Correlation and Spectrum of Dust Acoustic Waves in a Plasma Under Microgravity Conditions*

Dust acoustic waves under microgravity conditions were investigated in an experiment using the European Space Agency's facility PK-4 on the International Space Station. A dust cloud was confined in a neon plasma powered by a radio-frequency coil. Using video cameras, waves were observed to be spontaneously excited. The density fluctuations associated with the waves were characterized by calculating a microscopic particle density. The fluctuation spectrum indicates the emergence of collective modes in a broad range of wave numbers. The persistence of the coherence of the modes was characterized by density correlation functions. An experimental measurement of the wave's dispersion relation was also obtained.