Particle charge in PK-4 dc discharge from ground-based and microgravity experiments

2021

Molecules

Possible mechanisms of particle attraction providing formation of the field aligned microparticle strings in complex plasmas at elevated gas pressures are theoretically investigated in the light of the Plasmakristall-4 (PK-4) experiment on board the International Space Station. The particle interaction energy is addressed by two different approaches: (i) using the dynamically screened wake potential for small Mach numbers derived by Kompaneets et al., in 2016, and (ii) introducing effect of polarization of the trapped ion cloud by discharge electric fields. Is is found that both approaches yield the particle interaction energy which is independent of the operational discharge mode. In the parameter space of the performed experiments, the first approach can provide onset of the particle attraction and string formation only at gas pressures higher than 40–45 Pa, whilst the mechanism based on the trapped ion effect yields attraction in the experimentally important pressure range 20–40 Pa and may reconcile theory and observations.

“…Here, again, we have used the particle charges corresponding to

m estimated in the PK-4 set up in Ref. [ 24 ]. Larger grains have, therefore, even more chances to stay in the attractive potential well than smaller ones.…”

Section: Discussion Of the Particle Interaction Accounting For Thementioning

confidence: 99%

Possible Mechanisms of String Formation in Complex Plasmas at Elevated Pressures

Yaroshenko

2021

Molecules

“…For the particle charge Q, we adopted the values reported for our experimental conditions in Ref. [12]. For the particle neutral gas drag rate γ , we used the Epstein expression [13].…”

Section: Experimental Methodsmentioning

confidence: 99%

Shear flow in a three-dimensional complex plasma in microgravity conditions

Nosenko

Rubin-Zuzic

et al. 2020

Phys. Rev. Research

Self Cite

Shear flow in a three-dimensional (3D) complex plasma was experimentally studied in microgravity conditions using the Plasmakristall-4 laboratory on board the International Space Station. The shear flow was created in an extended suspension of microparticles by applying the radiation pressure force of the manipulation-laser beam. Individual particle trajectories in the flow were analyzed and from these, using the Navier-Stokes equation, an upper estimate of the complex plasma's kinematic viscosity was calculated in the range of 0.2-6.7 mm 2 /s. This estimate is much lower than previously reported in ground-based experiments with 3D complex plasmas. Possible reasons for this difference are discussed.

“…The microparticle charge according to the measurements in Ref. [33] was about 2100 elementary charges.…”

Section: Methodsmentioning

confidence: 97%

“…The oscillating electric field polarizes the shielding cloud of the microparticles, which leads to the appearance of the quadrupole term in their interaction potential [16]. Usage of dc electric field is not practical in complex plasmas since it causes instabilities in the microparticle suspensions [29][30][31] and under microgravity conditions also their drift [31][32][33]. In the present work, the so-called "polarity switching" mode [20] of the dc discharge in the PK-4 setup was used.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional structure of a string-fluid complex plasma

Klumov

Rubin-Zuzic

et al. 2020

Phys. Rev. Research

Self Cite

Three-dimensional structure of complex (dusty) plasmas was investigated under long-term microgravity conditions in the Plasmakristall-4 facility on the International Space Station. The microparticle suspensions were confined in a polarity-switched dc discharge. The experimental results were compared to the results of the molecular dynamics simulations with the interparticle interaction potential represented as a superposition of isotropic Yukawa and anisotropic quadrupole terms. Both simulated and experimental data exhibited qualitatively similar structural features, indicating the bulk liquid-like order with the inclusion of solid-like strings aligned with the axial electric field. Individual strings were identified and their size spectrum was calculated. The decay rate of the size spectrum was found to decrease with the enhancement of string-like structural features.