Reduced Fluid Descriptions of Toroidally Confined Plasma with Finite Ion Temperature Effects.

Fluid descriptions of toroidally confined plasma with FLR effects are studied, based on a generalized, energy conserving, self-consistent, nonlinear reduced fluid model (HHM). The model, derived via a fluid approach starting from moment equations, differs from Braginskii's fluid system in retaining O((rho)(,i)('2)) terms (where (rho)(,i) is the ion gyroradius) and most of the non-ideal effects. Hence, many of the well-known reduced fluid models can be reproduced from HHM by simply specifying scales of some parameters such as (rho)(,i) and (beta). On the other hand, a Pade approximation of the full FLR system, obtained from the simplified version of HHM, is also presented. This simplified model is not only energy conserving and much easier to access, but also can be shown to retain FLR effects quite accurately. We therefore remark that this version should deserve further analytical and numerical studies. The possible applications of HHM are discussed in a general way so that further detailed studies can readily follow. In particular, linear toroidal drift-tearing modes with finite ion temperature effects are studied. The eigenmode equations, derived from the linearized version of HHM, are analyzed both by a multi-scale variational principle for the sheared slab geometry; and by the conventional asymptotic matching process for the toroidal geometry. It is discovered that (1) without the effects of viscosity, the instability condition and the growth rate of the semicollisional drift-tearing modes are hardly affected by the finite ion temperature; (2) with the effects of viscosity, the instability condition and growth rate are characterized by the ion viscosity in a crucial manner. Since ion viscosity is sensitive to the ion temperature, we thus conclude that ion temperature could become an important parameter for controlling the drift-tearing instabilities in present and future day high temperature plasma devices. In addition, the non-canonical Hamiltonian theory and its application to our reduced system are discussed. This fast developing theory has been useful for studying the equilibria and nonlinear instability of fluid system.