A high-efficiency fast optimization method for focusing magnetic field of traveling wave tube under dynamic input

Abstract

The application discloses a high-efficiency traveling wave tube focusing magnetic field fast optimization method under dynamic input, and belongs to the field of microwave vacuum electron technology.The method firstly constructs a high-frequency structure model in an electromagnetic simulation software, imports an initial PCM magnetic field to perform PIC simulation to obtain electron trajectories and an initial current distribution;then, the electron trajectories are simulated in combination with a three-dimensional electron motion and a space charge force equation, y-direction projection is taken, the outermost two trajectories are selected, and an optimized PCM magnetic field is obtained through an optimization algorithm iteration; subsequently, the magnetic field is imported to perform PIC simulation to obtain a new current distribution, and after convergence is judged, the iteration optimization is repeated, and finally, an optimal PCM magnetic field is obtained.The application realizes accurate optimization of the magnetic field under dynamic signal input, greatly shortens the magnetic system optimization period, effectively reduces the intercepted current, improves the electron flow rate, and guarantees the output power of the traveling wave tube and the overall tube efficiency.

Description

Technical Field

[0001] This invention belongs to the field of microwave vacuum electronics technology, specifically relating to a method for rapid optimization of the focusing magnetic field of a high-efficiency traveling wave tube under dynamic signal input. Background Technology

[0002] A traveling wave tube (TWT) is a vacuum electronic device that amplifies high-frequency signals by utilizing the interaction between an electron beam and a traveling wave field in a high-frequency structure. This interaction modulates the electron's kinetic energy to continuously convert it into electromagnetic wave energy. TWTs are characterized by wide bandwidth and high gain. They have been widely used in military and industrial fields, covering important areas such as high-resolution radar, wireless communication, and electronic warfare.

[0003] As a key component of a traveling wave tube (TWT), the magnetic focusing system directly affects the stable transmission and interaction efficiency of the strip electron beam in high-frequency structures, thus determining the overall electrical performance of the tube. Compared to cylindrical electron beams, strip electron beams have higher current density and power capacity. However, during long-distance transmission, the electron beam is susceptible to the "Diocotron" instability, which can be effectively suppressed by using a periodic tangential magnetic field (PCM).

[0004] When optimizing the magnetic system of a PCM, traditional methods involve extensive parameter scanning using electromagnetic simulation software like CST to obtain suitable structural parameters. However, traditional biased magnetic pole PCMs suffer from limited pole width, resulting in independent magnetic field control in the narrow and wide sides of the electron beam. Furthermore, the simulation optimization process involving soft magnetic materials often requires hundreds of hours, consuming a significant amount of time and causing inconvenience to the design of focusing systems.

[0005] The patent "A design method for a focusing magnetic field to suppress dynamic defocusing in a high-efficiency traveling wave tube" (CN111414704A) effectively suppresses dynamic defocusing caused by the electron beam during beam-wave interaction by reducing the peak values ​​of the entire focusing magnetic field and the magnetic field near the output window. However, it requires continuous fine-tuning of the magnetic field peak value to reduce the interception current. This is achieved by manually adjusting the peak value until the beam shape remains stable and does not diverge while meeting the output power requirements. This process is cumbersome and difficult to control, and the magnetic field optimization design process is time-consuming.

[0006] Furthermore, as the output power increases, the electron clustering phenomenon caused by the increased disturbance of the electron beam by the high-frequency field makes focusing more difficult. Conventional periodic PCMs are unable to maintain stable confinement of the electron beam under high power conditions, resulting in a large intercept current and reducing the overall efficiency of the traveling wave tube. Existing magnetic system optimization work has not considered the situation under high-frequency dynamic signal input. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for rapidly optimizing the focusing magnetic field of a high-efficiency traveling wave tube under dynamic signal input, thereby solving the problem of difficulty in dynamic focusing of electron beams under high output power and shortening the optimization cycle of the magnetic system to meet design requirements.

[0008] The technical solution adopted in this invention is as follows:

[0009] A method for rapid optimization of the focusing magnetic field of a high-efficiency traveling wave tube under dynamic signal input includes the following steps:

[0010] S1. Construct a high-frequency structure model in electromagnetic simulation software, import the initial PCM magnetic field to perform PIC (Particle-in-Cell) simulation calculation, obtain electron trajectory data and calculate the initial current distribution.

[0011] S2. Based on the three-dimensional motion equation of electrons in high-frequency structures, combined with the current current distribution and space charge force equation, the space charge force on the electrons is calculated; then, the electron trajectory is simulated by combining the current PCM magnetic field, and the y-direction (narrow side) projection of the electron trajectory is obtained.

[0012] S3. Select the two outermost electron trajectories in the y-direction projection of the electron trajectory obtained in step S2 as optimization objects. Use the optimization algorithm to iterate and optimize the trajectories of these two electrons for Q1 times to obtain the electron narrow-side trajectory that meets the requirements and obtain the corresponding optimized PCM magnetic field.

[0013] Preferably, in step S3, the current PCM magnetic field is divided into M independent segments along the electron beam propagation direction (z-axis), and the peak value of the electron narrow-side trajectory profile is optimized segment by segment so that the electron trajectory profile decreases smoothly.

[0014] Preferably, in step S3, the optimization algorithm adopts the simulated annealing algorithm, which obtains new PCM magnetic field data by adjusting the optimization parameters, and re-simulates the electron trajectory under the new PCM magnetic field to solve for the PCM magnetic field parameters that minimize the optimization objective function.

[0015] The optimization parameters are set as Ky1, Ky2, ..., KyM, Kz1, Kz2, ..., KzM, representing the magnetic field variation coefficients in the y and z directions under different segments, and the initial values ​​are all set to 1.

[0016] The objective function S is set as follows:

[0017] ;

[0018] in, Let represent the i-th peak of the narrow-side trajectory of an electron, and n be the total number of peaks for two electrons.

[0019] Preferably, during the iterative optimization of the PCM magnetic field using the simulated annealing algorithm, the optimization range of the optimization parameters is set in segments according to the different electron interception conditions during PIC simulation; the optimization range is set as the initial value, initial value ±20%, or initial value ±30%.

[0020] S4. Import the PCM magnetic field obtained from step S3 into the electromagnetic simulation software for PIC simulation calculation, and obtain new electron trajectory data and corresponding current distribution.

[0021] S5. Determine if the current distribution has converged. If it has converged, proceed to the next step; if it has not converged, return to S2.

[0022] S6. Using the convergent current distribution and the optimized PCM magnetic field as initial conditions, repeat steps S2 to S4. At this time, the number of iterations for optimizing the two electron trajectories is set to Q2. After the iteration optimization is terminated, the final optimized PCM magnetic field is obtained.

[0023] Preferably, in step S3, the value of Q1 is 100~200; the value of Q2 is 300~400.

[0024] This invention considers the true three-dimensional motion of electrons in high-frequency structures and can simultaneously control the magnetic field on both the wide and narrow sides of the electron beam. Current distribution is calculated based on the actual electron distribution, and a locally increased current is used to represent the electron clustering effect under high-frequency signal input. Through a program-simulation iterative process, the current distribution without interception is calculated, thus achieving accurate simulation of the electron trajectory, and the simulated trajectory is optimized based on this. Compared to traditional focusing magnetic field optimization methods, this invention significantly reduces the optimization calculation time and can directly optimize the magnetic field under dynamic signal input. While ensuring output power and tube efficiency, it can effectively reduce interception current and improve electron flow rate. Attached Figure Description

[0025] Figure 1 This is an optimized flowchart of the present invention.

[0026] Figure 2 This is a comparison chart of static calculation and simulated trajectory.

[0027] Figure 3 Comparison chart of dynamic input calculation and simulation trajectory.

[0028] Figure 4 To capture the current convergence diagram.

[0029] Figure 5 A comparison of the dynamic input trajectory contours before and after optimization.

[0030] Figure 6 To optimize the power comparison chart before and after. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. It should be understood that the described embodiments are only a part of the implementation of the present invention, and not all of them. Based on the embodiments disclosed in the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The high-frequency structure in this embodiment adopts a traditional interleaved double-grid high-frequency structure, which uses the PCM magnetic field for electron focusing. Detailed operating parameters and structural parameters are shown in Table 1.

[0033] Table 1 List of Operating Parameters

[0034] parameter numerical values Operating voltage U (kV) 30 Operating current I (A) 0.73 Electron injection channel dimensions we × he (mm) 6 * 0.8 Waveguide dimensions w×h (mm) High-frequency structure length L (mm) 6.8 * 2185

[0035] S1. Construct an interlaced double-grid structure model in electromagnetic simulation software, import the initial PCM magnetic field for PIC simulation calculation, obtain electron trajectory data, and then calculate the initial current distribution based on the electron trajectory data.

[0036] S2. Based on the three-dimensional motion equation of electrons in the interleaved double grid, combined with the current current distribution and space charge force equation, the space charge force on the electrons is calculated; then, the electron trajectory is simulated by combining the current PCM magnetic field, and the y-direction (narrow side) projection of the electron trajectory is obtained.

[0037] Specifically, the three-dimensional equation of motion for electrons in the high-frequency structure is:

[0038] ;

[0039] in, This represents the acceleration of an electron in space. This represents the velocity of an electron in three-dimensional space. Indicates the magnitude of the applied external magnetic field. This indicates the magnitude of the space charge force experienced by an electron. Indicates the normalized electron mass. Represents the relativistic correction factor. It represents the amount of electron charge.

[0040] The equation for the space charge force on electrons in a high-frequency structure is as follows:

[0041] ;

[0042] in, Let x and y represent the space charge forces acting on electrons in the x and y directions, respectively, where x and y represent the coordinates of the wider side (x) and narrower side (y), respectively. For electron beam height, For charge quantity, For plasma frequency, For electron beam width, For the height of the electron injection channel, For narrow-side wavenumber, Representing different intrinsic modes, To normalize the electron mass, in this embodiment, the spatial step size is set to 0.2 mm, and one motion calculation is completed in the time it takes to move one spatial step.

[0043] The simulated electron trajectory is projected along the narrow side, and the simulation results are compared with the CST simulation results. Figure 2 , Figure 3 As shown, the simulated outermost electron trajectory profile can be seen under static input ( Figure 2 ) and dynamic input ( Figure 3 The outline of the simulation results is consistent with the actual results.

[0044] S3. Select the two outermost electron trajectories from the narrow-side electron trajectories simulated in step S2 as optimization objects. Use the simulated annealing algorithm to perform segmented optimization on the narrow-side electron trajectories in three segments: 0~73mm, 73~123mm, and 123~185mm. The optimization parameters are Ky1, Ky2, Ky3, Kz1, Kz2, and Kz3, which are the magnetic field change coefficients in the y and z directions in the three segments, respectively, and the initial values ​​of all parameters are set to 1.

[0045] The objective function S is set as follows:

[0046] ;

[0047] in, Let represent the i-th peak of the narrow-side trajectory of an electron, and n be the total number of peaks for two electrons.

[0048] In the initial PIC simulation, the electron beam narrow edge profile was relatively wide, and the electron interception was significant. Therefore, the optimization range of the optimization parameters was set to the initial value ±30%, and the number of optimization iterations was 100. In each iteration, the electron trajectory was re-simulated to find the minimum value of the objective function, thereby obtaining the electron narrow edge trajectory that meets the requirements and the corresponding optimized PCM magnetic field.

[0049] S4. Import the PCM magnetic field data obtained from step S3 into the electromagnetic simulation software to perform PIC simulation again, and obtain new electron trajectory data and corresponding current distribution.

[0050] S5. Determine whether the current distribution has converged. If it has converged, proceed to the next step. If it has not converged, return to step S2 and calculate the space charge force on the electron based on the optimized PCM magnetic field in step S4 and simulate the electron trajectory.

[0051] At this point, since the PIC simulation shows significant electron interception in the latter two sections under the current PCM magnetic field, only the magnetic field of the latter two sections needs to be optimized in step S3. The optimization parameters Ky1 and Kz1 remain unchanged, keeping their initial values ​​of 1. The optimization range for parameters Ky2, Ky3, Kz2, and Kz3 is set to ±20% of their initial values, and the iteration count is 100. The entire iteration process is as follows: Figure 4 As shown, after 4 iterations, the current distribution finally converges, and the intercepted current converges to 0.

[0052] S6. Using the convergent current distribution as the initial condition, repeat steps S2 to S4, where the number of iterations for optimizing the trajectories of the two electrons is set to 300. After the iteration optimization is terminated, the optimized PCM magnetic field is obtained, and the optimization process ends.

[0053] The optimized magnetic field obtained is imported into the electromagnetic simulation software CST for PIC simulation and output power calculation under dynamic signal input. The electron trajectory profile obtained under dynamic signal input is compared with the electron trajectory profile under the initial magnetic field. Figure 5 As shown, at a transmission distance of 185mm, the electron trajectory contour converges smoothly without significant divergence, and the electron interception phenomenon is significantly reduced.

[0054] Figure 6 The graph shows a comparison of the output power of the high-frequency structure before and after magnetic field optimization. As can be seen from the graph, the overall output power of the high-frequency structure increases due to the reduction in electron interception. From the above, we can conclude that the optimization process of this invention can effectively solve the electron interception problem under dynamic signal input while ensuring sufficient power output. Furthermore, the entire optimization process takes less than 10 hours, representing a significant improvement in optimization speed compared to traditional optimization methods.

Claims

1. A method for rapid optimization of the focusing magnetic field of a high-efficiency traveling wave tube under dynamic signal input, characterized in that, Includes the following steps: S1. Construct a high-frequency structure model in electromagnetic simulation software, import the initial PCM magnetic field for PIC simulation calculation, obtain electron trajectory data and calculate the initial current distribution; S2. Based on the three-dimensional motion equation of electrons in high-frequency structures, combined with the current current distribution and space charge force equation, the space charge force on electrons is calculated. Then, the electron trajectory is simulated by combining the current PCM magnetic field, and the y-direction projection of the electron trajectory is obtained; S3. Select the two outermost electron trajectories projected in the y-direction by the electron trajectory simulated in step S2 as optimization objects. Use the optimization algorithm to iterate and optimize the trajectories of these two electrons for Q1 times to obtain the electron narrow-side trajectory that meets the requirements and obtain the corresponding optimized PCM magnetic field. S4. Import the PCM magnetic field obtained from step S3 into the electromagnetic simulation software for PIC simulation calculation, and obtain new electron trajectory data and corresponding current distribution. S5. Determine if the current distribution converges. If it converges, proceed to the next step; if it does not converge, return to S2. S6. Using the convergent current distribution and the optimized PCM magnetic field as initial conditions, repeat steps S2 to S4. At this time, the number of iterations for optimizing the two electron trajectories is set to Q2. After the iteration optimization is terminated, the final optimized PCM magnetic field is obtained.

2. The method for rapid optimization of the focusing magnetic field of a high-efficiency traveling wave tube under dynamic signal input as described in claim 1, characterized in that, In step S3, the current PCM magnetic field is divided into M independent segments along the electron beam propagation direction, and the peak value of the electron narrow-side trajectory profile is optimized segment by segment.

3. A method for rapid optimization of the focusing magnetic field of a high-efficiency traveling wave tube under dynamic signal input as described in claim 1 or 2, characterized in that, In step S3, the optimization algorithm adopts the simulated annealing algorithm. By adjusting the optimization parameters, new PCM magnetic field data is obtained, and the electron trajectory is re-simulated under the new PCM magnetic field to solve for the PCM magnetic field parameters that minimize the optimization objective function. The optimization parameters are set as Ky1, Ky2, ..., KyM, Kz1, Kz2, ..., KzM, representing the magnetic field variation coefficients in the y and z directions under different segments, and the initial values ​​are all set to 1. The objective function S is set as follows: ； in, Let represent the i-th peak of the narrow-side trajectory of an electron, and n be the total number of peaks for two electrons.

4. The method for rapid optimization of the focusing magnetic field of a high-efficiency traveling wave tube under dynamic signal input as described in claim 3, characterized in that, In the process of iteratively optimizing the PCM magnetic field using the simulated annealing algorithm, the optimization range of the optimization parameters is set in segments according to the different electron interception conditions during PIC simulation; the optimization range is set as the initial value, initial value ±20%, or initial value ±30%.

5. The method for rapid optimization of the focusing magnetic field of a high-efficiency traveling wave tube under dynamic signal input as described in claim 4, characterized in that, In step S3, the value of Q1 is 100~200; the value of Q2 is 300~400.

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