Nonlinear entropy transfer of ETG turbulence via TEM driven zonal flow

A nonlinear interplay of the electron temperature gradient (ETG) mode and the trapped electron mode (TEM) is investigated by means of gyrokinetic simulation. It is found that the ETG turbulence can be suppressed by zonal flows driven by TEMs. The suppression process is quantitatively examined by the nonlinear entropy transfer analysis. In the statistically steady state where the TEM-driven zonal flows are dominant, the zonal flows induce the successive entropy transfer from ETG modes with low radial wavenumbers to those with high radial wavenumbers. The process is similar to the successive entropy transfer found in the ITG turbulence under the influence of ITG-driven zonal flows.