Dust-acoustic dispersion relation in three-dimensional complex plasmas under microgravity

A series of dedicated experiments with the Plasma Kristal Experiment (PKE)-Nefedov (Nefedov et al 2003 New J. Phys. 5 33) set-up were performed on board the International Space Station to measure the dispersion relation (DR) for the longitudinal dust-acoustic (DA) waves in quasi-isotropic three-dimensional (3D) complex plasmas. The waves were excited by applying ac electric modulation of variable frequency to the radio frequency (rf) electrodes. The amplitude of excitation was varied with frequency to ensure a 'sufficiently linear' regime of the dust density perturbations. The DR was obtained by measuring the induced density perturbations, revealing fairly good agreement with a simple multispecies theory of DA waves.