Effect of discharge polarity reversal on the self-excited dust density waves*

We report on the observation of the self- excited dust density waves in dc discharge plasma using the PK-4 facility. In the experiment, the trapped microparticles cloud was released to drift in a dc discharge of negative and, after some seconds, positive polarity. A DC plasma containing a drifting microparticle cloud was found to be asymmetric with respect to discharge polarity reversal in terms of microparticle drift velocity and plasma emission in accord with [Zobnin et.al., Phys. Plasmas 25, 033702 (2018)]. In addition to that, asymmetry in the self-excited wave pattern was observed. Also, after the polarity reversal, the wave pattern exhibited several bifurcations. These bifurcations are mainly observed in the head of the microparticle cloud. We show that spatial variations of electric field inside the drifting cloud play an important role in the formation of the wave pattern.