Numerical simulations of monolayer dust crystals in an RF complex plasma were performed to examine the crystal structure and quantify the effects of including the collision enhanced ion current in the charging model. A GEC cell similar to a previous experimental work was modeled for a range of RF voltages, using a continuum description for the plasma and a particle description for dust grains. The time history of each dust grain was monitored. The dust charge was computed using both the OML and the collision enhanced charging (CEC) model applicable to the sheath region. The dust model accounted for the electric force, ion drag force, neutral drag force, gravity, and the ion wake. The CEC model produced a lower charge and lower electric force which agreed better with the experimental data. Then dust crystals composed of 40 to 100 grains were modeled and the levitation height and inter-particle spacing of the resulting crystals was examined. Including the collision enhanced current reduced the inter-particle spacing but only had a minor effect on the levitation height.
Micron-sized dust grains have been successfully employed as non-perturbative probes to measure variations in plasma conditions on small spatial scales, such as those found in plasma sheaths. The dynamics of the grains can be used to map the forces due to electric fields present in the sheath, but the particle charge and electric field are difficult to measure independently. The problem is further complicated by the ion wake field which develops downstream of the dust grains in a flowing plasma. Within a sheath, ions are accelerated towards the charged boundary, and this ion flow creates a posi…
The role of hot electrons in charging of dust grains is investigated in a two-temperature hydrogen plasma. A variety of dust particles are introduced into the system and secondary electron emission (SEE) from each of the dust grains has been reported. A cylindrical Langmuir probe is used for determining the plasma parameters and a Faraday cup is connected to an electrometer in order to measure the dust current. The electrometer readings confirm the electron emission from the dust and SEE is observed from the tungsten dust in a low-pressure experimental plasma device for the first time.
Potential of a moving test charge in a dusty plasma in the presence of grain size distribution and grain charging dynamics
尘埃等离子体的线性介电响应受粒子尺寸分布的影响。在以前的结果[IEEE trans.Plasma Sci. 29，182（2001）]，表明对于一类尺寸分布，存在与单尺寸颗粒的洛伦兹分布的等价性。然后可以使用二阶近似法找到对缓慢移动的试探电荷的静电响应[Phys. Lett. A 305，79（2002）]。众所周知[Phys. Plasmas 10，3484（2003）]，尘埃等离子体中颗粒的动态充电增强了对试探电荷的屏蔽。在这一阶段，寻求颗粒尺寸分布和颗粒充电动力学对移动通过尘埃等离子体的试探电荷的组合效应似乎是自然的。在这里，我们考虑的晶粒尺寸分布和动态的晶粒充电的试探电荷在尘埃等离子体中缓慢移动的等离子体介电响应作为晶粒尺寸分布和晶粒充电动态的函数表示的影响。分析以及数值结果。值得注意的是，可以通过为不同的参数选择适当的值来检索以前的结果。这种研究对实验室和空间等离子体都有意义。
An approach was developed to describe the first passage time (FPT) in multistep stochastic processes with discrete states governed by a master equation (ME). The approach is an extension of the totally absorbing boundary approach given for calculation of FPT in one-step processes (Van Kampen 2007) to include multistep processes where jumps are not restricted to adjacent sites. In addition, a Fokker-Planck equation (FPE) was derived from the multistep ME, assuming the continuity of the state variable. The developed approach and an FPE based approach (Gardiner 2004) were used to find the mean fi…
To reveal the effect of secondary electron emission on the charging properties of a surface covered by micron-sized insulating dust particles and the migration characteristics of these particles, for the first time, we used a laser Doppler method to measure the diameters and velocities of micron-sized anorthite particles under electron beam irradiation with an incident energy of 350 eV. Here, anorthite particles are being treated as a proxy for lunar regolith. We experimentally confirm that the vertical transport of anorthite particles is always dominant, although the horizontal transport occu…
Dust particles immersed in a plasma environment become charged through the collection of electrons and ions at random times, causing the dust charge to fluctuate about an equilibrium value. Small grains (with radii less than 1 \mum) or grains in a tenuous plasma environment are sensitive to single additions of electrons or ions. Here we present a numerical model that allows examination of discrete stochastic charge fluctuations on the surface of aggregate grains and determines the effect of these fluctuations on the dynamics of grain aggregation. We show that the mean and standard deviation of…
Micron-size charged particles can be easily levitated in low-density plasma environments. At low pressures, suspended particles have been observed to spontaneously oscillate around an equilibrium position. In systems of many particles, these oscillations can catalyze a variety of nonequilibrium, collective behaviors. Here, we report spontaneous oscillations of single particles that remain stable for minutes with striking regularity in amplitude and frequency. The oscillation amplitude can also exceed 1 cm, nearly an order of magnitude larger than previously observed. Using an integrated experi…
The influence of a charge-gradient force, associated with variations of the particle charge in response to external perturbations, on the propagation of low-frequency waves in weakly coupled complex (dusty) plasmas is investigated. The magnitude of the effect is compared with that due to polarization force, studied previously in the literature. Numerical estimates are presented for the regime, where the orbital motion limited approach to particle charging is relevant.
A new method called `Configurational Temperature' is introduced in the context of dusty plasma, where the temperature of the dust particles, submerged in the plasma, can be measured directly from the positional information of the individual dust particles and the interaction potential between the dust grains. This method does not require the velocity information of individual particles which is a key parameter to measure the dust temperature in the conventional method. The technique is initially tested using two dimensional OpenMP parallel Molecular Dynamics and Monte-Carlo simulation and then…
Nonlinear frequency response analysis is a widely used method for determining system dynamics in the presence of nonlinearities. In dusty plasmas, the plasma-grain interaction (e.g., grain charging fluctuations) can be characterized by a single particle nonlinear response analysis, while grain-grain nonlinear interactions can be determined by a multi-particle nonlinear response analysis. Here, a machine learning-based method to determine the equation of motion in the nonlinear response analysis for dust particles in plasmas is presented. Searching the parameter space in a Bayesian manner allow…
The creation of a spatially extended stable DC complex plasma crystal is a big experimental challenge and a topical area of research in the field of dusty plasmas. In this paper we describe a newly built and commissioned dusty plasma experimental device, DPEx-II, at the Institute for Plasma Research. The device can support the formation of large sized Coulomb crystals in a DC glow discharge plasma. The plasma in this L-shaped table-top glass chamber is produced between a circular anode and a long tray shaped cathode. It is characterized with the help of various electrostatic probes over a rang…
Energetic electrons from the inner radiation belt provide significant electric charging of the surfaces of Jupiter's moons Thebe and Amalthea whose orbits are located within this radiation belt. We estimate theoretically the electric fields in the vicinity of the polar regions of Thebe and Amalthea and argue that these fields are sufficient for lofting of micron and submicron-sized dust grains from the surfaces of the moons. Thus, the lofting of charged dust grains in the electric fields can be considered as an additional source supplying dust to the gossamer rings in addition to dust ejection…
The formation of self-consistent dust crystal and its melting is a well known phenomenon in rf generated plasma but remains challenging in DC glow discharge plasma. Here, we report the melting of a two dimensional dusty plasma crystal, suspended in the cathode sheath of a DC glow discharge plasma. The experiments are carried out in a $Π-$shaped Dusty Plasma Experimental (DPEx) device where a stationary crystal of melamine formaldehyde particles is formed between the confining strips in a background of Argon plasma. The stable structure breaks and leads to a fluid state on reducing the neutral …
