| dc.description.abstract | When a projectile is moving in an extended background medium, the induced collective excitation of the background medium dissipates the kinetic energy of the projectile and exerts a drag force on the projectile. The wake trailing a moving boat on the water surface is a good example for the continuous medium. Down to the discrete level, if the projectile moves along the channel surrounded by lattice axes in the crystal, it can travel long distance due to small angle binary collision with the atoms in the background crystal. In this channeling process, various collective excitations of the background crystal can be induced, e.g. the excitation of phonons. For the liquid, if the mutual coupling is anisotropic, the stronger coupling along one dimension can cause the formation of chain bundles. The system behaves as a 2D liquid with poor bond-orientation order and short structural correlation length in the transverse plane, but has long range correlation length along the chain. The channels surrounded by long chains also provides an environment for projectile channeling. Nevertheless, the small atomic scale prevents the direct visualization of the channeling dynamics at the microscopic level.
Dusty plasma liquid is formed by negatively charged micrometer sized dusts suspended in a low pressure glow discharge plasma. The wake field of the downward ion wind on dusts with diameter > 3 micrometer provides strong vertical coupling and causes the formation of chain-bundle liquid with long vertical chains. The sub-mm interparticle distance and the sub-second response time of the system enable the microscopic observation of system’’s dynamics.
In this thesis, the channeling dynamics in the chain-bundle dusty plasma liquid is investigated experimentally through directly monitoring the channeling projectile motion and the spatiotemporal evolution of the background dusts of the induced wake field with high speed video-microscopy. The first direct observation of the resonant wave excitation, how the projectile is slowed down and exchanges energy back and forth with the background liquids through particle-wave interaction, are reported. It is found that, trailing the high speed projectile, a small amplitude narrow wake field in which dusts exhibit damped elliptical motion is excited. As the speed of the projectile approaches the speed of the acoustic wave along the chain, the resonant excitation increases the drag force on the projectile and the wave amplitude. The drag force oscillates its direction when the kinetic energy is exchanged between the projectile and the background wave which travels faster than the slowed down projectile. Furthermore, Long distance trapping by the large amplitude DAW excited by other perturbation is also observed.
| en_US |