Self-consistent modeling of plasma response to impurity spreading from intense localized source

Non-hydrogen impurities unavoidably exist in hot plasmas of present fusiondevices. They enter it intrinsically, due to plasma interaction with the wall ofvacuum vessel, as well as are seeded for various purposes deliberately. Normally,the spots where injected particles enter the plasma are much smallerthan its total surface. Under such conditions one has to expect a significantmodification of local plasma parameters through various physical mechanisms,which, in turn, affect the impurity spreading. Self-consistent modelingof interaction between impurity and plasma is, therefore, not possiblewith linear approaches. A model based on the fluid description of electrons,main and impurity ions, and taking into account the plasma quasi-neutrality,Coulomb collisions of background and impurity charged particles, radiationlosses, particle transport to bounding surfaces, is elaborated in this work. Todescribe the impurity spreading and the plasma response self-consistently,fluid equations for the particle, momentum and energy balances of variousplasma components are solved by reducing them to ordinary differential equationsfor the time evolution of several parameters characterizing the solutionin principal details: the magnitudes of plasma density and plasma temperaturesin the regions of impurity localization and the spatial scales of theseregions. The results of calculations for plasma conditions typical in tokamakexperiments with impurity injection are presented. A new mechanism for thecondensation phenomenon and formation of cold dense plasma structures isproposed