入射微粒於長鏈微粒電漿液體中之穿隙動力行為研究; Dynamics of Dust Channeling in Chain-Bundle Dusty Plasma Liquids

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題名:	入射微粒於長鏈微粒電漿液體中之穿隙動力行為研究;Dynamics of Dust Channeling in Chain-Bundle Dusty Plasma Liquids
作者:	曾鈺萍;Yu-Ping Tseng
貢獻者:	物理研究所
關鍵詞:	動力學;微粒電漿液體;dusty plasma liquid;channeling projectile;dust acoustic wave
日期:	2010-07-23
上傳時間:	2010-12-08 14:23:40 (UTC+8)
出版者:	國立中央大學
摘要:	一入射物體與可延展介質交互作用時，介質可被激發出集體的運動行為。入射物體在過程中不僅動能會損失，同時還會感受到介質所施加的阻力。若考慮物體於”連續”介質中移動，船於水面上移動激起尾跡波且感受到水的阻力即是自然中一個常見的例子。在探討微觀原子尺度的入射粒子與介質交互作用下，一般而言，入射粒子與介質中的原子碰撞使得入射粒子無法在介質中移動很長的距離。然而，若將粒子入射於固體介質中晶軸環繞的通道前進，將可達成長距離的穿隙運動，此現象亦稱作通道效應。穿隙過程中，入射粒子亦傳遞能量於介質，使得集體的晶格原子震動(晶格波或聲子 )被激發。對於一個液體介質，若分子彼此間的交互作用力沿著其中某一特定方向有較強的耦合性，可使液體分子沿著此強耦合方向排列成鏈狀的結構。這種液體中的分子結構沿著鍊狀方向有較高的空間關聯性，另外兩個維度的空間關聯性則較弱，與二維的均向性液體結構相似。此類液體介質亦可讓入射粒子沿著鏈狀結構所圍繞的通道中運動，因此提供另一個研究入射粒子穿隙運動的媒介。然而，由於原子尺度太小的限制，至今仍然無法直接觀測到穿隙運動的動力學過程。長鏈微粒電漿液體係由正離子、電子、中性原子與微粒所組成。平衡態下的微粒在電漿中帶負電。半徑大於三微米的微粒使得向下吹拂的離子風流經微粒後的聚焦效應變的顯著，此效應提供垂直方向的強耦合力，使得微粒形成長鏈狀的結構。微米等級的微粒間距與微秒等級的反應時間可經由顯微照相紀錄微粒運動，研究微粒的動力學行為。在此論文中，經由分析顯微影像中微粒運動情形，我們研究入射微粒在長鍊微粒電漿液體的穿隙動力學。首次發現適當速度的入射微粒可共振地激發出微粒集體的縱向波動。若入射微粒於長鍊微粒電漿液體中運動速度太高，則只在其後方形成狹窄的尾跡波。當入射微粒速度減弱接近於向下傳遞的微粒電漿聲波時，微粒電漿聲波 (即微粒集體的縱向波動) 可因而被激發。此外，我們進一步探討入射微粒減速過程中引發的背景微粒運動行為、激發的微粒聲波造成入射微粒減速過程阻力增加的情形及入射微粒受到的阻力因與微粒聲波交換能量而增減的過程。最後，我們發現若將微粒入射於大振幅的微粒電漿聲波中，入射微粒可被電漿聲波波前推進，產生長距離的運動, 是一個類似衝浪運動的有趣物理現象。 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.
顯示於類別:	[物理研究所] 博碩士論文

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