Correlation and spectrum of dust acoustic waves in a radio-frequency plasma using PK-4 on the International Space Station

Abstract

Dust acoustic waves were investigated in an experiment under microgravity conditions, using the European Space Agency-Roscosmos facility PK-4 on the International Space Station. A three-dimensional dust cloud was confined in a glow-discharge plasma powered by a radio-frequency coil in low-pressure neon gas. Low-frequency dust acoustic waves (DAWs) were spontaneously excited due to the flowing ions in the plasma. Dust motion was imaged using video cameras, yielding the position for individual dust particles. Besides these particle-level measurements, the dust was also measured as a fluid continuum to obtain its velocity and density fluctuations. A space–time diagram of the dust-fluid velocity reveals that the waves changed properties as they propagated across the dust cloud, in the direction of the ion flow. Density fluctuations were characterized by a wave spectrum, indicating the emergence of collective vibration modes in a broad range of wave numbers. The decay of the modes was characterized by density correlation functions. Fitting the correlation functions to an analytical model yields an experimental measurement of the dispersion relation for DAWs, which is compared to that of linear theory.

Nonlinear Wave Synchronization in a Dusty Plasma Under Microgravity on the International Space Station (ISS)

“…These waves were self-excited, due to flowing ions in an inductively coupled RF glow plasma. In [40], based on the same experiment on the ISS, we investigated linear features of the waves, including wave's spectrum and dispersion relation. Results presented here will reveal some nonlinear features of these waves, including indications of synchronization.…”

“…This microgravity experiment was carried out during the PK-4 Science Campaign 5, on orbit in the ISS. This article is based on data from the same experiment as in a previous article [40], which centered on different scientific topics, the decay of DAW modes as characterized by correlation functions, the usefulness of linear dispersion relation theory, and the spectrum of DAWs. The present article is based on different experimental runs (i.e., recorded at different times), as compared to [40].…”

“…Here, we briefly review our experiment, which was performed using the joint ESA-Roscosmos facility Plasma kristall-4 (PK-4) on the ISS [36]. Further details are presented in [40]. Fig.…”

“…In this article, we report a microgravity experiment using the PK-4 instrument [36]- [40] on the International Space Station (ISS), investigating the nonlinear wave synchronization in 3-D Fig. 1.…”

“…Our plasma was different from that in previous synchronization experiments; the RF power was inductively coupled, and the chamber was a glass tube. Our previous work in this plasma [40] has shown that it allows the spontaneous excitations of long-lived DAWs. Here, we will explore a nonlinear feature of the DAWs, a frequency clustering due to mutual synchronization among adjacent constituent elements in the dust cloud.…”