Machine-Learning Characterization of Intermittency in Relativistic Pair Plasma Turbulence: Single and Double Sheet Structures

TL;DR

This paper introduces a machine-learning method to identify and classify intermittent structures in relativistic pair plasma turbulence, revealing two main types of current structures crucial for modeling turbulence.

Contribution

The study applies a novel machine-learning segmentation technique to plasma turbulence simulations, distinguishing between current sheets and double sheets, advancing understanding of turbulence intermittency.

Findings

Intermittent fluctuations are classified into current sheets and double sheets.

Double sheets may be generated by interacting Alfvén-wave packets.

The distinction aids in developing realistic turbulence sub-grid models.

Abstract

The physics of turbulence in magnetized plasmas remains an unresolved problem. The most poorly understood aspect is intermittency -- spatio-temporal fluctuations superimposed on the self-similar turbulent motions. We employ a novel machine-learning analysis technique to segment turbulent flow structures into distinct clusters based on statistical similarities across multiple physical features. We apply this technique to kinetic simulations of decaying (freely evolving) and driven (forced) turbulence in a strongly magnetized pair-plasma environment, and find that the previously identified intermittent fluctuations consist of two distinct clusters: i) current sheets, thin slabs of electric current between merging flux ropes, and; ii) double sheets, pairs of oppositely polarized current slabs, possibly generated by two non-linearly interacting Alfv\'en-wave packets. The distinction is crucial for the construction of realistic turbulence sub-grid models.