Experimental study of the nonreciprocal effective interactions between microparticles in an anisotropic plasma

Abstract

There is a variety of cases in nature when the action–reaction symmetry is broken. In particular, suitable conditions for this are realized in colloidal suspensions and complex plasmas. Since the first theories and simulations of the nonreciprocal effective interactions between microparticles in complex plasmas were published in 1995–1996, there have been hundreds of studies in the theoretical development of this theme. However, despite such a rich theoretical background, one of the important unsolved problems is a direct experimental determination of the nonreciprocal interparticle interaction forces. Here, we studied experimentally in detail the forces of the nonreciprocal effective interaction between microparticles suspended a radio-frequency produced plasma sheath. For this purpose, an experimental method based on an analysis of the spectral density of random processes in an open dissipative two-particle system was developed. In contrast to previous investigations, the proposed method takes into account random and dissipative processes in the system, does not require a special design of the experimental setup and any external perturbations, pre-measurements of external fields and any assumptions about the type of interaction. We found that even small charge changes of one particle, caused by its thermal motion in a wake field of another particle, can lead to a significant change in the effective (measurable) interaction between the particles.

Active Brownian particle in homogeneous media of different viscosities: numerical simulations

“…In addition to Janus particles in a gas-discharge plasma, 14,15 suitable conditions can be realized for self-propelled particle pairs 41,42 formed by the effective nonreciprocal forces of the wake-mediated interaction between microparticles. 43 Another unusual example of underdamped active Brownian motion is the so-called vibrobots, which convert vibrational energy into directed motion using their tilted elastic legs. 27,44 A non-obvious question to ask is what kind of motion would one expect for a self-propelled particle in 'nonviscous' fluids.…”

Possible Mechanisms of String Formation in Complex Plasmas at Elevated Pressures

“…The downstream microparticle then experiences an attractive force towards the upstream particle wake, thus aligning grains along the ion flow direction. Many aspects of the ion wake formation and associated modifications of the particle interaction potential in various laboratory conditions have been studied theoretically, numerically and experimentally (see, e.g., References [ 11 , 12 , 13 , 14 , 15 ] and references herein). However, most of the theoretical results indicate that, to provide such an effective particle-wake interaction, the ion flow velocity should be in the order of the sound velocity.…”

Active Brownian motion of strongly coupled charged grains driven by laser radiation in plasma

“…These charged grains effectively interact with each other as well as with an external electrical field. The action of external forces and forces of interaction combined with dissipative mechanisms in these systems can lead to the self-organization of the system, resulting in the formation of quasistationary crystal- or liquid-like structures 21 – 33 .…”