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Simulation of high-Z impurity behaviour for ITER operational scenarios using the ZIMPUR impurity code

Results of the simulation of the transport and radiation losses of high-Z impurities (tungsten and argon) in the ITER reference operational scenarios are presented. The impurity dynamics was modelled by the ZIMPUR impurity code, a description of which is presented. This code was integrated with the ASTRA transport code for the background plasma behaviour modelling and with the NCLASS code to take into account the neoclassical impurity fluxes. Simulations show that for flat plasma density profiles the neoclassical thermal diffusion contributes to plasma core screening from heavy impurities in all considered scenarios. Thus, a radiating layer is formed near the plasma column periphery. It is more essential for the steady-state scenario with the reversed shear region and an improved confinement in the plasma core. An appreciable effect is also found for the reference inductive ELMy H-mode scenario, where the plasma is more strongly influenced by anomalous transport. The calculated radiated power near the plasma edge exceeds by about twice the value obtained in the coronal model approximation. This can be explained as being due to the reduction of impurity ion charge states, due to their charge exchange with deuterium/tritium neutrals, fuelling the plasma. It offers the possibility of decreasing the total impurity contamination, which is necessary for re-radiation of the given power.