2D numerical simulations of the boundary plasma parameters in the toroidal limiter configuration of the FTU tokamak

The problem of the choice of suitable materials for the plasma facing components in the reactor is recognized as very important and yet not solved. Low Z materials, mostly used in operating tokamaks, may present problems in application to reactor parameters since large erosion rates are foreseen for them. As regard the high Z materials they are at present under discussion and investigation. The main advantages in using high Z materials are their high melting points, high sputtering yield thresholds and acceptable thermomechanical properties. The main problem concerning high Z materials rely on the strong energy losses from the core, if high Z ions accumulate in the centre. However radiation losses, if located at the plasma periphery, could be beneficial for the reactor. In order to analyze the influence of the wall facing components on the discharge parameters, an experimental campaign has been carried out on the FTU (Frascati Tokamak Upgrade). Edge plasma parameters have been investigated intensively for different poloidal limiter materials (Ni, Si, Mo, W). Simultaneously the 2D multifluid numerical code EPIT (Edge Plasma Impurity Transport) has been used to analyze plasma parameters of the FTU tokamak SOL. A new toroidal molybdenum limiter has been installed on the FTU tokamak and the code EPIT has been applied to study the transport of plasma and molybdenum ions in the new configuration of the FTU scrape-off layer. The problem of the existence of the self-regulating mechanism limiting impurity production and the electron temperature in the FTU SOL is investigated. (orig.)