PIC Simulations Of Fast Ion Dynamics In Magnetized Plasmas

The interaction between charged particles and plasmas has always been an interesting topic in the past decades.It can not only reveal basic physical problems but also be widely applied in many practical fields,such as inertial confinement fusion driven by ion beam,high-energy and high-density matter,and auxiliary heating means of neutral beam in magnetic confinement fusion.The plasma heating by neutral beam is considered to be a mature auxiliary heating method with high efficiency and clear physics.And the neutral beam injected into the plasma will be quickly ionized to fast ions with high energy.The dynamic behavior of these fast ions interacting with plasmas and the energy deposition process have always been the focus of researches.In addition,various instability modes excited by the interaction between high-energy particles generated by thermonuclear fusion and plasmas are also concerned.In this paper,the self-consistent two-dimensional electrostatic particle simulation(Particle-in-Cell Simulation Method,PIC)is used to study the energy deposition process and the wake effect of isolated ion cluster(continuous ion beam)in the shear magnetic field.The effects of shear magnetic field,injected ion energy and correlation between injected ions are investigated.Moreover,a three-dimensional hybrid model is used to study the influence of the dynamic effect of energetic particles on the ballooning mode instability.The research background and progress of the interaction between charged particles and plasmas are described in the first chapter.In chapter 2.the two-dimensional electrostatic particle model adopted to study the interaction of charged particles with plasmas is introduced,and the detailed simulation parameters are also given.In chapter 3.the effect of shear magnetic field perpendicular to the simulation area on fast ion energy deposition is studied.The results show that the shear magnetic field is more conducive to the energy deposition of fast ions compared with the uniform magnetic field.And the wake field will be easily induced by these fast ions in the shear magnetic field which would promote the energy deposition from fast ions to the background plasmas.In the early stage of the ion cluster penetration into the plasma,the volume of the ion cluster will be compressed to one-third of the original one under the focus of the wake field.And then,due to the difference between the phase velocity of the wake field and the drift speed of the fast ions,the ion cluster will gradually spread a lot.Besides,increasing the incident energy and density of the ion cluster will also enhance the energy deposition of the ion cluster.In chapter 4.the effect of shear magnetic field parallel to the simulation area on the energy deposition of fast ions is investigated.The simulation results show that when there is an injection angle between the ion cluster and the magnetic field,the wake field will be induced by the ion cluster in the lateral direction.And then these fast ions will lose amounts of energy do against with the wake field.What's more,the stratification occurs during ion cluster transportation.As the continuous ion beam penetrates into the plasma with an injection angle,the ion beam will also be stratified under the modulation of wake field.Afterwards,the ion beam moves along the direction of the magnetic field under the constraint of the Lorentz force and the ion beam diffuses uniformly in space.The stopping power of the ion cluster increases with the injection angle.Besides,the energy deposition efficiency of isolated ion cluster tends to flatten as the injection angle reaches a certain threshold.In addition,this chapter compares the energy deposition efficiency of ion cluster(continuous beam)under different magnetic field configurations.In the case of shear magnetic field which is perpendicular to the simulation area,the energy deposition efficiency of isolated ion cluster gradually catches up with that for the case of continuous ion beam,as the strength of the magnetic field increases.However,the energy deposition efficiency of continuous ion beam under the shear magnetic field which is parallel to the simulation area is always better than that of isolated ion cluster.In chapter 5.the dynamic effect of energetic particles on the ballooning instability is studied by using the three-dimensional hybrid model(magnetohydrodynamic model coupled with particle model).It has been found that the increase of the energetic particle beta?_h will shorten the nonlinear stage of system instability mode,while at the nonlinear stage there will be a secondary growth which will accelerate the system disruption.By analyzing the Fourier component of the perturbation magnetic field amplitude,it is found that the dynamic behavior of energetic particles can effectively suppress the growth of the low-order ballooning mode.But the n=0 instability mode grows rapidly at the nonlinear stage,resulting in the system disruption.In addition,the dynamic effect of energetic particles can stimulate various instability modes in the system.And the ballooning-like perturbation can be observed at the linear stage.Furthermore,the clockwise rotation of the mode structure could enhance the stability of the system.However,due to the multiple modes coupling,the spatial topological structure of magnetic lines is gradually destroyed until the system disruption.