Simulation Study On The Evolution Of Rough Surface Of The Tungsten Target By Deuterium Ion Bombardment

The process of plasma-wall interactions mainly includes physical sputtering, chemical erosion, backscattering and desorption. It also includes other physical and chemical mechanism. These reactions will threaten the wall performance and reduce the lifetime of the wall. In addition, they seriously affect the proceeds of fusion reactions. In different fusion devices, the non-uniform erosion and deposition behavior caused by rough divertor target are confirmed by a large number of experiments. The convex part of rough target surface are much more easily eroded, while the sunken part will deposit a lot of erosion materials. The Monte Carlo code SURO made great achievement in the research on the 13C deposition behavior on rough surface by injecting 13CH4 into TEXTOR limiter. Recently, there are few investigations on the evolution of three-dimensional rough surface topography under the bombardment of deuterium ions. However, the interactions between the plasma and rough target under three-dimensional model are indispensable and it can help us to further understand the internal reaction mechanism.In this paper, we combined three-dimensional Monte Carlo code SURO and one-dimensional PIC-MCC code SDPIC to study the evolution of rough surface topography of tungsten target under the bombardment of deuterium ions in fusion devices. We can get the edge plasma information from SDPIC code simulation. The results of simulation can be used as input parameters for SURO. Adding that, SURO code can be used to calculate local angle (the angle between incident direction and rough surface normal direction), rough divertor target erosion/deposition and the evolution of rough surface. This paper can be divided into four parts. The first part is mainly to study the deposition and erosion of tungsten particles on the roughness target surface under different plasma densities. The second part is mainly to study the nominal angle/local angle and surface evolution under different magnetic field angles. In the third part, we simulated the erosion/deposition, surface evolution and the distribution of local angle under different characteristic length. Lastly, we studied the influence of different initial surface morphologies on the surface evolution.Under different plasma densities, the simulation results show that azimuthal angle distribution can be elongated due to the effect of magnetic field and electric field. The nominal angle distribution of the majority of particles can be maintained at between 50-70 degrees. The uneven phenomenon of erosion and deposition are presented in different simulation areas. The erosion mainly occurs in a convex surface, while the deposition mainly occurs in the concave part. At the beginning of the simulation, the erosion rate is low and the deposition rate is high. When it reaches the stable state, the opposite situation showed up. Through the simulation of evolution in different magnetic field angles, we found that the erosion rate of deuterium ions increased with magnetic field angle increasing. The erosion rate even changed an order magnitude. The larger the magnetic field angle is, the higher the deposition rate is, and we can see that the topography evolution of rough target surface is more and more apparent. Under different characteristic length, the probability density of the local angle of background deuterium ions becomes much narrower and the asymmetry becomes much more pronounced with length increasing. And, the peak angle increases. At the beginning of the simulation, the larger the characteristic length is, the higher the erosion of rough target is. The larger the characteristic length is, the lower the deposition rate is and the surface evolution has a much more obvious change. Comparing the simulation investigations of roughness surface evolution under different initial surface morphology, it is found that, contrast to that of real rough target surface, the erosion rate of the surface topography using a reference case is higher and the deposition rate is lower. However, the impact caused by the deposition can’t be ignored.