Modeling of impurity effect on drift instabilities in plasmas with many ion species

Abstract

Drift microinstabilities, being the main cause of anomalous transport of charged particles and energy in fusion plasmas, can be strongly influenced by the presence of impurities. Normally a large amount of different ion species from diverse charge states and chemical elements is present. An approach, providing a possibility to take into account an arbitrary number of ion species in analysis of instabilities, is proposed and applied to study the impurity effect on unstable modes due to ion temperature gradient and trapped electrons described in a linear fluid approximation. The method is validated by comparing with the results from direct calculations in a one impurity ion case. The dependence of instability characteristics and anomalous transport coefficients on the absolute level and radial gradient of impurity density is investigated. Plasmas with several impurity ion species, including C+6, N+7, O+8, Ne+10, and Ar+18 whose density peaking factors are determined self-consistently from the impurity zero flux condition, are considered as an example of applications.