Nonlinear Energy Transfer Analysis between Coherent Modes in Developing Plasma Turbulence

Abstract

Energy transfer among various spectral components of fluctuating physical parameters in plasma occurs due to the nonlinear interactions, but these effects are typically not captured by the traditional linear spectral methods. Plasma density fluctuations measured in the Inverse Mirror Plasma Experimental Device (IMPED) have signatures of nonlinear mode interactions among various instability modes, i.e. Rayleigh-Taylor (RT) and Drift-Wave (DW) modes. In this paper, the energy transfer among these modes as a result of nonlinear wave interactions (through the quadratic coupling processes) have been investigated in detail. The existing computational methods for single field model such as Ritz method and Kim method have been explored to understand the dynamics of nonlinear interaction between coherent modes. Both methods are applied and validated in simulation as well as experimental data from IMPED for coherent modes in plasma. We find that the validity and applicability of the methods depend on the statistical nature of the data, particularly higher-order moments such as kurtosis, and on spatial stationarity. Energy transfer analysis using these methods reveals primarily the transfer of energy from a RT mode and a mix mode of DW and RT to a comparatively low-frequency DW mode, demonstrating the capability of the method to quantify spectral energy transport between the coherent modes.