A low magnetic field and high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output

Abstract

The present invention relates to a microwave source device in the field of high-power microwave technology, in particular to a low-magnetic-field high-efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output, belonging to the field of high-power microwave technology; the whole device adopts a coaxial structure, which can reduce the space charge effect and is conducive to the device working in a low magnetic field; the whole device works in a quasi-TEM and TM 01 Under the dual-mode mechanism, a non-uniform slow-wave structure is simultaneously used to strengthen the electric field and electron beam modulation, thereby improving the microwave conversion efficiency; pure TEM mode microwaves can be output only through an output waveguide with a transition section; the present invention can solve the problem that the prior art is difficult to obtain high efficiency under low magnetic fields, obtain a conversion efficiency greater than 40% under a guided magnetic field of 0.5T, and achieve single-mode output.

Description

Technical Field

[0001] The invention relates to a microwave source device in the field of high-power microwave technology, in particular to a low-magnetic-field high-efficiency coaxial relativistic backward-wave tube with dual-mode operation and single-mode output, belonging to the field of high-power microwave technology. Background Art

[0002] High-power microwaves generally refer to electromagnetic waves with a peak power exceeding 100MW and an operating frequency between 1GHz and 300GHz. A high-power microwave source refers to a device that converts the energy of a strong relativistic electron beam into microwave energy in a high-power microwave system, that is, a device that generates high-power microwaves. In existing high-power microwave sources, a strong guiding magnetic field is generally required to obtain a higher conversion efficiency. Technicians generally use solenoid magnets or superconducting magnets to provide the required magnetic field. The volume of these two types of magnet systems increases sharply with the increase of the magnetic field. Therefore, the volume of the excitation system of a high-power microwave source working in a low magnetic field (less than 1T) is greatly reduced compared to a high-power microwave source working in a strong magnetic field (greater than 1T), but it also causes the problem of low conversion efficiency.

[0003] In order to solve the problem of low conversion efficiency under low magnetic field, high-power microwave sources working in dual mode have been proposed in recent years. Unlike traditional high-power microwave sources in which the electron beam only converts energy with a single surface wave or body wave, high-power microwave sources working in dual mode convert energy with both surface wave and body wave at the same time, which greatly improves the conversion efficiency. At present, researchers mostly use relativistic backward wave oscillators (also known as relativistic backward wave tubes) working in dual mode to obtain high conversion efficiency under low magnetic field. The mechanism of relativistic backward wave oscillators to generate high-power microwaves is Cherenkov radiation.

[0004] At present, the research on dual-mode relativistic backward wave oscillators mainly includes the following related work:

[0005] In 2018, Vladislav V. Rostov and others from the Institute of High Currents of the Siberian Branch of the Russian Academy of Sciences studied an over-moded two-mode relativistic backward wave oscillator [VV Rostov, AV Gunin, RV Tsygankov, et al. Two-Wave Cherenkov Oscillator WithModerately Oversized Slow-WaveStructure [J]. IEEE Transactions on Plasma Science, 2018, 46(1): 33-42.] (hereinafter referred to as prior art 1, such as Figure 1The structure consists of a hollow cathode, an absorbing material, an anode, a matching section, a slow wave structure 1, a slow wave structure 2, a collector, an output waveguide and a solenoid magnetic field. The entire device is rotationally symmetrical about the center. 01 , Body WaveTM 02 The beam-wave interaction improves the conversion efficiency. Simulations show that the conversion efficiency of the device can reach 47% and 30% respectively when working in a strong magnetic field (about 4T) and a low magnetic field (about 1T). This solution has achieved high conversion efficiency under magnetic fields of different strengths, but under low magnetic fields, the conversion efficiency needs to be further improved due to the quality of the electron beam.

[0006] In 2020, Xiao Renzhen and others from the Northwest Institute of Nuclear Technology studied a low-magnetic-field, high-efficiency relativistic backward wave oscillator [Renzhen Xiao, Yanchao Shi, Huida Wang, et al. Efficient generation of multi-gigawatt power by an X-band dual-mode relativistic backward wave oscillator operating at low magnetic field [J]. Physics of Plasmas, 2020, 27(4): 043102.] (hereinafter referred to as prior art 2, such as Figure 2 As shown). The structure consists of a cathode, an internal reflector, a dual pre-modulation cavity, a non-uniform slow-wave structure, and an output waveguide. The entire device is rotationally symmetrical about the center. The internal reflector of this solution does not isolate the diode and the slow-wave structure, and the entire device works in dual mode: TM 01 and TM 02 , and also outputs TM 01 and TM 02 The simulation shows that the device working in dual mode can make full use of the body wave to participate in the beam-wave interaction, thereby improving the efficiency. Under the conditions of diode voltage 880kV, current 12.5kA, and guiding magnetic field 0.66T, the output power is 4.6GW and the conversion efficiency is 42%. This scheme achieves a conversion efficiency of more than 40% under a magnetic field of 0.66T, but its guiding magnetic field can be further reduced, the efficiency can be further improved, and the output of this scheme is TM 01 and TM 02 In the mixed mode, an additional mode converter is required to purify the output mode.

[0007] Analyzing the above research status, it is not difficult to see that the research on dual-mode relativistic backward wave oscillators has achieved a conversion efficiency of more than 40% under a magnetic field of 0.6 T, but the guiding magnetic field of most technical solutions is still above 0.6 T, and the guiding magnetic field needs to be further reduced; and the microwave output mode is complex and needs further purification before it can be used.

[0008] Therefore, there is an urgent need to study a relativistic backward wave tube that can operate in dual modes, has a pure output mode (single mode), a low magnetic field (<0.5T), and a high conversion efficiency (>40%). The technical solution has not yet been publicly reported. Summary of the invention

[0009] The technical problem to be solved by the present invention is: the present invention proposes a low magnetic field high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output. The whole device adopts a coaxial structure, which can reduce the space charge effect and is conducive to the device working in a low magnetic field. The whole device works in quasi-TEM and TM 01 Under the dual-mode mechanism, a non-uniform slow-wave structure is simultaneously used to strengthen the electric field and electron beam modulation, thereby improving the microwave conversion efficiency. Pure TEM mode microwaves can be output only through an output waveguide with a transition section. The present invention can solve the problem that the prior arts 1 and 2 are difficult to obtain high efficiency under low magnetic fields, obtain a conversion efficiency greater than 40% under a guided magnetic field of 0.5T, and achieve single-mode output.

[0010] The technical solution of the present invention is:

[0011] A low magnetic field high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output, comprising a cathode seat 301, a cathode 302, an inner conductor 303, an anode outer cylinder 304, a first drift cavity 305, a first modulation cavity 306, a second drift cavity 307, a second modulation cavity 308, a third drift cavity 309, a slow wave structure 310, a trapezoidal collector 311, an output waveguide 312, and a solenoid magnetic field 313; the entire structure is rotationally symmetric about the central axis.

[0012] The cathode 302 is a thin-walled cylinder with a wall thickness of 2 mm and a radius of R1, which is sleeved on the right end of the cathode seat 301; the outer surface of the inner conductor 303 and the inner surface of the anode outer cylinder 304 have irregular corrugations, and the two constitute a coaxial high-frequency structure. The first drift cavity 305 is an annular cavity with an outer radius of R2 and an inner radius of R3, and a width of L1, which is generally 0.5-0.7 times the working wavelength 𝜆; the first modulation cavity 306 is an annular cavity with an outer radius of R4 and an inner radius of R5, satisfying R4>R2, R3>R5, and a width of L2, which is generally 0.3-0.5 times the working wavelength 𝜆; the second drift cavity 307 is an annular cavity with an outer radius of R2 and an inner radius of R6, satisfying R6>R5, and a width of L3, which is generally 0.6-0. 8 times; the second modulation cavity 308 is a circular ring cavity with an outer radius of R7 and an inner radius of R5, satisfying R7>R4, and a width of L4, which is generally 0.8-1 times the working wavelength 𝜆; the third drift cavity 309 is a circular ring cavity with an outer radius of R8 and an inner radius of R6, satisfying R8>R2, and a width of L5, which is generally 0.5-0.7 times the working wavelength 𝜆; the part of the slow-wave structure 310 located on the outer surface of the inner conductor is a cylinder with a radius of R9, and the part located on the inner surface of the anode outer cylinder is 9 slow-wave blades: the first slow-wave blade is composed of an inner radius R 10 , a ring with a width of L6 and an inner radius of R 23 , a ring with a width of L7, satisfying R 10 >R 23 , L6 is generally 1mm-6mm, L7 is generally 6mm-15mm; the second slow wave blade is composed of an inner radius R 11 , a ring with a width of L8 and an inner radius of R 24 , a ring with a width of L9, satisfying R 11 >R 24 , L8 is generally 1mm-6mm, L9 is generally 6mm-15mm; the third slow wave blade is composed of an inner radius R 12 , Width L 10 The ring and the inner radius R 25 , Width L 11 The ring composition satisfies R 12 >R 25 , L 10 The general value is 1mm-6mm, L 11 The general value is 6mm-15mm; the fourth slow wave blade is from the inner radius R 13 , Width L 12 The ring and the inner radius R 25 , Width L 13 The ring composition satisfies R 13 >R 25 , L 12The general value is 1mm-6mm, L 13 The value is usually 6mm-15mm; the fifth slow wave blade is from the inner radius R 14 , Width L 14 The ring and the inner radius R 26 , Width L 15 The ring composition satisfies R 14 >R 26 , L 14 The general value is 1mm-6mm, L 15 The general value is 6mm-15mm; the sixth slow wave blade is from the inner radius R 15 , Width L 16 The ring and the inner radius R 26 , Width L 17 The ring composition satisfies R 15 >R 26 , L 16 The general value is 1mm-6mm, L 17 The general value is 6mm-15mm; the seventh slow wave blade is from the inner radius R 16 , Width L 18 The ring and the inner radius R 26 , Width L 19 The ring composition satisfies R 16 >R 26 , L 18 The general value is 1mm-6mm, L 19 The general value is 6mm-15mm; the eighth slow wave blade is from the inner radius R 17 , Width L 20 The ring and the inner radius R 26 , Width L 21 The ring composition satisfies R 17 >R 26 , L 20 The general value is 1mm-6mm, L 21 The value is generally 6mm-15mm; the ninth slow wave blade is composed of the inner radius R 18 , Width L 22 The ring and the inner radius R 19 , Width L 23 The ring composition satisfies R 18 >R 19 , L 22 The general value is 1mm-6mm, L 23 It needs to be designed comprehensively according to the electron beam bombardment position and magnetic field configuration, and is generally taken as 0.2-0.5 times the working wavelength 𝜆. The trapezoidal collector 311 is a truncated cone-shaped cavity with a parallelogram cross section and an outer radius of R 20 , the inner radius is R 19 , the length of the base is L25 , the projection length of the hypotenuse is L 24 , L 24 and L 25 It needs to be designed comprehensively according to the electron beam bombardment position and magnetic field configuration. 24 The value is generally 1.2-1.6 times the working wavelength 𝜆, L 25 The value is generally taken as 0.4-1 times of the working wavelength 𝜆; the inner conductor 303 is projected at a length L from the trapezoidal collector 311. 26 The radius at the position increases from R9 to R 22 , from R9 to R 22 The projection length at the transition section is L 27 , L 26 The value is generally taken as 0.7-1.2 times of the working wavelength 𝜆, L 27 The value is generally 0.2-0.7 times the working wavelength 𝜆. The output waveguide 312 is an outer radius R 21 , the inner radius is R 22 , length is L 28 The coaxial waveguide, L 28 1-2 times of the working wavelength 𝜆; the output waveguide with transition section is used to make the output waveguide cutoff TM 01 mode, thereby outputting pure TEM mode microwaves, avoiding the need for an additional mode converter behind the device; the solenoid magnetic field 313 surrounds the outer wall of the anode outer cylinder 304 to generate a guiding magnetic field.

[0013] The cathode seat 301, the inner conductor 303 and the anode outer tube 304 are usually made of non-magnetic stainless steel, the cathode 302 can be made of high-hardness graphite or heat-resistant glass cloth-epoxy resin copper foil (FR-5) material, and the solenoid magnetic field 313 is made of enameled copper wire or glass fiber copper wire. The left end of the cathode seat 301 is connected to the inner conductor of the pulse power driving source, and the left end of the anode outer tube 304 is connected to the outer conductor of the pulse power driving source.

[0014] The working process of the present invention is as follows: the pulsed high voltage generated by the front device (such as a pulse power source) acts on the cathode 302 through the cathode seat 301, and the cathode 302 generates a strong relativistic electron beam based on the explosive emission, which is transmitted to the coaxial high-frequency structure under the guidance of the solenoid magnetic field 313. The electron beam passes through the first drift cavity 305, the first modulation cavity 306, the second drift cavity 307, the second modulation cavity 308, the third drift cavity 309, the slow-wave structure 310, and finally bombards the trapezoidal collector 311. Under a low magnetic field, the first modulation cavity and the second modulation cavity can pre-modulate the strong relativistic electron beam. The pre-modulated electron beam enters the slow-wave structure and first interacts with the quasi-TEM eigenmode in the slow-wave structure. Since the device is in a coaxial over-modulation state, the quasi-TEM mode excited first will be converted into a TM of the same frequency.01 The two modes are mixed and interact with the electron beam. The generated microwaves are finally radiated outward through the output waveguide 312.

[0015] Compared with the prior art, the present invention can achieve the following technical effects:

[0016] 1. The present invention provides a dual-mode working single-mode output low magnetic field high efficiency coaxial relativistic backward wave tube working in coaxial quasi-TEM and TM 01 In the dual-mode mechanism, unlike devices operating in single mode where only surface waves (coaxial quasi-TEM mode) participate in beam-wave interaction, this device enables bulk waves (coaxial TM 01 mode) also participates in the beam-wave interaction. The maximum electric field of the body wave is farther away from the device surface than that of the surface wave, so that the electron beam diffusing laterally under low magnetic field can move away from the surface of the slow-wave structure for efficient beam-wave interaction, thereby improving the conversion efficiency of the device under low magnetic field.

[0017] 2. Compared with the traditional hollow relativistic backward wave tube working in a low magnetic field, the low-magnetic-field high-efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output provided by the present invention introduces an inner conductor, so that the high-frequency structure is transformed into a coaxial structure. The coaxial structure can further reduce the space charge effect of the electron beam and improve the quality of the electron beam under the same magnetic field strength, thereby reducing the guiding magnetic field of the dual-mode working high-power microwave device.

[0018] 3. Compared with the hollow dual-mode working relativistic backward wave tube, the low-magnetic field high-efficiency coaxial dual-mode working single-mode output relativistic backward wave tube provided by the present invention does not need to be connected with a mode converter separately. The mixed mode working in the slow-wave structure can be output in a single TEM mode only through an output waveguide with a transition section, which solves the problem that traditional dual-mode working devices output mixed modes and need to be connected with a mode converter separately. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of an over-moded dual-mode relativistic backward wave oscillator disclosed in the prior art 1 in the background introduction;

[0020] Figure 2 A schematic diagram of the structure of a low magnetic field and high efficiency relativistic backward wave tube oscillator disclosed in the prior art 2 in the background introduction;

[0021] Figure 3 A - A cross-sectional view of a preferred embodiment of a low magnetic field high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output provided by the present invention;

[0022] Figure 4 A-A sectional stereoscopic schematic diagram of a preferred embodiment of a dual-mode working single-mode output low magnetic field high efficiency coaxial relativistic backward wave tube provided by the present invention;

[0023] Figure 5 A dispersion curve of a uniform periodic slow-wave structure of a preferred embodiment of a low-magnetic-field high-efficiency coaxial relativistic backward-wave tube with dual-mode operation and single-mode output provided by the present invention;

[0024] Figure 6 The first modulation cavity and the second modulation cavity of the preferred embodiment of the dual-mode working single-mode output low magnetic field high efficiency coaxial relativistic backward wave tube provided by the present invention are S 11 Plot of changes with frequency;

[0025] Figure 7 The spatial distribution diagram of the electric field axial component of a preferred embodiment of a dual-mode working single-mode output low magnetic field high efficiency coaxial relativistic backward wave tube provided by the present invention when the output microwave reaches saturation (t=23ns);

[0026] Figure 8 The spatial distribution diagram of the radial component of the electric field of a preferred embodiment of a dual-mode working single-mode output low magnetic field high efficiency coaxial relativistic backward wave tube provided by the present invention when the output microwave reaches saturation (t=23ns);

[0027] Fig. 9 A graph showing the variation of injected electric power over time in a preferred embodiment of a dual-mode working single-mode output low magnetic field high efficiency coaxial relativistic backward wave tube provided by the present invention;

[0028] Fig.10 An output microwave power diagram of a preferred embodiment of a dual-mode working single-mode output low magnetic field high efficiency coaxial relativistic backward wave tube provided by the present invention;

[0029] Fig.11 An output microwave spectrum diagram of a preferred embodiment of a dual-mode working single-mode output low magnetic field high efficiency coaxial relativistic backward wave tube provided by the present invention;

[0030] Fig.12 The electric field spatial distribution diagram of a preferred embodiment of a dual-mode working single-mode output coaxial relativistic backward wave tube provided by the present invention when the output waveguide has no transition section;

[0031] Fig.13 The electric field spatial distribution diagram of a preferred embodiment of a dual-mode working single-mode output coaxial relativistic backward wave tube provided by the present invention when the output waveguide has a transition section;

[0032] Fig.14 The output microwave of the low magnetic field high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output provided by the present invention is R 22 ;

[0033] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention. DETAILED DESCRIPTION

[0034] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] The present invention is composed of a cathode seat 301, a cathode 302, an inner conductor 303, an anode outer cylinder 304, a first drift cavity 305, a first modulation cavity 306, a second drift cavity 307, a second modulation cavity 308, a third drift cavity 309, a slow wave structure 310, a trapezoidal collector 311, an output waveguide 312, and a solenoid magnetic field 313. The entire structure is rotationally symmetric about the central axis.

[0036] When the present invention is in operation, the pulse power driving source loads the pulse voltage onto the cathode holder 301, and the cathode 302 emits a strong relativistic electron beam, which is first pre-modulated in the first modulation cavity 306 and the second modulation cavity 308, i.e., initial velocity modulation. In the non-uniform slow-wave structure, the fundamental quasi-TEM mode in the slow-wave structure is first excited, and then the quasi-TEM mode is converted into the TM mode of the same frequency. 01 The two modes interact with the electrons together. The electrons are further modulated in speed at the first few slow-wave blades of the slow-wave structure. The speed modulation gradually turns into density modulation, and clustering occurs. The clustered electron beam generates Cherenkov radiation at the last few slow-wave blades of the slow-wave structure, and hands over energy to microwaves, thereby generating high-power microwaves.

[0037] In the particle simulation, under the conditions of diode voltage 625kV, current 11.9kA, and guide magnetic field 0.5T, the high-power microwave with an output frequency of 8.40GHz, an output microwave power of 3.5GW, and a conversion efficiency of 47% were output. From the above results, it can be seen that the present invention overcomes the difficulty of obtaining high conversion efficiency of the relativistic backward wave tube under low magnetic field, and obtains a conversion efficiency of more than 45%.

[0038] See also Figure 5It can be seen that the dispersion curves of the electron beam line and the quasi-TEM mode intersect at point a, with a frequency of about 8.48 GHz. At this time, the electron beam and the quasi-TEM mode interact with each other synchronously, and then the quasi-TEM mode is converted into the TM with the same frequency. 01 mode (points b and c), with which the electron beam undergoes asynchronous beam-wave interaction.

[0039] See also Figure 6 It can be seen that the S of the first modulation cavity and the second modulation cavity for the TEM mode at the operating frequency of 8.40 GHz 11 It is 0.87, which can effectively isolate the beam-wave interaction region and the diode region.

[0040] See also Figure 7 and Figure 8 It can be seen that when the device outputs microwave saturation, there are strong axial electric fields and radial electric fields in the coaxial slow-wave structure, and different longitudinal modes are shown on the side close to the outer conductor surface of the device and the side far from the conductor surface, indicating that there are quasi-TEM modes (surface waves) and TM modes in the slow-wave structure area. 01 modes (bulk waves) rather than a single quasi-TEM mode or TM 01 Mode, that is, working in dual mode.

[0041] See also Fig. 9 , it can be seen that the input power of the device is 7.45GW.

[0042] See also Fig.10 It can be seen that when the guided magnetic field is 0.5T, the output microwave power of the device is 3.5GW, and the corresponding conversion efficiency is 47%.

[0043] See also Fig.11 It can be seen that the center frequency of the device's output microwave is 8.40GHz, and the spectrum is pure without any noise, indicating that there is no competition from other frequencies.

[0044] See also Fig.12 and 13 It can be seen that the output waveguide without a transition section will output TEM mode and TM mode. 01 The output waveguide with a transition section can achieve pure TEM mode output without further loading of a mode converter.

[0045] See also Fig.14 , we can know that the inner conductor radius R at the output waveguide 22 It has an impact on the conversion efficiency because it affects the output port's TEM mode and TM mode. 01 Reflection of the module, R 22 When the optimal value is 36mm, the conversion efficiency reaches the maximum.

[0046] Of course, in this preferred embodiment, other connection methods can also be used between the components, and the device structure can also be processed with other materials. The above is only a preferred implementation method of the present invention. The protection scope of the present invention is not limited to the above embodiment. All technical solutions under the concept of the present invention belong to the protection scope of the present invention.

[0047] It will be clear to those skilled in the art that the scope of the present invention is not limited to the examples discussed above, and that several changes and modifications may be made thereto without departing from the scope of the present invention as defined in the appended claims. Although the present invention has been illustrated and described in detail in the drawings and the specification, such illustration and description are merely illustrative or schematic and not restrictive. The present invention is not limited to the disclosed embodiments.

[0048] By studying the drawings, the description and the claims, those skilled in the art can understand and implement variations of the disclosed embodiments when practicing the invention. In the claims, the term "comprising" does not exclude other steps or elements. The fact that certain measures are cited in mutually different dependent claims does not mean that a combination of these measures cannot be used to advantage. Any reference signs in the claims do not constitute a limitation of the scope of the invention.

Claims

1. A low magnetic field high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output, characterized by: It comprises a cathode seat (301), a cathode (302), an inner conductor (303), an anode outer cylinder (304), a first drift cavity (305), a first modulation cavity (306), a second drift cavity (307), a second modulation cavity (308), a third drift cavity (309), a slow wave structure (310), a trapezoidal collector (311), an output waveguide (312), and a solenoid magnetic field (313); the entire structure is rotationally symmetric about a central axis; The cathode (302) is a thin-walled cylinder with a radius of R1, which is sleeved on the right end of the cathode seat (301); the outer surface of the inner conductor (303) and the inner surface of the anode outer cylinder (304) have irregular corrugations, and the two constitute a coaxial high-frequency structure; the first drift cavity (305) is a circular ring cavity with an outer radius of R2, an inner radius of R3, and a width of L1, where L1 is 0.5-0.7 times the working wavelength 𝜆; the first modulation cavity (306) is a circular ring cavity with an outer radius of R4, an inner radius of R5, and satisfies R4>R2, R3>R5, and a width of L2, where L2 is 0.3-0.5 times the working wavelength 𝜆; the second drift cavity (307) is a circular ring cavity with an outer radius of R2, an inner radius of The first modulation cavity (308) is a circular ring cavity with an outer radius of R7 and an inner radius of R5, satisfying R7>R4, and a width of L4, which is 0.8-1 times the working wavelength 𝜆; the third drift cavity (309) is a circular ring cavity with an outer radius of R8 and an inner radius of R6, satisfying R8>R2, and a width of L5, which is 0.5-0.7 times the working wavelength 𝜆; the portion of the slow-wave structure (310) located on the outer surface of the inner conductor is a cylinder with a radius of R9, and the portion located on the inner surface of the anode outer cylinder is 9 slow-wave blades: the first slow-wave blade is composed of an inner radius of R 10 , a ring with a width of L6 and an inner radius of R 23 , a ring with a width of L7, satisfying R 10 >R 23 , L6 is 1mm-6mm, L7 is 6mm-15mm; the second slow wave blade is composed of inner radius R 11 , a ring with a width of L8 and an inner radius of R 24 , a ring with a width of L9, satisfying R 11 >R 24 , L8 is 1mm-6mm, L9 is 6mm-15mm; the third slow wave blade is composed of inner radius R 12 , Width L 10 The ring and the inner radius R 25 , Width L 11 The ring composition satisfies R 12 >R 25 , L 10 The value is 1mm-6mm, L 11 The value is 6mm-15mm; the fourth slow wave blade is from the inner radius R 13 , Width L 12 The ring and the inner radius R 25 , Width L 13 The ring composition satisfies R 13 >R 25 , L 12 The value is 1mm-6mm, L 13 The value is 6mm-15mm; the fifth slow wave blade is from the inner radius R 14 , Width L 14 The ring and the inner radius R 26 , Width L 15 The ring composition satisfies R 14 >R 26 , L 14 The value is 1mm-6mm, L 15 The value is 6mm-15mm; the sixth slow wave blade is from the inner radius R 15 , Width L 16 The ring and the inner radius R 26 , Width L 17 The ring composition satisfies R 15 >R 26 , L 16 The value is 1mm-6mm, L 17 The value is 6mm-15mm; the seventh slow wave blade is from the inner radius R 16 , Width L 18 The ring and the inner radius R 26 , Width L 19 The ring composition satisfies R 16 >R 26 , L 18 The value is 1mm-6mm, L 19 The value is 6mm-15mm; the eighth slow wave blade is from the inner radius R 17 , Width L 20 The ring and the inner radius R 26 , Width L 21 The ring composition satisfies R 17 >R 26 , L 20 The value is 1mm-6mm, L 21 The value is 6mm-15mm; the ninth slow wave blade is from the inner radius R 18 , Width L 22 The ring and the inner radius R 19 , Width L 23 The ring composition satisfies R 18 >R 19 , L 22 The value is 1mm-6mm, L 23 It needs to be designed comprehensively according to the electron beam bombardment position and magnetic field configuration, and the value is 0.2-0.5 times the working wavelength 𝜆; the trapezoidal collector (311) is a truncated cone-shaped cavity with a parallelogram cross section and an outer radius of R 20 , the inner radius is R 19 , the length of the base is L 25 , the projection length of the hypotenuse is L 24 , L 24 and L 25 It needs to be designed comprehensively according to the electron beam bombardment position and magnetic field configuration. 24 The value is 1.2-1.6 times of the working wavelength 𝜆, L 25 The value is 0.4-1 times of the working wavelength 𝜆; the inner conductor (303) is projected at a length L from the trapezoidal collector (311) 26 The radius at the position increases from R9 to R 22 , the radius increases from R9 to R 22 The projection length is L 27 , L 26 The value is 0.7-1.2 times of the working wavelength 𝜆, L 27 The value is 0.2-0.7 times of the working wavelength 𝜆; the output waveguide (312) is an outer radius of R 21 , the inner radius is R 22 , length is L 28 The coaxial waveguide, L 28 1-2 times of the working wavelength 𝜆; the output waveguide with transition section is used to make the output waveguide cutoff TM 01 mode, thereby outputting pure TEM mode microwaves, avoiding the need for an additional mode converter behind the device; the solenoid magnetic field (313) surrounds the outer wall of the anode outer cylinder (304) to generate a guiding magnetic field.

2. A low magnetic field high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output according to claim 1, characterized in that: The cathode (302) wall thickness is 2 mm.

3. A low magnetic field high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output according to claim 1, characterized in that: The cathode seat (301), the inner conductor (303) and the anode outer cylinder (304) are made of non-magnetic stainless steel material.

4. A low magnetic field high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output according to claim 1, characterized in that: The cathode (302) is made of high-hardness graphite or heat-resistant glass cloth-epoxy resin copper-clad foil material.

5. A low magnetic field high efficiency coaxial relativistic backward wave tube with dual-mode operation and single-mode output according to claim 1, characterized in that: The solenoid magnetic field (313) is wound with enameled copper wire or glass-fiber-wrapped copper wire.

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