Simulation Optimization Design Of Dynamic Focusing With Broad-Width Scanning Electron Beam

The importance of selective electron beam melting technology is becoming more and more prominent with the extensive application of complex precision parts in various industries.Among them,the processing of large complex parts puts forward higher requirements for broad-width scanning and dynamic focusing of electron beam.The research objective of this project is to design an electron gun system which can realize the dynamic focusing of broad-width scanning electron beam.In order to achieve this goal,the electron beam generation system,focusing system,deflection system and dynamic focusing fuzzy control system of the electron gun are simulated and optimized,and the related laws are summarized to guide the actual research and development of the electron gun.Firstly,based on the principle of electron optics and the design principle of electron gun,taking an electron gun with a gross power of 3 k W,cathode accelerating voltage of-60 k V and beam currents' adjustment range of 0 ? 50 m A as an example,the generation system,focusing system and deflection system of electron beam are calculated and designed.CST software is used to simulate this electron gun system.Based on the simulation results,the parameters of the key parts in the electron gun are optimized.At the same time,the following general conclusions applicable to the design of the electron gun are obtained.In the design of the electron beam generation system,the cathode,the beam-forming electrode and the anode mainly affect the accelerating electric field of the electron gun,and then affect the characteristics of the electron beam: The large gap between the beamforming electrode and the cathode causes the electric field to expand towards the cathode,and the potential in front of the cathode increases,which weakens the electron emission ability of the cathode.If the anode aperture is too large,the electric field will expand to the anode,the potential in front of the cathode will decrease,and the electron emission ability of the cathode will be enhanced.Under the condition that the cathode-60 k V and the anode 0 V,reducing the voltage of the beam-forming electrode will reduce the electron beam current,the focal length and reduce the diameter of the focus.Until the cut-off voltage of the electron gun model is-65.5 k V,at which time the electron beam current is0.In addition,the equal potential of the electron beam transmission space and the anode would make the electron beam have no energy loss in transmission.The design of the focusing system and the deflection system is the key to realize the broad-width scanning of the electron beam.The main goal of design is to get the focusing coil with enough central magnetic field intensity,and the deflection coil with relatively simple electromagnetic environment and high magnetic field uniformity,so as to get the electron beam with high stiffness and easy to be controlled during wide scanning.Simulation results show that the magnetic field strength of the focusing coil can be improved by increasing the inner diameter of the focusing coil and adding iron shell outside the coil.In the polyphase deflection coil,the magnetic field uniformity increases first and then weakens with the increase of the number of phases,and the magnetic field uniformity decreases with the increase of magnetic core.In contrast,although the magnetic field uniformity of saddle coil decreases,it greatly simplifies the electromagnetic environment and makes the electron beam deflection easier to control.Moreover,the magnetic field uniformity can be improved by using the quantitative distribution of windings.Another important point of electron beam broad-width scanning is the realization of dynamic focusing,for which a fuzzy control system is developed.A BP neural network with 2 inputs and 3 outputs was constructed using Py Charm software,which contained two hidden layers,each layer containing 16 neurons.A fixed plane was selected to focus the electron beam at the plot position of the plane,and 481 sets of data,such as the coordinates of the plot position,the corresponding focusing compensation current and the deflection current,were collected for the training of the neural network.Then the neural network is used to control the dynamic focusing of the electron beam.The simulation results show that the deviation is less than 1%,which is of practical value.