Nonlinear Energy Transfer Analysis in Developing Plasma Turbulence

TL;DR

This paper investigates nonlinear energy transfer among plasma instability modes using computational methods validated on experimental data, revealing energy flow from Rayleigh-Taylor to Drift-Wave modes.

Contribution

It applies and compares Ritz and Kim methods to analyze nonlinear wave interactions in plasma turbulence, highlighting their dependence on data statistics and stationarity.

Findings

Energy transfer from RT to DW modes demonstrated

Methods validated with experimental plasma data

Energy transfer quantified across different radial locations

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 turbulence model such as Ritz method and Kim method have been explored to understand the turbulence dynamics. Both methods are applied and validated in simulation as well as experimental data from IMPED for developing plasma turbulence. 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 at different radial locations using these methods reveals the transfer of energy from RT modes to a comparatively low-frequency DW mode, demonstrating the capability of the method to quantify spectral energy transport in the plasma turbulence.