This paper reports the development of a fully 3-D finite-element (FE) design tool for the design of electron guns and collectors called the electron optics simulator (EOS). It is a module of the microwave tube simulator suite (MTSS) developed by the University of Electronic Science and Technology of China. EOS specifically targets problem classes including axisymmetric gun, gridded gun, multibeam gun, and multistage depressed collector. EOS is a steady-state trajectory code, which is a solver of electrostatic field and trajectory that takes into account secondary electrons, space-charge effects, and the external magnetic field. The simulator is dependent on the following two front-end features in MTSS: preprocessing that includes a solid modeling tool and a fully 3-D tetrahedral FE mesh automatic generator, and post processing for analysis and display of the results. A friendly interface is provided to design, test, optimize, and validate the electron optics systems. The aforementioned theoretical models are discussed in detail in this paper. In the end, some comparisons between simulation and experiment are presented.

Electron Optics Simulator: A Three-Dimensional Finite-Element Electron Gun and Collector Design Tool

In this paper a novel parallel meta-heuristic algorithm called MeTEO is presented, applied to the shape optimization of multistage depressed collectors, simulated by means of a Finite Element collector and electron gun simulator, COLLGUN, which uses the Constructive Solid Geometry for the description of the device shape. METEO is a hybrid algorithm composed by three different heuristics: FSO (Flock of Starlings Optimization), PSO (Particle Swarm Optimization), and BCA (Bacterial Chemotaxis Algorithm); it performs the optimization using both the topological and the metric rules and offers a natural parallel implementation that allows speeding up the whole process of optimization by the fitness modification (FM).

Shape Optimization of Multistage Depressed Collectors by Parallel Evolutionary Algorithm

In this paper, a novel inverse-based multifrontal block incomplete LU preconditioner is proposed, which is derived from the complete multifrontal method and the inverse-based dropping strategy. The new preconditioner is used to solve the large-scale complex unsymmetrical linear systems arising from the 3-D finite-element (FE) eigenvalue analysis of lossy slow-wave structures (SWSs) of traveling-wave tubes (TWTs). An update-matrix-free multifrontal method and an adaptive super-block incomplete factorization framework are proposed and utilized to improve the computational performance and decrease the memory requirements of this preconditioner. Moreover, the inverse-based dropping strategy is introduced to the incomplete multifrontal method for the first time making this preconditioner more effective. By utilizing the proposed preconditioner, the cold characteristic parameters of SWSs can be calculated quickly and accurately. In the simulations of many SWSs, the 3-D FE eigenvalue analysis of lossy SWSs based on this preconditioner has shown the high-efficiency computational performance and the low memory requirements. It is shown that this novel preconditioner is very useful to design lossy SWSs for high-efficiency TWTs.

An Inverse-Based Multifrontal Block Incomplete LU Preconditioner for the 3-D Finite-Element Eigenvalue Analysis of Lossy Slow-Wave Structures

Purpose – The purpose of this paper is to present the application of a novel hybrid algorithm, called MeTEO (Metric‐Topological‐Evolutionary‐Optimization), based on the combination of three heuristics inspired by artificial life to the solution of optimization problems of a real electronic vacuum device.Design/methodology/approach – The Particle Swarm Optimization (PSO), the Flock‐of‐Starlings Optimization (FSO) and the Bacterial Chemotaxis Algorithm (BCA) were adapted to implement a novel meta‐heuristic MeTEO the FSO has been powerfully employed for exploring the whole space of solutions, whereas the PSO is used to explore local regions where FSO had found solutions, and BCA to refine the solutions found by PSO, thanks its better performances in local search.Findings – The optimization of the focusing magnetic field of a Travelling Wave Tubes (TWT) collector is presented in order to show the effectiveness of MeTEO, in combination with COLLGUN FE simulator and equivalent source representation. The optimiz...

TWT magnetic focusing structure optimization by parallel evolutionary algorithm

This work reports some initial results of a 2-D electron gun design code (XMGUN) based on the finite-element method (FEM). Using the Galerkin weak formulation, the nodal analysis, and the first-order elements, the Poisson equation was solved for the electron gun electrostatic potential. The nonrelativistic particle paths were numerically calculated by a fourth-order Runge-Kutta method. An iterative scheme was repeated until the electron paths convergence was achieved under full space-charge limited condition. In order to validate the algorithm, the focusing properties of a 2-D Pierce electron gun with planar symmetry were studied. The quality of the beam was evaluated based on the particle's final position, the transit time, and the particle energy evaluations. Using these three parameters, a good agreement was found between the theoretical and calculated results. Absolute current density errors of less than 1% were found, even with a coarse discretization of the domain. The XMGUN tool was used to design a 30-kV, 7.1-A, and 1.37-μPerv axis-symmetric high-power electron gun for use in vacuum microwave devices. The figure of merit used as reference to measure the quality of the electron beam was the normalized transverse velocity.

The XMGUN Particle Path FEM Code

A novel three-dimensional FE procedure for the analysis of electron guns inside traveling wave tubes (TWTs) is presented, illustrating its main features. In this procedure, electron trajectories modeling cathode emission are obtained by solving a Vlasov-Poisson system of equations together with the relativistic dynamical equations of motion, under consistent particle injection conditions. This coupled electromechanical problem is solved iteratively by assuming stationary conditions. Simulation results concerning a gridded electron gun are presented, showing good agreement with available experimental data

3-D Finite Element Analysis of TWT grid electron guns

The application of radio frequency (RF) vacuum electronics for the betterment of the human condition began soon after the invention of the first vacuum tubes in the 1920s and has not stopped since. Today, microwave vacuum devices are powering important applications in health treatment, material and biological science, wireless communication—terrestrial and space, Earth environment remote sensing, and the promise of safe, reliable, and inexhaustible energy. This article highlights some of the exciting application frontiers of vacuum electronics.

/pdf/frontiers-in-the-application-of-rf-vacuum-electronics-1983wjld.pdf

Frontiers in the Application of RF Vacuum Electronics

In this paper, the authors present a 3-D dedicated finite-element tool expressly conceived for the analysis of traveling wave tool helicoidal slow wave structures (SWSs). Accurate analysis of the SWS is a difficult task due to its complex geometry. Moreover, in order to achieve the design parameters a specific post-processing is required. Consequently, specialized 3-D numerical simulators are needed to carry out the design process. The developed tool includes a dedicated mesh generator, an eigenmode and a driven mode solver, and a post-processing module. An example of a typical SWS analysis performed by using the tool is also given

An FE Tool for the Electromagnetic Analysis of Slow-Wave Helicoidal Structures in Traveling Wave Tubes

COLLGUN: a 3D FE Simulator for the Design of TWTs Electron Guns and Multistage Collectors

A novel slow wave structure (SWS) consisting in a planar helix with straight-edge connections, operating in the K-band with a very low cathodic voltage, is herein proposed. The structure has been designed so to have a working band centered around 20 GHz. Considering an electron beam generated by a cathode with voltage and current of 1700V and 15mA respectively, we have predicted a gain of 35dB and a saturated output power of 5.5W at 20GHz in a 100 periods structure. Furthermore, our SWS has been designed in order to be more promising in terms of fabrication, if compared with other similar structures already reported in the literature.

Design of a Planar Helix Slow Wave Structure for TWT applications in the K-Band

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