Modification of local plasma parameters by impurity injection

Plasma behavior in the vicinity of strong sources of impurities is considered. A model, based on a fluid description of electrons, main and impurity ions and taking into account the plasma quasi-neutrality, Coulomb collisions of background and impurity charged particles, radiation losses, sinks of particles to bounding material surfaces, is elaborated. Particle, momentum and energy balances are deduced by integrating transport equations within the clouds of neutral and singly charged impurities, both inside and beyond the scrape-off layer of the puffing limiter. These provide algebraic non-linear equations for the characteristic densities and temperatures of the plasma components in the cloud and for the cloud dimension itself. Computations are done for the conditions of impurity seeding experiments in the tokamak TEXTOR. The model allows us to simulate two-dimensional images of radiation losses which can be directly compared with experimental observations.