Characterizing filamentary magnetic structures in counter-streaming plasmas by Fourier analysis of proton images

TL;DR

This paper uses Fourier analysis of proton images to better interpret filamentary magnetic structures in plasmas, revealing that observed features correspond to filament size rather than spacing, aiding experimental analysis.

Contribution

It introduces a Fourier-based method to accurately interpret proton images of filamentary magnetic fields, clarifying the relationship between image features and filament properties.

Findings

Proton image features correspond to filament size, not spacing.

Fourier analysis effectively distinguishes filamentary magnetic structures.

Results improve interpretation of proton imaging in plasma experiments.

Abstract

Proton imaging is a powerful tool for probing electromagnetic fields in a plasma, providing a path-integrated map of the field topology. However, in cases where the field structure is highly inhomogeneous, inferring spatial properties of the underlying field from proton images can be difficult. This problem is exemplified by recent experiments which used proton imaging to probe the filamentary magnetic field structures produced by the Weibel instability in collisionless counter-streaming plasmas. In this paper, we perform analytical and numerical analysis of proton images of systems containing many magnetic filaments. We find that, in general, the features observed on proton images do not directly correspond to the spacing between magnetic filaments (the magnetic wavelength) as has previously been assumed, and that they instead correspond to the filament size. We demonstrate this result by Fourier analysis of synthetic proton images for many randomized configurations of magnetic filaments. Our results help guide the interpretation of experimental proton images of filamentary magnetic structures in plasmas.