Vortex spectrum in superfluid turbulence: interpretation of a recent experiment

TL;DR

This paper analyzes a recent superfluid turbulence experiment, explaining the observed vortex spectrum by decomposing the vortex line density into polarized and isotropic components, resolving previous discrepancies with classical vorticity spectra.

Contribution

It introduces a novel interpretation of vortex line density by decomposing it into polarized and isotropic fields, clarifying the spectrum measurement.

Findings

The observed $f^{-5/3}$ spectrum is explained by the isotropic component.

Decomposition resolves the disagreement with classical vorticity spectra.

Polarized field carries most of the energy.

Abstract

We discuss a recent experiment in which the spectrum of the vortex line density fluctuations has been measured in superfluid turbulence. The observed frequency dependence of the spectrum, $f^{-5/3}$, disagrees with classical vorticity spectra if, following the literature, the vortex line density is interpreted as a measure of the vorticity or enstrophy. We argue that the disagrement is solved if the vortex line density field is decomposed into a polarised field (which carries most of the energy) and an isotropic field (which is responsible for the spectrum).