Effects Of Particle Recycling And The Carbon Impurities On The Divertor Plasma: A Particle-in-cell Simulation

Energy is vital to the survival and development of mankind,the controlled fusion energy is considered to be the most promising ultimate energy,and tokamak is the most important magnetically confined controllable fusion device.The divertor is the main component of the tokamak,which is used to remove the particle and heat flux from the core plasma and to shield the impurities,and it is the main plasma-wall interactions(PWIs)area.PWIs play important role on both plasma and wall,on one hand,they may produce intrinsic impurity through the wall sputtering to pollute the plasma,and on the other hand,the divertor target may be damaged under the bombardment of the intense flux plasma,which can reduce the lifetime of the tokamak device.Therefore,it is necessary to reduce the plasma temperature and energy flux load to the target effectively,which requires the divertor to have strong power radiation capability.The particle recycling can radiate energy in the divertor region by releasing neutral particles,and the plasma temperature and density in turn have great impact on the particle recycling.In addition,the generated neutral particles have an opposite effect on the plasma,thus affecting the whole divertor operation.Different target materials also have different effects on particle recycling.Therefore,further study is required.Impurity radiation is another important method to raise the power radiation,and carbon impurity is a very important radiator as an inherent impurity(for carbon divertor target).Thus,it is important to quantitatively analyze the effects of carbon impurity and recycled neutral particles on divertor plasma.In this thesis,the effects of particle recycling and carbon impurity on the divertor plasma are studied by the particle simulation(particle-in-cell Monte Carlo collision,PIC-MCC).The whole thesis is divided into five chapters.In Chapter 1,the current status of magnetic controlled fusion,the background and motivation of the thesis are summarized.In Chapter 2,the PICMCC model,the particle simulation software VSim and corresponding simulation method are introduced.In Chapter 3,a one-dimensional in space three-dimensional in velocity(1D3V)PIC-MCC model by using VSim software,is applied to study the effects of particle recycling on divertor plasma.The simulation domain is the whole scrape-off layer of the tokamak in onedimension along the magnetic field.The mechanism of influence of particle recycling on the plasma under different parameters is studied.The effects of different collision processes and the different target materials(carbon or tungsten)on plasma are also studied.The simulation finds that the particle recycling on divertor target plate can produce deuterium atom(D)and deuterium molecules(D2)with certain density,which can collide with plasma,with various reactions(e.g.ionization collisions,charge exchange,electric dissociation,excitation collision and elastic collision).By analyzing the temperature and density of plasma and neutral particle in the whole simulation domain,as well as the energy flux and particle flux to the target plate,it is found that the recycled neutral particles have a great impact on the divertor plasma,and the collision reaction can radiate energy,thus reducing the plasma temperature and energy flux load to the divertor target,and promoting the realization of detached divertor.The simulation results also demonstrate that the plasma energy and momentum loss with the carbon target is greater than that with the tungsten target in the divertor region.By only considering the particle recycling,the plasma detachment is beneficial from carbon target,while the tungsten target has a more significant impact on the core plasma.In Chapter 4,the same 1D3 V PIC-MCC model is applied to study the effect of carbon impurity on the divertor plasma,and the difference between the carbon and recycled deuterium on the plasma detachment.When considering the role of carbon impurity in the divertor,it is found that carbon impurity has a great influence on the divertor plasma.The ionization collision of carbon can effectively increase the electrons density near the divertor target,and the excitation reaction radiate energy effectively and reduce the electrons temperature near the target.The carbon impurity is a more effective power radiator than the neutral deuterium particle,and thus it can promote the achievement of divertor detachment.In Chapter 5,the summaries of the present thesis and future work are presented.