Agglomeration of microparticles in complex plasmas

TL;DR

This study investigates how highly charged microparticles in complex plasmas form aggregates due to dust density waves, combining experimental observations with theoretical estimates to understand the underlying mechanisms.

Contribution

It provides experimental evidence of microparticle agglomeration driven by dust density waves and compares the observed agglomeration rate with theoretical predictions.

Findings

Agglomeration occurs when particle velocities overcome Coulomb repulsion.

Agglomeration rate matches theoretical estimates.

Dust density waves trigger microparticle clustering.

Abstract

Agglomeration of highly charged microparticles was observed and studied in complex plasma experiments carried out in a capacitively coupled rf discharge. The agglomeration was caused by strong dust density waves triggered in a particle cloud by decreasing neutral gas pressure. Using a high-speed camera during this unstable regime, it was possible to resolve the motion of individual microparticles and to show that the relative velocities of some particles were sufficiently high to overcome the mutual Coulomb repulsion and hence to result in agglomeration. After stabilising the cloud again through the increase of the pressure, we were able to observe the aggregates directly with a long-distance microscope. We show that the agglomeration rate deduced from our experiments is in good agreement with theoretical estimates. In addition, we briefly discuss the mechanisms that can provide binding of highly charged microparticles in a plasma.