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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 (DPEx-II) device 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 range of discharge conditions. The dust particles are introduced by a dust dispenser to form a strongly coupled Coulomb crystal in the cathode sheath region. The unique asymmetric electrode configuration minimizes the heating of dust particles and facilitates the formation of crystalline structures with a maximum achievable dimension of 40 cm × 15 cm using this device. A larger crystal has numerous advantages over smaller ones, such as higher structural homogeneity, fewer defects, lower statistical errors due to finite size effects etc. A host of diagnostics tools are provided to characterize the Coulomb crystal. Results of a few initial experiments aimed at demonstrating the technical capabilities of the device and its potential for future dusty plasma research, are reported. [ABSTRACT FROM AUTHOR]

This paper presents recent progress on the development of the new multi-purpose particle modeling and simulation tool VizGrain. A unique aspect of VizGrain is that it allows computational modeling of particle dynamics in a variety of systems, including rarefied gas dynamics, macroscopic particle dynamics (e.g., dust particles, droplets, etc), particle-in-cell modeling, and hybrid continuum-particle modeling within a single integrated framework. VizGrain allows working with atomic sized particles and particles with finite macroscopic sizes. The former approach is used to model rarefied gas dynamics and conventional non-equilibrium plasmas, while the finite sized macro-particles are considered for the modeling of dusty plasmas, aerosols, droplets etc. In this latter case, the electrical charge up of particles in a plasma environment is considered. The model features a comprehensive variety of drag forces that can act on both atomic and macro-particles. A detailed description of the physical models implemented within VizGrain is presented, to provide insights into the approach that can be taken in other particle-based codes in the community. These models are scrupulously validated against the benchmark problems proposed in the research literature for a variety of applications from the plasma reactors used in semiconductor industry to high-speed rarefied gas dynamics problems. [ABSTRACT FROM AUTHOR]

In this paper, the formation of the electron energy distribution function (EEDF) in the argon dusty plasma of the positive column of glow discharge at low pressure is investigated. A model for calculating EEDF in the local approximation is adapted to find the nonlocal EEDF via the Holstein–Tsendin model. The results show that, contrary to the prevalent opinion in the literature, the presence of dust has little effect on the EEDF up to the limiting values of the density of dust particles that can be injected into the plasma for the considered conditions. It is also shown that, when obtaining the nonlocal EEDF, the spatial profiles of the axial (heating) and radial (ambipolar) fields should be chosen from a self-consistent solution. Additionally, the differences between the local and nonlocal EEDFs increase in the peripheral regions of the discharge due to a sharp decrease of fast electrons in the nonlocal case. Significant changes in the form of the nonlocal EEDF along the radius also lead to noticeable changes in other characteristics of the electrons in this area, especially for those with a large energy threshold (e.g. due to excitation, ionization). [ABSTRACT FROM AUTHOR]

Atmospheric pressure low-temperature plasmas are often utilized to perform particle synthesis, treatment, and removal. It is well-known that dust particles are highly negatively charged in these plasmas; however, little is known about dust particle charging behavior as particles leave the plasma volume and pass through the spatial afterglow region. In this work, monodisperse particles of various sizes and work functions were introduced into an atmospheric pressure radiofrequency capacitively coupled flow-through plasma. Dust particle electrical mobility distributions downstream of the flow-through plasma were measured utilizing a differential mobility analyzer in conjunction with a condensation particle counter at various gas flow velocities. Charge distributions were determined from the measured electrical mobility distributions. Experiments confirm that particles become less negatively charged, and even net-positively charged after leaving the plasma volume, with a distribution that follows a shifted Boltzmann charge distribution. Additionally, particle charge in the effluent of the flow-through plasma is negligibly dependent on work function but highly size and flow velocity dependent. Larger particles were shown to have a higher magnitude of charge under all studied conditions; however, particle polarity was switchable by varying gas flow velocity. The charging dynamics were simulated utilizing a constant number Monte Carlo model that accounts for electron temperature decay and the transition from ambipolar to free diffusion of electrons and ions in the spatial afterglow. Simulation results also suggest that, at the same flow velocity, larger particles obtain a greater magnitude of charge, negative or positive. The decrease in electron mobility and the difference between ion and electron convective loss rates create an ion-rich region in the plasma effluent that promotes ion–particle collisions and drives particle charge removal and even reversal of polarity. Larger particles more favorably collide with energetic species in these environments, which results in higher charge states. [ABSTRACT FROM AUTHOR]

The COVID-19, viral influenza, tuberculosis, and other widespread infectious diseases evidence that pathogenic biological aerosols (PBAs) are a serious threat to public health. Different from traditional inactivation methods, such as ultraviolet (UV) light which are only safe to use when people are not present, and high-efficiency particulate filters (HEPA) which merely filter microbes without killing them, atmospheric pressure nonequilibrium plasma (APNP) has shown its tremendous potential in drastically diminishing the aerosol transmission route of the infectious agents through the abatement of PBAs. The key issues to develop high performance APNP based air purification system are critically reviewed. Systematic studies on the hazards of different PBAs and the spread of PBAs in indoor environments guide the development of APNP sources to control communicable diseases. The key six sampling and seven detection methods on PBAs are introduced to analyze the PBA abatement efficiency by APNP. Seven common APNP sources which can remove viruses and bacteria aerosols efficiently developed during the past 8 years are introduced. For the APNP sources with small plasma volume, the electric field and diffusion driven charging are the dominant mechanisms to charge PBAs, while the common methods of dusty plasma research can be adapted to atmospheric-pressure conditions to describe the charging effects of APNP sources with large plasma volume. Plentiful long- and short-lifetime reactive oxygen and nitrogen species (RONS) generated by APNP effectively contribute to inactivation of bacterial aerosols. Current studies suggest that viral aerosols are mainly inactivated by short-lifetime RONS including 1O2, ONOO− and ONOOH. The study on the dissolution and reaction of gaseous RONS in microdroplets and accurate measurements on the evolution of charged PBAs are envisaged to be the focus of future research. Opportunities for multidisciplinary collaborative research to advance the development of next-generation high-performance plasma-based air purifiers are highlighted. [ABSTRACT FROM AUTHOR]

We present an electrostatic particle extractor system (EPEX) which extracts particles from a reactive, particle-growing plasma by using the electrostatic force. The system is able to extract eight samples during a single growth cycle without the need to interrupt the plasma process. Using video microscopy, imaging-Mie, and Mie polarimetry we demonstrate the minimal invasiveness of EPEX. The extraction voltage and its duration are optimized to tune the particle density on the sample wafer. Compared to other invasive extraction methods, EPEX is fast and reliable. Using atomic force microscopy the size of the particles can be determined from samples extracted from the nanodusty plasma during one growth cycle and can be compared to the results of simultaneously performed in situ Mie polarimetry for the first time. We show that the extraction process can be divided in three distinct phases and that its physics can be understood in the simple framework of the force balance for a single dust particle. Using this single particle model, we present a new method for determining the particle charge of dust particles in dense dusty plasmas. The determined particle charge of (−9.2 ± 2.8) elementary charges reveals a strong Havnes effect. [ABSTRACT FROM AUTHOR]

The PK-4 system is a micro-gravity dusty plasma experiment currently in operation on-board the International Space Station. The experiment utilizes a long DC discharge in neon or argon gases. We apply our 2D particle-in-cell with Monte Carlo collisions discharge simulation to compute local plasma parameters that serve as input data for future dust dynamics models. The simulation includes electrons, Ne+ ions, and Nem metastable atoms in neon gas and their collisions at solid surfaces including secondary electron emission and glass wall charging. On the time scale of the on-board optical imaging, the positive column appears stable and homogeneous. On the other hand, our simulations show that on microsecond time scales the positive column is highly inhomogeneous: ionization waves with phase velocities in the range between 500 m s−1 and 1200 m s−1 dominate the structure. In these waves, the electric field and charged particle densities can reach amplitudes up to 10 times of their average value. Our experiments on ground-based PK-4 replica systems fully support the numerical findings. In the experiment, the direction of the DC current can be alternated, which has been found to favor dust particle chain formation. We discuss possible mechanisms for how the highly oscillatory plasma environment contributes to the dust particle chain formation. [ABSTRACT FROM AUTHOR]

A dusty plasma was created in a stratified glow discharge in longitudinal magnetic fields above 1 T. Experimental conditions were selected and dust structures were first created in the neon working gas in the magnetic field range B = 1.1–2.2 T. Under realized conditions, the electron cyclotron radius is close to the dust particle radius, and the ion cyclotron radius is less than the Debye screening length. Images of dust structure cross sections perpendicular to the magnetic field were obtained. They contain about 10 particles. The dependence of the angular velocity of the dust structure rotation for its widest cross section on magnetic field was measured. The direction of the angular velocity vector coincides with the direction of the magnetic induction vector. In contrast to the previously obtained dependence of the rotation velocity on magnetic field in the region B < 1 T, at B > 1 T the rotation angular velocity ceases to grow, reaching a value of about 3 rad s−1. To explain the experimental results on the dust structure rotation velocity, an analytical model of the rotation mechanism is proposed. The model is based on the concept of eddy currents in striations and the influence of the magnetic field on the striation length. The obtained estimates of the rotation velocity are in a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Sectional models of the dynamics of aerosol populations are well established in the aerosol literature but have received relatively less attention in numerical models of dusty plasmas, where most modeling studies have assumed the existence of monodisperse dust particles. In the case of plasmas in which nanoparticles nucleate and grow, significant polydispersity can exist in particle size distributions, and stochastic charging can cause particles of given size to have a broad distribution of charge states. Sectional models, while computationally expensive, are well suited to treating such distributions. This paper presents an overview of sectional modeling of nanodusty plasmas, and presents examples of simulation results that reveal important qualitative features of the spatiotemporal evolution of such plasmas, many of which could not be revealed by models that consider only monodisperse dust particles and average particle charge. These features include the emergence of bimodal particle populations consisting of very small neutral particles and larger negatively charged particles, the effects of size and charge distributions on coagulation, spreading and structure of the particle cloud, and the dynamics of dusty plasma afterglows. [ABSTRACT FROM AUTHOR]

In the present work, various scenarios of the spatial distributions of argon dusty plasma parameters are considered, focusing on the case of a large density of dust particles. It is shown that in this case a scenario with the inversion of the ambipolar field sign, considered in earlier studies by authors for plasma with heavy negative ions, can be realized. In this case, the ionization inside the dust cloud becomes small in comparison with the volume loss of charges inside the dust cloud, and the lack of charges is compensated by their arrival from the outer peripheral plasma region. This transition is accompanied by the phenomenon of the reversal of the sign of the radial electric field at the boundary of the dust cloud, and the formation of nonmonotonic profiles of the electron density with a shift of the maximum electron density from the center to the periphery. The radial stability of the dust particles cloud is provided by the balance of the increasing dust charge density gradient in the presence of the pushing out ambipolar field. [ABSTRACT FROM AUTHOR]

Incandescent dust particles are observed with the naked eye in plasmas excited at the electron cyclotron resonance produced in pure acetylene. To investigate the heating mechanisms involved and their potential impact on the dust particle charge, as a first approach, a probe is used to measure the floating potential and to estimate the temperature reached by the material. Both highly depend on the position in the magnetic field and on the plasma conditions (pressure and gas, namely argon or helium). Numerical simulations based on the balance of the currents and of the heat fluxes on the probe emphasize a key role of primary electrons: they are responsible for the very negative floating potential as well as for the high probe temperature. Numerical simulations are also adapted to the case of a dust particle in a non-reactive plasma. However, even it can reach temperatures higher than 1600 K, the dust particle remains negatively charged. [ABSTRACT FROM AUTHOR]

The forced vertical oscillations of a single dust particle trapped in a standing striation are investigated. The particle oscillations associated with the displacement of the striation are induced by square wave modulation of the discharge current. Amplitude−frequency characteristics with respect to pressure are measured. The resonance frequency, the logarithmic decrement and the amplitude of resonance peak are determined. In order to obtain the eigenfrequency value, the phase shift of the forced dust particle oscillations is measured and the velocity resonance investigated. The calculation of the dust particle charge is made with the help of the eigenfrequency. A quantitative description of the resonance behaviour of the dust particle based on the theory of the forced harmonic oscillator is made. The Q-factor of a dusty plasma system is measured for the first time, and the obtained value compared with Q-factors of dusty plasma oscillatory systems previously investigated in rf plasma. [ABSTRACT FROM AUTHOR]

Dusty plasma has been studied in dc glow discharge with standing striation formed in neon. The theoretical method of dust particle charge determination is proposed. This method is based on the calculation of the ion and electron fluxes on the dust particle surface in a spatially periodic field of striation. The electron flux is calculated through the use of non-local electron energy distribution function (EEDF), which is formed by inhomogeneous strata potential. The calculation of dust particle charge using proposed theoretical method are compared with those in which the used EEDF was assumed to be Maxwell EEDF. Under the conditions of standing P-striations at low pressures of neon the numerical calculations and the measurements are performed. An experimental method of dust particle charge determination is applied in the dc discharge condition. Discharge current is modulated at low-frequency in order to determine the dust charge through the relaxation oscillation of a single dust particle. The calculation of the dust particle charge with the help of measured frequency and damping coefficient of the oscillations is made. The dust particle charges obtained by using two independent methods are in good agreement. [ABSTRACT FROM AUTHOR]

Strongly coupled plasmas in which the interaction energy exceeds the kinetic energy play an important role in many astrophysical and laboratory systems including compact stars, laser plasmas and dusty plasmas. They exhibit many unusual collective properties, such as liquid or crystalline behaviour, peculiar oscillation spectra and transport properties. Recently, strongly coupled plasmas were studied in the presence of a strong magnetic field by computer simulations, and strong modifications of their transport properties and oscillation spectra were observed. While strong magnetization is common in stellar systems it is practically impossible to achieve in complex plasmas due to the large mass of the dust particles. Here we discuss a recently demonstrated approach to achieve very strong 'magnetization' by a rotation of the neutral gas, and we present new results for macroscopic two-dimensional systems. [ABSTRACT FROM AUTHOR]

The electric charge on silica microparticles (5µm in diameter) levitating in the sheath of an rf discharge plasma is determined in a newly installed device for dusty plasma experiments at the IASST. The sheath potential profile is measured using an emissive probe and the electric field is obtained in order to determine the dust charge. The measured dust charge in the pressure range 0.50-5.0 Pa using the electric field value at the levitation height is found to be of the order of 104 elementary charges. Dust charge is also examined using the vertical resonance method which gives a similar order of charges. The experimentally measured charge is compared with the estimated values based on the orbital motion limited charging model. The coupling strength between the particles forming a 2D plasma crystal lattice is estimated using the measured dust charge. [ABSTRACT FROM AUTHOR]

Anions in low-pressure magnetically confined Ar–C2H2 plasmas were investigated using the laser-induced photodetachment technique. In particular, the influence of the magnetic field (B) was studied. We observed that the density of negatively-charged species n– increases with B and slightly decreases when the C2H2 percentage grows. These phenomena are the result of changes in the plasma kinetics. We also observed that n– decreases as the pressure increases from 2 to 10 mTorr due to the corresponding rise of the collision frequency, which leads to enhanced losses of the negatively-charged species. In parallel, the photodetachment cross-section was deduced from the energy dependence of the photodetachment signal and was found to be close to that of C2H− anions, which indicates that these anions are likely to dominate the negative ion population. [ABSTRACT FROM AUTHOR]

A variety of experimental techniques for the generation of subsonic/supersonic dust fluid flows and means of measuring such flow velocities are presented. The experiments have been carried out in a -shaped dusty plasma experimental device with micron size kaolin/melamine formaldehyde particles embedded in a background of argon plasma created by a direct current glow discharge. A stationary dust cloud is formed over the cathode region by precisely balancing the pumping speed and gas flow rate. A flow of dust particles/fluid is generated by additional gas injection from a single or dual locations or by altering the dust confining potential. The flow velocity is then estimated by three different techniques, namely, by super particle identification code, particle image velocimetry analysis and the excitation of dust acoustic waves. The results obtained from these three different techniques along with their merits and demerits are discussed. An estimation of the neutral drag force responsible for the generation as well as the attenuation of the dust fluid flow is made. These techniques can be usefully employed in laboratory devices to investigate linear and non-linear collective excitations in a flowing dusty plasma. [ABSTRACT FROM AUTHOR]

We developed a model for the nucleation, growth and transport of carbon dust particles in a DC discharge. The carbon source comes from the sputtering of a graphite cathode resulting in the production of primary clusters and then of nanoparticles. We consider the ionic cluster growth as well as the particle growth and charging and the influence of both on the discharge equilibrium. We found that the discharge becomes electronegative for long duration when particle density reaches 109 cm−3 and particle size 45 nm. The corresponding transition modifies the electric field profile in the vicinity of the field reversal region in the negative glow. We then analyze the space and time evolution of the different discharge characteristics and the mechanisms involved in the discharge. We showed that particle density is governed by nucleation, coagulation and transport, while particle size is mainly governed by the deposition of the small neural clusters emitted at the cathode on the particle surface. [ABSTRACT FROM AUTHOR]

A void (i.e. the complete absence of macroscopic dust particles) can be generated in the bulk plasma region of a cogenerated dusty plasma with the help of a positively dc-biased ring electrode placed between two electrodes of dc discharge. This void region can then be dynamically controlled by varying the external positive bias voltage through the ring electrode. [ABSTRACT FROM AUTHOR]

A capacitively coupled radio-frequency discharge in a nitrogen–methane (N2–CH4) gas mixture is used to simulate the formation of solid aerosols in Titan's atmosphere. The present work is focused on the time evolution of the plasma parameters, such as self-bias potential, Vdc, and electron density. The time evolution of the electron temperature is evaluated from the correlation of the optical emission spectroscopy and the electron density. In situ mass spectrometry is used to monitor the neutral composition of the gas phase. After a few seconds, a drastic change is observed for all of the parameters, which is related to the formation of solid particles in the discharge. The electron density decreases simultaneously with an increase of the electron temperature, which induces an increase of the methane consumption. [ABSTRACT FROM AUTHOR]

The occurrence of low frequency instabilities in a plasma can be due to the presence of a high density of grown dust particles. These instabilities are characterized by analyzing the discharge current, evidencing the existence of successive phases marked by distinct frequency evolutions. The main characteristics of these phases are determined as a function of the gas pressure. Particular attention is paid to the changes of the instability appearance time, duration and frequencies. These parameters seem to be related to global amount of grown dust particles. The instability appearance time is the first parameter that can be easily measured during an experiment and all the other parameters can be estimated from this simple measurement. [ABSTRACT FROM AUTHOR]

In Ar and He radio-frequency (RF) plasmas with admixtures of C2H2 and CH4 the hydrocarbon chemistry has been studied in relation to dust particle formation by means of infrared tunable diode laser absorption spectroscopy (TDLAS) combined with Fourier transform infrared (FTIR) spectroscopy. The experiments were performed in a RF capacitively coupled parallel plate reactor at a frequency of f = 13.56 MHz, a pressure of p = 0.1 mbar and a flow rate of Φ = 8 sccm of Ar or He with admixtures of 0.5 sccm C2H2 or 1 sccm CH4. The power was P = 15 W. Using TDLAS, the temporal evolution of the concentrations of the methyl radical and of four stable molecules, C2H2, CH4, C2H4 and CO, was monitored in the plasma. Simultaneously, the growth process of the dust particles was analysed by FTIR spectroscopy. The degree of dissociation of the acetylene precursor was found to be nearly constant in the range of 96% under stabilized conditions for both the Ar and He plasmas. In contrast, the degree of dissociation of the methane precursor varied between 45% and 90% depending (i) on the appearance of dust particles in the reactor volume and (ii) on the Ar or He plasma conditions. The methyl radical concentration was found to be in the range of 1011 molecules cm−3. The concentrations of all hydrocarbon species were strongly correlated with the dynamic of the dust formation. Fragmentation efficiencies of acetylene (RF (C2 H2) = 3.2 × 1016 molecules J−1) and of methane (RF (CH4) = (0.16–2.5) × 1016 molecules J−1) and conversion efficiencies to the produced hydrocarbons (RC = (0.23–8.5) × 1014 molecules J−1) could be estimated in dependence on the discharge conditions in the RF plasma. [ABSTRACT FROM AUTHOR]