In fusion devices strongly localized intensive sources of impurities may arise unexpectedly, e.g., if the wall is excessively demolished by hot plasma particles, or can be created deliberately through impurity injection done for diverse purposes. The spreading of impurities from such sources, both along and perpendicular to the magnetic field, is affected by Coulomb collisions with background particles, ionization, acceleration by electric field, etc. Simultaneously the plasma itself can be significantly disturbed by these interactions. To describe self-consistently the impurity spreading process and the electron density response, three-dimensional fluid equations for the particle, parallel momentum and energy balances of various ion species are solved by reducing them to one-dimensional equations for the time evolution of the radial profiles of several parameters which allow finding the main characteristics of solutions: the maximum densities of impurity ions of different charges, the dimensions along and across the magnetic field of 'shells', i.e. the cross-sections of the regions occupied with these particles by magnetic surfaces, and characteristic temperatures of impurity ions. The results of modelling of the penetration process for carbon impurity into a relatively cold edge of ohmic TEXTOR plasma and of argon into hot H-mode plasma in JET are presented.
Interplay of light and heavy impurities in a fusion device