Cherenkov oscillator using a composite fine-tuning magnetic field

Abstract

The present application relates to a kind of Cherenkov oscillator using composite fine adjustment magnetic field, the present application includes oscillator cavity and the composite fine adjustment magnetic field being arranged outside oscillator cavity, composite fine adjustment magnetic field includes positive solenoid external magnetic field and fine adjustment magnetic field system, fine adjustment magnetic field system is located between positive solenoid external magnetic field and oscillator cavity, fine adjustment magnetic field system includes first positive solenoid fine adjustment magnetic field, second positive solenoid fine adjustment magnetic field and negative solenoid fine adjustment magnetic field, oscillator cavity includes extraction cavity, extraction cavity is arranged with negative solenoid fine adjustment magnetic field outside, negative solenoid fine adjustment magnetic field is arranged with first positive solenoid fine adjustment magnetic field and second positive solenoid fine adjustment magnetic field outside respectively, the present application uses composite hetero solenoid magnetic field combination magnetic field model in magnetic field design and optimally designs, changes magnetic force line configuration, in turn changes electron beam running track.This kind of design guarantees the distance between electron beam and outer cavity, while using local magnetic field to change electron beam configuration method reduces the distance between electron beam and extraction cavity, improves microwave extraction efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to a microwave source device in the field of high power microwave technology, in particular to a Cerenkov oscillator using a composite fine-tuning magnetic field to improve extraction efficiency, and belongs to the field of high power microwave technology. BACKGROUND

[0002] High power microwave generally refers to electromagnetic waves with a peak power greater than 100 MW and a frequency of 1 GHz-300 GHz, and high power microwave technology is a new research field emerging with the development of pulsed power technology, plasma physics and electric vacuum technology. It has a bright application prospect in plasma heating, high power radar, particle radio frequency acceleration and future space energy utilization.

[0003] A high power microwave source is a core device of a high power microwave system, and its operation is based on coherent radiation of an electron beam. The coherent radiation mechanism of the electron beam is divided into three categories: Cerenkov radiation, transition radiation and bremsstrahlung. The high power microwave source based on the Cerenkov radiation mechanism mainly includes a relativistic Cerenkov oscillator and a relativistic Cerenkov amplifier. The high power microwave source based on the transition radiation mechanism mainly includes a relativistic klystron oscillator and a relativistic klystron amplifier. The high power microwave source based on the bremsstrahlung mechanism mainly includes a free electron laser and a virtual cathode.

[0004] The relativistic Cerenkov oscillator is one of the most potential high power microwave source devices at present. It utilizes the interaction between a relativistic electron beam and an electromagnetic wave mode (structure wave) in a slow wave structure to produce self-oscillation and amplification, form coherent microwave radiation, and has the characteristics of high power, high efficiency and suitability for repeated frequency operation.

[0005] Generally speaking, for a relativistic Cerenkov oscillator working in TM01 mode, the closer to the outer conductor, the stronger the transverse electric field, so the annular electron beam is generally closer to the outer conductor in the design of the device. However, since the outer conductor has a potential of 0, the electron beam has a negative voltage of tens to hundreds of kilovolts, and if the distance between the electron beam and the outer conductor is too close, the electron beam will break through the constraint of the guiding magnetic field under the action of the strong potential difference, hit the outer conductor earlier than expected, and reduce the efficiency.

[0006] According to research, the extraction structure plays a great role in improving the electromagnetic wave extraction efficiency of the Cerenkov oscillator. The extraction structure is generally located behind the slow wave structure, and utilizes the principle of resonant cavity to form a standing wave of a specific frequency in the cavity. When the clustered electron beam passes through, the strong standing wave in the cavity converts the kinetic energy of the electron beam into the energy of the electromagnetic wave. However, as described in the previous paragraph, the distance between the electron beam and the extraction cavity is greatly restricted, which affects the microwave extraction efficiency. SUMMARY

[0007] The technical problem this invention aims to solve is to provide a Cherenkov oscillator that improves extraction efficiency using a composite fine-tuning magnetic field. This invention employs a magnetic field model combining composite anisotropic solenoid magnetic fields and optimizes its design, altering the magnetic field line configuration and thus the electron beam trajectory. This design ensures the distance between the electron beam and the external cavity while reducing this distance by using a local magnetic field to change the electron beam configuration, thereby improving microwave extraction efficiency. This provides a new approach to improving the microwave output efficiency of Cherenkov oscillators, and the structure is simple and easy to manufacture.

[0008] The technical solution of this invention is as follows: This invention is a Cherenkov oscillator using a composite fine-tuning magnetic field, characterized in that: the Cherenkov oscillator using a composite fine-tuning magnetic field includes an oscillator cavity and a composite fine-tuning magnetic field surrounding the outside of the oscillator cavity. The composite fine-tuning magnetic field includes a positive solenoid external magnetic field and a fine-tuning magnetic field system. The fine-tuning magnetic field system is located between the positive solenoid external magnetic field and the oscillator cavity. The fine-tuning magnetic field system includes a first positive solenoid fine-tuning magnetic field, a second positive solenoid fine-tuning magnetic field, and a negative solenoid fine-tuning magnetic field. The oscillator cavity includes an extraction cavity, and a negative solenoid fine-tuning magnetic field is surrounding the outside of the extraction cavity. A first positive solenoid fine-tuning magnetic field and a second positive solenoid fine-tuning magnetic field are respectively surrounding the negative solenoid fine-tuning magnetic field on both sides. The negative solenoid fine-tuning magnetic field, the first positive solenoid fine-tuning magnetic field, and the second positive solenoid fine-tuning magnetic field are located between the oscillator cavity and the positive solenoid external magnetic field.

[0009] Furthermore, the external magnetic field of the positive solenoid is divided into three parts. The first part of the external magnetic field of the positive solenoid is of length L. m1 The outer radius is R m2 The inner radius is R m5 The magnetic field of the solenoid, the second part of the positive external magnetic field of the solenoid is of length L. m2 The outer radius is R m5 The inner radius is R m1 The magnetic field of the solenoid, the third part of the positive external magnetic field of the solenoid is of length L. m1 The outer radius is R m2 The inner radius is R m5 The solenoid magnetic field consists of a first part of the positive solenoid external magnetic field and a third part of the positive solenoid external magnetic field, which are respectively arranged around the two ends of the second part of the positive solenoid external magnetic field.

[0010] Furthermore, the first positive solenoid fine-tuning magnetic field is of length L. m3 The outer radius is R m1 The inner radius is R m3 The first positive solenoid magnetic field; the second positive solenoid fine-tuning magnetic field is of length L. m3 The outer radius is R m1 The inner radius is Rm3 a solenoid magnetic field with a length of L m4 , an outer radius of R m1 , and an inner radius of R m4 .

[0011] Further, the oscillator cavity comprises, from left to right, an anode outer cylinder, a cutoff neck, a resonant reflection cavity, a slow wave structure, an extraction cavity, and an output waveguide; the anode outer cylinder is internally provided with a cathode.

[0012] Further, the cathode is a thin-walled cylinder with a wall thickness of 2mm and an inner radius R1 equal to the electron beam radius, the anode outer cylinder is a metal shell with an inner radius R2, the cutoff neck is disc-shaped with an inner radius R3, R3>R1, and a length L2, the length L1 between the cutoff neck and the cathode is the anode-cathode spacing, L1 is greater than 2cm, the resonant reflection cavity is disc-shaped with an inner radius R3 and an outer radius R4, R4>R3, and a length L3 equal to 0.4-0.5 times the working wavelength λ; the slow wave structure is at a length L4 from the resonant reflection cavity, L4 is equal to 0.2-0.3 times the working wavelength λ.

[0013] Further, the slow wave structure is composed of 6 trapezoidal slow wave vanes, each two trapezoidal slow wave vanes are connected by a circular ring with a length L7 and an inner radius R3, among the 6 trapezoidal slow wave vanes, the first slow wave vane is a right-angled trapezoid with an upper base length L5, an oblique side width L6, and an outer radius R5; the second, third, and fifth slow wave vanes are isosceles trapezoids with an upper base length L5 and an oblique side width L6, and the outer radii R6, R7, and R9, respectively, satisfying R9>R7>R6; the fourth trapezoidal slow wave vane has an upper base length L8, satisfying L8>L5, an oblique side width L6, and an outer radius R8, satisfying R8>R9; the sixth slow wave vane is also a right-angled trapezoid with an upper base length L5, an oblique side width L6, and an outer radius R 10 , satisfying R8>R 10 >R9, and L5 and L7 are equal to 0.1 times the working wavelength λ.

[0014] Further, the slow wave structure is followed by a drift section with an inner radius R3 and a length L9, L9 is equal to 0.8-1 times the working wavelength λ; the drift section is followed by the extraction cavity, the extraction cavity is disc-shaped with an outer radius R 11 , a length L 10 , satisfying R 11 >R8, and a depth equal to the difference between the outer radius R 11 of the extraction cavity and the inner radius R3 of the drift section.

[0015] Further, the extraction cavity is connected with an output waveguide with a radius R3.

[0016] Further, the minimum radius of the outer magnetic field of the solenoid should not be less than R m1 , and R m1 >R2.

[0017] Further, the anode outer cylinder, the cutoff neck, the resonant reflector cavity, the slow wave structure, the extraction cavity and the output waveguide are made of non-magnetic stainless steel, the cathode is made of graphite, and the forward solenoid outer magnetic field, the first forward solenoid fine-tuning magnetic field, the negative solenoid fine-tuning magnetic field and the second forward solenoid fine-tuning magnetic field are wound with copper wires.

[0018] Compared with the prior art, the present application can achieve the following technical effects:

[0019] The present application adopts a composite fine-tuning magnetic field, and the main effects are as follows:

[0020] 1) Although the solenoid flat wires of all magnetic field parts are actually one wire, when all magnetic field parts are energized, the negative solenoid fine-tuning magnetic field 110 can generate a reverse magnetic field due to the reverse winding, and at this time, due to the fine-tuning shaping effect of the magnetic lines of force of the positive solenoid fine-tuning magnetic field A 109 and the positive solenoid fine-tuning magnetic field B 111 on the front and rear sides of the negative solenoid fine-tuning magnetic field 110, the magnetic lines of force will produce outward bending at this position. After adopting the composite fine-tuning magnetic field, the magnetic field, the magnetic line of force and the relative relationship profile of the device designed by SuperFish software are shown in Figure 3 , wherein the thin gray line in the figure is the magnetic line of force cluster after adopting the magnetic field, and the thick gray line is the actual running track of the electron beam in the PIC (particle simulation simulation) simulation. It can be seen that the magnetic line of force track produces outward bending at the extraction cavity, and the radius of the electron beam running according to the magnetic line of force track increases at the extraction cavity, and after passing through the extraction cavity, the radius decreases and finally hits the output waveguide. The advantage of this design is that the distance between the electron beam and the outer conductor of the slow wave structure and other parts remains unchanged, ensuring that the electron beam passes through the position with the strongest transverse electric field and does not contact the outer conductor in advance, improving the microwave extraction efficiency, and no additional materials are required except copper wires for solenoid magnetic field.

[0021] 2) The single solenoid magnetic field and the composite fine-tuning magnetic field are adopted, and the comparison chart of the Cherenkov oscillator model containing the electron beam in the PIC software is shown in Figure 4 . It can be seen that the electron beam part of the Cherenkov oscillator using the composite fine-tuning magnetic field extends into the extraction cavity Figure 5 , and the electron beam of the Cherenkov oscillator using the single solenoid magnetic field is far away from the extraction cavity Figure 5The closer the extraction cavity is to the electron beam, the higher the microwave extraction efficiency is, because a strong standing wave field is generated at the extraction cavity. Figure 5 The microwave output power of the Cherenkov oscillator using single solenoid magnetic field is 3.15 GW after saturation. The microwave output power of the Cherenkov oscillator using composite fine-tuning magnetic field is 3.86 GW after saturation. In the figure, it can be obviously observed that the microwave output power is greatly improved at the cost of 5 ns delay of saturation time after the Cherenkov oscillator using composite fine-tuning magnetic field is used, which proves that the use of composite fine-tuning magnetic field to change the electron beam shape is helpful to improve the output efficiency of the device. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A cross-sectional perspective view of a preferred embodiment of the Cherenkov oscillator using composite fine-tuning magnetic field according to the present application is provided.

[0023] Figure 2 A cross-sectional structure view of a preferred embodiment of the Cherenkov oscillator using composite fine-tuning magnetic field according to the present application is provided.

[0024] Figure 3 A corresponding diagram of magnetic field magnetic lines and electron running track of a preferred embodiment of the Cherenkov oscillator using composite fine-tuning magnetic field according to the present application is provided.

[0025] Figure 4 A comparison diagram of relative positions of electron beam and device when single solenoid magnetic field and composite fine-tuning magnetic field are used in a preferred embodiment of the Cherenkov oscillator using composite fine-tuning magnetic field according to the present application is provided.

[0026] Figure 5 A comparison diagram of microwave output power changing with time when single solenoid magnetic field and composite fine-tuning magnetic field are used in a preferred embodiment of the Cherenkov oscillator using composite fine-tuning magnetic field according to the present application is provided.

[0027] The reference signs are explained as follows:

[0028] 101, cathode; 102, anode outer cylinder; 103, cutoff neck; 104, resonant reflection cavity; 105, slow wave structure; 106, extraction cavity; 107, output waveguide; 108, positive solenoid external magnetic field; 109, first positive solenoid fine-tuning magnetic field; 110, negative solenoid fine-tuning magnetic field; 111, second positive solenoid fine-tuning magnetic field; 112, oscillator cavity. DETAILED DESCRIPTION

[0029] The overall scheme of the present application is further explained in detail in combination with the drawings and specific embodiments as follows:

[0030] Reference is made to Figure 1 , 2The application provides a Cherenkov oscillator using a composite fine-tuning magnetic field, and the structure of a specific embodiment of the Cherenkov oscillator includes an oscillator cavity 112 and a composite fine-tuning magnetic field arranged outside the oscillator cavity 112, wherein the composite fine-tuning magnetic field includes a forward solenoid external magnetic field 108 and a fine-tuning magnetic field system, the fine-tuning magnetic field system includes the forward solenoid external magnetic field 108, a first forward solenoid fine-tuning magnetic field 109, a negative solenoid fine-tuning magnetic field 110 and a second forward solenoid fine-tuning magnetic field 111; the oscillator cavity 112 includes, from left to right, an anode outer cylinder 102, a cutoff neck 103, a resonant reflection cavity 104, a slow wave structure 105, an extraction cavity 106 and an output waveguide 107; a cathode 101 is arranged in the anode outer cylinder 102. The whole structure is rotationally symmetrical about a central axis, the left end of the cathode 101 is externally connected to an inner conductor of a pulse power source, the left end of the anode outer cylinder 102 is externally connected to an anode of the pulse power source, and the right end of the output waveguide 107 is connected to a mode converter and an antenna; the forward solenoid external magnetic field 108, the first forward solenoid fine-tuning magnetic field 109, the negative solenoid fine-tuning magnetic field 110 and the second forward solenoid fine-tuning magnetic field 111 are installed on a magnetic field support. The Cherenkov oscillator part is as follows:

[0031] The cathode 101 is a thin-walled cylinder with a wall thickness of 2 mm and an inner radius R1 equal to the electron beam radius;

[0032] The anode outer cylinder 102 is a metal shell with an inner radius R2, and the left end is externally connected to the anode of the pulse power source;

[0033] The cutoff neck 103 is disc-shaped, has an inner radius R3 and a length L2, and R3>R1; the length L1 between the cutoff neck 103 and the cathode 101 is referred to as the anode-cathode spacing; if L1 is too small, the cathode plasma will expand to the anode too early, resulting in anode-cathode closure and shortening of the pulse, so L1 is generally greater than 2 cm;

[0034] The resonant reflection cavity 104 is disc-shaped, has an inner radius R3 and an outer radius R4, and R4>R3; the length L3 is generally 0.4-0.5 times the working wavelength λ;

[0035] The slow wave structure 105 is located at a length L4 away from the resonant reflection cavity 104; L4 is generally 0.2-0.3 times the working wavelength λ;

[0036] The slow wave structure 105 is composed of six trapezoidal slow wave vanes, and the trapezoidal slow wave vanes are connected by a circular ring with a length L7 and an inner radius R3;

[0037] The first slow wave vane is a right-angled trapezoid, has a length L5 as the upper base of the trapezoid and a width L6 as the hypotenuse, and has an outer radius R5;

[0038] The second, third and fifth slow wave vane are isosceles trapezoids, the upper base length of the trapezoid is L5, the oblique side width is L6, the outer radius of the slow wave vane is R6, R7 and R9 respectively, and R9>R7>R6 is satisfied;

[0039] The fourth trapezoidal slow wave vane has an upper base length of L8, and L8>L5 is satisfied, the oblique side width is L6, and the outer radius of the slow wave vane is R8, and R8>R9 is satisfied;

[0040] The sixth slow wave vane is also a right trapezoid, and the upper base length of the trapezoid is also L5, the oblique side width is L6, and the outer radius of the slow wave vane is R 10 , and R8>R 10 >R9 is satisfied, and L5 and L7 are generally 0.1 times of the working wavelength λ;

[0041] The slow wave structure 105 is followed by a drift section with an inner radius of R3 and a length of L9, and the length L9 of the drift section affects the matching between the slow wave structure 105 and the extraction cavity 106, and L9 is generally 0.8 to 1 times of the working wavelength λ;

[0042] The drift section is followed by the extraction cavity 106, and the extraction cavity 106 is in the shape of a disc, has an outer radius of R 11 , and a length of L 10 , and R 11 >R8 is satisfied, and the outer radius and the depth of the extraction cavity 106 determine the extraction effect of the extraction cavity 106 on the microwave, and the depth is the difference between the outer radius R 11 of the extraction cavity and the inner radius R3 of the drift section;

[0043] The extraction cavity 106 is followed by the output waveguide 107 with a radius of the inner radius R3 of the drift section, and the right end of the output waveguide 107 is connected to the mode converter and the antenna.

[0044] The magnetic field part is as follows:

[0045] The forward solenoid outer magnetic field 108 is a solenoid magnetic field wrapped outside the Cerenkov oscillator, and the minimum radius of the entire forward solenoid outer magnetic field 108 should not be less than R m1 , and R m1 >R2 is satisfied;

[0046] The forward solenoid outer magnetic field 108 is an entirety, but for the convenience of description, the forward solenoid outer magnetic field 108 is divided into three parts for description, the first part of the forward solenoid outer magnetic field is a solenoid magnetic field with a length of L m1 , an outer radius of R m2 , and an inner radius of R m5 , the second part of the forward solenoid outer magnetic field is a solenoid magnetic field with a length of L m2 , an outer radius of R m5 , and an inner radius of R m1the third part of the positive solenoid outer magnetic field is a solenoid magnetic field with a length of L m1 , an outer radius of R m2 , and an inner radius of R m5 . The first part of the positive solenoid outer magnetic field and the third part of the positive solenoid outer magnetic field are arranged around the two ends of the second part of the positive solenoid outer magnetic field. The first part of the positive solenoid outer magnetic field and the third part of the positive solenoid outer magnetic field mainly adjust the magnetic field line configuration at the two ends; the second part of the positive solenoid outer magnetic field mainly provides the main magnetic field line distribution.

[0047] The fine-tuning magnetic field system includes a first positive solenoid fine-tuning magnetic field 109, a negative solenoid fine-tuning magnetic field 110, and a second positive solenoid fine-tuning magnetic field 111, wherein the outer side of the extraction cavity 106 is arranged around the negative solenoid fine-tuning magnetic field 110, the two sides of the negative solenoid fine-tuning magnetic field 110 are arranged around the first positive solenoid fine-tuning magnetic field 109 and the second positive solenoid fine-tuning magnetic field 111 respectively, and the negative solenoid fine-tuning magnetic field 110, the first positive solenoid fine-tuning magnetic field 109, and the second positive solenoid fine-tuning magnetic field 111 are located between the oscillator cavity 112 and the positive solenoid outer magnetic field 108.

[0048] The first positive solenoid fine-tuning magnetic field 109, the negative solenoid fine-tuning magnetic field 110, and the second positive solenoid fine-tuning magnetic field 111 form a fine-tuning magnetic field system, which is also the core part of the present application, wherein:

[0049] The first positive solenoid fine-tuning magnetic field 109 is a solenoid magnetic field with a length of L m3 , an outer radius of R m1 , and an inner radius of R m3 ;

[0050] The second positive solenoid fine-tuning magnetic field 111 is a solenoid magnetic field with a length of L m3 , an outer radius of R m1 , and an inner radius of R m3 ;

[0051] The negative solenoid fine-tuning magnetic field 110 is a solenoid magnetic field with a length of L m4 , an outer radius of R m1 , and an inner radius of R m4 , but different from other magnetic field parts, the wire in the negative solenoid fine-tuning magnetic field 110 solenoid is reversely wound, that is, from the -z to z direction;

[0052] The magnetic field parameters (the positive solenoid outer magnetic field 108, the first positive solenoid fine-tuning magnetic field 109, the negative solenoid fine-tuning magnetic field 110, and the second positive solenoid fine-tuning magnetic field 111) are obtained by continuous calculation, adjustment, and optimization of the target magnetic field line configuration and particle simulation software, so there is no general range of length and radius.

[0053] Anode outer cylinder 102, cutoff neck 103, resonant reflection cavity 104, slow wave structure 105, extraction cavity 106, output waveguide 107 are made of non-magnetic stainless steel, cathode 101 is made of graphite, magnetic field (forward solenoid outer magnetic field 108, first forward solenoid fine adjustment magnetic field 109, negative solenoid fine adjustment magnetic field 110, second forward solenoid fine adjustment magnetic field 111) is made of copper wire.

[0054] This embodiment realizes a C-band Cherenkov oscillator with a center frequency of 4.26 GHz (corresponding to a microwave wavelength λ = 7 cm). The corresponding size design is: R1 = 27 mm, R2 = 80 mm, R3 = 50 mm, R4 = 61 mm, R5 = 54 mm, R6 = 54 mm, R7 = 56 mm, R8 = 64 mm, R9 = 57 mm, R 10 = 58 mm, R 11 = 73 mm, R m1 = 86 mm, R m2 = 118 mm, R m3 = 56 mm, R m4 = 74 mm, R m5 = 102 mm; L1 = 21 mm, L2 = 44 mm, L3 = 31 mm, L4 = 6 mm, L5 = 6 mm, L6 = 8 mm, L7 = 6 mm, L8 = 8 mm, L9 = 56 mm, L 10 = 13 mm, L m1 = 48 mm, L m2 = 450 mm, L m3 = 10 mm, L m4 = 18 mm). In the particle simulation, under the conditions of diode voltage 676 kV, current 12.9 kA, guiding magnetic field 1.2 T, the output microwave power is 3.86 GW, and the power conversion efficiency is 43%.

[0055] Referring to Figure 3 , the fine gray line in the figure is the magnetic field line cluster after the magnetic field is adopted, and the thick gray line is the actual running track of the electron beam in the PIC (particle simulation simulation) simulation. It can be observed Figure 3 that the electron beam running track in the device in the PIC diffuses outward according to the magnetic field line distribution at the extraction cavity and extends into the extraction cavity.

[0056] Referring to Figure 4 , it can be seen that the distance between the device electron beam and the slow wave structure is close when the single solenoid magnetic field and the composite fine adjustment magnetic field are adopted, that is, when the composite fine adjustment magnetic field is adopted, the device beam wave interaction is also sufficient, and the extraction efficiency is higher.

[0057] Referring to Figure 5The Cherenkov oscillator with the composite fine-tuning magnetic field has a saturated microwave output power of 3.86 GW, which is higher than that of the Cherenkov oscillator with a single solenoid magnetic field. It can be proved that the composite fine-tuning magnetic field can change the electron beam shape and help to improve the output efficiency of the device.

[0058] Of course, in the preferred embodiment, other connection modes can also be used between the cutoff neck 103, the resonant reflection cavity 104, the slow wave structure 105, the extraction cavity 106 and the output waveguide 107, and other materials can also be used for processing the device structure. The above description is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical solution falling within the idea of the present application belongs to the protection scope of the present application.

[0059] The technical content not specifically described in the content of the present application and the above-mentioned embodiments is the same as the prior art.

[0060] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A Cherenkov oscillator using a composite fine-tuning magnetic field, characterized in that: The Cherenkov oscillator using the composite fine-tuning magnetic field comprises an oscillator cavity and a composite fine-tuning magnetic field arranged outside the oscillator cavity, the composite fine-tuning magnetic field comprises a forward solenoid external magnetic field and a fine-tuning magnetic field system, the fine-tuning magnetic field system is located between the forward solenoid external magnetic field and the oscillator cavity, the fine-tuning magnetic field system comprises a first forward solenoid fine-tuning magnetic field, a second forward solenoid fine-tuning magnetic field and a negative solenoid fine-tuning magnetic field, the oscillator cavity comprises an extraction cavity, the negative solenoid fine-tuning magnetic field is arranged outside the extraction cavity, and the first forward solenoid fine-tuning magnetic field and the second forward solenoid fine-tuning magnetic field are arranged outside the negative solenoid fine-tuning magnetic field in sequence.

2. The Cherenkov oscillator using a composite fine-tuned magnetic field according to claim 1, characterized in that: The positive solenoid outer magnetic field is divided into three parts, the first part of the positive solenoid outer magnetic field is a solenoid magnetic field with a length of L m1 , an outer radius of R m2 , and an inner radius of R m5 , the second part of the positive solenoid outer magnetic field is a solenoid magnetic field with a length of L m2 , an outer radius of R m5 , and an inner radius of R m1 , and the third part of the positive solenoid outer magnetic field is a solenoid magnetic field with a length of L m1 , an outer radius of R m2 , and an inner radius of R m5 , and the first part and the third part of the positive solenoid outer magnetic field are respectively arranged around the two ends of the second part of the positive solenoid outer magnetic field.

3. The Cherenkov oscillator using a composite fine-tuned magnetic field according to claim 2, characterized in that: The first positive solenoid fine tuning magnetic field is a solenoid magnetic field with a length L m3 , an outer radius R m1 , and an inner radius R m3 ; the second positive solenoid fine tuning magnetic field is a solenoid magnetic field with a length L m3 , an outer radius R m1 , and an inner radius R m3 ; and the negative solenoid fine tuning magnetic field is a solenoid magnetic field with a length L m4 , an outer radius R m1 , and an inner radius R m4 .

4. The Cherenkov oscillator using a complex fine-tuned magnetic field according to any of claims 1 to 3, characterized in that: The oscillator cavity comprises, in sequence from left to right, an anode outer cylinder, a cutoff neck, a resonant reflection cavity, a slow wave structure, an extraction cavity and an output waveguide; and the anode outer cylinder is internally provided with a cathode.

5. The Cherenkov oscillator using a composite fine-tuned magnetic field according to claim 4, characterized in that: The cathode is a thin-walled cylinder with a wall thickness of 2 mm and an inner radius R1 equal to the electron beam radius, the anode outer cylinder is a metal shell with an inner radius R2, the cutoff neck is disc-shaped with an inner radius R3 and a length L2, R3>R1, and the length L1 between the cutoff neck and the cathode is the anode-cathode spacing, L1 is greater than 2 cm, the resonant reflection cavity is disc-shaped with an inner radius R3 and an outer radius R4 satisfying R4>R3, and the length L3 is 0.4-0.5 times the working wavelength λ; the slow wave structure is at a distance L4 from the resonant reflection cavity, and L4 is 0.2-0.3 times the working wavelength λ.

6. The Cherenkov oscillator using a composite fine-tuned magnetic field according to claim 5, characterized in that: The slow wave structure is composed of six trapezoidal slow wave blades arranged in a row, and each two trapezoidal slow wave blades are connected by a circular ring with a length L7 and an inner radius R3, among the six trapezoidal slow wave blades, the first slow wave blade is a right-angle trapezoid with an upper base length L5 and a hypotenuse width L6, and the outer radius of the slow wave blade is R5. The second, third and fifth slow wave vanes are isosceles trapezoids, the upper base length of the trapezoid is L5, the inclined side width is L6, the outer radius of the slow wave vane is R6, R7 and R9 respectively, and R9>R7>R6 is satisfied; the fourth trapezoidal slow wave vane has an upper base length L8, and L8>L5 is satisfied, the inclined side width is L6, the outer radius of the slow wave vane is R8, and R8>R9 is satisfied; the sixth slow wave vane is also a right trapezoid, the trapezoidal upper base length is also L5, the inclined side width is L6, and the outer radius of the slow wave vane is R 10 , and R8>R 10 >R9 is satisfied, and L5 and L7 are 0.1 times of the working wavelength λ.

7. The Cherenkov oscillator using a composite fine-tuned magnetic field according to claim 6, characterized in that: The slow-wave structure is followed by a drift section with an inner radius R3 and a length L9, L9 being 0.8 to 1 times the operating wavelength λ; the drift section is followed by an extraction cavity, the extraction cavity being disc-shaped, with an outer radius R 11 , a length L 10 , satisfying R 11 >R8, the depth of the extraction cavity being the difference between the outer radius R 11 of the extraction cavity and the inner radius R3 of the drift section.

8. The Cherenkov oscillator using a composite fine-tuned magnetic field according to claim 7, characterized in that: The extraction cavity is followed by an output waveguide with a radius equal to the inner radius R3 of the drift section.

9. The Cherenkov oscillator using a composite fine-tuned magnetic field according to claim 5, characterized in that: The minimum radius of the solenoid outer magnetic field should not be less than R m1 , and satisfies R m1 > R2.

10. The Cherenkov oscillator using a composite fine-tuned magnetic field according to claim 4, characterized in that: The anode outer cylinder, the cutoff neck, the resonant reflection cavity, the slow wave structure, the extraction cavity and the output waveguide are all made of non-magnetic stainless steel, the cathode is made of graphite, and the forward solenoid external magnetic field, the first forward solenoid fine-tuning magnetic field, the negative solenoid fine-tuning magnetic field and the second forward solenoid fine-tuning magnetic field are all wound by copper wires.

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