A New fast velocity-diffusion modelling for impurity transport in integrated edge plasma simulation

Shimizu, Katsuhiro; Takizuka, Tomonori; Kawashima, Hisato

For compatibility of high confinement core plasma with strong radiative divertor, it is necessary to establish the control method for impurity retention in the divertor region. We have been studying the impurity behavior in divertor plasmas with a simulation code, IMPMC. A conventional Monte-Carlo algorithm for scattering process in velocity space has a disadvantage that the impurity ions must be traced with a time step shorter than the slowing down time. The IMPMC code demands huge computational time in case of detached plasma. We have developed a new diffusion model using the analytical solution of Langevin equations. By the new diffusion model, we got a prospect of the self-consistent modeling of divertor plasmas and impurity transport, i.e. combining the SOLDOR/NEUT2D and the IMPMC Code. The unified code named SONIC clarifies the impurity transport in the MARFE plasma in consideration of kinetic effects. We carried out the simulation analysis for the JT-60U plasma at first with the IMPMC code. It was found that the radiation near the X-point during MARFE is caused dominantly by deeply penetrating carbons, which are dissociated from the methane (CH) chemically sputtered from the private region.