Dust acoustic waves in three-dimensional complex plasmas with a similarity property. (arXiv:1506.08686v2 [physics.plasm-ph] UPDATED)

Dust acoustic waves in the bulk of a dust cloud in complex plasma of low-pressure gas discharge under microgravity conditions are considered. The complex plasma is assumed to conform to the ionization equation of state (IEOS) developed in our previous study. This equation implies the ionization similarity of plasmas. We find singular points of IEOS that determine the behavior of the sound velocity in different regions of the cloud. The fluid approach is utilized to deduce the wave equation that includes the neutral drag term. It is shown that the sound velocity is fully defined by the particle compressibility, which is calculated on the basis of the used IEOS. The sound velocities and damping rates calculated for different three-dimensional complex plasmas both in ac and dc discharges demonstrate a good correlation with experimental data that are within the limits of validity of the theory. The theory provides interpretation for the observed independence of the sound velocity on the coordinate and for a weak dependence on the particle diameter and gas pressure. Predictive estimates are made for the ongoing PK-4 experiment.

Study of the top-quark pair production in association with a bottom-quark pair from fast simulations at the LHC

Abstract A large number of top quarks will be produced at the Large Hadron Collider (LHC) during the Run II period. This will allow us to measure the rare processes from the top sector in great details. We present a study of top-quark pair production in association with a bottom-quark pair ( \(t\bar tb\bar b\) ) from fast simulations for the Compact Muon Solenoid (CMS) experiment. The differential distributions of \(t\bar tb\bar b\) are compared with the top-quark pair production with two additional jets ( \(t\bar tjj\) ) and with the production in association with the Higgs ( \(t\bar tH\) ), where the Higgs decays to a bottom-quark pair. The significances of the \(t\bar tb\bar b\) process in the dileptonic and the semileptonic decay modes are calculated with the data corresponding to an integrated luminosity of 10 fb-1, which is foreseen to be collected in the early Run II period. This study will provide an important input in searching for new physics beyond the standard model, as well as in searching for the \(t\bar tH\) process where the Yukawa coupling with the top quark can be directly measured.

Complex plasma in g×B configurations: Stability switching and stationary structure

In a low-pressure magneto-gravitated complex plasma, the stability state of dust gravitational drift wave is switched at a critical wavenumber and the propagating dust magneto-gravitational drift wave is transformed into an aperiodic stationary structure at a cut-off wavenumber. In this paper, two analytical formulas have been derived for the critical wavenumber of stability switching and the cut-off wavenumber of stationary structure. The critical wavenumber is equal to the ratio of ion plasma frequency to ion streaming velocity and the cut-off wavenumber is proportional to the ratio of dust plasma frequency to dust g × B drift velocity. These scaling formulas are in excellent agreement with exact numerical solutions of dispersion relations. These scenarios are expected to be observed in fully magnetized dusty plasma experiments as the next frontier for complex plasma research.

Dust acoustic waves in three-dimensional complex plasmas with a similarity property

Author(s): D. I. Zhukhovitskii

Dust acoustic waves in the bulk of a dust cloud in complex plasma of low-pressure gas discharge under microgravity conditions are considered. The complex plasma is assumed to conform to the ionization equation of state (IEOS) developed in our previous study. This equation implies the ionization simi…

[Phys. Rev. E 92, 023108] Published Fri Aug 28, 2015

Zakharov equations in quantum dusty plasmas

By generalizing the formalism of modulational interactions in quantum dusty plasmas, we derive the kinetic quantum Zakharov equations in dusty plasmas that describe nonlinear coupling of high frequency Langmuir waves to low frequency plasma density variations, for cases of non-degenerate and degenerate plasma electrons.

Dust-void formation in a dc glow discharge

Author(s): A. V. Fedoseev, G. I. Sukhinin, M. K. Dosbolayev, and T. S. Ramazanov

Experimental investigations of dusty plasma parameters of a dc glow discharge were performed in a vertically oriented discharge tube. Under certain conditions, dust-free regions (voids) were formed in the center of the dust particle clouds that levitated in the strong electric field of a stratified …

[Phys. Rev. E 92, 023106] Published Mon Aug 24, 2015

Gas phase synthesis of two ensembles of silicon nanoparticles

Dusty plasmas provide a very favorable environment for the growth of silicon nanocrystals. For application of silicon nanocrystals in a solar cell, the fabrication of monodisperse silicon quantum dots has been challenging. We report a single step method to synthesize silicon (Si) nanoparticles in a custom designed dedicated plasma reactor. The nanoparticles produced in the gas phase belong to two different phases exhibiting different structural and optical properties. Particles made in the bulk of the plasma are aggregates of crystalline particles with a mean size of 100 nm. Particles made in locally enhanced plasma regions produced at holes present in the grounded electrode contain free-standing quantum sized particles with crystallites (with mean size of 2.95 nm) embedded within an amorphous matrix. We provide insight on different plasma processes leading to the formation of aggregates and free-standing particles. We hypothesize that the free standing particles are formed due ...

A molecular dynamics study of phase transition in strongly coupled pair-ion plasmas

Existence of phase transition in strongly coupled pair-ion plasmas with soft core is investigated. Extensive Molecular Dynamics (MD) simulations are performed in the canonical ensemble, for such plasmas, at different temperatures, to analyze phase stability. Our studies show interesting phase co-existence between liquid-like and vapor-like phases. The different phases are identified by calculating the ensemble averaged density. This and the corresponding critical properties are calculated directly from MD simulation. The critical temperature of vapor-liquid coexistence is obtained, and the corresponding critical value of density is also estimated for different sizes of the soft core. We have used a novel method that allows the location of phase coexistence through a constant density simulation in which the temperature is changed in a single time-step (quenching) in order to place the system in a thermodynamically and mechanically unstable state, resulting in spontaneous separation of two coexisting phases. The results obtained from this temperature quench MD method also show the coexistence of vapor-liquid phase in pair-ion plasmas. The critical exponents obtained directly from MD simulation are found to be in close agreement with the values predicted by a mean-field theory.

Effective potentials of interactions and thermodynamic properties of a nonideal two-temperature dense plasma

Author(s): T. S. Ramazanov, Zh. A. Moldabekov, and M. T. Gabdullin

In this article a dense nonideal, nonisothermal plasma is considered. New effective screened interaction potentials taking into account quantum-mechanical diffraction and symmetry effects have been obtained. The effective potential of the ion-ion interaction in plasmas with a strongly coupled ion su…

[Phys. Rev. E 92, 023104] Published Wed Aug 19, 2015

Dusty Plasma Experimental (DPEx) device for complex plasma experiments with flow. (arXiv:1507.08647v2 [physics.plasm-ph] UPDATED)

A versatile table-top dusty plasma experimental (DPEx) device to study flow induced excitations of linear and nonlinear waves/structures in a complex plasma is presented. In this {$\Pi$}-shaped apparatus a DC glow discharge plasma is produced between a disc shaped anode and a grounded long cathode {tray} by applying a high voltage DC in the background of a neutral gas {(Argon)} and subsequently a dusty plasma is created by introducing micron sized dust particles that get charged and levitated in the sheath region. A flow of the dust particles is induced in a controlled manner by adjusting the pumping speed and the gas flow rate into the device. A full characterisation of the plasma, using Langmuir and emissive probe data, and that of the dusty plasma using particle tracking data with the help of an idl based (super) Particle Identification and Tracking (sPIT) code is reported. Experimental results on the variation of the dust flow velocity as a function of the neutral pressure and the gas flow rate are given. {The neutral drag force acting on the particles and the Epstein coefficient are estimated from the initial acceleration of the particles}. The potential experimental capabilities of the device for conducting fundamental studies of flow induced instabilities are discussed.