Effects Of Fast Ion Injection On Magnetized Sheath Near A Floating Wall

Fast-ion populations play an increasingly important role in the dynamics of magnetically confined fusion plasmas and related studies, which have spanned a period of more than several decades, including the dynamics of fast ions and their interaction with the bulk plasma. However, due to the collective instabilities driven by the fast ions and interactions with magnetohydrodynamic instabilities, some of the fast ions cannot be confined by the magnetic field and lose to the wall. These fast ions have significant effects on the plasma-wall interaction and have to be taken into consideration. Also, the sputtered material from the wall, due to the bombardment of fast ions, can affect the core plasma effectively. Plasma sheath, a transition region between the plasma and wall, plays an important role on the plasma-wall interaction. So the investigation of fast ions interactions with magnetized plasma sheath is significance. This passage will use the PIC/Monte Carlo simulation method to study the interaction between the injection fast ions and the suspended magnetized sheath.In the second chapter, we first introduce the physics model adopted in the simulation, including the boundary conditions, external magnetic field and so on. Then describe the specific process of the particle simulation method that we used, including the plasma initialization process, the motion of the charged particles at the presence of magnetic field, besides the one-dimensional, two-dimensional case under the weight distribution and the Poisson equation solving process. In addition, the treating of Coulomb collisions between the charged particles with the model proposed by Nanbu is discussed in detail. In this procedure, we will focus on considering two major factors:the impact of collisions between charged particles and the effects of external magnetic field.In the third chapter, the influence of injection fast-ion velocity, density, magnetic field, plasma temperature and angle θ0formed by the magnetic field and x-axis on sheath potential and electric field are discussed, respectively. One-and two-dimensional simulations are performed, and numerical results show that increasing fast-ion injection density or decreasing velocity increases the sheath potential as well as electric field. The enhancement of sheath potential is explained by the increasing net space charge in the sheath due to the injection of fast ions. Magnetic field significantly affects theme evolution of ion flux and velocity distribution on the wall. We also find that strong magnetic field can advance the time of injected ion reaching its maximum velocity. The injection of fast ion disturbs the background charged particle distribution. Furthermore, our results indicate that the magnetic field and injected ion beam have significant effects on sheath properties at the wall in the magnetically confined fusion plasmas.