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Gyrofluid Turbulence Models with Kinetic Effects

W. Dorland
G. Hammett
Journal / Anthology

Physics of Fluids B
Year: 1993
Volume: 5
Issue: 3
Page range: 812-835

Nonlinear gyrofuid equations are derived by taking moments of the nonlinear, electrostatic gyrokinetic equation. The principal model presented includes evolution equations for the guiding center n, u parallel, T parallel, and T perpendicular, along with an equation expressing the quasineutrality constraint. Additional evolution equations for higher moments are derived that may be used if greater accuracy is desired. The moment hierarchy is closed with a Landau damping model [G.W. Hammett and F.W. Perkins, Phys. Rev. Lett. 64, 3019 (1990)], which is equivalent to a multipole approximation to the plasma dispersion function, extended to include finite Larmor radius effects (FLR). In particular, new dissipative, nonlinear terms are found that model the perpendicular phase-mixing of the distribution function along contours of constant electrostatic potential. These "FLR phase-mixing" terms introduce a hyperviscositylike damping variation k 2 perpendicular bar Phi sub k kl time k prime bar, which should provide a physics-based damping mechanism at high k perpendicular rho which is potentially as important as the usual polarization drift nonlinearity. The moments are taken in guiding center space to pick up the correct nonlinear FLR terms and the gyroaveraging of the shear. The equations are solved with a nonlinear, three-dimensional initial value code. Linear results are presented, showing excellent agreement with linear gyrokinetic theory.

*Science > Physics > Fluid Mechanics