Observation of high phase velocity of dust acoustic waves with elongated dust grains in a cryogenic dusty plasma experiment

Self-excited dust acoustic waves (DAWs) with a high phase velocity were observed in the cryogenic dusty plasma experiment, where submillimeter, elongated, and fractal-like water-ice dust grains are formed. The phase velocity of the observed DAWs was obtained by the fast Fourier transform of the sequential images of the DAWs and it ranges from 8 to 15 cm s(-1). The length of the dust grains was measured between 100 and 250 mu m and the thermal speed of the dust grains was obtained between 1.5 and 2.8 cm s(-1). It is shown that the linear theory including the effect of the dust thermal speed can explain the observed fast phase velocity. The possible mechanisms by which the submillimeter dust grains gain such high kinetic energies are discussed.