High Frequency Geodesic Acoustic Modes in Electron Temperature Gradient   Mode Turbulence
  In this work the first demonstration of a high frequency branch of the geodesic acoustic mode (GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for high frequency GAMs driven nonlinearly by ETG modes is derived. A new saturation mechanism for ETG turbulence through the interaction with high frequency GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared to the mixing length estimate. 
Johan Anderson, Hans Nordman, Raghvendra Singh and Predhiman Kaw
physics.plasm-ph