
Author(s):
H. Sugama and S. Nishimura

Title:
Momentequation methods for calculating neoclassical transport coefficients in general toroidal plasmas
Date of publication:
Jan. 2008

Key words:
neoclassical transport, collisional momentum conservation, momentequation methods, Onsager symmetry, ambipolar diffusion

Abstract:
A detailed comparison is made between momentequation methods presented by Sugama and Nishimura [Phys. Plasmas 9, 4637 (2002)] and by Taguchi [Phys. Fluids B 4, 3638 (1992)] for calculating neoclassical transport coefficients in general toroidal plasmas including nonsymmetric systems. It is shown that these methods can be derived from the drift kinetic equation with the same collision model used for correctly taking account of collisional momentum conservation. In both methods, the Laguerre polynomials of the energy variable are employed to expand the guidingcenter distribution function and to obtain the moment equations, by which the radial neoclassical transport fluxes and the parallel flows are related to the thermodynamic forces. The methods are given here in the forms applicable for an arbitrary truncation number of the Laguerrepolynomial expansion so that their accuracies can be improved by increasing the truncation number. Differences between results from the two methods appear when the Laguerrepolynomial expansion is truncated up to a finite order because different weight functions are used in them to derive the moment equations. At each order of the truncation, the neoclassical transport coefficients obtained from the SugamaNishimura method show the Onsager symmetry and satisfy the ambipolardiffusion condition intrinsically for symmetric systems. Also, numerical examples are given to show how the transport coefficients converge with the truncation number increased for the two methods.

