RU2535924C1 - Microwave generator with virtual cathode of coaxial type - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention can be used for generation of high-power pulses of electromagnetic emission with high-current electron beams. A microwave generator with a virtual cathode of coaxial type includes high voltage source (1), the negative electrode of which is connected to earthed cylindrical vacuum chamber (2), high-voltage insulator (3) installed in the end face of the chamber, cylindrical grid anode (7) located along the chamber axis and connected to positive electrode (9) of high voltage source (1) through anode holder (8) and high voltage insulator (3), a cathode assembly with cylindrical cathode (11), which is located inside anode (7) on its axis and connected to vacuum chamber (2) through coaxial conical line (4), which is connected with a wide end to a free end face of chamber (2) and with a narrow end to coaxial waveguide junction (5), to which antenna (6) and matching element (14) are connected.

EFFECT: enlarging functional capabilities; improving reliability of the device.

5 cl, 2 dwg

Description

The invention relates to microwave technology and can be used to generate powerful pulses of electromagnetic radiation by high-current electron beams.

The generation of pulses of electromagnetic radiation obtained using high-current electron beams is of great interest in connection with the prospects for their use in both scientific and technological purposes. In particular, a microwave pulse pulled into the atmosphere can be used to initiate a number of biochemical processes, modify materials, and other applications, the number of which increases as we understand the physics of the processes of generating these pulses and improve the technique for producing powerful electromagnetic radiation. Thus, the relevance of research and development of devices for the generation of powerful pulses of electromagnetic radiation by high-current electron beams is confirmed.

A device for generating electromagnetic radiation by a high-current electron beam [A.N. Didenko et al. Relativistic triode microwave generators // Relativistic high-frequency electronics. Publishing House of the Institute of Applied Physics, Academy of Sciences of the USSR, Gorky. - 1984. - issue 4. - p. 104-117]. The device contains a source of pulsed high voltage, a flat cathode located under the ground potential, and a flat grid anode located under a high positive potential, a vacuum chamber, which is also the electrodynamic system of the generator and a window for outputting microwave energy. In contrast to the known microwave generators operating on high-current beams, in this device the generation of microwave radiation is carried out during the formation of a virtual cathode behind the grid anode. With the formation of a virtual cathode (VC), the electrons emitted from the cathode begin to oscillate around the grid anode and between the real and virtual cathode, resulting in powerful microwave radiation. Electromagnetic radiation from the vacuum chamber is discharged into the free space through the exit window. The advantage of this generator is that it is simple in design, compact, does not require additional equipment to create magnetic fields and transport an electron beam into them. The disadvantage is multimode generation in this device, associated with the geometry of the system: the geometric dimensions of the electrodynamic system (vacuum chamber) of the generator are many times greater than the wavelength of the generated radiation.

A device is known [Relativistic microwave generator. USSR Copyright Certificate No. 1522317, H01J 25/68, Bull. No. 42, 1989], which allows to improve the overall dimensions of the generator. The microwave generator contains a high voltage source in which the negative electrode is connected to a grounded cylindrical vacuum chamber, in the end of which a high-voltage insulator is installed, and on the other end there is a window for outputting microwave radiation into free space. The cylindrical cathode is located on the inner surface of the vacuum chamber. Inside the vacuum chamber, a cylindrical grid anode is mounted coaxially with it, which is connected to the high voltage electrode of a positive polarity of the power source using an anode holder. Inside the anode, a virtual cathode is formed by a stream of electrons emitted from the cathode and passed through the anode. Due to the electron oscillation between the real and virtual cathodes, single-mode electromagnetic radiation on a wave of the TM ₀₁ type arises in the device, which forms a radiation pattern in free space with a minimum radiation power on its axis [A.G. Zherlitsyn. Generation of microwave radiation in a triode with a virtual cathode of a coaxial type // Letters in ZhTF. - 1990. - v.16. - issue 22. - S.78-80].

The disadvantage of this device is the limited functionality of the microwave generator associated with the formation of a radiation pattern having a minimum radiation power on its axis, which limits the use of this generator for practical purposes.

A device of the coaxial type [A.G. Zherlitsyn et al. Investigation of the excitation of electromagnetic waves in a planar-coaxial triode with a virtual cathode // News of Universities. Physics. - 2011. - T.54. - No. 11/2. - S.209-214], wherein the electromagnetic radiation is excited in the TE ₁₁ wave in circular waveguide that allows the formation of the radiation pattern with the maximum power of the radiation on its axles. On the basis of the technical features of this analogue is selected as a prototype of the invention.

The device contains a high voltage source, in which the negative electrode is connected to a grounded cylindrical vacuum chamber, in the end of which a high-voltage insulator is installed, and at the other end there is an output window made in the form of a horn antenna for outputting microwave radiation. Inside the vacuum chamber along its axis there is a grid anode having the shape of a rectangular cylinder connected through the anode holder and the vacuum insulator to the positive electrode of the high voltage source. Inside the anode, a cathode assembly is located along its axis. The cathode assembly is connected to a grounded vacuum chamber by four electrodes, which are simultaneously the supports of the assembly, which pass through the holes of the anode holder. The diameter of the holes provides electrical isolation of the vacuum gaps between the electrodes and the holes in the anode holder body. Four flat cathodes are installed in the cathode assembly. A rectangular cylindrical anode is formed by four grids connected in a square straight prism with rounded ribs, which smoothly passes into a hollow cylinder, at the end of which a cone is installed. Four flat cathodes and four anode grids form four flat cathode-anode gaps. A virtual cathode is formed in the space between the anode and the wall of the vacuum chamber by the flow of electrons passing through the anode.

The prototype device operates as follows. When a high voltage pulse of positive polarity is applied to the anode, electron flows arise in the cathode-anode spaces, which, passing through the anode grids in the space between the anode and the wall of the vacuum chamber, create virtual cathodes. During the formation of virtual cathodes in electron flows, an oscillatory movement of electrons occurs between real and virtual cathodes, which is accompanied by powerful electromagnetic radiation, and microwave waves of the microwave range are excited in a vacuum chamber. The vacuum chamber together with the electrode system located inside the chamber form the electrodynamic system of the generator, which is not simply connected in the field of interaction of the beam with the fields of the electrodynamic system (resonator). It is not uniform along the axis of the chamber and consists of segments of waveguide lines:

coaxial, planar-coaxial and cylindrical. Waves of the TEM, TE, TM type can be excited in it. The lowest type of oscillations in this system are waves of the TEM type. The first highest type of waves are waves of type TE ₁₁ . Therefore, the most efficient excitation and energy transfer will be carried out by TEM and TE ₁₁ waves. In this case, in order for the excitation to be on one type, namely, on TE ₁₁ type, it is necessary to have an axially asymmetric electron flux. This is achieved in the device due to the asymmetric arrangement of the flat cathodes. Experimental studies performed on the prototype device showed that when axially asymmetric electron flows are generated in the generator, microwave radiation is generated _on type ₁₁ TE, in which a radiation pattern with maximum power on the axis is formed in free space. When an axially symmetric electron beam diverging from the camera axis is formed, a TEM wave is excited in this system, which is transformed into a TM ₀₁ wave in a segment of a cylindrical line and a radiation pattern with a minimum power on the axis is formed in the free space [A.G. Zherlitsyn et al. Generation of microwave oscillations in a coaxial vircator with a diverging beam // Bulletin of the Tomsk Polytechnic University. - 2012. - T. 21. - No. 2. - S.31-35]. The axial symmetry of the electron flow was achieved in the device by replacing the rectangular cylindrical grid anode with a round cylindrical grid anode and replacing the flat cathodes in the cathode assembly with a round cylindrical cathode.

The disadvantage of the prototype device is the limitation of its functionality, low reliability of the device associated with the electrical strength of the vacuum gaps in the area of the cathode assembly with the vacuum chamber. Namely, with an increase in the microwave radiation power, it is necessary to increase the high voltage, which entails an increase in the vacuum gaps in the area of the cathode assembly connecting to the vacuum chamber and, as a result, an increase in the geometric dimensions of the overall dimensions of the generator, as well as an increase in the probability of the generation transition from single-mode, to multi-mode generation.

The technical result of the invention is to expand the functionality of a microwave generator with a virtual coaxial cathode, increasing the reliability of the device.

The specified technical result is achieved by the fact that in a microwave generator with a virtual cathode of a coaxial type, containing, like the prototype, a high voltage source in which the negative electrode is connected to a grounded cylindrical vacuum chamber, a high-voltage insulator installed at the end of the chamber, a cylindrical grid anode, located along the axis of the chamber, connected to the positive electrode of the high voltage source through the anode holder and high voltage insulator, cathode assembly with a cylindrical cathode, The antenna for outputting microwave radiation located inside the anode on its axis and connected to the vacuum chamber, unlike the prototype, the cathode assembly is connected to the vacuum chamber through a coaxial conical line connected at the wide end to the free end of the chamber, and the narrow end to the coaxial waveguide junction to which the antenna and matching element are connected.

It is advisable that the coaxial waveguide transition was made in the form of a coaxial waveguide transition of a button type.

It is advisable that the coaxial conical line was connected to the coaxial waveguide transition through a grounded emitter.

It is advisable that the matching element was made in the form of a short-circuited high-frequency piston and connected to a coaxial-waveguide transition through a vacuum-tight radio-transparent window.

It is advisable that a radio-transparent vacuum-tight window be installed at the output of the antenna.

Since button-type coaxial waveguide transitions can be electrically broken only at a microwave power equal to the microwave power of the electrical breakdown of a coaxial line [Centimeter wave transmission lines / edited by G.A. Remeza. - M .: Soviet radio. 1951. - vol. 1-415. - S.357], then to improve the reliability of the device at high levels of radiation power generated in the generator, it is advisable to use a button type transition.

Figure 1 schematically shows the design of the claimed device. Figure 2 illustrates the use of a button-type coaxial waveguide transition in a device.

A microwave generator with a coaxial-type virtual cathode comprises a high voltage source 1, in which the negative electrode is grounded; a grounded cylindrical vacuum chamber 2, in the end of which a high-voltage insulator 3 is installed. The other end of the chamber is connected to a coaxial conical line 4, to which a coaxial waveguide transition 5 is connected with a rectangular antenna 6 for outputting microwave radiation. Inside the vacuum chamber, a cylindrical grid anode 7 is installed along its axis, which is connected via an anode holder 8 to a high-voltage electrode of positive polarity 9 of a high voltage source 1. Inside the anode, a cathode holder 10 with a cylindrical cathode 11 is installed along the axis of the cathode. 8 and the vacuum chamber 2 form two interconnected coaxial lines. The cathode holder 10, which is the inner conductor of the coaxial line, is connected through the inner conductor 12 of the coaxial cone line 4 to the grounded emitter 13 of the coaxial waveguide transition (FIG. 1, view A-A). The emitter 13 serves as an element of communication between the coaxial conical line 4 and the rectangular waveguide of the coaxial waveguide transition. To coordinate the coaxial line and the coaxial-waveguide transition, a matching element 14 is connected to the transition in the form of a section of the waveguide line that can be adjusted using a short-circuit piston. To maintain the vacuum in the coaxial waveguide transition and inside the device, the matching element 14 is connected to the coaxial waveguide transition with a radio-transparent vacuum-tight window 15, and a radio-transparent vacuum-tight window 16 is installed at the antenna output. Inside the vacuum chamber 2, opposite the cathode-anode gap 17 , behind the grid anode, a stream of electrons passing through the anode forms a virtual cathode 18.

In another embodiment (Figure 2), the cathode holder 10 is connected via an inner conductor 12 of the coaxial cone line 4 to a grounded emitter 13 of a coaxial waveguide transition 5 of a button type.

The proposed device operates as follows.

A high-voltage pulse of positive polarity from the high-voltage source 1 through the high-voltage electrode 9, the insulator 3 and the anode holder 8 is applied to the grid anode 7. Under the influence of the potential difference between the cathode 11 and the anode 7, the electrons emitted from the surface of the cylindrical cathode are accelerated in the gap between the cathode-anode 17 forming a radially diverging stream of electrons, which, after passing through the anode grid, form a virtual cathode 18 behind the anode. In a potential well in the region of the cathode – anode – virtual cathode I am a radially symmetric electron stream oscillating between the real and virtual cathodes, which is a source of high-power microwave radiation, which, in the case of a radially symmetric electron stream in a coaxial resonant system, excites TEM waves. The TEM wave excited through the coaxial cone line is transmitted to the coaxial waveguide transition. In a coaxial waveguide transition, a TEM wave transforms into a TE ₁₀ wave in a rectangular waveguide. To ensure minimal energy loss of electromagnetic radiation during wave transformation in a coaxial waveguide device, a customizable matching element 14 is used, made in the form of a short-circuited high-frequency piston. This element is connected to a coaxial waveguide transition through a vacuum-tight radiolucent window 15. The TE10 wave formed in the coaxial waveguide transition through a rectangular horn antenna 6 is emitted into the free space and a radiation pattern with maximum power is generated in the far zone from the antenna window 16 on the axis of the antenna.

Thus, by connecting the cathode to a grounded vacuum chamber through a coaxial line and a coaxial waveguide junction, the implementation of the proposed device allows you to expand the functionality of the microwave generator, to increase the reliability of its operation.

In a specific example of the implementation of the proposed microwave generator with a virtual cathode, the geometric dimensions of the vacuum chamber 2, the cathode assembly with the cathode, the anode with the anode holder, the parameters of the power source are the same as in the prototype, namely, the vacuum chamber 2 has a diameter of 35 cm, length 52 cm, the cathode 11 is made in the form of a stainless steel disk with a diameter of 11 cm and is attached to the cathode holder 10 of stainless steel with a diameter of 10 cm; a cylindrical mesh anode 7 with a diameter of 13.4 cm, made of steel mesh with a geometric transparency of 0.7, and mounted on the anode holder 8, made of stainless steel pipe with a diameter equal to the diameter of the anode; power source 1 generates a voltage pulse of positive polarity with an amplitude of 450-500 kV, a duration of ~ 120 nsec and provides a current in the cathode-anode gap of 45-50 kA.

As follows from the results of studies conducted on a microwave generator - prototype, in this geometry a radial axially-symmetric oscillating electron flow is generated, exciting in a vacuum chamber with electrode systems of the anode and cathode of a wave of the TEM type [A.G. Zherlitsyn et al. Generation of microwave oscillations in a coaxial vircator with a diverging beam // Bulletin of the Tomsk Polytechnic University. - 2012 .-- v.21. - No. 2. - S.31-35].

In the proposed device, the cathode holder 10 is connected to the inner conductor 12 of the coaxial conical line 4 using threaded connections. The outer conductor of the coaxial conical line 4 through a flange vacuum-tight connection is attached with a wide end to the vacuum chamber. The geometric dimensions of the coaxial conical line 4 are selected from the conditions: firstly, the wave impedance of the coaxial line formed by the cathode holder 10 and the vacuum chamber 2 and the coaxial conical line 4 should be equal; secondly, the length of the cone line ℓ _{C. L.} > 2λ, where λ is the radiation wavelength. In this case, the standing wave coefficient (SWR) of the line is close to unity [Transmission lines of centimeter waves / edited by G.A. Remeza. - M .: Soviet radio. - 1959. - T.1. - 415 p.].

равно Z_л=75 Ом. Тогда для конусной линии с волновым сопротивлением Z_к.л.=Z_л=75 Ом углы, образованные осью конусной линии и образующими конусов внутреннего и внешнего проводников конусной линии, соответственно будут равны θ₁=5° и θ₁=17° [Х. Мейнке и Ф.В. Гундлах радиотехнический справочник. - М.: Государственное энергетическое издание. - 1960. - т.1. - 516 с.]. С учетом полученных углов длина конусной линии ℓ_к.л. будет равна ℓ_к.л.≈57 см. Эта длина достаточна для того, чтобы выполнялось второе условие согласования коаксиальных линий, при котором КСВ≈1, а именно ℓ_к.л.>2λ для длины волны излучения λ=10 см.The characteristic impedance of the coaxial line outer conductor with a diameter equal to the diameter of the cathode holder _cathode d = 10 cm, according to the formula $$Z_l=60\ln \frac{D_{\mathrm{to}\mathrm{but}meR\mathrm{but}}}{d_{\mathrm{to}\mathrm{but}t\mathrm{about}d}}$$

equal to Z _l = 75 Ohms. Then the tapered line with impedance Z _KL = Z _l = 75 Ohm, the angles formed by the axis of the cone line and forming the cones of the inner and outer conductors of the cone line, respectively, will be θ ₁ = 5 ° and θ ₁ = 17 ° [X. Meinke and F.V. Gundlach radio technical reference. - M.: State energy publication. - 1960 .-- v. 1. - 516 p.]. Taking into account the obtained angles, the length of the cone line is ℓ _k.l. will be equal to ℓ _k.l. ≈57 cm. This length is sufficient to satisfy the second condition for matching coaxial lines, at which the SWR is ≈ 1, namely, ℓ _k.l. > 2λ for a radiation wavelength of λ = 10 cm.

In a specific embodiment, to connect the coaxial conical line to the coaxial waveguide junction, a collet connection of the inner conductors 12 and 13 and a flange connection of the outer conductors are used. The wave impedance of a segment of the coaxial line of the coaxial waveguide transition is equal to the wave impedance of the cone line: Z _q.v.n. = Z _kl = 75 ohms. As noted earlier, to increase the reliability of the device at high levels of radiation power, it is advisable to use a coaxial waveguide transition of the button type. In this transition, the breakdown strength of the electric field is equal to the breakdown strength in coaxial lines. In an example of a specific embodiment, it is proposed to use a coaxial waveguide transition of a button type with a rectangular waveguide with a cross section of 45 × 90 mm ² . The diameters of the inner and outer conductors of the segment of the coaxial transition line are determined from the condition of the electric strength of the vacuum coaxial line. For nanosecond pulses, the breakdown electric field strength in a vacuum is E _pr ≥600 kV / cm [V.Ya. Ushakov. Isolation of high voltage installations. - M .: Energoatomizdat. - 1994. - 466 p.]. In this case, the maximum microwave power transmitted along the vacuum coaxial line is related to the breakdown electric field strength by the following formula [Design of microwave devices and screens: Textbook. A manual for universities / AM Chernushenko, N.E. Melanchenko, L.G. Manoratsky, B.V. Petrov / Ed. AM Chernushenko. - M .: Radio and communication. - 1983. - 400 p.]:

, $$P_{PR.}=\frac{E_{PR.}^2{d}^2}{480}\ln \frac{D}{d}$$

,

where P _ave - ultimate microwave power,

E _ave - the breakdown intensity of the electric field in the line,

d is the diameter of the inner conductor of the line,

D is the diameter of the external conductor of the line.

, тогда предельная СВЧ-мощность, передаваемая по вакуумной коаксиальной линии, будет равна:For a line with wave impedance Z _kl = 75 ohms $$\ln \frac{D}{d}=\frac{75}{60}=1.25$$

then the ultimate microwave power transmitted along the vacuum coaxial line will be equal to:

$$P_{PR.}=\frac{1.25\cdot E_{PR.}^2{d}^2}{480}$$

and the diameter of the inner conductor of the segment of the coaxial line of the coaxial waveguide transition can be determined from the expression:

. $$d=\frac{19.6\sqrt{P_{PR}}}{E_{PR.}}$$

.

For P≥10 generated power ⁹ W and E _ave = 6 · 10 ⁵ V / cm, d≥1 cm.

From structural considerations chosen d = 1,6 cm, while the diameter of the outer conductor of the coaxial-waveguide transition coaxial line with the wave impedance Z line _KL = 75 Ohms, will be equal to D = 5.5 cm.

Ultimate microwave power transmitted through a vacuum waveguide of a coaxial waveguide junction with a cross section of 45 × 90 mm to an antenna on a traveling wave of type TE _{10 is} determined by the formula:

, $$P_{PR.\mathrm{at}\mathrm{about}l{n}_{T{E}_{10}}}\le \frac{a\cdot b}{\mathrm{four}}\cdot \frac{E_{PR}^2}{Z_c}\cdot \sqrt{\mathrm{one}-{\left(\frac{{\lambda }_0}{{\lambda }_{\mathrm{to}R{.}_{T{E}_{10}}}}\right)}^2}$$

,

- предельная СВЧ-мощность в волноводе на волне типа ТЕ₁₀, Вт;Where $$P_{PR.\mathrm{at}\mathrm{about}l{n}_{T{E}_{10}}}$$

- ultimate microwave power in a waveguide on a wave of type TE ₁₀ , W;

a and b are the internal size of the waveguide, cm;

E _CR - the breakdown intensity of the electric field in a vacuum waveguide, V / cm;

Z _c = 376.7 Ohms is the characteristic resistance of a plane wave in vacuum;

- длина волны колебаний в волноводе и критическая длина волны типа ТЕ₁₀ в волноводе [Конструкция СВЧ- устройств и электронов: Учеб. пособие для Вузов / А.М. Чернушенко, Н.Е. Меланченко, Л.Г. Малорацкий, Б.В. Петров / Под ред. А.М. Чернушенко. - М.: Радио и связь. - 1983. - 400 с.]. Тогда согласно этой формуле при a=9 см; b=4,5 см; E_пр=6·10⁵ В/см; Z_c=376,7 Ом; λ₀=10 см; $${\lambda }_{кр{.}_{Т{Е}_{10}}}=18$$

см; $$P_{пр.вол{н}_{Т{Е}_{10}}}\le \mathrm{6,5}\cdot {10}^9$$

Вт.λ ₀ and $${\lambda }_{\mathrm{to}R{.}_{T{E}_{10}}}=2a$$

- wavelength of oscillations in the waveguide and the critical wavelength of type TE ₁₀ in the waveguide [Design of microwave devices and electrons: Textbook. manual for universities / A.M. Chernushenko, N.E. Melanchenko, L.G. Maloratsky, B.V. Petrov / Ed. A.M. Chernushenko. - M .: Radio and communication. - 1983. - 400 p.]. Then according to this formula at a = 9 cm; b = 4.5 cm; E _ol = 6 · 10 ⁵ V / cm; Z _c = 376.7 ohms; λ ₀ = 10 cm; $${\lambda }_{\mathrm{to}R{.}_{T{E}_{10}}}=\mathrm{eighteen}$$

cm; $$P_{PR.\mathrm{at}\mathrm{about}l{n}_{T{E}_{10}}}\le 6.5\cdot {10}^9$$

Tue

Thus, as an example of a specific embodiment shows, the use of the inventive device allows for the generation of microwave radiation of a gigawatt power level in a ten-centimeter wavelength range in a microwave generator with a virtual cathode to transform TEM type waves into a TE ₁₀ wave in a rectangular waveguide and expand the functionality of the microwave -generator, increase the reliability of its work.

Claims (5)

1. A microwave generator with a virtual cathode of a coaxial type, comprising a high voltage source, in which a negative electrode is connected to a grounded cylindrical vacuum chamber, a high voltage insulator installed at the end of the chamber, a cylindrical grid anode located along the axis of the chamber, connected to a positive electrode of a high source voltage through the anode holder and the high voltage insulator, the cathode assembly with a cylindrical cathode located inside the anode on its axis and connected to the vacuum chamber, ntennu to output microwave radiation, characterized in that the cathode assembly is connected to the vacuum chamber through a tapered coaxial line, the wide end of which is connected to the free end face of the chamber, and the narrow end to the coaxial-waveguide transition which is connected to an antenna and a matching element. 2. A microwave generator with a virtual coaxial type cathode according to claim 1, characterized in that the coaxial waveguide transition is made in the form of a coaxial waveguide transition of a button type. 3. A microwave generator with a virtual coaxial type cathode according to claim 1, characterized in that the coaxial cone line is connected to the coaxial waveguide transition through a grounded radiator. 4. A microwave generator with a coaxial-type virtual cathode according to claim 1, characterized in that the matching element is made in the form of a short-circuited high-frequency piston and connected to a coaxial-waveguide transition through a vacuum-tight radio-transparent window. 5. A microwave generator with a coaxial-type virtual cathode according to claim 1, characterized in that a radio-transparent vacuum-tight window is installed at the output of the antenna.

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