Quasi-three-dimensional modelling of penetration and influence of impurities in plasma

In fusion devices strongly localized intensive sources of impurities may arise unexpectedly from plasma-wall interactions or can be created deliberately through impurity injection. The spreading of impurities from such sources is essentially a three-dimensional and non-stationary phenomenon involving physical processes of extremely different time scales. Numerical modelling of such events is still a very challenging task, even using most modern computers. To diminish the calculation time drastically, a new quasi-three-dimensional description is proposed, combining a 'shell' model for the impurity penetration process and a two-zone approximation for the main plasma components. This approach allows us to reduce fluid equations for particle, parallel momentum and energy balances of the main and impurity plasma species to one-dimensional equations describing the time evolution of radial profiles of the most characteristic parameters. The assumptions in the approach are verified by comparing its predictions with direct numerical solutions of transport equations. The results of modelling for the penetration process of argon species into hot H-mode plasma during impurity puffing experiments are presented.