'Shell' approach to modeling of impurity spreading from localized sources in plasma

In fusion devices, strongly localized intensive sources of impurities may arise unexpectedly or can be created deliberately through impurity injection. The spreading of impurities from such sources is essentially three-dimensional and nonstationary phenomenon involving physical processes of extremely different time scales. Numerical modeling of such events is still a very challenging task even by using most modern computers. To diminish the calculation time drastically a "shell" model has been elaborated that allows to reduce equations for particle, parallel momentum and energy balances of various ion species to one-dimensional equations describing the time evolution of radial profiles for several most characteristic parameters. The assumptions of the "shell" approach are verified by comparing its predictions with a numerical solution of one-dimensional time-dependent transport equations