EP0384813A1 - Durch eine optische Vorrichtung modulierter Elektronenstrahlerzeuger - Google Patents

Durch eine optische Vorrichtung modulierter Elektronenstrahlerzeuger Download PDF

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Publication number
EP0384813A1
EP0384813A1 EP90400431A EP90400431A EP0384813A1 EP 0384813 A1 EP0384813 A1 EP 0384813A1 EP 90400431 A EP90400431 A EP 90400431A EP 90400431 A EP90400431 A EP 90400431A EP 0384813 A1 EP0384813 A1 EP 0384813A1
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EP
European Patent Office
Prior art keywords
frequency
electron gun
photocathode
source
optical modulator
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP90400431A
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English (en)
French (fr)
Inventor
Georges Faillon
Alexis Dubrovin
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Thales Electron Devices SA
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Thomson Tubes Electroniques
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Publication date
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Publication of EP0384813A1 publication Critical patent/EP0384813A1/de
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    • 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
    • H01J25/04—Tubes having one or more resonators, without reflection of the electron stream, and in which the modulation produced in the modulator zone is mainly density modulation, e.g. Heaff tube

Definitions

  • the present invention relates to electron guns which can be used to provide a modulated electron beam in oscillator or amplifier electron tubes, or in injectors of particle accelerators or the like.
  • lasertrons which use an electron gun with an electron beam modulated by pulses of a laser illuminating the photocathode.
  • the present invention provides improvements to this technique by eliminating the laser.
  • a photocathode is illuminated by a laser beam whose wavelength is chosen as a function of the output work of the material from which the photocathode is made.
  • a pulsed laser beam at frequency F tears out of the photocathode, at this same frequency F, packets of electrons.
  • These electron packets are then accelerated in an electrostatic electric field and thus gain kinetic energy. They then pass through a cavity resonating at frequency F and their kinetic energy is transformed into electromagnetic energy at frequency F. The energy from the cavity is taken by coupling it to an external use circuit.
  • the reference 1 denotes the photocathode, the reference 2, the laser beam and the reference 3, the electron beam.
  • the photocathode 1 is illuminated obliquely by the laser beam 2 and the electron beam 3 propagates along the longitudinal axis XX 'of the tube.
  • the laser beam 2 and the electron beam 3 propagate along the longitudinal axis XX ′ of the tube, but in the opposite direction.
  • the laser beam 2 is therefore normal to the emissive surface of the photocathode.
  • the electron beam 3 is accelerated by the electrostatic electric field created by an anode 4, then enters a cavity 5 resonating at the frequency F.
  • a collector 6 then receives the electron beam.
  • the electromagnetic energy is taken at the frequency F from the cavity 5 by coupling it to an external use circuit, by a waveguide 7, associated with a window 8, as in FIG. 1 or by a loop 9, as in figure 2.
  • the electrons are therefore naturally grouped from the start, whereas in tubes such as klystrons, we must use several cavities to form the electrons of a beam initially continuous in bundles.
  • the electron packets can also be injected into a particle accelerator which operates at frequency F.
  • the embodiments of electron guns which are represented in FIGS. 1 and 2 have the following drawbacks, relating to the use of lighting by laser beam: -
  • the photoelectric efficiency of the cathode is not optimal at the wavelengths commonly supplied by lasers.
  • the modulation frequency F is limited by the state of the art of the modulation of the laser pulses.
  • additional equipment is added to the system to provide a more suitable wavelength, and to better control the laser modulation.
  • the size, weight, complexity and cost of the pulsed laser beam lighting system are restrictive for practical applications.
  • the lasertron could develop very high powers of HF energy with excellent efficiency (a few hundred megawatts of peak power with an efficiency of around 70%, twice or one and a half times that obtained with a pulsed klystron). Nevertheless, in the current state of the art, there remain technical problems in the existing constructions.
  • the technology of the laser-excited gun is mainly based on the cathode and the laser.
  • the progress of photocathodes (AsGa ... field emission cathodes) is encouraging, although still insufficient.
  • Several tens of amps are easily obtained in the laboratory; but the objective is of the order of kA for 50 to 100 picoseconds.
  • the laser outside the tube itself, several basic difficulties must be resolved before deciding.
  • the invention which is the subject of this patent proposes to replace the laser by another much simpler source.
  • Lasers which are YAG lasers for example, have low yields and their implementation is critical.
  • the excitation of the photocathode requires very short wavelengths, in the ultraviolet (UV) for example to have a good efficiency of conversion of photons into electrons. Since the wavelength of lasers is generally longer than necessary, a light frequency multiplier is added to the system. This multiplier works well but it further complicates the whole system, which becomes even more critical. In addition, the yield decreases further.
  • UV ultraviolet
  • the object of the invention is precisely to remedy the drawbacks and to overcome the performance limits imposed by the use of a pulsed laser to stimulate the photocathode of an electron gun. These aims are achieved, as will be seen below in detail, by replacing the laser with another light source and a device for modulating this light interposed between this light source and the photocathode.
  • the light source according to the invention which could be a gas lamp, for example, can be chosen as a function of the wavelength emitted so as to optimize the photoelectric efficiency of the cathode without using a multiplier device of light frequency, necessary according to the prior art.
  • the modulation frequency F of the electron gun according to the invention is not limited by the characteristics of the light source as in the prior art.
  • the maximum modulation frequency depends on the time required to switch the modulation device interposed between the light source and the photocathode according to the invention, which makes it possible to modulate at much higher frequencies than before (an order more frequency is easily obtained in the laboratory).
  • the size, the weight, the complexity, and the cost of the electron gun system according to the invention are considerably reduced by the elimination of the laser, the frequency multiplier, and the related control electronics, in favor of a more common and less critical light source, modulated by a device that is very simple to implement.
  • the present invention provides an electron gun intended for emitting a microwave modulated beam at a frequency F, comprising as photon source a photocathode and a photocathode lighting source characterized in that a modulator optical is interposed between the light source and the photocathode, this optical modulator being controlled at the frequency F to modulate the lighting arriving from the source to the cathode at this high frequency F.
  • a much simpler light source is used, which need not be a source of coherent, monochromatic, parallel, nor pulsed light, since it is subsequently modulated by an optical modulator establishing the frequency desired by the light pulses; by varying the optical modulation rate, the amplitude of the variation in the lighting of the photocathode is controllable - unlike laser lighting - giving the possibility of using the electron gun thus modulated in an amplifier tube whose the signals can be coded either in amplitude modulation (AM) or in frequency modulation (FM).
  • AM amplitude modulation
  • FM frequency modulation
  • the theoretical photoelectric efficiency of an AsGaCs cathode is of the order of 60 mA / watt light, in an appropriate spectral band (UV, for example), which corresponds to results already obtained in the laboratory (4A for 187 W).
  • This lamp is followed by an optical modulator, for example electrooptic.
  • the modulator can be composed of several optical modulation elements, for example crystals with variable polarization controlled by an electromagnetic field associated with polarizers and filters, sensitive to an HF signal and with an extremely short response time.
  • the optical modulator allows the modulation of light beams from an HF signal.
  • This HF signal in the form of an electromagnetic field surrounding the modulator controls the latter directly.
  • modulators are, for example, Pockels cells, the main element of which is a crystal with variable polarization, sensitive to the electric field and whose response time is extremely short.
  • polarizing plate With such cells associated with a so-called polarizing plate and a second playing the role of filter, it is commonly known to make a 100% modulation (opaque black with total transparency) at a few hundred MHz.
  • new processes verified experimentally make it possible to obtain very good modulations up to 5 to 10 GHz.
  • the modulation of the Pockels cell can be obtained by placing the crystal with variable polarization in a resonator or an electromagnetic microwave circuit, in a place where the electric field is important. If the bandwidth of this modulator circuit is large, nothing prevents the vacuum tube from having this same bandwidth.
  • the size of the system is small, 5cm cube at 5 GHz, for example.
  • the optical modulator is for example a Kerr cell containing an insulating liquid which has a variable birefringence in the presence of a variable electric field.
  • Using a Cotton-Sheep cell may cause response time problems.
  • the modulation of the electron gun according to the invention is controlled very simply and allows the gun to be used in an oscillator tube by carrying out the modulation control with part of the signal taken at the HF output of the tube, or in an amplifier tube by controlling the modulation with the HF signal to be amplified.
  • the electron gun according to the invention can be used for oscillator or amplifier microwave tubes, as well as an injector for particle accelerators.
  • Microwave tubes can be of the klystrode, klystron, traveling wave tube or lasertron type, for example.
  • the electron gun excited according to the invention by a non-coherent lamp, modulated by an electrooptical system such as a high frequency Pockels cell (Ghz) can be used to provide a modulated electron beam for electron tubes, particle accelerators or any application that requires a large electron beam, pulsed at high frequency.
  • a non-coherent lamp modulated by an electrooptical system such as a high frequency Pockels cell (Ghz)
  • Ghz high frequency Pockels cell
  • the frequency and amplitude of the modulation are simultaneously controllable, as well as the shape of the pulse of the micro-pulses. Consequently, the lasertron using the proposed system is a real amplifier whose linearity can be excellent as long as the micro pulses are similar to those of a grid tube operating in class C.
  • this device can be used not only in place of the lasertron for high frequencies, but also and even more easily in place of the klystrode for low frequencies. And thus would disappear certain criticizable elements of the klystrode: namely its mechanically fragile grid and whose lifetime depends on the evolution of its secondary emission, and its very voluminous coaxial input cavity, with low bandwidth. But like the klystrode, it will be a linear amplifier in C band and this point remains unchanged.
  • the electronic tube fitted with the device according to the invention does not operate in class A: the unmodulated beam cannot exist, the cathode remaining cold. This explains why the yields can be significant.
  • this invention can be used, either for an amplifier, the input signal being the signal which modulates the crystals and which is then the signal to be amplified; either for a oscillator where the input signal is taken from the microwave output signal.
  • This possibility is completely absent from conventional lasertron where - even assuming that the laser works properly - there is no microwave signal in the input system.
  • Figure 3 shows the ideal shape of the light pulses to obtain the best functioning of a high current and high frequency pulsed electron gun.
  • a series of pulses of regular and uniform shape, of duration t at half height (measured at half the maximum intensity), spaced in time by a regular delay T 1 / F, where F is the high frequency of modulation, is provided during a period ⁇ .
  • ⁇ greater than or equal to 10 ⁇ 6 sec, with a repetition frequency or a rate ranging from 1 KHz to continuous.
  • the number of electrons released from the cathode during each light pulse varies as the integral of the intensity of the pulse, so the photoelectric efficiency is maximum for pulses of square shape or almost.
  • FIG. 4 shows the shape of the pulses obtained in the state of the art, using the signal at the output of a pulsed laser, operating at 250 MHz maximum.
  • FIG. 4 shows how far the state of the art is still far from the theoretical performances hoped for for the lasertron.
  • FIG. 5 shows a longitudinal section view of a lasertron system in which the laser has been replaced by a non-coherent lamp modulated by an optical modulator, according to the invention.
  • the modulated electron gun comprises a photocathode 1, a non-coherent light source 11 which emits light rays 2 which are modulated by an optical modulator which can be composed of several optical modulation elements, by example an active polarization modulation element 15 placed between a polarizer 13 and a filter 14, the light rays then being focused on the photocathode by optical means 19 which can be constituted by a lens, for example.
  • an optical modulator which can be composed of several optical modulation elements, by example an active polarization modulation element 15 placed between a polarizer 13 and a filter 14, the light rays then being focused on the photocathode by optical means 19 which can be constituted by a lens, for example.
  • the active optical modulation element 15 can be a Pockels cell, for example.
  • a Pockels cell can be positioned in a waveguide 16 supplied with electromagnetic energy 17 at the desired frequency; it is the surrounding electromagnetic field which controls the modulation, and not an electrical signal brought by conductors on electrodes of the cell; possibly a suitable load 18 in the guide 16 can help stabilize the spectral purity of the HF signal.
  • the light 2 is focused by a lens 19 through a transparent window 21 sealed against the vacuum which prevails inside the lasertron, on the photocathode 16 which emits packets 3 of electrons at the frequency of light stimulation determined by the optical modulator. 13 + 14 + 15.
  • the electron packets are accelerated in the direction of the lasertron axis by a high voltage applied between the cathode and the anode 4 and other surrounding metal parts 26,31 which are generally grounded.
  • the high voltage insulation between these parts is provided by a ceramic 25 and conventional anti-corona means 23.
  • the pulsed electron beam in bundles 3 is focused at the start of the cathode by a focusing electrode 24 and through the cavities 5 and sliding zones 26 by a system of coils 30 which generate a substantially axial magnetic field confined between the parts polar 31.
  • the electrons After having passed through the cavities and slides, the electrons are no longer subject to the focus fields and repel each other, so they take divergent paths 12 to arrive at the collector 6 which dissipates their kinetic energy in a cooling system which is not not shown.
  • a small transverse magnetic field is applied by magnets or electromagnets 20 to deflect the trajectories of the electrons to prevent them from falling on the optical window 21.
  • the HF energy generated in the cavities 5 by the bundle of electron packets 3 passes through an iris 27 and can be extracted towards a charge 10 (not shown) by means of a microwave window 8 which is vacuum-tight but transparent to HF radiation. .
  • the lasertron using a non-coherent light source modulated by an optical modulation device according to the invention and as shown schematically in Figure 5 has many advantages.
  • Optical modulation offers the possibility of obtaining much higher frequencies.
  • the photoelectric efficiency is better depending on the choice of lighting type. Also the light power output of a gas lamp is better than that of a laser. System performance is the product of these two effects.
  • the system can be used as an HF amplifier.
  • an active polarization modulation element such as a Pockels cell, for example, controlled by a microwave electromagnetic field surrounding this active element, the degree of polarization and therefore the intensity of transmitted light is controllable by the amplitude of the control microwave electromagnetic field, while the modulation is at the frequency of the same microwave electromagnetic field.
  • an HF oscillator tube is obtained, the frequency of which depends on the dimensions of the resonant cavities of the tube using the barrel according to the invention.
  • the invention relates to an electron beam microwave electron gun modulated by an optical device with non-coherent light.
  • the invention also relates to electronic tubes using an electron gun modulated according to the invention, in particular lasertrons, klystrodes, klystrons and traveling wave tubes.

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  • Lasers (AREA)
  • Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
  • Microwave Tubes (AREA)
EP90400431A 1989-02-21 1990-02-16 Durch eine optische Vorrichtung modulierter Elektronenstrahlerzeuger Withdrawn EP0384813A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8902236A FR2643507A1 (fr) 1989-02-21 1989-02-21 Canon a electrons a faisceau electronique module par un dispositif optique
FR8902236 1989-02-21

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EP0384813A1 true EP0384813A1 (de) 1990-08-29

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EP90400431A Withdrawn EP0384813A1 (de) 1989-02-21 1990-02-16 Durch eine optische Vorrichtung modulierter Elektronenstrahlerzeuger

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US (1) US5043630A (de)
EP (1) EP0384813A1 (de)
JP (1) JPH02260352A (de)
FR (1) FR2643507A1 (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0485266A1 (de) * 1990-11-09 1992-05-13 Thomson Tubes Electroniques Durch optoelektronische Umschaltung modulierte Elektronenkanone
WO1992020088A1 (fr) * 1991-05-03 1992-11-12 Thomson Tubes Electroniques Tube hyperfrequence a cavite resonante accordable en frequence

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2737340B1 (fr) * 1995-07-28 1997-08-22 Thomson Tubes Electroniques Tube electronique multifaisceau a couplage cavite/faisceau ameliore
FR2756970B1 (fr) * 1996-12-10 2003-03-07 Thomson Tubes Electroniques Tube hyperfrequence a interaction longitudinale a cavite a sortie au dela du collecteur
FR2764730B1 (fr) * 1997-06-13 1999-09-17 Thomson Tubes Electroniques Canon electronique pour tube electronique multifaisceau et tube electronique multifaisceau equipe de ce canon
JP3268237B2 (ja) * 1997-07-29 2002-03-25 住友重機械工業株式会社 フォトカソードを用いた電子銃
JPH11111174A (ja) * 1997-10-03 1999-04-23 Sony Corp 電子銃の位置ずれ検出方法及び検出装置
FR2780809B1 (fr) 1998-07-03 2003-11-07 Thomson Tubes Electroniques Tube electronique multifaisceau avec champ magnetique de correction de trajectoire des faisceaux
FR2803454B1 (fr) * 1999-12-30 2003-05-16 Thomson Tubes Electroniques Generateur d'impulsions hyperfrequences integrant un compresseur d'impulsions
US6828574B1 (en) * 2000-08-08 2004-12-07 Applied Materials, Inc. Modulator driven photocathode electron beam generator
FR2854728B1 (fr) * 2003-05-06 2005-07-29 Thales Sa Tube hyperfrequence a faible rayonnement parasite
JP6578529B1 (ja) * 2019-06-10 2019-09-25 株式会社Ｐｈｏｔｏ ｅｌｅｃｔｒｏｎ Ｓｏｕｌ 電子銃、電子線適用装置、および、電子銃の制御方法

Citations (4)

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US3239670A (en) * 1961-11-17 1966-03-08 Bloembergen Nicolaas Microwave modulation of optical radiation in a waveguide
US3388282A (en) * 1965-03-29 1968-06-11 Hallicrafters Co Biased crossed field dynamic electron multiplier
US4703228A (en) * 1985-08-28 1987-10-27 Ga Technologies Inc. Apparatus and method for providing a modulated electron beam
EP0298817A1 (de) * 1987-06-25 1989-01-11 Commissariat A L'energie Atomique Verfahren und Vorrichtung zur Elektronenerzeugung mittels einer Feldkopplung und des photoelektrischen Effekts

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US4608569A (en) * 1983-09-09 1986-08-26 General Electric Company Adaptive signal processor for interference cancellation
US4763996A (en) * 1984-11-20 1988-08-16 Hamamatsu Photonics Kabushiki Kaisha Spatial light modulator
FR2599565B1 (fr) * 1986-05-30 1989-01-13 Thomson Csf Lasertron a faisceaux multiples.

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3239670A (en) * 1961-11-17 1966-03-08 Bloembergen Nicolaas Microwave modulation of optical radiation in a waveguide
US3388282A (en) * 1965-03-29 1968-06-11 Hallicrafters Co Biased crossed field dynamic electron multiplier
US4703228A (en) * 1985-08-28 1987-10-27 Ga Technologies Inc. Apparatus and method for providing a modulated electron beam
EP0298817A1 (de) * 1987-06-25 1989-01-11 Commissariat A L'energie Atomique Verfahren und Vorrichtung zur Elektronenerzeugung mittels einer Feldkopplung und des photoelektrischen Effekts

Non-Patent Citations (3)

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Title
IEEE TRANSACTIONS ON NUCLEAR SCIENCE, vol. NS-32, no. 5, partie 2, octobre 1985, pages 2906-2908, IEEE, New York, US; E.L. GARWIN et al.: "An experimental program to build a multimegawatt lasertron for super linear colliders" *
ITERNATIONAL ELECTRON DEVICES MEETING, Washington, DC, 1-4 décembre 1985, pages 342-345, IEEE, New York, US; M. SHRADER et al.: "Pre-bunched beam devices-efficient sources of UHF and microwave power" *
THE MICROWAVE JOURNAL, vol. 7, no. 8, août 1964, pages 51-56, Horizon House, Dedham, US; K.M. JOHNSON: "Microwave light modulation by the pockel effect" *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0485266A1 (de) * 1990-11-09 1992-05-13 Thomson Tubes Electroniques Durch optoelektronische Umschaltung modulierte Elektronenkanone
FR2669145A1 (fr) * 1990-11-09 1992-05-15 Thomson Tubes Electroniques Canon a electrons module par commutation optoelectronique.
US5313138A (en) * 1990-11-09 1994-05-17 Thomson Tubes Electroniques Electron gun modulated by optoelectronic switching
WO1992020088A1 (fr) * 1991-05-03 1992-11-12 Thomson Tubes Electroniques Tube hyperfrequence a cavite resonante accordable en frequence

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Publication number Publication date
US5043630A (en) 1991-08-27
JPH02260352A (ja) 1990-10-23
FR2643507A1 (fr) 1990-08-24

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