Time-evolution of velocity distributions of impurity ions in deuterium plasma due to Coulomb interaction

Abstract

Due to Plasma - Surface Interaction fusion plasmas with ITER-like conditions contain impurities existing out of sputtered and eroded wall particles. These impurities affect the plasma fusion yield and reduce the life time of the containing vessel. Therefore, basic understanding of these impurities is essential. We have made a Coulomb-interaction based diffusion model that quantifies both the velocities and directions of these particles as a function of time, with temperature, background plasma, type of impurities and density as parameters. In doing so, we can monitor the time-dependent velocity distribution of the impurity particles. With this model, we can make precise calculations for the time it takes impurities to slow down. We define a parameter H, which will be a measure for the dominant term in the plasmas motion; gyration or diffusion, ranging from zero for gyration-dominated plasmas, to infinity for diffusion dominated situations. We find that for hydrogen plasmas with a temperature of 3 eV and density of 2 *10^14 cm^-3, our parameter H is roughly 6.2, meaning that the plasmas behaviour is dominated by diffusion.