We consider the excitation and dispersion of ion acoustic waves in expanding ultracold plasmas, taking into account the influence of boundary conditions. A cylindrical plasma geometry is assumed. We show that temporal changes in the medium lead to a wave frequency shift, associated with an evolving radial and standing wave mode structure, and to the temporal change of the background plasma parameters. A non-collisional model for the cylindrical geometry is also proposed.

Investigation of arbitrary amplitude nonlinear ion-acoustic solitary waves which accompany collisionless positive–negative ion plasmas with high-energy electrons (represented by kappa distribution) is presented. Arbitrary amplitude solitary waves are investigated by deriving an energy-integral equation involving a Sagdeev-like pseudopotential. The existence regions of solitary pulses are, defined precisely, modified by the superthermality of energetic electrons. Furthermore, numerical calculations reveal that both compressive and rarefactive pulses may exist for negative ion mass groups in Titan's atmosphere. The superthermality of energetic electrons are found to modify the existence domains of large amplitude ion-acoustic waves in Titan's atmosphere. The dependence of solitary excitation characteristics on the superthermal parameter, the negative ion concentration, the positive-to-negative ions mass ratio, and the Mach number have been investigated. The present study might be helpful to understand the excitation of fully nonlinear ion-acoustic solitary pulses that may appear in the interplanetary medium and/or in the astrophysical plasmas in general.

Solitary waves are investigated in a charge-varying dusty plasma involving dust trapping. A potentially useful neuronal method that may handle a wide variety of non-analytic pseudo-potentials is used. This method could be advantageously exploited in rendering a cumbersome pseudo-potential analytically more tractable. Making use of the approximate Sagdeev pseudo-potential, our results show the possibility of development of localized dust structures in a dusty plasma with variable charge trapped dust grains.

The Rosetta–Philae mission to comet 67P/Churyumov–Gerasimenko in 2014 will provide a unique opportunity to observe the variable nature of the interaction of a comet with the solar radiation and the solar wind, as the comet approaches the Sun. In this short paper we will focus on the varying global structure of the cometary plasma environment. Specifically we make predictions on the varying locations of the two basic transitions in the global, contaminated solar wind flow toward the comet: the outer bow shock and the ionopause.

Waves in a dusty plasma over the lunar dayside are considered. It is shown that the relative motion of the solar wind with respect to the photoelectrons over the lunar surface leads to the excitation of high-frequency oscillations with frequencies in the range of Langmuir and electromagnetic waves. The dust acoustic wave excitation is possible in the vicinity of the lunar terminator.

The linear dust lattice waves propagating in a two-dimensional honeycomb configuration is investigated. The interaction between particles is considered up to distance 2a, i.e. the third-neighbor interactions. Longitudinal and transverse (in-plane) dispersion relations are derived for waves in arbitrary directions. The study of dispersion relations with more neighbor interactions shows that in some cases the results change physically. Also, the dispersion relation in the different direction displays anisotropy of the group velocity in the lattice. The results are compared with dispersion relations of the waves in the hexagonal lattice.

The nonlinear propagation of dust ion-acoustic (DIA) solitary waves (SWs) as well as double layers (DLs) in a dusty plasma containing warm adiabatic ions, non-extensive electrons, and arbitrarily (positively or negatively) charged immobile dust are studied. Based on the energy-like integral equation, a new relationship between the localized electrostatic disturbances and dust polarity in the non-extensive dusty plasma is derived. It is shown that the effect of electron non-extensivity, in contrast to the influence of extensive electrons, is destructive for the formation of the SWs and DLs. It is also found that the negative (positive) dust number density raises (reduces) the possibility for the formation of these localized states.

An exact nonlinear solution for a cold fluid in presence of a gravitational field and viscous dissipation is obtained using Lagrange variable. It is shown that with a density-dependent viscosity the nonlinear equation can be exactly solved. The solution indicates that in absence of viscosity and initial fluid velocity shear, density collapse occurs at time of the order of inverse Jeans frequency. The effect of viscosity is to delay the collapse but it can not halt the collapse. The initial fluid velocity shear can act in both directions: a positive one leads to delay, a negative one to a speeding up of the density collapse. This nonlinear solution may have some bearing with the structure formations in the universe.

The processes responsible for initiation of electrical breakdown in xenon-filled tube with two spherical iron electrodes at 2.7-mbar pressure have been analyzed. The analysis is based on the experimental data of electrical breakdown time delay as a function of afterglow period. It is shown that positive ions remaining from previous discharge, as well as positive ions created in mutual collisions of metastable atoms in afterglow, have a dominant role in secondary emission of electrons from the cathode which lead to initiation of breakdown in early afterglow. In late afterglow, dominant role in initiation of breakdown is taken by N(4S) atoms formed during the discharge by dissociation of ground state nitrogen molecules that are present as impurities in xenon. When the concentration of N(4S) atoms decreases sufficiently, the initiation of breakdown is caused by cosmic radiation. Small doses of gamma-ray irradiation also contribute to the initiation of breakdown, but only for large values of the afterglow period.

In this work we investigate the effect of relativistic degeneracy on different properties of low-dimensional quantum plasmas. Using the dielectric response from the conventional quantum hydrodynamic model, including the quantum diffraction effect (Bohm potential) on free electrons, we explore the existence of the Shukla–Eliasson attractive screening and possibility of the ion structure formation in low-dimensional, completely degenerate electron–ion plasmas. A generalized degeneracy pressure expression for arbitrary relativity parameter in two-dimensional case is derived, indicating that change in the polytropic index (change in the equation of state) for the two-dimensional quantum fluid takes place at the electron number-density of n0 ≃ 1.1 × 1020cm−2 whereas this is known to occur for the three-dimensional case in the electron density of n0 ≃ 5.9 × 1029cm−3. Also, a generalized dielectric function valid for all dimensionalities and densities of a degenerate electron gas is calculated, and distinct properties of electron–ion plasmas, such as static screening, structure factor and Thomson scattering, are investigated in terms of plasma dimensionality.

A fluid model is used to describe the propagation of envelope structures in an ion plasma under the influence of the action of weakly relativistic electrons and positrons. A multiscale perturbative method is used to derive a nonlinear Schrödinger equation for the envelope amplitude. Criteria for modulational instability, which occurs for small values of the carrier wavenumber (long carrier wavelengths), are derived. The occurrence of rogue waves is briefly discussed.

In this paper, turbulent transport in the edge plasma of the IR-T1 tokamak (r/a = 0.9) in the presence of a resonant helical magnetic field (RHF) and a biased limiter has been investigated and analyzed. The time evolution of potential fluctuation, and electric field and turbulent transport have been measured by using two arrays of the Langmuir probes in both the radial and poloidal directions. The experiments have been done in different regimes such as limiter biasing and RHF, and both of them. The analyses have been done by the fast Fourier transport method and their spectral features are obtained with the help of the standard autocorrelation technique. The results show that radial turbulent transport decreases about 60% after positive biasing application, while it increases about 40% after negative biasing. The effect of positive biasing on poloidal turbulent transport displays an increase of about 55%, while the negative bias voltage decreases the poloidal turbulent transport about 30%. Consequently, confinement is improved and plasma density rises significantly due to the applied positive biasing in IR-T1. However, the results are reversed when negative biasing is applied. Also, in this work, the results of the applied RHF (L = 3) are compared with biasing results and analyzed.

The nonlinear coupling of two high-power laser beams in plasmas in the presence of a transverse, static electric field is investigated to generate a difference frequency terahertz (THz) radiation. The relativistic variation of electron mass in the presence of two high-power laser beams is responsible for producing a nonlinear current driving the THz radiation. For typical laser and plasma parameters, we report the efficiency of the order of ~10−4 for the current scheme.

To describe the transverse nonlinear and collective self-consistent interaction of a long relativistic electron or positron beam with an unmagnetized plasma, a pair of coupled nonlinear differential equations were proposed by Fedele and Shukla in 1992 (Fedele, R. and Shukla, P. K. 1992a Phys. Rev. A 45, 4045). They were obtained within the quantum-like description provided by the thermal wave model and the theory of plasma wake field excitation. The pair of equations comprises a 2D Schrödinger-like equation for a complex wave function (whose squared modulus is proportional to beam density) and a Poisson-like equation for the plasma wake potential. The dispersion coefficient of the Schrödinger-like equation is proportional to the beam thermal emittance. More recently, Fedele–Shukla equations have been further applied to magnetized plasmas, and solutions were found in the form of nonlinear vortex states and ring solitons. They have been also applied to plasma focusing problems and extended from thermal to quantum regimes. We present here a review of the original approach, and subsequent developments.

The large-amplitude ion-acoustic double layers in a collisionless plasma consisting of isothermal positrons, warm adiabatic ions and two-temperature distribution of electrons are investigated. Using the pseudo-potential approach, an energy-integral equation for the system has been derived which encompasses complete nonlinearity for the plasma system. The existence region of the double layers is analyzed numerically. It is found that for a selected set of physical parameters, the rarefactive double layer exists in the electron–positron–ion plasma. It is found that the existence regime of the double layer is very sensitive to the plasma parameters, e.g. cold electron concentration (μ) and temperature ratio of two electron species (β). An increase in the finite ion temperature ratio increases the amplitude of the rarefactive double layer. To study small-amplitude double layers, we have expanded the Sagdeev potential. In the case of small amplitude, it is found that the amplitude of the double layer increases with increase in ion temperature ratio (σ) and cold electron concentration (μ). However increase in positron concentration (α) and temperature ratio of positrons to electrons (γ) decreases the amplitude of the double layer. The effect of various plasma parameters on the characteristics of the double layers is discussed in detail. The results of the investigation may be helpful to understanding basic plasma characteristics in space.

Gyro-phase drift is a guiding center drift that is directly dependent on the charging rate limit of dust grains. The effect of introducing a gyro-phase-dependence on the grain charge leads to two orthogonal components of guiding-center drift. One component, referred to here as grad-q drift, results from the time-varying, gyro-phase angle dependent, in-situ-equilibrium grain charge, assuming that the grain charging is instantaneous. For this component, the grain is assumed to be always in its in-situ-equilibrium charge state and this state gyro-synchronously varies with respect to the grain's average charge state. The other component, referred to here as the gyro-phase drift, arises from any non-instantaneous-charging-induced modification of the diamagnetic drift and points in the direction of -∇RLd (where RLd is the grain gyro-radius), i.e. the direction associated with increasing magnitude of in-situ-equilibrium charge state. For this component, the grain gyro-synchronously undercharges and overcharges with respect to its gyro-synchronously varying, in-situ-equilibrium charge state. These characteristics are illustrated with a single-particle code for predicting grain trajectory that demonstrates how gyro-phase drift magnitude and direction could be exploited, using an extended version of the presented model, as sensitive indicators of the charging time of dust grains because of the cumulative effect of the ever-changing charge state of a grain making repeated excursions in inhomogeneous plasma over many gyro-periods.

We report experimental observations of a low-frequency (≪ ion gyrofrequency) electrostatic wave mode in a magnetized cylindrical (Q machine) plasma containing positive ions, very few electrons and a relatively large fraction (n−/ne > 103) of heavy negative ions (m−/m+ ≈ 10), and no magnetic field-aligned current. The waves propagate nearly perpendicular to B with a multiharmonic spectrum. The maximum wave amplitude coincided spatially with the region of largest density gradient suggesting that the waves were excited by a drift instability in a nearly electron-free positive ion–negative ion plasma

Experimental observations of supersonically flowing dusty plasmas and their interaction with an electrically biased circular cylinder are presented. Two methods for producing flowing dusty plasmas are described. The dusty plasma is produced in a DC anode glow discharge plasma. In Configuration I, a secondary dust cloud, initially formed near a biased grid, flowed away from the grid at supersonic speeds when the grid voltage was suddenly changed. In Configuration II, a pencil-like dust beam was produced using a nozzle-like (converging-diverging) electrostatic potential structure. Using Configuration I, the streaming dust encountered a biased cylinder (wire) whose axis was oriented transverse to the dust flow. The flowing dust particles were repelled by the electrostatic field of the negatively charged cylinder, and a dust void was formed around the cylinder. A detached electrohydrodynamic bow shock, akin to the Earth's magnetohydrodynamic bow shock, was formed on the upstream side of the cylinder, while an extended teardrop-shaped wake region was formed on the downstream side. Video imaging of the dust stream allowed for observations of the structure and evolution of the bow shock. Configuration II was used to produce a narrow beam of dust particles and observe how the beam was deflected around the biased cylinder. Three multimedia files (movies) of the observed phenomena are provided in the online Supplementary material.

The excitation of drift waves by an electron current parallel to the magnetic field is investigated in a nonuniform plasma composed of electrons, positive ions, negative ions, and massive, negatively charged dust. Electrostatic drift waves with frequencies smaller than the ion gyrofrequencies and wavelengths larger than the ion gyroradii are considered. Linear kinetic theory is used, and collisions of charged particles with neutrals are taken into account. The present results may be relevant to laboratory collisional magnetoplasmas containing negative ions and dust.

In this paper, electrical and optical emission spectrometer (OES) characteristics of an Ar/air atmospheric-pressure plasma jet (APPJ) based on the plasma needle and plasma pencil systems were investigated and analyzed. Electrical measurement results showed that the breakdown and working voltage of the jet increased with the increase of the ratio of air/Ar, and the emission intensity of Ar* significantly decreased. For the plasma needle, when the ratio of air/Ar reached 1, the OES characteristics of Ar/air were similar to those of air plasma, and the main excited species was N2*. For the plasma pencil, when a little air impurity was added in Ar, the emission intensities of N2* species will be significantly increased. Based on these two APPJ systems, photoresist materials were etched, etched results showed that the etched surface was easier to be oxidized with the addition of air into Ar. The etched surface was cleaner with pure Ar plasma with scanning substrate methods than that with the Ar/air mixture. Etched results of higher ratios of air/Ar plasma were similar to those of air plasma.