Data-driven analysis of anomalous transport and three-wave-coupling effects in E x B plasma discharges

TL;DR

This study uses spectral and phase analysis of simulation data to uncover the nonlinear wave interactions driving anomalous electron transport in E x B plasma discharges, highlighting the role of three-wave coupling and energy cascades.

Contribution

It introduces a spectral model based on three-wave coupling equations to explain the energy transfer mechanisms in plasma transport, supported by simulation data.

Findings

Transport dominated by in-phase oscillations of E and density

Existence of a secondary mode not predicted by linear theory

Evidence of inverse energy cascade through three-wave interactions

Abstract

Collisionless cross-field electron transport in an E x B configuration relevant for electric propulsion is studied using data from a (z, {\theta}) full-PIC simulation. Higher-order spectral analysis shows that transport is dominated by the in-phase interaction of the oscillations of the azimuthal electric field and the electron density associated to the first electron cyclotron drift instability (ECDI) mode. A secondary contribution emanates from a lower-frequency mode, not predicted by linear ECDI theory, while higher modes have a minor direct impact on transport. However, a bicoherence analysis reveals that strong phase couplings exist among the ECDI modes, and a sparse symbolic regression spectral model, based on the three-wave coupling equations, suggests an inverse energy cascade as the most likely explanation, thus suggesting that higher modes contribute indirectly to transport by quadratic power transfer to the first mode. This work provides new insights into the dynamics of anomalous plasma transport in E x B sources and the underlying processes governing energy distribution across different scales, and supports the validity of weak turbulence theory to examine their behavior.