Theory Weekly Highlights for January 2005

January 28, 2005

A new Gyro-Landau Fluid (GLF) model was tested against the full database of 1799 Gyro-Kinetic Stability (GKS) runs and found to agree markedly better overall with the GKS results than the GLF23 model. The database is divided into three groups representing three different plasma conditions: STD for the core of L and H-modes, NCS for the internal transport barrier region of negative central shear discharges, and PED for the steep gradient region of the H-mode edge. For only four Hermite basis functions in the ballooning mode wavefunction expansion, the errors for the new GLF growth rates were 12% for the STD and NCS group and 17% for the PED group. The frequency errors were respectively 20%, 23% and 41%.

January 21, 2005

GYRO simulations of D-T plasmas show that in an initial 50-50 D-T mixture, tritium experiences better confinement than deuterium. This asymmetry will give rise to a small (but likely insignificant) build-up of tritium in the core. This effect is robust, and persists over a wide temperature gradient and collisionality range. In related studies, the D-V (diffusion versus convective velocity) model of impurity flow was shown to be consistent with fully nonlinear gyrokinetic simulations. These results, accepted for publication in Phys. Plasmas, represent the first systematic gyrokinetic study of particle transport in tokamak plasmas.

January 14, 2005

In collaboration with scientists at NIFS (National Institute for Fusion Science, Japan), a method has been formulated to compute the growth rate of a weakly unstable RWM in 3D configurations using results from ideal stability codes. It is shown that the growth rate of the RWM is given reasonably well by the rate at which the available free energy for the ideal external kink can be dissipated by the resistive wall. The eigenfunction is also approximately that of the external kink mode (the mode rigidity condition). This formulation is demonstrated numerically by coupling the computation of dissipation on the resistive wall to the computation of the ideal MHD stability code KSTEP that computes ideal stability of 3D toroidal systems by transforming them into their 2D equivalent systems.

These highlights are reports of research work in progress and are accordingly subject to change or modification