Research Objectives
Modeling of ion temperature gradient driven turbulence as a cause of anomalous plasma transport in magnetic fusion devices is at the core of the Numerical Tokamak Turbulence Project (NTTP), one of the Department of Energy's Phase II Grand Challenges. The model developed at Oak Ridge National Laboratory is a full-torus gyrofluid model for this type of tokamak turbulence, covering the entire plasma cross section. This model is complementary to global gyrokinetic models and local flux tube gyrofluid and gyrokinetic models curently in use within the NTTP to understand and control plasma turbulence and transport in tokamak fusion devices.
Computational Approach
The three-dimensional toroidal gyrofluid model under development solves a set of fluid equations, augmented by a closure describing linear wave-particle resonances leading to Landau damping over the whole plasma cross section. The linear terms are treated implicitly in time, while the nonlinear terms give rise to convolutions which are treated explicitly in time. Finite differences are used in the radial direction, while Fourier mode expansion is used in the angles covering the long way around the torus (toroidal direction) and the short way around the torus (poloidal direction). This model has been implemented in parallel on the vector parallel machines at NERSC and on the massively parallel Cray T3E. Message passing has been implemented for the T3E version using PVM (Parallel Virtual Machine.) Both linear and nonlinear calculations have been performed on these machines.
Accomplishments
Appropriate gyrofluid equations for describing ion temperature gradient turbulence over the full plasma cross section have been derived and implemented in both cylindrical and toroidal geometry. This model of core plasma transport in tokamak fusion devices has been parallelized for the Cray T3E using message passing and PVM. Large scale nonlinear calculations performed on the T3E show that the turbulence in steady-state is dominated by short scale structures on the order of a few plasma Larmor radii, much smaller than the full plasma cross section. Extensive linear tests have been performed in toroidal geometry in anticipation of large scale nonlinear calculations. These studies are part of the fusion community-wide Cyclone Team's effort at benchmarking the various approaches to modeling ion temperature gradient driven turbulence pursued to date.
Significance
This work contributes to the fundamental understanding of anomalous transport in magnetic plasma fusion devices. Control of anomalous transport is one of the key issues for present and future fusion reactors to become efficient energy producing devices.
Publications
Lynch, V. E., J.-N. Leboeuf, B. A. Carreras, J. D. Alvarez, and L. Garcia. 1997. Plasma turbulence calculations on the Cray T3E. SC'97, San Jose, California, November 15-21.
Leboeuf, J.-N., V. E. Lynch, B. A. Carreras, and L. Garcia. Full torus Landau fluid calculations of ion temperature gradient driven turbulence. 1997. Paper lWepP2.19, Plasma Physics Division Meeting, American Physical Society, November 17-21, Pittsburgh, PA.
A typical linear toroidal eigenmode for circular and D-shaped tokamak plasmas.