Numerical experiments quantifying the role of both 'residual' Rosenbluth-Hinton zonal flows and geodesic acoustic modes (GAMs) in saturating drift-wave turbulence have revealed several key findings. The GAMs can represent an important source of shear stabilization, as they can be excited to sufficiently strong levels to counter-act the reduced 'per-unit' shearing efficiency due to their finite frequency. Also, the ExB component of the zonal flow shear is stabilizing for finite-n drift-waves, while the diamagnetic component appears to destabilize the finite-n modes, and that the entropy generation peaks at wavelengths corresponding to peak transport production, but entropy dissipation is spread broadly over many wave numbers (including the n=0 zonal modes). These results appear to hold for ITG, TEM and mixed ITG/TEM turbulence. The results have been published in the December 2008 issue of Physics of Plasmas.

C. Holland gave a seminar on validation and high performance computing in fusion plasmas at the Fermilab weekly colloquium on Wednesday, Dec. 17. A video of the seminar will be made available on the Fermilab website.