Transition to defect-mediated dust acoustic turbulence wave

Jun-Yi Tsai^1*, Po-Cheng Lin¹, Lin I¹

¹Department of Physics and Center for Complex Systems, National Central University, Taoyuan, Taiwan

* Presenter:Jun-Yi Tsai, email:zazartsai@gmail.com

The transition from an ordered wave to a weakly disordered wave with increasing drive is a ubiquitous phenomenon in many extended nonlinear open systems. In the weakly disordered wave, also named as defect-mediated turbulence, modulation instability associated with amplitude and phase modulation and broadening sharp peaks in the power spectrum, induces undulated waveform and formation of defect filaments at the trough of an envelope with an undefined phase in a three-dimensional system. The previous study shows that defect filaments are winded by helical waveforms, named acoustic vortices (AVs). AVs should be pair generated and annihilated with opposite helicities, through rupturing and reconnection of sequential wave crest surfaces. Before the onset of defect-mediated turbulence, how AVs are spontaneously excited from an ordered plane wave and their correlation with modulation instability are still open issues. In this work, using self-excited dust acoustic wave as a platform, we demonstrate the generation of a single AV from ruptured wave crest at the boundary or from the repelling of another pair-generated AV to the boundary. It is found that the onset of modulation instability, the formation of sharp side-peaks around the main peak and its harmonics in power spectrum, is related to the wiggling motion of single AV which distorted the surrounding waveform.

Keywords: dusty plasma, dust acoustic wave, defect-mediated turbulence, acoustic vortex