Energetic study of the transition to nonlinear state in two-dimensional electron temperature gradient fluid turbulence

Eigenmode projection has been used in analysis of the two-dimensional numerical solution of electron temperature gradient ETG turbulence. The secondary Kelvin–Helmholtz instability KHI that breaks up the primary ETG structure at the onset of saturation is found to be associated with strong excitation of damped eigenmodes and strong energy damping. While the KHI structure induces some fine scale motions, which can be dissipated by collisional damping, the structure also damps directly at low poloidal wavenumbers through stable eigenmodes. The latter process is persistent in time, while the former occurs only transiently at the initial breakdown of the linearly dominant ETG structure. The persistence of energy damping by stable eigenmodes during and after the transition is enabled by nonlinear advection of electron pressure. Thus, KHI in this system couples with electron pressure advection to generate a dissipative structure at low poloidal wavenumber. © 2010 American Institute of Physics. doi:10.1063/1.3496394