Theoretical Research And Algorithm Implementation Of Absorbing Boundary Conditions In Particle-in-cell Simulation

In scientific research,when faced with a complex physical system,beside theoretical or experimental approach,numerical simulation method is an effective way to study and solve these problems.Since 1970 s,with the development of computer technology and PIC(particle-in-cell)simulation,computer simulation plays a more and more important role in solving the physical problems hard to be solved by theory or experiment,which can shorten the research cycle,reduce the verification experiment,reduce the cost of experiments and so on.In the simulation of electric vacuum devices,a limited space is often needed to simulate the cavity structure,which requires take a variety of boundary conditions into account.Among these boundaries,the absorbing boundary plays a key role in the PIC simulation by absorbing the electromagnetic wave without reflection.Thus,realizing the absorbing boundary function of CHIPIC has very important meaning.The paper's main works are below:Firstly,after a brief introduction of CHIPIC,the absorbing boundary algorithm is alalyzed.According to the program flow chart,the absorbing boundary module is realized in the 3D modeling platform.And then the electric dipole and magnetically insulated line oscillator are used to verify the absorbing boundary module.The simulation result show the correctness of the absorbing boundary module.Secondly,according to the simulation of high power electric vacuum device,the central difference absorption boundary algorithm is improved,the field update iteration formulas of absorb boundary region in time-biased method and HIGH-Q algorithm are derived,and are implemented in CHIPIC software.And then a backward wave tube is simulated by the new CHIPIC,comparing with the simulation data acquired by central difference algorithm,the result indicate the two algorithm have good effects.Finally,the particle backflow phenomenon of absorbing boundary is studied in all respects.According to the analyze of numerical simulation,the reason of backflow is caused by the differential treatment of the particle and electromagnetic in algorithm,which cause the charged particle accumulation on the next grid layer.And then the reflect field of the accumulated particle caused the backflow phenomenon.To solve this problem,according to the current continuity equation,the iteration equations of the particle in the absorbing boundary are derived,by which the conductivity parameter is determined to modify the absorbing boundary algorithm.After these work,the diode and 140 GHz confocal waveguide gyrotron traveling wave amplifier are simulated to verify the correctness of the modified module,which are compared with the MAGIC results.The results present the valuable of method.