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|Title: ||微粒電漿缺陷紊波波型與缺陷演變之微觀動力行為;Lagrangian-Eulerian micro-dynamics of waveform and defect evolution in defect-mediated dust acoustic wave turbulenc|
|Issue Date: ||2015-09-23 11:32:47 (UTC+8)|
上述未探討之議題在此研究中，藉由實驗上觀測微粒電漿系統產生自發性的微粒電漿紊流波，直接追蹤微粒運動與波形演變並建立清楚的波-粒子動力行為圖像。實驗結果發現，局部的粒子在波峰前堆積與波峰後耗散行為，影響該局部區域之波移動速度、波高增減與波形演變。此外也發現，影響粒子在二維上堆疊與耗散主因──波峰越高波移動速度越快、粒子聚散特性藉由受力方向由高至低密度與非均勻波高的不整齊波導致。以上發現可解釋觀測到的叉型波與缺陷演化。隨著叉型波移動的移動座標觀測，叉型波中，前方的微彎的波峰被拉直且伴隨著缺陷朝著叉型波開口方向的運動。緊接著後方緩慢移動的波峰因為強烈的彎曲而與前方波斷開連結。這斷開連結的單一波峰隨後會因頂點的耗散場而造成重新與尾隨的波峰重新連結而形成新的叉型波。;An acoustic type wave can be self-excited in the nonlinear dissipative system with the ordered waveform. Increasing the power of the system, the ordered wave becomes weakly disordered, and the sharp spikes in power spectrum are broadened through the modulation instability. In a 2D system, a weakly disordered plane wave is accompanied with the emergence of defects at the vertices of pitchfork shape waveforms, where the amplitudes are null and the phases are undefined. It leads to the name of defect mediated turbulence. Microscopically, longitudinal density waves such as acoustic type waves in plasmas and gases are constituted by particles exhibiting longitudinal motion. Particle motions are affected by the waveform through wave-particle
interactions, which in turn determines waveform evolution. Nevertheless, the generic behaviors of how particles move in the above unstable wave, which affect waveform and defect evolutions are still fundamental unexplored issues.
In this work, a clear Lagrangian-Eulerian wave-particle dynamic picture is constructed for the above unexplored issues experimentally in a weakly disordered self-excited dust acoustic wave in a rf dusty plasma system, by direct tracking dust particle motion and waveform evolution. It is found that local accumulation and depletion of particles in the wave front and rear, respectively, affects the local crest propagation speed, and the growth and decay of the local crest height, which also affect the waveform evolution. The higher crest traveling faster, and particle focusing and defocusing from the transverse force field and the non-uniform wave height distribution along a tilted wave crest, are the key factors to determine the particle accumulation and depletion. The above findings can explain the observation of the pitchfork waveform evolution and the defect motion. In the wave moving frame of the pitchfork waveform, the leading front waveform is straightened and associated with the transverse motion of defect to the open side of the pitchfork. The slow propagation of the trailing crest is detached from the strongly kinked pitchfork branch. This detached single crest is reconnected to the trailing crest because of the spreading field at the vertex.
|Appears in Collections:||[物理研究所] 博碩士論文|
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