Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
  • H01J25/02—Tubes with electron stream modulated in velocity or density in a modulator zone and thereafter giving up energy in an inducing zone, the zones being associated with one or more resonators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
  • H01J25/74—Tubes specially designed to act as transit-time diode oscillators, e.g. monotrons

Definitions

• the present invention relates to a microwave amplifier device, as well as an oscillator obtained from the previous device.
• speed modulation electronic tubes such as klystrons or traveling wave tubes.
• This type of tube includes an electron gun, providing an electron beam; the electrons in the beam undergo a periodic change in speed which causes them to regroup in packets in certain areas of space; these packets then excite by impulse, according to their own period, the oscillations of a microwave circuit (resonant cavity or line) by borrowing the energy necessary for their own kinetic energy.
• the effects of space charge are very important.
• vircators which, unlike the previous tubes, take advantage of the space charge effects.
• a current of electrons is injected into a space, most often equal to several times the maximum current that could actually cross this space.
• This virtual cathode is unstable, that is to say it oscillates in space, thus creating electromagnetic fields.
• the signal transmitted is of poor quality, that is to say that the power is transmitted on numerous modes in a series of simultaneous or successive frequencies, and the applications of this type of signals are quite reduced.
• the conversion efficiency is poor (of the order of 2 to 1 at best) compared to the efficiency that it is possible to obtain ⁇ r with speed modulation tubes (often greater than 40%) .
• the present invention has ofciet a device intended to produce hyperfrequency energy from an electron beam, which makes it possible to avoid the preceding limitations, that is to say an efficiency as energy conversion of the electron beam in microwave energy and a quality of the signal emitted comparable to those of speed modulation tubes, with a weight and in -an volume comparable to those of vircators.
• the device according to the inversion comprises:
• an electronic gun capable of producing an electron beam such that the current that i carries is slightly lower than the maximum current likely to be transported in the generator; a so-called modulation microwave circuit, making it possible to apply an alternating voltage whose amplitude is sufficient to trigger, during one of its alter ⁇ nances, the formation of a virtual cathode no longer allowing the passage of electrons, the current carried by the beam thus being modulated at the frequency called modulation of the alternating voltage;
• FIG. 3 a third embodiment of the device according to the invention, in which the electron beam used is a solid cylindrical beam.
• the same references relate to the same elements.
• FIG. 1 therefore represents a first embodiment of the device according to the invention, seen in longitudinal schematic section.
• the generator according to the invention is a structure of revolution around a longitudinal axis ZZ. It comprises an electron gun 1, formed by a cathode 11 and an anode composed of an armature 20 and a screen 21.
• the cathode 11 is in the form of a conductive cylinder of axis ZZ, whose circumference protrudes 10 so that the electrons emitted by this cathode form an annular beam, represented by a dotted area 8 in the figure.
• the direction of propagation of the electrons of the beam 8 is shown by arrows.
• the armature 20 of the anode consists of a hollow cylinder, of the same axis ZZ as the cathode; it is closed by an annular shoulder 23 and a screen 21 in the form of a disc, leaving an annular slot 22 for the passage of the electron beam 8 to remain; the screen 21 is for example fixed by three tabs on the shoulder 23.
• the generator according to the invention also comprises an output microwave circuit 4 which is, in this embodiment, of the coaxial type, formed by an internal conductive cylinder 5 and an external conductor 4, arranged in the extension of the armature 20, between which is defined an annular space 44.
• the output circuit is substantially symmetrical of the electron gun 1 with respect to a plane normal to the plane of the figure, that is to say that the outer conductor 40 has a shoulder 43 annular and a screen 41 bearing, for example by legs, on the shoulder 43 and defining with this shoulder a circular slot 42 for the passage of the electron beam 8; the latter is received by an annular projection 50 of the inner conductor 5.
• the generator according to the invention further comprises a microwave modulation circuit 7, which is in this embodiment of the coaxial type; the central conductor of the circuit is formed by the wall 40 and the external conductor by a wall 70 in the form of a hollow cylinder, always of axis ZZ, defining with the wall 40 an annular space 74, the outer conductor 70 coming to be connected to part 25 of the frame 20.
• the operation of this device is as follows.
• the application to the cathode 11 of a negative voltage with respect to that of the anode causes the emission of the annular electron beam 8.
• the armature 20, the screen 21 and the elements of the output circuit 4 are at ground potential and a voltage -V is applied to the cathode 11.
• a longitudinal magnetic field is preferably applied to the structure, using means not shown.
• the mechanism for forming a virtual cathode is recalled below. Inside an electron beam there is a charge of space: on the axis of the beam, the potential and the speed of the electrons are lower than at the periphery. If the density of electrons and consequently the current transport increase, the potential and the speed of the electrons decrease until zero: the electrons then form a heap, negatively charged, called virtual cathode.
• This electron cluster oscillates on the longitudinal axis, giving rise to an electromagnetic field. The frequency of the oscillations depends in particular on the injection current and it is commonly measured in Gigahertz.
• the maximum current intensity beyond which the electrons form a virtual cathode is a function of the potential of the electron beam as well as of the dimensions of the beam and of the injection region 3; more precisely, the maximum current for a given electron beam is lower when the injection zone 3 is of larger diameter.
• the dimensions of the device (electron gun and injection zone) and the current of the electron beam are chosen so that it is slightly less than the maximum current likely to travel through region 3, current beyond which there is virtual cathode formation.
• the voltage between parts 25 and 45 resulting from this field must be of sufficient amplitude so that, for one of the alternations, the electron beam 8 is stopped by a mechanism of the virtual cathode type and no longer reaches the circuit. outlet 4, the electrons then being absorbed by the walls delimiting the injection zone 3; at the next alternation, the voltage applied between the same elements 25 and 45 restores the beam; the beam current is thus modulated in intensity at the frequency of the modulation signal.
• the output circuit 4 is then excited by the preceding modulated current and thus ensures the transformation into hyper-frequency energy of at least part of the energy of the electrons of the beam.
• Screens 21 and 41 conventionally have the function of absorbing divergent electrons. It should be noted that the modulation (7) and output (4) microwave circuits make it possible, by the choice of their dimensions, to precisely define the frequency of the modulation signal and, which is the aim sought, the frequency of the signal. output, thus obtaining a good quality signal.
• the maximum period of the alternating modulation field may be only a fraction of the beam switching time between the on state and the virtual cathode; in practice it can be of the order of the transit time of the electrons in the structure.
• the generator described here is, like a vircator, particularly compact; the length of the injection region 3, limited by the screens 21 and 41 happens to be in fact, in practice, of the order of the operating wavelength.
• V direct voltage
• MV voltages
• KA currents
• the reinjection means can be produced by any known means, such as a coupling loop produced in an opening in the wall 40 or a circuit outside the generator shown.
• FIG. 2 represents a second embodiment of the device according to the invention, in which means are provided for post-acceleration of the beam after modulation, in order to improve the efficiency of the assembly.
• the output circuit 4 is also formed as in FIG. 1 by the cylindrical inner conductor 5 surrounded by the conductor 40, the shoulder 43 and the screen 41.
• the injection zone is no longer closed by the screen 21 and the shoulder 43 but by a conductive element 61 similar to the screen 41 and an external conductor 60, arranged in the extension of the armature 20 and providing with the latter the slot 71 to which the modulation circuit is connected; the element 60 also houses an annular slot 62 with the screen 61 to allow the passage of the electron beam 8.
• the elements 60 and 61 are therefore electrically isolated both from the barrel 1 and from the output circuit 4.
• a voltage -V is applied to the cathode relative to the anode, the modulation signal via circuit 7 and, in addition, a post-acceleration voltage + V 1 to the output circuit. relative to the wall 60, which is for example at the potential of the anode. From the outlet ⁇ an acceleration of the electrons is carried out from the injection zone 3.
• FIG. 3 represents a third embodiment of the device according to the invention, in which the electron beam is a full cylinder.
• the emitted surface if ve of the cathode, now marked 12, of the barrel 1 is in the form of a disc so as to emit a solid cylindrical electron beam.
• the inner conductor of the output circuit 4, now marked 51 is constituted by a flat surface in the form of a disc.
• the screens 21 and 41 of FIG. 1 have been replaced here by the elements marked 26 and 46, constituted by grids or metallic sheets sufficiently thin for their absorption of electrons to be very low.
• the diameter of the cathode 12 must be substantially less than the wavelength of the energy. microwave obtained at the output, for example of the order of half the wavelength.

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• Particle Accelerators (AREA)
• Microwave Tubes (AREA)

Applications Claiming Priority (3)

Publications (2)

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• 1989
  • 1989-01-27 FR FR8901007A patent/FR2642584B1/fr not_active Expired - Fee Related
• 1990
  • 1990-01-26 WO PCT/FR1990/000059 patent/WO1990009029A1/fr active IP Right Grant
  • 1990-01-26 JP JP2502651A patent/JPH03503818A/ja active Pending
  • 1990-01-26 EP EP90902637A patent/EP0407558B1/de not_active Expired - Lifetime
  • 1990-01-26 CA CA002026111A patent/CA2026111C/fr not_active Expired - Fee Related
  • 1990-01-26 DE DE69021290T patent/DE69021290T2/de not_active Expired - Fee Related
  • 1990-01-26 US US07/576,443 patent/US5164634A/en not_active Expired - Fee Related

Non-Patent Citations (1)

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