微粒電漿系統由微米大小的顆粒在弱游離的電漿中所組成。透過微粒的慣性力、屏蔽效應下之庫倫作用力、背景電漿壓力與離子風之交互作用，此微粒電漿系統會自發的產生向下傳播的三維電漿微粒聲波，或稱電漿微粒疏密波。藉由非線性之聲波場與微米粒子的交互作用，電漿微粒聲波場影響微米粒子的運動，而受影響之微米粒子震盪伴隨著聲波密度的變化進而影響微粒聲波在時空中的傳播。透過高速數位攝影技術，藉由直接記錄微米粒子影像而監測聲波場的密度變化，無論從電漿角度或是從非線性角度，微粒聲波提供一個好的觀測平台以研究波動現象。例如，電漿微粒聲波紊流態展現不同時間尺度下之，不同的幕次尺度率與多重碎形特性。然而，電漿微粒聲波如何從規則週期性的震盪轉變至紊流態，卻沒有被探討。在此研究中，藉由精細的調控系統參數，並監測疏密波形在水平面與縱向面之時空中的變化，我們首度觀察到介於三維電漿微粒規則聲波與微粒紊流聲波之間，存在著缺陷介導紊波。隨著聲波從規律的週期性傳播轉變為缺陷介導紊波，其時間中功率頻譜的分布從窄的諧波往兩邊擴散。發現缺陷介導紊波的密度在時間上的變化經歷振幅與相位的調製，是由於聲波在空間中的波形起伏。聲波在縱向面之起伏則產生缺陷，並藉由波峰之彎曲、斷裂和重聯之行為影響缺陷的動力學行為。聲波在水平面之起伏產生高密度和低密度變化的區塊。進一步藉由希爾伯特轉換與複數平面之分析，量測缺陷介導紊波之振福與相位變化，發現低振幅洞與缺陷同時發生。藉由觀測三維時空的低振幅洞軌跡，發現缺陷可以透過產生與結合，導致低振幅洞擁有不同生存時間與移動速度。此外，越亂的缺陷介導紊波將導致更多的幅度與相位的調製，亦導致更混亂的三維時空低振幅洞軌跡。The dust acoustic wave (DAW) with longitudinal dust particle oscillation can be self-excited by ion streaming in the dusty plasma. From the plasma side, it is a fundamental plasma wave. From nonlinear dynamics view, it is also a good platform to investigate the generic behavior of wave dynamics from the ordered wave to the wave turbulence for the 3D traveling acoustic type waves, due to the capability of monitoring its spatiotemporal waveform evolution through direct particle imaging. It has been found that the regular DAW can be tuned to the wave turbulence state, exhibiting multifractal dynamics. However, the intermediate state on the way to the wave turbulence has never been investigated.In this work, by monitoring the spatiotemporal waveform evolutions in the transverse (xy) plane and the longitudinal (xz) planes, we demonstrate the first laboratory observations of the defect-mediated wave turbulence with fluctuating phase defects, dust depletion bubbles and chaotic low amplitude hole filament bundles in a downward propagating 3D plane DAW by reducing pressure. It is found that the onset of the waveform undulation leads to the fluctuating phase defect excitations, the amplitude and the phase modulations of the local dust density oscillation, and the broadening of the sharp peaks in the power spectrum. The bending, breaking, and connecting of wave crests in the longitudinal (xz) plane lead to the phase defect motion. High and low density patches in the transverse (xy) plane, and dust depletion bubbles surrounded by high density walls are observed. The trajectories of the low oscillation amplitude holes appear in the form of chaotic filament bundles along the defect trajectories in the xyt space. Holes with uncertain life times and speeds can be generated and annihilated through defect pair generation and recombination. The more irregular state leads to more amplitude/phase modulations of waveform undulations and more chaotic hole filaments.
