Study Of The Nonlinear Interaction Between Electrostatic Wave And Energetic Particles By BOT Model

Wave-particles interaction is a fundamental problem in plasma physics.In magnetic confinement fusion devices,the interaction between plasma waves and energetic particles is very important.The wave resonating with the energetic particles that have a similar velocity can gain energy from the interaction,and be stimulated during the slowing down process of energetic particles.Meanwhile,the wave with a certain amplitude can also redistribute the energetic particles during this process,which seriously affects the heating efficiency of the particles.Besides,energetic particles can damage the device first wall,leading to the further reduction of plasma confinement.Therefore,study of the interaction between the wave-particles is an important topic in plasma research.In this thesis,based on the Bump-On-Tail model of one-dimensional electrostatic wave,the distribution function of energetic particles is studied numerically using the spectral method.Scanning the coefficients of diffusion,drag and Krook collision with BOT code,the thresholds for generating nonlinear sweeping phenomenon are given,and the effects of these three factors on wave-particles interaction are discussed as well as the related physical mechanisms.Based on the finite difference method,the BOT model is numerically calculated,and a program with filter module had been developed to study the multi-mode coupling problem in self-adaptive system.The thesis structure as follows:In chapter ?,it introduces the current researching situation at home and abroad and describes several typical wave-particles interaction models in plasma.In chapter ?,it introduces the kinetic theory of wave-particles interaction,the physical model BOT used,and the Landau damping and growth mechanism,the hole-clumps formation and sweeping that appear in wave-particles interaction.In chapter ?,the spectral method is used to handle the distribution function of energetic particles.Scanning the coefficients of diffusion,drag,and Krook collision with BOT code,the thresholds of nonlinear sweeping phenomenon are given,together with the efficiency analysis of these three factors on sweeping.When the ratio of the background damping rate ?d to the linear growth rate yLof the wave is around one,the system is in threshold instability.The results show that:(1)the sweeping is found that can be achieved when it is far away(?d/?L=0.3)or close to(?d/?L=0.8)the threshold,drag itself cannot cause the sweeping while it shows more influence when the sweeping threshold is approched.(2)Both diffusion and Krook collision can effectively suppress the sweeping at near the instability threshold(?d/?L=0.9),and the latter suppression effect is more obvious.On the contrary,the drag can promote the formation of the sweeping,the drag effect is enhanced,the clump structure in the velocity distribution function is obvious as well as the downward sweeping.In chapter ?,the numerical calculation of the BOT model based on finite difference method.The code with filter module is written by solving the wave-particles equations,which can be used to study the problem of multi-mode coupling in self-consistent systems.The code can well exhibit the process of both the electrostatic oscillation and the wave-particles energy exchange.The benchmark of the code with the original BOT code proves the reliability of the code,lays a foundation for the subsequent discussion of the wave-particles resonance multi-mode problem.