Modeling Of Ion Impinging On Rough Test Limiter Exposed To The Edge Plasma Of TEXTOR

Carbon materials have been widely used as plasma facing materials(PFMs) in magnetic confinement nuclear fusion due to the low atomic number and their excellent thermal properties. However, eroded carbon can co-deposit on wall materials with tritium, forming a co-deposition layer. Tritium is radioactive which will result in severe danger on long-term operation of fusion reactor. Thus, to investigate the transport, erosion and deposition of carbon material in edge plasma is of great importance. Dedicated experiments carried out on TEXTOR showed carbon deposition efficiency on rough test limiter is much larger than on a relative smooth one, and pattern of deposition is much broader. The ERO code can successfully simulate the transport of impurities in Scrape Off Layer (SOL) of TEXTOR and the interaction between impurities and smooth test limiter. However surface roughness effect has not been incorporated into ERO code. The aim of this research is to provide the surface roughness module dealing with the surface roughness effect to ERO code.The ERO code is utilized to investigate the ionization, collision, transport of deuterium atoms and a certain amount of carbon impurities in edge plasma of TEXTOR under variable parameters, and the distribution of their resulting incident angle and impact energy on smooth test limiter is calculated. The detailed parameters include the temperture of background palsma, strength of magnetic field, initisive energy and moving direction of impurities, limiter tilt angle (the angle between limiter surface and magnetic field) and electron density. Simulation results show that the distribution of incident angle of dueterium ions and carbon ions on smooth test limiter only depends on the tilt angle of the test limiter, while the distribution of their impact energy only on the temperature of plasma in the SOL region. These modelled distributions of incident angle and impact energy will be set as input parameters for the surface roughness code.Based on the sputtering yield and reflection coefficient when ions impinging on wall materials depend on the incident angle, a Monte-Carlo code is developed to model the interaction between ions and rough surfaces. It is mainly considered in this code that erosion and deposition on different regions of rough surface under ions impinging would be different. Meanwhile eroded atoms and reflected impurities may impinge on materials after transport within the rough surface region, which can result in a second erosion and deposition on the rough surface. Taking into above issues, the evolution of rough test limiter surface via impinging time of ions can be produced. If the limiter surface is near to the Last Closed Flux Surface (LCFS), where the amount of carbon is small, the evolution of rough surface behaves an erosion dominating scenario; for the region far from the LCFS, the evolution of rough surface behaves a deposition dominating scenraio due to lager amount of carbon. Different from smooth surface, carbon can redeposit within the rough surface, which will not be easily eroded away from the surface. This can lead a Smoothening effect of rough test limiter surface by ions impinging. Those results make sense for further understanding of the application of carbon materials in fusion facilities and how to solve the problem of tritium retention co-deposited with carbon.