Transverse oscillations in a single-layer dusty plasma under microgravity

Abstract

A single-layer suspension of microparticles was formed in a plasma under microgravity conditions. This single layer is confined at a void boundary by a balance of ion drag and electric forces, where the ion flow velocity is much slower than in the sheath of laboratory plasmas. Using a high-resolution camera that allows measurements of velocities at a low level, the microparticle kinetic temperature was found to be close to that of the neutral gas. The random motion transverse to the single layer was found to have oscillations of the form expected for harmonic oscillators driven by white noise. The driving of the oscillation is mostly attributed to the Brownian motion of neutral atoms, while the damping is mostly due to neutral gas friction. An observed resonance frequency of 25 s−1 allows us to quantify the electric and ion drag forces as being in the range of 0.2–0.4mpg, where mp is the microparticle mass and g is the acceleration of gravity on Earth’s surface. No signature of wave dispersion was detected for this experiment with neon at a pressure of 0.12 Torr.