The ion-acoustic (IA) mode exhibiting various orbital angular momentum (OAM) states is examined in a plasma with drifting electrons. The constituent plasma species are modeled with a non-gyrotropic Maxwellian distribution and discussion of dispersion relation and growth rate of twisted IA waves under various conditions is presented. In the domain of kinetic model, the twisted IA waves are characterized by Laguerre-Gaussian (LG) solutions, where plasma distribution function and electric field are decomposed into axial and azimuthal components. The plasma response function is obtained under paraxial approximations and investigated for threshold condition of instability growth rate with helical electric field structures. The impact of an extra electron specie on the instability is demonstrated through a comparison of twisted waves for single and double electron species.

We have investigated the twisted dust-acoustic waves (TDAWs) in an electrostatic self-gravitating dusty plasma whose electrons and ions are modelled by nonextensive q-distribution function while massive dust particles are Maxwellian distributed. A well-known kinetic theory is employed for this purpose where perturbed distribution function, electrostatic and gravitational potentials are expressed with Laguerre–Gauss functions. The governing equations of kinetic theory are solved together under paraxial approximations. The dispersion relations and instability growth rates are obtained for two situations; a) super-extensivity ( q < 1) and b) sub-extensivity ( q > 1). Significant modifications concerning the wave frequencies and growth rates are presented with respect to self-gravitation parameter, twist parameter, nonextensive parameter and streaming speed. It is observed that wave frequency and growth rate of TDAWs reduces in the presence of self-gravitating effects. Furthermore, the growth rates exhibit a significant enhancement in amplitude with the increase in twist parameter, q -parameter and streaming speed. Our present results may have applications in interstellar dust clouds and in the dusty plasma environments of Halley’s Comet.

The effects of dust–dust self-gravitational force and nonextensive characteristics of plasma species on the low frequency twisted waves owing to the helical wave structure in complex (dusty) plasmas are analyzed. The electrons and ions of the plasma are modelled by nonextensive q -distribution function while massive dust particles are Maxwellian distributed. The self-gravitational effects are incorporated in the Vlasov equation of kinetic theory where perturbed distribution function, electrostatic and gravitational potentials are expressed with Laguerre–Gauss functions. The governing equations of kinetic theory are solved together under paraxial approximations. The dispersion relations and damping rates of twisted dust-acoustic waves (TDAWs) are obtained for two situations; (a) super-extensivity ( q < 1) and (b) sub-extensivity ( q > 1). The effects of self-gravity, nonextensivity and twist parameter significantly modified the basic features of dust-acoustic waves. This study contributes to our understanding of the complex dynamics of TDAWs in interstellar dust clouds, considering the interplay of self-gravity, nonextensivity, and helical phase structures. The obtained theoretical and numerical results provide valuable insights into the behavior of these waves and offer a foundation for further investigations in this field. However, understanding of the topic can be enhanced through a combination of theoretical models, numerical simulations and observational data.

Dust-acoustic waves (DAWs) are examined in an electrostatic self-gravitating dusty plasma whose electrons and ions are modeled by nonextensive q-distribution function while massive dust particles are Maxwellian distributed. A Vlasov–Poisson’s set of equations is used for the derivation of plasma dispersion relation and growth rate of instability. The real wave frequency and instability growth rates are obtained for two situations; a) super-extensivity (q<1) and b) sub-extensivity (q>1). Significant modifications concerning the real wave frequencies and growth rates are presented with respect to self-gravitation parameter, nonextensive parameter, dust concentration and streaming speed. It is observed that parametric variation significantly modifies the threshold conditions and associated growth rates of instability of DAWs. The applicability of the present results in interstellar dust clouds is discussed.

Twisted ion-acoustic waves with finite orbital angular momentum (OAM) states are numerically investigated in a plasma containing electrons, positrons and dynamical ions. For this purpose, the well-known Vlasov–Poisson equations are solved together under the paraxial approximation. The perturbed quantities are assumed to follow the Laguerre–Gaussian type solutions and a generalized plasma response function for finite OAM states is derived. The generalized response function is numerically analyzed to investigate dispersion characteristics of the twisted ion-acoustic waves. Consequently, a computer code is developed which is based on the very famous numerical technique known as the Newton–Raphson method. The dependence of the (real) wave oscillation frequency and damping rate involving the twisted ion-acoustic waves is highlighted with different plasma parameters. It is found that the dynamics of ion-acoustic waves are strongly influenced by the twist parameter owing to OAM states. The results obtained in the present study are useful in the understanding of the particle transport and trapping phenomena.

The linear characteristics of electron-acoustic waves and associated kinetic instability are investigated in an unmagnetized electron-ion plasma containing streaming warm (hot) electrons, dynamical cool electrons and static background of the positive ions. The plasma under consideration is modeled by using a non-gyrotropic nonextensive q-distribution function in which the free energy source for wave excitation is provided by the relative directed motion of streaming warm electrons with respect to the cool electrons. In the frame work of kinetic theory, the Vlasov–Poisson equations are solved to derive the expressions for linear dispersion relation and Landau damping rate. The results are analyzed for threshold condition of wave dispersion and instability growth rate in the presence of nonextensive effects. The relevance of study to the observed situations is also described.

In this work, a type-III heterojunction based on a pulsed-laser-deposited vanadium dioxide (VO 2 ) and p-type silicon (p-Si) substrate is realized. The device shows a large self-powered and room-temperature photoresponse to IR (950 nm), green (515 nm) and blue (456 nm) LEDs. A short-circuit current ( I sc ) of ∼3 µ A and an open-circuit voltage ( V oc ) of ∼−120 mV are observed under IR LED illumination. The work function data in literature along with the sign of V oc measurement is used to sketch the energy band diagram of the heterojunction. The temperature-dependent I sc properties of the junction, contrary to conventional photodetectors, show an initial rise and then a sharp transition from maximum (3.5 μ A) to almost zero near 337 K, corresponding to a metal–insulator phase transition, paving the way for photodetectors with temperature-tunable photoresponsivity.

The linear characteristics of the unstable mode of ion-acoustic waves are examined in an electrostatic electron-ion plasma composed of streaming hot electrons, non-streaming cold electrons and dynamical positive ions. The plasma under consideration is modeled by using a non-gyrotropic nonextensive q-distribution function in which the free energy source for wave excitation is provided by the relative directed motion of streaming hot electrons with respect to the other plasma species. In the frame work of kinetic model, a linearized set of Vlasov–Poisson’s equations are solved to obtain the analytical expressions for dispersion relation and Landau damping rate. The threshold condition for the unstable ion-acoustic wave is derived to assess the stability of the wave in the presence of nonextensive effects. Growth in the wave spectrum and nontrivial effects of q-nonextensive parameter on the ion-acoustic waves can be of interest for the readers in the regions of Saturns’s magnetosphere.

The electrostatic twisted ion-acoustic waves with finite orbital angular momentum states and associated kinetic instability are investigated in an electron-ion plasma. The plasma consisting of superthermal electrons and ions is modeled by using a non-gyrotropic Kappa distribution function in which the free energy source for wave excitation is provided by the relative directed motion of streaming electrons with respect to the ions. In the frame work of kinetic theory, the VlasovPoisson equations are employed to derive the expressions for dispersion relation and Landau damping rate under paraxial approximation. The results are analyzed for threshold condition of wave dispersion and instability growth rate in the presence of helical electric field structure. The relevance of study to the observed situations is also described.

S Ali , S Bukhari , M Ikram and J T Mendonca National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000, Pakistan Department of Physics, The University of Azad Jummu and Kashmir, Muzaffarabad 13100 Azad Kashmir, Pakistan Department of Physics, Hazara University, Mansehra 21300, Pakistan 4 IPFN, Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal

Making use of the kinetic approach for plasma species, the electrostatic twisted dust-acoustic (DA) waves are studied in a collisionless unmagnetized multi-component dusty plasma consisting of electrons, singly ionized positive ions and charged massive dust grains. The Vlasov-Poisson equations are coupled together to obtain a generalized response function by using the Laguerre-Gaussian (LG) perturbed electrostatic potential and distribution function in the paraxial limit. The dispersive properties and growth rate instability of twisted DA waves are examined with distinct OAM states in a multi-component dusty plasma. Various significant modifications associated with the real wave frequency and growth rate are shown with respect to twist parameter and dust concentration. It is examined that dust concentration enhances the growth rate of twisted DA waves, whereas an increase in twist parameter reduces the growth rate instability. The excitation of twisted DA mode is also found to enhance with streaming speed of inertialess electrons. Our results may be useful for particle transport and trapping phenomena due to wave excitation in laboratory dusty plasmas.

The electrostatic twisted modes with orbital angular momentum and associated kinetic instability are studied in a permeating space plasma containing streaming particle species. The plasma containing superthermal electrons and ions is modeled by using a non-gyrotropic Kappa distribution function which penetrates through a relatively slow moving (static) plasma and gives rise to dispersion, damping and growth of ion-acoustic mode under various conditions. Using the Vlasov-Poisson model, the solutions of twisted modes are defined by Laguerre-Gaussian mode functions, which decompose the plasma distribution function and electric field into components characterized by the axial and azimuthal wave numbers. The dielectric constant is derived and analyzed for threshold condition of wave dispersion and instability in the presence of helical electric field with illustrations. The wave excitations due to penetration of solar wind into cometary clouds or interstellar electron-ion plasmas is examined.

Dust oscillons, or dust waves carrying distinct states of orbital angular momentum (OAM), are studied in a self-gravitating unmagnetized dusty plasma, whose constituents are the inertialess electrons and ions with negatively charged mobile massive dust grains. Starting from the linearized fluid equations, an evolution equation in terms of dust density perturbation is derived. By using the beam type solution, the wave is assumed to propagate around the beam axis with slowly varying amplitude proportional to exp(ikz). It leads to a paraxial equation of the wave that admits more generalized Laguerre-Gaussian beam solutions within paraxial limits. It is also shown that dust oscillons carry finite amount of energy flux and OAM density and are modified significantly by the azimuthal mode index and group velocity including the dust Jeans effects. Numerically, the dust Jeans frequency, azimuthal phase angle, as well as radial and azimuthal mode indices have strong dependence on the profiles of dust density perturbations. The present findings may prove useful to understand the dynamics of dust oscillons caused by the Brillouin backscattering of laser beams in a self-gravitating dusty plasma.

The electrostatic twisted waves with finite orbital angular momentum (OAM) states are studied in a doubly κ− distributed plasma, containing superthermal hot and cool electrons in addition to positive ions. In the framework of Vlasov-Poisson model, the expression for a generalized plasma response function is derived by considering the Laguerre-Gaussian (LG) solutions for the perturbed distribution function and electrostatic potential. Modified dispersion relations and instability growth rates of the twisted electron-acoustic (TEA) and twisted ion-acoustic (TIA) waves are derived in an unmagnetized double κ−distributed superthermal plasma. For parametric analysis, the effects of spectral indices (κh and κc), twisted parameter (η) and hot-to-cool electron density ratio (f) are numerically examined on the real and imaginary frequencies of TEA and TIA waves. The threshold conditions for TEA and TIA waves are also analyzed to investigate their instability growth rates both analytically and numerically. The relevance of the present results to Saturn's outer magnetosphere is discussed, where two groups of electrons with different finite temperatures are modeled by the double κ−distributions.

New features of the twisted dusty plasma modes and associated instabilities are investigated in permeating plasmas. Using the Vlasov–Poisson model equations, a generalized dispersion relation is obtained for a Maxwellian distributed plasma to analyse the dust-acoustic and dust-ion-acoustic waves with finite orbital angular momentum (OAM) states. Existence conditions for damping/growth rates are discussed and showed significant modifications in twisted dusty modes as compared to straight propagating dusty modes. Numerically, the instability growth rate, which depends on particle streaming and twist effects in the wave potential, is significantly modified due to the Laguerre–Gaussian profiles. Relevance of the study to wave excitations due to penetration of solar wind into cometary clouds or interstellar dusty plasmas is discussed.

The kinetic instability of twisted dust-acoustic (DA) wave with distinct orbital angular momentum states is studied in an unmagnetized self-gravitating superthermal dusty plasma. For this purpose, the linearized Vlasov–Poisson equations are solved together by expressing the perturbed distribution function, electrostatic and gravitational potentials in terms of Laguerre–Gauss functions or solutions. A generalized plasma dielectric constant is derived and the existence conditions for the damping/growth rates are identified. The impact of streaming speed, dust self-gravitation, superthermality and twist parameters are numerically examined on the growth rate instability. It has been found that parametric variation significantly modifies the threshold conditions and associated growth rate instability of twisted DA waves. The relevance of the present results to interstellar dust clouds is illustrated, where massive dust grains follow a Maxwellian distribution in addition to superthermal electrons and ions.

Twisted ion–acoustic excitations and the existence of kinetic instability are investigated in this study, accounting for finite orbital angular momentum states. For this purpose, a quasi‐neutral electron–ion plasma is considered, which permeates through another (target) plasma. The Vlasov‐Poisson model is used to obtain explicit expressions for wave dispersion and kinetic instability, including the contributions from the orbital angular momentum. It is shown that the existence of instability is a result of the exceeding electron speed as compared to the ion–acoustic speed, with a strong contribution of twist in the wave. Furthermore, it is found that a planner ion–acoustic wave propagates as a slow wave in comparison with the non‐planar (twisted) wave. The results are analysed numerically for typical plasmas found in space and astrophysical environments.

A generalized response (dielectric) function for twisted electrostatic waves is derived for an un‐magnetized self‐gravitating thermal dusty plasma, whose constituents are the Boltzmann‐distributed electrons and positive ions in the presence of negatively charged micrometre‐sized massive dust particulates. For this purpose, a set of Vlasov–Poisson coupled equations is solved along with the perturbed Laguerre–Gauss distribution function, as well as the electrostatic and gravitational potentials in the limit of paraxial approximation. For plane wave solution, the wavefronts of the dust‐acoustic (DA) wave are assumed to have a constant phase with electric and gravitational field lines propagating straight along the propagation axis. On the other hand, non‐planar wave solutions show helical (twisted) wavefronts, in which field lines spiral around the propagation axis owing to the azimuthal velocity component to account for the finite orbital angular momentum (OAM) states. The dispersion relation and damping rate for twisted DA waves are studied both analytically and numerically. It is shown that finite OAM states, the dust to electron temperature ratio, and dust self‐gravitation effects significantly affect the linear dispersion and Landau damping frequencies. In particular, the phase speed of twisted DA waves is reduced with the variation of the twist parameter η (= k/lqϕ), dust concentration δ (= nd0/ni0), and dust self‐gravitation α (= ωJd/ωpd). The relevance of our findings to interstellar dust clouds is also discussed for micrometre‐sized massive dust grains.

Keeping in view the kinetic treatment for plasma particles, the electrostatic twisted dust-acoustic (DA) and dust-ion-acoustic (DIA) waves are investigated in a collisionless unmagnetized multi-component dusty plasma, whose constituents are the electrons, singly ionized positive ions, and negatively charged massive dust particulates. With this background, the Vlasov–Poisson equations are coupled together to derive a generalized dielectric constant by utilizing the Laguerre-Gaussian perturbed distribution function and electrostatic potential in the paraxial limit. The dispersion and damping rates of twisted DA and DIA waves are analyzed with finite orbital angular momentum states in a multi-component dusty plasma. Significant modifications concerning the real wave frequencies and damping rates appeared with varying twisted dimensionless parameter and dust concentration. In particular, it is shown that dust concentration enhances the phase speed of the DIA waves in contrary to DA waves, whereas the impact of twisted parameter reduces the frequencies of both DA and DIA waves. The results should be useful for the understanding of particle transport and trapping phenomena caused by wave excitation in laboratory dusty plasmas.

With interest in establishing baseline concentrations of 137Cs in soil from the Qatarian peninsula, we focus on determination of the activity concentrations in 129 soil samples collected across the State of Qatar prior to the 2011 Fukushima Dai-ichi nuclear power plant accident. As such, the data provides the basis of a reference map for the detection of releases of this fission product. The activity concentrations were measured via high-resolution gamma-ray spectrometry using a hyper-pure germanium detector enclosed in a copper-lined passive lead shield that was situated in a low-background environment. The activity concentrations ranged from 0.21 to 15.41Bq/kg, with a median value of 1Bq/kg, the greatest activity concentration being observed in a sample obtained from northern Qatar. Although it cannot be confirmed, it is expected that this contamination is mainly due to releases from the Chernobyl accident of 26 April 1986, there being a lack of data from Qatar before the accident. The values are typically within but are sometimes lower than the range indicated by data from other countries in the region. The lower values than those of others is suggested to be due to variation in soil characteristics as well as metrological factors at the time of deposition.