Study of nonlinear spectral energy transfer in frequency domain

A method for measuring nonlinear energy transfer in the frequency domain using a two-field model of drift turbulence is proposed, and the theoretical motivation and experimental results are presented. The approach is based on the cross-bispectral analysis of quadratic nonlinearities in the turbulent internal and kinetic energy balance equations directly derived from the fluid plasma continuity and momentum equations. Application of the technique to data from a laboratory plasma experiment reveals the nonlinear energy transfer in weak collisional plasma drift turbulence; the results show a transfer of density fluctuation energy toward higher frequency (which correspond to smaller azimuthal spatial scales) and a transfer of kinetic energy to lower frequencies (corresponding to larger azimuthal scales).