Fluid models of phase mixing, Landau damping, and nonlinear gyrokinetic dynamics
- Princeton Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543 (United States)
Fluidlike models have long been used to develop qualitative understanding of the drift-wave class of instabilities (such as the ion temperature gradient mode and various trapped-particle modes) which are prime candidates for explaining anomalous transport in plasmas. Here, the fluid approach is improved by developing fairly realistic models of kinetic effects, such as Landau damping and gyroradius orbit averaging, which strongly affect both the linear mode properties and the resulting nonlinear turbulence. Central to this work is a simple but effective fluid model (Phys. Rev. Lett. {bold 64}, 3019 (1990)) of the collisionless phase mixing responsible for Landau damping (and inverse Landau damping). This model is based on a nonlocal damping term with a damping rate {similar to} {ital v}{sub {ital t}}{vert bar}{ital k}{sub {parallel}}{vert bar} in the closure approximation for the {ital n}th velocity space moment of the distribution function {ital f}, resulting in an {ital n}-pole approximation of the plasma dispersion function {ital Z}. Alternatively, this closure approximation is linearly exact (and therefore physically realizable) for a particular {ital f}{sub 0} which is close to Maxwellian. Gyrofluid'' equations (conservation laws for the {ital guiding}-{ital center} density {ital n}, momentum {ital mnu}{sub {parallel}}, and parallel and perpendicular pressures {ital p}{sub {parallel}} and {ital p}{sub {perpendicular}}) are derived by taking moments of the gyrokinetic equation in guiding-center coordinates rather than particle coordinates. This naturally yields nonlinear gyroradius terms and an important gyroaveraging of the shear. The gyroradius effects in the Bessel functions are modeled with robust Pade-like approximations.
- DOE Contract Number:
- AC02-76CH03073
- OSTI ID:
- 7182277
- Journal Information:
- Physics of Fluids B; (United States), Vol. 4:7; ISSN 0899-8221
- Country of Publication:
- United States
- Language:
- English
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