Neoclassical transport coefficients for ion and impurity species are computed in a large aspect ratio toroidal magnetic confinement system for intermediate-to-high collision frequencies. A large range of values of the relevant density and charge parameters is explored and terms of order (m i/ml)1/2 are retained. The behavior of the transport coefficients is found to depend on the collisionality of both the ions and the impurities. A simple approximate analytic representation of these results which incorporates the correct asymptotic plateau and Pfirsch-Schlüter behavior is presented. In the plateau regime, when (n l/ni)(ml/mi)1/2≪1, the inward impurity flux is found to be suppressed for experimentally obtainable plasma parameters, implying that the time scale for impurity concentration could be too long to be observable.
All Science Journal Classification (ASJC) codes