Particle Simulation Of Open Cavity Electron Beam With High-frequency Field In The Sp Fel Interaction

Smith-Purcell free electron laser shortened as SP FEL is an important branch of free electron laser. This paper presents a more deeply and comprehensive study of Smith-Purcell effect and the SP free-electron laser devices in an open resonator, and good results are achieved.In this paper, at first, according to the theory of quasi-optical resonator diffraction and Smith-Purcell free-electron laser, we discussed the characteristics of a new structure free-electron laser, which mainly includes analysis of the electron movement equation and beam-wave interaction, and also introduction of the stable solution of the spherical cavity.With the help of two-dimensional particle-in-cells simulation, we adopt a flat gating in an open rectangular cavity model to simulate the Smith-Purcell radiation. By setting multitude observe point and observing the bitmap of longitude magnetic field, the frequency of the observe point and space momentum distribution of the beam, simulation for a single bunch is carried out first, from which we can observe the process of generation of SP radiation and the evanescent wave, and find the difference of them. When the single bunch passes over the grating surface, the SP radiation will be inspired. The SP radiation frequency changes with the angle. According to simulation results, the curve that radiation frequency changes with the angle is familiar with the curve draw follow the SP theoretical formula. Then, by observing the bitmap of longitude magnetic field, we simulate a train of periodic bunch to demonstrate the properties of the super-radiant radiation, the output angle of second harmonic and third harmonic frequency are also following the theoretical formula. By changing the shape of the grating, we can achieve different evanescent wave frequency. A cylindrical grating structure is designed to research the SP radiation, too. We used the same method above and also get satisfied results which rectified the correctness of the above model.We suppose the new structure of the SP FEL in an open resonator. And the cold test and electron beam-wave interaction in such system is performed by a two dimensional particle-in-cell simulation. By supposing two different structure and changing the shape of grating, the output result of all kinds FEL is given and made analysis. The entity of laser is completed and the cold test is carried out. The results match the simulation results well. By debugging the parameter of the simulation structure, we can design more satisfied SP FEL, achieving 3mm wave output with high power.