| dc.description.abstract | 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. | en_US |