Abstract and subjects
The two-fluid equations of Braginskii miss heat-flux terms in the viscosity. In this work we employ drift orderings to recover these missing terms and obtain a fully self-consistent system of short mean-free path two-fluid equations. These equations cannot be recovered from the short mean-free path limit of the well-known drift kinetic formalism of Hazeltine since this formalism is only accurate through first order in the small gyroradius expansion parameter, whereas second order accuracy is required. We propose a way of generalizing this formalism to make it second-order accurate. We also use the results to derive the gyroviscosity and ion perpendicular viscosity for plasmas of arbitrary collisionality, provided the leading order distribution function is velocity-space isotropic. As an application, we consider electrostatic turbulence in a tokamak and use our expressions for ion viscosity in the toroidal angular momentum conservation equation to show that the ion perpendicular viscosity can be important for determining the axisymmetric radial electric field (and, therefore, zonal flow amplitude), especially if the turbulent radial particle flux is small.