Meter-scale Observations of Equatorial Plasma Turbulence

TL;DR

This paper reports high-resolution measurements of equatorial plasma turbulence using a multi-Needle Langmuir Probe on the ISS, revealing detailed turbulent structures and spectral features down to a few meters.

Contribution

It introduces a novel high-frequency plasma measurement technique on the ISS and presents initial observations of plasma turbulence at unprecedented spatial scales.

Findings

Detection of detailed plasma density fluctuations at meter scales.

Identification of spectral break-points indicating turbulent dissipation.

Observation of kilometer-scale plasma swirls related to gradient-drift instability.

Abstract

The multi-Needle Langmuir Probe collects an electron current through four fixed-bias cylindrical copper needles. This allows for an extremely high sampling frequency, with plasma properties being inferred through polynomial fitting in the current-voltage plane. We present initial results from such a multi-needle probe mounted on the International Space Station, orbiting Earth at an altitude of around 400 km. That altitude, and its orbital inclination (~50 degrees), place the ISS as a suitable platform for observing equatorial plasma bubbles. In case studies of such turbulent structuring of the F-region plasma, we observe density timeseries that conserve considerable detail at virtually every level of magnification down to its Nyquist scale of 2-5 meters. We present power spectral density estimates of the turbulent structuring found inside equatorial plasma bubbles, and we discuss apparent break-points at scale-sizes between 1 m and 300 m, which we interpret in the light of turbulent dissipation as kilometer-scale swirls produced by the gradient-drift instability dissipate in the plasma.