Impacts Of Rough Surface On Impurity Erosion And Deposition In Tokamaks

With the decrease of the fossil energy,energy crisis is threatening human being and the renewable energy resources exists various problems,so control and using the nuclear fusion is the problem of all countries in the world concerns.Nowadays,tokamak is the device which is seen as the most realized fusion reactor.And tungsten（W）has been widely considered as a major material for the divertor and the first wall in the next-step fusion devices due to is high thermal conductivity and melting point,low sputtering yield and tritium retention.The process of plasma-wall interaction is important in researching tokamak,which is directly impacts the life of tokamak.The process of plasma-wall interaction is very complicated mainly includes physical sputtering,chemical erosion,back sputtering,desorption and other physical or chemical mechanism.It is very important to select the wall’s material,due to the plasma-wall interaction damages the wall serious and has a great impact on the fusion reaction in the device.Divertor target will suffer great damage due to the high energy plasma and the edge localized modes,thus the life of tokamak will be shorted.Different flux density,plasma temperature and the target surface topography in the device make different damage in the target.In addition to the study of target material,to study the surface topography of target also has the great significance.The major works of the thesis are summarized as follows:the first part is mainly about the reason of study nuclear fusion,the progress of nuclear fusion at home and abroad,the device of tokamak and divertor,the plasma-wall interaction and some material of target.The second part is about studies of impurity erosion and deposition on tungsten rough surfaces under plasma conditions suing the three-dimensional code SURO.The modelling results of SDPIC are used as an input data to simulate the erosion and deposition of impurity by changing surface topography,plasma temperature and impurity flux.The third part is the simulation of the carbon deposition and substrate erosion on the rough surfaces with the method of Monte-Carlo code SURO.Then we study the impurity erosion and deposition under different rough surface topography,different plasma temperature and different material of substrate.The simulation showed that the deposition of the beryllium impurity mainly occurs at the valley region on the two rough surfaces for the small beryllium flux when the impurity erodes and deposits on rough tungsten surface.The relatively uniform distribution of the deposited beryllium impurity is obtained on both rough surfaces.The detailed analysis of the impact of the background beryllium flux on the evolution of the tungsten rough surface has been performed,which shows that the deposition of the beryllium impurity can result in a possible smoothing of the tungsten rough surface even though the erosion of background plasma is negligible.The complex rough surface with more local wrinkles would lead to a higher deposition of the beryllium impurity and a lower erosion of the tungsten substrate.The increase of the plasma temperature with the range from 5 to 10 eV would lead to a significant enhancement of the erosion of the tungsten substrate.The modelling of the carbon deposition on tungsten and carbon rough surfaces has been carried out with the 3D SURO code.At the plasma temperature of 10 eV,the rough and smooth surfaces are in the deposition dominated regime.Some segments of the rough surfaces are not completely covered by the deposition from incident C³⁺ions due to the leading edge effect of rough surfaces,which results in a higher eroded C areal density.The increase of the plasma temperature leads to a stronger modulation of the concentration of the deposited C in the surface and also a faster smoothing phenomenon of the rough surface,which is in the erosion dominated regime.The rough and smooth surfaces cannot be fully covered by the deposition from incident C³⁺ions,which can establish a dynamic balance with the substrate material in the surface.