section waveguide or a coaxial waveguide.

 This waveguide is arranged transversely to the electron beam. The outlet cavity can be connected to several transmission lines.

 The coupling between the outlet cavity and the waveguide is made by an orifice placed in a side wall of the cavity; a coupling iris is thus obtained. A microwave window made up of a thin strip of dielectric material can be placed at the level of the coupling orifice so as to completely block it. This window is intended to allow microwave waves to pass through to the member of use while maintaining a high vacuum inside the cavity.

This microwave window could also be fixed inside the waveguide.

 In other so-called "external cavity" klystrons, sleeves made of dielectric material, coaxial with the axis of the electron beam, are tightly mounted inside the cavities. Each sleeve defines an inner cavity portion subjected to high vacuum and an outer cavity portion subjected to atmospheric pressure. In this construction, it is the outer portion of the crimped cavity which is connected by a coupling orifice to the member for use.

 The transmission line connected to the output cavity being transverse to the axis of the electron beam, the klystron is asymmetrical. This asymmetry has Ru minus two unfortunate consequences.

 The focusing device cannot completely surround the outlet cavity. The magnetic field is considerably reduced in the exit cavity whereas it is the place where it is most needed, the magnitude of the electromagnetic field then being maximum and likely to disturb the trajectory of the beam in a significant way.

 In the prior art, we used electromagnet coils scalloped at the level (the transmission line. But this construction does not really allow to find a correct value of the magnetic field and more there is a risk of obtaining a radial component too strong magnetic field which causes defocusing of the beam.

 This asymmetry also causes a significant difficulty during the assembly of the klystron. In fact, it is necessary to slide and very precisely adjust the barrel-cavity-manifold assembly a. inside the focusing device. This manipulation is always very difficult to re-install due to the precision required, the masses used and the fragility of the connection between the outlet cavity and the transmission line. It should be noted that the barrel-cavity-manifold assembly often weighs several hundred kilograms.

 The object of the present invention is to produce a microwave tube of the klystron type which does not have the drawbacks mentioned above.

 The present invention provides a particularly simple solution for producing such tubes with preexisting elements. The modifications take place mainly only at the level of the outlet cavity.

 To meet these aims, the present invention provides a microwave tube with a longitudinal axis, At at least one longitudinal electron beam passing through at least one outlet cavity and collected in a collector Aligned with the axis of the tube, this outlet cavity being coupled to a user member via a transmission line characterized in that the transmission line surrounds the collector and in that the transmission line and the collector are coaxial.

 According to a preferred construction, the transmission line is a coaxial waveguide comprising an inner conductor surrounded by an outer conductor.

 The diameter of the inner conductor is close to the diameter of the collector.

 The diameter of the outer conductor is close to the large dimension of the end wall of the outlet cavity.

 At least one orifice passes through the end wall of the outlet cavity and opens into a space between the outer conductor and either the collector or the inner conductor.

 According to a first - variant at least one microwave window seals the orifice.

 According to a second variant, the microwave window is sealed in a space between the outer conductor and the inner conductor or the collector. Preferably, the window will be placed beyond the collector.

 According to a third variant, a sleeve of dielectric material, coaxial with the axis of the tube, is mounted in leaktight manner inside the outlet cavity. It defines an internal part and an external part. The orifice passes through the end wall of the external part of the outlet cavity.

 A cooling fluid circulates around the collector, this fluid is conveyed by at least a first conduit and is evacuated by at least a second conduit, these conduits passing near the coupling orifice.

The invention will be better understood and other characteristics and advantages will appear on reading the following description illustrated by the appended figures which represent
- Figure 1 a longitudinal section of a classic klystron
- Figure 2a a longitudinal section of a klystron 1 according to the invention
- Figure 2b a cross section at a plane
AA 'of the same klystron
- Figure 3 a longitudinal section of a variant of a klystron according to the invention
- Figure 4 a longitudinal section of another variant of a klystron according to the invention
- Figure 5 an exploded view of "klystron multibeam according to the invention.

The klystron shown in Figure 1 has four cavities 1,2,3. A longitudinal electron beam 4 of axis XX 'is produced by a gun 5. The electron beam 4 successively crosses the cavities 1,3,2. They are aligned with the axis
XX '. They are separated by sliding tubes 6. The axis
XX 'coincides with the main axis of the tube.

 The first cavity 1 near the barrel 5 is the inlet cavity. It comprises a coupling device 7 intended to introduce a microwave wave to be amplified. The last cavity 2 crossed by the electron beam 4 is the exit cavity. It is connected to a user member via a transmission line 8. The user member is not shown. By transmission line is meant both a coaxial line as a waveguide or a coaxial waveguide.

 The transmission line 8 shown is here a waveguide. It is perpendicular to the axis XX '.

 A microwave window 9 has been mounted in leaktight manner inside the waveguide 8. This window 9 is intended to maintain a high vacuum inside the tube while letting out the microwave waves veF D The organ d 'use.

The coupling between the outlet cavity 2 and the transmission line 8 is effected by means of a coupling orifice 10 situated in a side wall 11 of the outlet cavity 2, this wall being substantially parallel to the axis XX '. We thus realize a
Coupling iris. The 1,2,3 cavities of klystrons generally have the shape of cylinders of revolution or rectangular parallelepipeds.

 The microwave window 9 could have closed the coupling orifice 10 instead of being located in the waveguide 8.

 After passing through the output cavity 2 the electron beam 4 is collected in a collector 12 located downstream of IR output cavity. This manifold often has the shape of a hollow cylinder of revolution, coaxial with the axis XX '. A refrigerant, for example water, is circulated in conduits suitably arranged around the manifold 12. These conduits are not shown.

 A first pole piece 13 is placed between the outlet of the barrel 5 and the inlet cavity 1. A second pole piece 24 is placed between the outlet cavity 2 and the manifold 12. These pole pieces help to converge the beam d 'electrons 4.

 A focusing device 14 almost completely surrounds the cavities 1,2,3. This focusing device has the shape of a hollow revolution cylinder of axis XX '. It produces a magnetic field parallel to the XX 'axis. The focusing device 14 consists of successive electromagnet coils 15, 16.

This focusing device serves as an envelope for the klystron.

 The coil 16 which surrounds the outlet cavity 2 has two notches 17,18.

 One of the notches 17 allows the waveguide 8 to pass, the other notch 18 is diametrically opposite for reasons of symmetry. Such a coil 16, despite the two symmetrical notches 17, 18, risks causing a parasitic radial magnetic field to defocus and in any case reduces the magnetic field on the axis XX '.

 Figure 2a shows a longitudinal section of a formless klystron according to the invention. Compared to Figure 1, the differences between the two klystrons are only in an area between the outlet cavity and the collector. The other elements of the tube are arranged as in Figure I and they have the same references. For reasons of clarity the proportions are not respected.

 The output cavity bears the reference 30. It is surrounded by a coil 31 of electromagnet identical to the other coils 15. The electron beam 4 after passing through the output cavity 30 is collected by a collector 32 in the form of a cylinder. of hollow revolution, coaxial with axis XX '. The collector 32 includes a cooling device operating by circulation of a coolant. This cooling device will be described later.

The outlet cavity 30 is always connected to a member of use not shown, by means of a transmission line 35 but this transmission line is no longer transverse to the axis XX '. This transmission line 35 is now in the axis. of the tube. For this, the end wall 33 of the outlet cavity 30 which is opposite the manifold 32 has at least one coupling orifice 56. This strip 33 is substantially transverse to the axis XX '. In Figure 2b which is a cross section in the plane AA 'at the end wall 33 there is shown four coupling holes 56 of oblong shape. These orifices 56 could have been circular or of another shape. For reasons of mechanical strength, if possible, use several coupling orifices,
The transmission line 35 is a coaxial waveguide.

Its axis coincides with the axis of the tube and consequently of the collector 32. This coaxial waveguide comprises an internal conductor 36 surrounded by an external conductor 37. These two conductors 36, 37 are hollow cylinders, of revolution, coaxial;
The two conductors 36, 37 each have respectively one end 38, 39 connected to the tooling member, this is their upper end. Their other end 40, 41 or base is integral with .u klystron.

 The base 41 of the outer conductor 37 is fixed in a leaktight manner, using screws 42 and a gasket 43 to the electromagnetic waves on a part 44. This disc-shaped plate 44 is integral with both the end wall 33 of the outlet cavity 30 and of the electromagnet coil 31.

This part 44 has holes 49 of the same size as the orifices 56. These holes 49 are located opposite the orifices 56.

The coupling orifices 56 open into a space between the external conductor 37 and the collector 32.

 It could be envisaged that the base 41 of the conductor 37 is fixed in a sealed manner directly on the end wall 33 of the outlet cavity 30 or on the coil 31. This depends on the diameter of the conductor 37.

 The outer conductor 37 will have a diameter substantially close to the outer diameter of the outlet cavity, if the latter is cylindrical. If the outlet cavity is parallelepiped on another shape, the diameter of the external conductor will be close to the largest dimension of the end surface 33 of the outlet cavity 30.

 The base 40 of the Inner conductor 36 is integral with a stirrup 46 which is itself fixed in a leaktight manner using screws 47 and a seal 48 sealed against microwave waves at the top of the collector 32. The diameter of the inner conductor 36 will be close the outside diameter of the manifold 32.

 Other means of fixing the inner conductor and the outer conductor can be envisaged.

 In all cases it is necessary that the diameter of the inner conductor 36 be less than the diameter of the outer conductor 37. This constraint requires that the outer diameter of the collector 32 be less than the largest dimension of the end surface 33 of the outlet cavity 30.

 The collector 32 comprises an internal envelope 50 generally in the form of a hollow cylinder of revolution closed at its upper end. It is inside this envelope 50 that the electrons are collected. This envelope 50 is surrounded by an external envelope 51 also in the form of a cylinder of revolution closed at its upper end, coaxial with the internal envelope 50. It is between these two envelopes 50, 51 that the refrigerant will circulate. For this, an intermediate wall 52 is placed, in the form of a hollow cylinder of revolution having an open upper end. A space 53 is arranged between the upper end of the intermediate wall 52 and the top of the external envelope 51. The lower ends of the internal envelope. 50, of the external casing 51 and of the intermediate wall. ') 2 are open and are fixed in a sealed manner either to the part 44, or to the end surface 33 of the outlet cavity 30.

 The refrigerant circulates on the one hand between the external envelope 51 and the intermediate wall 52 and on the other hand between the intermediate wall 52 and the internal envelope 50.

 This fluid is injected through conduits 54 located at the base of the manifold 32 at the level of the part 44 or of the end wall 33 of the outlet cavity. These conduits 54 are placed between the orifices 56 in the case where there are several orifices.

 I1 penetrate inside the external envelope 51.

 This fluid is evacuated by other conduits 55 also located at the base of the collector 32 at the level of the part 44 or of the end wall 33 of the outlet cavity 30. These conduits 55 are placed between the orifices 56 in the case where there are several orifices. These conduits 55 penetrate inside the intermediate wall 52.

 Sealed windows 20 are arranged in the orifices 56. These windows are blades of a dielectric material such as ceramic for example. They are transparent to electromagnetic waves while they maintain a high vacuum inside the klystron.

 FIG. 3 represents a variant of a klystron according to the invention. Several differences exist between Figures 2a, 2b and Figure 3.

 A first difference is seen in the diameter of the internal conductor C; of the transmission line. The internal conductor 66 instead of being fixed to the top of the collector 32 will now be fixed to the end wall 33 of the outlet cavity 30. The diameter of the internal conductor 66 will be greater than the diameter of the collector 32. The diameter of the internal conductor 66 will always be less than the diameter of the outer conductor 37.

We did not represent any part playing the role of the part
44 of FIG. 2a and now the bases of the outer conductor 37 and of the inner conductor 66 are fixed in leaktight manner to the end wall 33 of the outlet cavity 30. At least one orifice 56 has been drilled through this wall 33.

 This orifice 56 opens into a space between the outer conductor 37 and the inner conductor 66. Two orifices 56 have been shown. There may be more. Now these orifices 56 are free and a microwave window 67 is placed between the outer conductor 37 and the inner conductor 66, transverse to the axis XX beyond the collector 32. It consists of a generally thin plate of ceramic for example. The other elements of the figure are identical to those of Figures 2a, 2b.

 FIG. 4 represents yet another variant of a klystron according to the invention. The difference between this klystron and that shown in FIGS. 2a and 2b is located at the outlet cavity 70. The klystron is with an external cavity. A ceramic sleeve 71, for example, coaxial with the axis XX ′, has been placed inside the outlet cavity 70. This sleeve 71 delimits, inside the outlet cavity 70, an internal part 73 subjected to the vacuum and an external part 72 subjected to a different pressure, the latter pressure possibly being atmospheric pressure. As in FIG. 3, the outer conductor 37 of the transmission line 35 is secured to the end wall 74 of the outlet cavity 70 while, as in FIGS. 2a 2b, the inner conductor 36 is secured to the top of the collector 32. The terminal paro 74 of the outlet cavity 70 comprises at least one f. if Ice 76 not closed, which allows microwave waves to propagate from the outlet cavity 70 to the transmission line 35.

 FIG. 5 represents an exploded view of a multibeam klystron of axis XX '. This multi-beam klystron has a barrel 80 which produces four longitudinal electron beams 81 parallel to the axis XX '. These four electron beams 81 pass through successive cavities 82, 83 aligned with the axis XX 'A device. focusing 84 surrounds the cavities 82, 83. After having crossed the last cavity 83 or exit cavity the four electron beams 81 are collected in a collector 85. In this type of tube, the barrel, the collector, the focusing device and the cavities are common to the four electron beams 81.

 The outlet cavity 83 is coupled to a transmission line which is collnear with the axis XX '. This transmission line is in this example a coaxial waveguide 90 of axis XX 'which surrounds the collector 85. The coaxial waveguide 90 comprises an outer conductor 91 surround an inner conductor 92. The inner conductor 92 is fixed at its base in a leaktight manner at the top of the collector 85. The base of the external conductor 91 is secured to an intermediate piece 86 as in FIGS. 2a, 2b. This intermediate disc-shaped part is fixed to the end wall 87 of the outlet cavity 83. The end wall 87 of the outlet cavity 83 is pierced with at least one orifice 88. The intermediate piece 86 has at least one hole 89 of the same dimension as the orifice 88. The orifice 88 and the hole 89 are located opposite.

 A sealed window 93 is arranged in each orifice 88.

Instead of closing the orifices 88, a window could have been placed inside the coaxial waveguide 90 preferably beyond the collector 85. We would have. pu also dispf v ~ in the outlet cavity 83 a sleeve as shown in FIG. 4. A cooling device for the manifold 85 has not been shown.

 The present invention applies to kly trons and to B all the tubes of the klystron family. Single-beam, multi-beam, hollow beam klystrodes, lasertrons, relativistic klystrons etc. belong to this family.

 This invention applies to tubes of moderate average power because the possibility of supplying the collector with coolant is somewhat restricted.

 A tube according to the invention is perfectly of revolution and if necessary can be easily inserted into a housing.

 The invention is not limited to the examples described and other variants are possible without departing from the scope of the invention.

Claims (9)

 1 - Microwave tube of axis XX 'with at least one beam  longitudinal electron (4) passing through at least one cavity  outlet (30) and collected in a collector (32) allocated with  the axis of the tube, this cavity being coupled to a member  of use via a 'transmission line  (35) characterized in that the transmission line (35) surrounds  the collector (32) and in that the transmission line (35) and  the manifold (32) are coaxial.  an external conductor (37).  coaxial wave including an inner conductor (36) surrounded  characterized in that the transmission line (35) is a guide  2 - Microwave tube according to claim 1  3 - Microwave tube according to claim 2  characterized in that at least one orifice (56) passes through the wall  end (33) of the outlet cavity (30) so that the outlet cavity (30) communicates with a space included  between the outer conductor (37) and either the conductor  interior (36) or the manifold (32).  4 - Microwave tube according to one of claims 2  or 3 characterized in that the diameter of the inner conductor  (36) is close to the diameter of the manifold (32)  5 - Microwave tube according to one of claims 2 to  4 characterized in that the diameter of the outer conductor (37)  is close to the large dimension of the end wall (33) of  the outlet cavity (30).  6 - Microwave tube according to claim 3  characterized in that at least one microwave window (20)  sealing the orifice (56).  7 - Microwave tube according to one of claims 2 to  5 characterized in that at least one microwave window  (67) seals a space between the inner conductor (66) and the outer conductor (37).  8 - Microwave tube according to one of claims 3 to 5 characterized in that a sleeve (71) of dielectric material, coaxial with the axis of the tube is sealingly mounted inside the outlet cavity (70 ) defining an internal part (73) and an external part (72), the orifice (76) passing through the end wall (74) of the external part (72).  9 - Microwave tube according to one of claims 3 to 8 characterized in that a cooling fluid circulates around the collector (32), this fluid being conveyed by at least one premler conduit (54) and discharged by at least a second conduit (55), these conduits passing near the coupling orifice (56).