Local energy transfer rate and kinetic processes: the fate of turbulent energy in two-dimensional Hybrid Vlasov-Maxwell numerical simulations

TL;DR

This study investigates how turbulent energy transfers across scales in collisionless plasmas using 2D Hybrid Vlasov-Maxwell simulations, focusing on the Local Energy Transfer rate as a key proxy.

Contribution

It introduces and validates the Local Energy Transfer rate as a reliable proxy for turbulent energy cascade in collisionless plasmas, linking it to kinetic processes and distribution deviations.

Findings

The LET correlates with kinetic activity and distribution deviations.

Statistical laws of LET confirm its role in turbulent cascade.

Large positive LET regions are associated with energy dissipation processes.

Abstract

The nature of the cross-scale connections between the inertial range turbulent energy cascade and the small-scale kinetic processes in collisionless plasmas is explored through the analysis of two-dimensional Hybrid Vlasov-Maxwell numerical simulation (HVM), with alpha particles, and through a proxy of the turbulent energy transfer rate, namely the Local Energy Transfer rate (LET). Correlations between pairs of variables, including those related to kinetic processes and to deviation from Maxwellian distributions, are first evidenced. Then, the general properties and the statistical scaling laws of the LET are described, confirming its reliability for the description of the turbulent cascade and revealing its textured topology. Finally, the connection between such proxy and the diagnostic variables is explored using conditional averaging, showing that several quantities are enhanced in the presence of large positive energy flux, and reduced near sites of negative flux. These observations can help determining which processes are involved in the dissipation of energy at small scales, as for example ion-cyclotron or mirror instabilities typically associated with perpendicular anisotropy of temperature.