Structure for inhibiting interaction of front cavities in frequency-adjustable high-power gyrotron

Abstract

The invention discloses a structure for inhibiting front cavity interaction in a frequency-adjustable high-power gyrotron, which is used for carrying out PIC analogue simulation on the basis of a frequency-adjustable gyrotron developed in a laboratory, and verifying the front cavity interaction by utilizing a gyrotron linear theory and a generalized scattering matrix theory according to a generation principle of the front cavity interaction. And on the basis, adjustment and simulation analysis are carried out on the cavity structure of the gyrotron, a feasible way for inhibiting the interaction of the front cavity is found out, and stable work of the gyrotron during frequency tuning is ensured. The structure is composed of the periodic loading dielectric waveguide from the rear end of the electron gun to the beam-wave interaction front end, the design is simple, the cost is low, and the problems that the overall efficiency of the gyrotron is reduced and the working stability of the gyrotron is damaged due to interaction of the front cavity of the non-interaction section in the existing gyrotron are solved.

Description

Technical Field

[0001] The invention relates to the field of terahertz technology, and in particular to a technology for suppressing front cavity interaction in a frequency-adjustable high-power gyrotron. Background Art

[0002] In recent years, many parasitic oscillations, including low-frequency (LF, up to several hundred MHz) and high-frequency (RF, at the same order of magnitude as the frequency of the operating mode) oscillations have been observed in MW-level gyrotron research projects. These parasitic oscillations can deteriorate the working state of the gyrotron in different ways, such as reducing the working efficiency of the gyrotron, unexpectedly increasing the temperature of certain locations of the gyrotron, and thus limiting the pulse width of the gyrotron, making the gyrotron unable to work under the pre-designed working parameters. Among these parasitic oscillations, the front cavity interaction has been widely discussed as an important factor affecting the overall efficiency and device stability.

[0003] After the electron beam is emitted from the electron gun, before entering the beam-wave interaction zone, it will first pass through a uniform beam tunnel. The parasitic resonance generated by the parasitic beam-wave interaction in this tunnel is a pre-cavity interaction with adverse effects. This oscillation will generate further electromagnetic waves, specifically the resonance of the parasitic mode at a high or low frequency. On the one hand, the pre-cavity interaction will modulate the output power of the working mode at the working frequency, limit the stable region of the working mode, make it difficult for the gyrotron to achieve the desired output power, and increase the gyrotron stray radiation level; on the other hand, this parasitic beam-wave interaction will affect the working state of the electron beam, further leading to the discreteness of the electron beam energy and velocity, so that the electron beam cannot be in the most suitable state in the interaction cavity section, thereby reducing the observed working performance of the gyrotron. In recent years, a large number of scholars have tried to suppress the parasitic interaction phenomenon in the beam tunnel by different means. In addition to the special correction of the magnetic field distribution in the input cavity front area to suppress parasitic oscillations, a major solution is to modify the inherent parameters of the beam tunnel to destroy the resonance conditions of the parasitic mode. On the one hand, the geometry of the channel is changed, and on the other hand, other media are added to the inner side of the channel. In 2010, a team studied the parasitic oscillations in the injection wave channel and proposed an improved spectral measurement system and a new analysis method. The results verified the theoretical prediction of the parasitic oscillations and effectively verified the corresponding improved injection wave channel structure. An improved injection wave channel structure based on the destruction of azimuthal symmetry by ripples was also proposed, and the parasitic oscillations in the injection wave channel were completely eliminated. In 2012, a team conducted another experiment to parametrically study the influence of lossy ceramic material properties and geometry on the parasitic modes in the stacked gyrotron injection wave channel. From the numerical results, it can be found that changing the geometric dimensions and adding ceramic materials affect the parasitic oscillations in a similar way. In addition, it was observed that high-loss materials do not necessarily lead to higher attenuation of parasitic modes. In 2020, the experimental results of a team showed that for all observed signals, the parasitic interaction occurred before the main interaction, especially in the compression zone close to the cavity. In addition, the reason for the elimination of parasitic oscillations after adding ceramic media was pointed out: the oscillating current of the parasitic mode was increased, making it impossible for the parasitic mode to oscillate. In addition, a team has made a parasitic-free gyrotron, which verifies that the direction of changing the geometric dimensions and adding ceramic materials is feasible. In addition, in 2021, a team used the PIC algorithm to establish a wave injection channel model with lossy ceramic materials based on the W-band gyrotron, and found that the parasitic mode TE52 excited in the wave injection tunnel was effectively suppressed under the influence of ceramic materials.

[0004] In recent years, it has been found that in the parasitic oscillations occurring before the interaction cavity section, in addition to the oscillations generated by the parasitic injection wave interaction mechanism at the injection wave tunnel, it may also originate from the reverse wave generated by the interaction cavity. This reverse wave can extend to the transition region between the electron gun and the interaction cavity, thereby affecting the working state of the electron beam. In 2023, Konstantinos A. Avramidis et al. used two codes to perform multi-mode simulations on two existing gyrotrons to verify the possibility of parasitic RF oscillations of the reverse wave. Studies have shown that this parasitic oscillation can cause the power of the working mode to be reduced by 10% in its order of magnitude when its own power is 1% lower than the working mode power. The reason for this decrease in power performance is that the reverse wave can extend to the front of the interaction cavity, that is, the transition section between the electron gun and the interaction cavity, which may lead to an increase in the energy and velocity discreteness of the electron beam at this position, causing the electron beam to deviate from the appropriate working state. Therefore, this reverse wave, which is different from the front cavity interaction and is generated by the interaction cavity but can act on the electron beam at the front cavity position, also needs further research and appropriate means to suppress it. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to propose a structure for suppressing the front cavity interaction in a frequency-adjustable high-power gyrotron. The structure is based on a frequency-adjustable gyrotron developed in the laboratory, and PIC simulation is performed. According to the generation principle of the front cavity interaction, the front cavity interaction is verified by using the gyrotron linear theory and the generalized scattering matrix theory, and on this basis, the gyrotron cavity structure is adjusted and simulated and analyzed to find a feasible way to suppress the front cavity interaction and ensure that the gyrotron works stably during frequency tuning. The structure consists of a periodically loaded dielectric waveguide from the rear end of the electron gun to the front end of the injection wave interaction. The design is simple and low-cost, and solves the problem that the interaction of the front cavity in the non-interaction section of the existing gyrotron will reduce the overall efficiency of the gyrotron and destroy its working stability.

[0006] In order to achieve the purpose of the present invention, the present invention is implemented through the following technical scheme: based on the frequency-adjustable gyrotron developed in the laboratory, PIC simulation is carried out, and according to the principle of generation of front-cavity interaction, the front-cavity interaction is verified by using gyrotron linear theory and generalized scattering matrix theory, and on this basis, the gyrotron cavity structure is adjusted and simulated and analyzed to find a feasible way to suppress the front-cavity interaction and ensure that the gyrotron works stably during frequency tuning.

[0007] Further improvements are: modeling and simulation of the same size based on the existing gyrotron in the laboratory. The PIC electromagnetic simulation algorithm in the three-dimensional electromagnetic simulation software is used for simulation. The model background material, model structure, and simulation frequency range are set according to the existing gyrotron in the laboratory. The input end electron beam is set according to the guide radius, starting current voltage, and horizontal and vertical speed ratio calculated in the early stage, and the boundary conditions, external magnetic field, and field distribution monitor are set. The solver is further used to solve the simulation and adjust the simulation settings based on the obtained simulation results.

[0008] Further improvements are: in order to calculate the possible resonant frequency of the parasitic mode in the front cavity section, we intend to use the scattering matrix theory method to calculate the S parameter-frequency diagram of the mode within a certain frequency band near the electron cyclotron frequency. By observing the extreme value of the S parameter, we can preliminarily determine the possible resonance point of the mode.

[0009] Further improvements are: based on the simulation and program calculation results of the front-cavity interaction, the influence of various gyrotron parameters on the front-cavity interaction is analyzed. We consider the geometric parameters of dielectric loading, such as the width and thickness of the dielectric ring, and adjust the parameters to increase the starting current of the parasitic mode generated by the front-cavity interaction, so that the mode cannot be started under the electron injection current state of the working mode, thereby eliminating or reducing the phenomenon of the parasitic mode generated by the front-cavity interaction.

[0010] Further improvements are: using a self-written nonlinear beam interaction program, using the parameters of a 0.5THz gyrotron in the laboratory, simulating the corresponding front-cavity interaction results obtained with the electromagnetic simulation software, and verifying each other. After adjusting the cavity parameters, simulation analysis was performed to observe the changes in the front-cavity interaction.

[0011] The beneficial effects of the present invention are as follows: a structure for suppressing front-cavity interaction in a frequency-adjustable high-power gyrotron is proposed. The structure is based on a frequency-adjustable gyrotron developed in the laboratory, and PIC simulation is performed. According to the generation principle of the front-cavity interaction, the front-cavity interaction is verified using the gyrotron linear theory and the generalized scattering matrix theory. On this basis, the gyrotron cavity structure is adjusted and simulated and analyzed to find a feasible way to suppress the front-cavity interaction, thereby ensuring that the gyrotron works stably during frequency tuning.

[0012] The structure consists of a periodically loaded dielectric waveguide from the rear end of the electron gun to the front end of the injection wave interaction. The design is simple and low-cost, and solves the problem that the interaction in the front cavity of the non-interaction section of the existing gyrotron will cause the overall efficiency of the gyrotron to decrease and destroy its working stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0014] Figure 1 is a schematic diagram of a periodically loaded dielectric waveguide of the present invention;

[0015] Figure 2 It is a schematic diagram of the system design process of the present invention;

[0016] Figure 3 is a diagram of the simulation result of the starting current in the embodiment of the present invention;

[0017] Figure 4 is a graph showing the relationship between the beam-wave interaction efficiency and the operating frequency as a function of the operating magnetic field in an embodiment of the present invention;

[0018] Figure 5 4 is a graph showing the relationship between the injection-wave interaction efficiency and the operating frequency as a function of the voltage in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Example

[0021] See also Figure 1 This embodiment proposes a structure for suppressing front-cavity interaction in a frequency-adjustable high-power gyrotron. The structure is based on a frequency-adjustable gyrotron developed in the laboratory, and PIC simulation is performed. According to the generation principle of front-cavity interaction, the front-cavity interaction is verified using gyrotron linear theory and generalized scattering matrix theory, and on this basis, the gyrotron cavity structure is adjusted and simulated and analyzed to find a feasible way to suppress the front-cavity interaction and ensure that the gyrotron works stably during frequency tuning. The structure consists of a periodically loaded dielectric waveguide from the rear end of the electron gun to the front end of the injection wave interaction. The design is simple and low-cost, and solves the problem that the interaction in the front cavity of the non-interaction section of the existing gyrotron will reduce the overall efficiency of the gyrotron and destroy its working stability.

[0022] Figure 2The flowchart of the embodiment. First, a preliminary judgment is made on the possible front cavity interaction modes, and it is analyzed which modes may produce front cavity interaction in the injection wave channel section of the front cavity under the magnetic field conditions and electron injection conditions. The resonant frequency of each mode under this size is compared and calculated with the electron cyclotron frequency under the external magnetic field conditions, and the parasitic modes that may be excited are preliminarily judged. According to the existing gyrotron in the laboratory, the same size modeling and simulation are carried out, and the PIC electromagnetic simulation algorithm with the three-dimensional electromagnetic simulation software is used for simulation. According to the existing gyrotron in the laboratory, the model background material, model structure, and simulation frequency range are set. According to the guide radius, starting current voltage, and transverse and longitudinal velocity ratio obtained in the previous calculation, the input end electron beam is set, the boundary conditions, external magnetic field and field distribution monitor are set, and then the solver is further used for solving the simulation. Based on the results obtained in the preliminary stage of the study, the injection wave channel section is loaded with a medium, and the front cavity part is modeled and simulated using the control variable method. Observe the parasitic modes excited by the front cavity and record the data. According to the obtained results, the linear theory of gyrotron is used to judge and verify the reliability of the parasitic oscillation generated by the injection wave interaction in the front cavity. Then, according to the synchronization conditions of the electron cyclotron interaction, the relevant parameters of the injection wave channel in the front cavity of the gyrotron are adjusted, such as the width and thickness of the dielectric ring. The particle simulation of the electromagnetic simulation software is used for simulation again, and the parasitic mode excited by the front cavity is observed and the data is recorded. The oscillation of the parasitic mode before and after the adjustment is compared. After adjusting the parameters, the front cavity interaction is significantly suppressed, indicating that the method is effective. Then, the self-compiled time domain program based on the self-consistent nonlinear theory is used to simulate the front cavity interaction, and the simulation results are analyzed and verified by comparing the actual measured experimental data. According to the self-consistent nonlinear theory of the gyrotron, the initial conditions and boundary conditions are used to calculate the injection wave interaction process. In the process of writing the program, a series of numerical analysis methods need to be used, such as the equation of motion of the electron and the equation of the injection wave interaction field can be solved by the fourth-order Runge-Kutta method, and the optimization method for the treatment can be the shooting method, the variable polyhedron method, etc.

[0023] See also Figure 3 In order to further study the potential mode competition in the cavity from the principle, the starting current is used to further study the potential mode competition in the cavity from the principle, and the magnetic field and electron beam current required for the excitation working mode are analyzed. The starting current formula based on linear theory has the following form:

[0024]

[0025] Among them, μ mn is the nth root of the derivative of the mth-order Bessel function, R g is the radius of the electron beam guide center, I start is the starting current, Q is the total quality factor of the cavity, Z 0and λ is the free space impedance and wavelength, m 0 and e 0 are the rest mass and charge of the electron, γ 0 is the relativistic factor, f(z) is the normalized field amplitude, k mn is the transverse beam, c is the speed of light in vacuum, C mn is the normalization constant, β ⊥0 and β z0 are the normalized transverse and longitudinal velocities of the electrons, respectively, L is the length of the interaction cavity, and s is the harmonic order.

[0026] See also Figure 4 , Figure 5 In order to obtain the performance parameters of the gyrotron such as the frequency and injection-wave interaction efficiency in the working mode, it is necessary to further analyze the injection-wave interaction process of the gyrotron. The self-consistent nonlinear theory combines the effect of the electromagnetic field on the electrons and the excitation of the electrons on the electromagnetic field, and can accurately calculate the key parameters such as the gyrotron resonant frequency and injection-wave interaction efficiency. The self-consistent nonlinear theory equation is:

[0027]

[0028] Where: f(z) is the axial field distribution, e mn is the transverse modulus vector, J ω is the lateral current density distribution, ρ and I 0 are the linear charge density and the DC electron beam current, v t and v z are the transverse and longitudinal velocities of the electron, respectively.

[0029] The relationship between the start current and the magnetic field of the working mode is plotted on Figure 3 It can be seen that near the external magnetic field of 4.8 T, TE 3,3 The starting current of the mode increases from 100mA to 500mA as the longitudinal index increases.

[0030] The relationship between the working frequency (Frequency) and beam-wave interaction efficiency (Efficiency) of the working mode and different magnetic fields (Magnetic) is plotted on Figure 4 It can be seen that the operating frequency of the working mode increases from 263.71 GHz to 263.75 GHz with the increase of the working magnetic field, and the beam-wave interaction efficiency increases from 0.2% to 28.7% with the increase of the working magnetic field.

[0031] The relationship between the working frequency (Frequency) and the beam-wave interaction efficiency (Efficiency) of the working mode and different voltages (Voltage) is plotted on Figure 5 It can be seen that the operating frequency of the working mode increases from 263.71 GHz to 263.73 GHz with the increase of the working magnetic field, and the beam-wave interaction efficiency increases from 2.2% to 25.2% with the increase of the working magnetic field.

[0032] The simulation experiment was conducted on the structure for suppressing the front cavity interaction in the frequency adjustable high-power gyrotron of the present invention. The results are as follows: Figure 4 , Figure 5 As shown:

[0033] In the simulation, the electron transverse velocity ratio α = 1.5, the guide center radius R g =0.966mm;

[0034] In the simulation, the voltage is 10 kV and the electron beam current I 0 =180mA;

[0035] The relationship between the beam-wave interaction efficiency and the operating frequency with the operating voltage In the simulation, the electron beam current I 0 =180mA, magnetic field is 4.8T.

[0036] Figure 3 It is the curve result of the starting current of the working mode changing with the working magnetic field;

[0037] Figure 4 The relationship between the beam-wave interaction efficiency and the operating frequency as a function of the operating magnetic field;

[0038] Figure 5 This is the relationship between the beam-wave interaction efficiency and the operating frequency as the operating voltage changes.

[0039] The performance and effect of the gyrotron structure with a gradual output section are analyzed by using Matlab calculation linear and nonlinear theory, and the analysis results are presented in a graphical way, which is very convincing. It shows that the structure that suppresses the front-cavity interaction in the frequency-adjustable high-power gyrotron can solve the problem of low output efficiency caused by the existing competition mode. It is proved that the structure that suppresses the front-cavity interaction can be applied to the frequency-adjustable high-power gyrotron and maintain good performance.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A structure for suppressing front cavity interaction in a frequency-adjustable high-power gyrotron. It is characterized by: This structure is based on a frequency-adjustable gyrotron developed in the laboratory. It consists of a periodically loaded dielectric waveguide from the rear end of the electron gun to the front end of the injection wave interaction. The design is simple and low-cost, which solves the problem that the interaction in the front cavity of the non-interaction section of the existing gyrotron will cause the overall efficiency of the gyrotron to decrease and destroy its working stability.

2. The structure for suppressing front cavity interaction in a frequency-adjustable high-power gyrotron according to claim 1, characterized in that: The generalized scattering matrix is ​​used to characterize the field and S parameters of the injection wave channel section of the gyrotron front cavity. The PIC electromagnetic simulation algorithm in the three-dimensional electromagnetic simulation software is used for simulation. According to the existing gyrotron in the laboratory, the model background material, model structure, and simulation frequency range are set. The guide center radius R is obtained according to the previous calculation. g =0.966mm, electron injection current I0=180mA, electron transverse and longitudinal velocity ratio α=1.

5.

3. The structure for suppressing front cavity interaction in a frequency-adjustable high-power gyrotron according to claim 1, characterized in that: Using a self-written nonlinear beam-wave interaction program and the parameters of a 0.5THz gyrotron in the laboratory, the corresponding front-cavity interaction results obtained with the electromagnetic simulation software were simulated and verified with each other.

4. A structure for suppressing front cavity interaction in a frequency-adjustable high-power gyrotron, characterized in that: The following steps are involved: First, we make a preliminary judgment on the possible front-cavity interaction modes, and analyze which modes may produce front-cavity interaction in the injection wave channel section of the front cavity under the magnetic field conditions and electron injection conditions. We compare and calculate the resonant frequency of each mode at this size with the electron cyclotron frequency under the external magnetic field conditions, and make a preliminary judgment on the parasitic modes that may be excited. According to the existing gyrotron in the laboratory, the same size modeling and simulation were carried out, and the PIC electromagnetic simulation algorithm in the three-dimensional electromagnetic simulation software was used for simulation. According to the existing gyrotron in the laboratory, the model background material, model structure, and simulation frequency range were set. According to the guide radius, starting current voltage, and transverse and longitudinal velocity ratio obtained in the previous calculation, the input end electron beam was set, the boundary conditions, the external magnetic field, and the field distribution monitor were set, and then the solver was used for further solution and simulation. Based on the results obtained in the preliminary stage of the study, the injection wave channel section was loaded with dielectric, and the front cavity part was modeled and simulated using the control variable method. The parasitic mode excited by the front cavity was observed and the data was recorded. Based on the results obtained, the linear theory of the gyrotron was used to judge and verify the reliability of the parasitic oscillation generated by the injection wave interaction at the front cavity. Then, according to the synchronization conditions of the electron cyclotron interaction, the relevant parameters of the injection wave channel of the front cavity of the gyrotron were adjusted, such as the width and thickness of the dielectric ring, and the particle simulation of the electromagnetic simulation software was used for simulation again. The parasitic mode excited by the front cavity was observed and the data was recorded, and the parasitic mode oscillation before and after the adjustment was compared. After adjusting the parameters, the front-cavity interaction was significantly suppressed, indicating that the method was effective. Then, a self-compiled time-domain program based on self-consistent nonlinear theory was used to simulate the front-cavity interaction, and the simulation results were compared with the actual measured experimental data for analysis and verification. According to the self-consistent nonlinear theory of gyrotron, the initial conditions and boundary conditions are used to calculate the beam-wave interaction process. In the process of programming, a series of numerical analysis methods need to be used. For example, the equation of motion of electrons and the equation of beam-wave interaction field can be solved by the fourth-order Runge-Kutta method. For the optimization method of treatment, the shooting method and the variable polyhedron method can be used.

Images