| dc.description.abstract | Subjected to a strong localized perturbation in an open-dissipative nonlinear extended media, the formation of the acoustic type nonlinear coherent localized structures, such as bubbles, cavities, and solitons, is an interesting nonlinear dynamical problem in our daily life. Down to the discrete level, however, the local heterogeneity of density fluctuations becomes prominent and seriously affects the formation and the dynamics of the coherent localized structures, especially when the spatial scale of the coherent localized structures is in only few inter-particle distances. How the localized collective excitations interact with the particle motions and how the particle motions in turn affect the formation of the localized collective excitations are important issues and poorly understood due to the difficulty of direct observation at discrete level.
Dusty plasma liquid formed by micrometer sized dust particles negatively charged and suspended in a low-pressure weakly ionized discharge background is an inspiring system to mimic and understand the generic dynamical behaviors of the acoustic type nonlinear coherent localized structures in nature at the discrete level because of the capability of direct optical visualization. The nonlinear coherent structures excited by dust density perturbation in dusty plasma systems have been extensively studied previously, but rare studies have been done on the spatiotemporal responses of a dusty plasma liquid subjected to a spatially and temporally localized strong density perturbation. Our previous study done by Chu et al. in 2003 firstly demonstrates the formation of various kinds of nonlinear collective excited localized structures (soliton-like dusty plasma bubbles) in 3D dusty plasma liquid subjected to a spatially and temporally localized strong density perturbation via an intense focused pulsed laser. However, the detailed micro-dynamics of the dust particles constituting the soliton-like bubble cannot be well resolved at that time owing to the sampling limit of the slow CCD.
In this work, using a high speed CCD, we experimentally study the detailed dust micro-dynamics of the dusty plasma bubble generated by an intense focused pulsed laser in the 3D dusty plasma liquid. Under the symmetry breaking by the downward ion flow, asymmetric bubble expansion and collapse, and a damped solitary wake field composed of a leading ultrasonic downward rarefaction wave trailed by a series of compressional dense crests with descending crest speeds and crest heights are observed. The dust density waves propagating not along the downward ion flow directions are quickly damped, leading to the formation of a narrow-width wake field. The micro-dynamics of dust particles are well resolved by directly tracking the trajectories for each dust. A clear Eulerian/Lagrangian picture is then constructed to correlate the dust motions and the associated dust density fluctuations during the bubble expansion and collapse, and in the later damped solitary wake field. The mutual support of the dust oscillations and the downward compressional crests is found.
In addition, the spatiotemporal responses of a single plasma bubble with different bubble sizes and under different background pressures are also investigated to study the effect of different strengths of external perturbations and the effect of different excitabilities of the 3D dusty plasma liquid respectively. Furthermore, the interaction between two vertically aligned plasma bubbles is studied to understand how nonlinear collective excitations of each bubble interfere with each other. Finally, an interesting phenomenon regarding the falling energetic particle enhanced dust acoustic wave in the damped solitary wake field of a plasma bubble is briefly reported. | en_US |