F L Hinton | PubMed Health

PubMed2001

Neoclassical radial electric field and transport with finite orbits.

Neoclassical transport in a toroidal plasma with finite ion orbits is studied, including for the first time the self-consistent radial electric field. Using a low-noise deltaf particle simulation, we demonstrate that a deep electric-field well develops in a region with a steep density gradient, because of the self-collision-driven ion flux. We find that the electric field agrees with the standard neoclassical expression, when the toroidal rotation is zero, even for a steep density gradient. Ion thermal transport is modified by the electric-field well in a way which is consistent with the orbit squeezing effect, but smoothed by the finite orbits.

Journal Article↗

PubMed2001

Modified lattice Boltzmann method for compressible fluid simulations.

A modified lattice Boltzmann algorithm is shown to have much better stability to growing temperature perturbations, when compared with the standard lattice Boltzmann algorithm. The damping rates of long-wavelength waves, which determine stability, are derived using a collisional equilibrium distribution function which has the property that the Euler equations are obtained exactly in the limit of zero time step. Using this equilibrium distribution function, we show that our algorithm has inherent positive hyperviscosity and hyperdiffusivity, for very small values of viscosity and thermal diffusivity, which are lacking in the standard algorithm. Short-wavelength modes are shown to be stable for temperatures greater than a lower limit. Results from a computer code are used to compare these algorithms, and to confirm the damping rate predictions made analytically. Finite amplitude sound waves in the simulated fluid steepen, as expected from gas dynamic theory.

Journal Article↗