Effect of arbitrary temperature degeneracy and ion magnetization on shear Alfven waves in electron-positron-ion plasmas

Linear properties of low-frequency electromagnetic shear Alfven waves (SAWs) are studied in quantum electron-positron-ion plasmas with effect of arbitrary temperature degeneracy for magnetized () and unmagnetized ( ) ions by using the quantum hydrodynamic model. Dispersion relations are derived for nearly degenerate () and nearly non-degenerate () plasmas. Bohm potential due to density correlation and temperature degeneracy due to Fermi–Dirac statistics of electron–positron, and their effects on the dispersion of SAWs are studied in detail both analytically and numerically. The relevance of the work regarding dense astrophysical plasmas is highlighted.     

Numerical study of the effect of secondary electron emission on the sheath characteristics in q-non-extensive plasma

In this paper, a plasma sheath containing primary electrons, cold positive ions, and secondary electrons is studied using a one-dimensional fluid model in which the primary electrons are described by q-non-extensive distribution according to the Tsallis statistics. Based on the Sagdeev potential method and the current balance relation, a modified sheath criterion, and floating potential are established theoretically. The effect of secondary electron emission on q-non-extensive plasma sheath characteristics have been numerically examined. A significant change is observed in the quantities characterizing the non-extensive plasma sheath with the presence of the secondary electrons. It is found that the sheath properties with super-extensive distribution and sub-extensive distribution are different compared with plasma sheath with Maxwell distribution .     

Damped dust-ion-acoustic solitons in collisional magnetized nonthermal plasmas

A multispecies magnetized collisional nonthermal plasma system, containing inertial ion species, noninertial electron species following nonthermal -distribution, and immobile dust particles, is considered to examine the characteristics of the dissipative dust-ion-acoustic soliton modes, theoretically and parametrically. The electrostatic solitary modes are found to be associated with the low-frequency dissipative dust-ion-acoustic solitary waves (DIASWs). The ion-neutral collision is taken into account, and the influence of ion-neutral collisional effects on the dynamics of dissipative DIASWs is investigated. It is reported that most of the plasma medium in space and laboratory are far from thermal equilibrium, and the particles in such plasma system are well fitted via the -nonthermal distribution than via the thermal Maxwellian distribution. The reductive perturbation approach is adopted to derive the damped KdV (dKdV) equation, and the solitary wave solution of the dKdV equation is derived via the tangent hyperbolic method to analyse the basic features (amplitude, width, speed, time evolution, etc.) of dissipative DIASWs. The propagation nature and also the basic features of dissipative DIASWs are seen to influence significantly due to the variation of the plasma configuration parameters and also due to the variation of the supethermality index in the considered plasma system. The implication of the results of this study could be useful for better understanding the electrostatic localized disturbances, in the ion length and time scale, in space and experimental dusty plasmas, where the presence of excess energetic electrons and ion-neutral collisional damping are accountable.     

Magnetoacoustic waves with effect of arbitrary degree of temperature and spin degeneracy in electron-positron-ion plasmas

The linear properties of magnetosonic waves are studied in nearly degenerate and nearly non-degenerate quantum plasmas composed of electrons, positrons and ions in the presence of spin- effect. Using the fluid equations, a generalized dispersion relation for perpendicular and oblique propagation is derived. It is found that degree of temperature and spin degeneracy modify the dispersive properties of the given modes. The results of analysis are beneficial for understanding the collective phenomena in dense quantum astrophysical plasmas.     

Thermodynamics of the uniform electron gas: Fermionic path integral Monte Carlo simulations in the restricted grand canonical ensemble

The uniform electron gas (UEG) is one of the key models for the understanding of warm dense matter—an exotic, highly compressed state of matter between solid and plasma phases. The difficulty in modelling the UEG arises from the need to simultaneously account for Coulomb correlations, quantum effects, and exchange effects, as well as finite temperature. The most accurate results so far were obtained from quantum Monte Carlo (QMC) simulations with a variety of representations. However, QMC for electrons is hampered by the fermion sign problem. Here, we present results from a novel fermionic propagator path integral Monte Carlo in the restricted grand canonical ensemble. The ab initio simulation results for the spin-resolved pair distribution functions and static structure factor are reported for two isotherms (T in the units of the Fermi temperature). Furthermore, we combine the results from the linear response theory in the Singwi-Tosi-Land-Sjölander scheme with the QMC data to remove finite-size errors in the interaction energy. We present a new corrected parametrization for the interaction energy and the exchange–correlation free energy in the thermodynamic limit, and benchmark our results against the restricted path integral Monte Carlo by Brown et al. [Phys. Rev. Lett. 110 , 146405 (2013)] and configuration path integral Monte Carlo/permutation-blocking path integral Monte Carlo by Dornheim et al. [Phys. Rev. Lett. 117 , 115701 (2016)].     

Plasma phase transition (by the fiftieth anniversary of the prediction)

At first, we present a brief review of the problem. Then, we consider plasma phase transition (PPT) as a mechanism of the first order fluid–fluid phase transition in warm dense hydrogen. The pros and cons are analysed. The properties of warm dense hydrogen are investigated by ab initio methods of molecular dynamics using the density functional theory. Strong ionization during the fluid–fluid phase transition in warm dense hydrogen makes this transition close to the prediction of the PPT. Finally, we present differences in the real phase transition from the prediction 1968–1969. Structures are observed with inter‐proton separations that are equal to the distances between protons in the and ions. The transition is not only ionization, but also structural. An analysis of the phase transition counterpart in solid hydrogen under high pressure allows us to reveal partially the character of the new structure. The ionized phase includes complex cluster ions. Van der Waals loops are of abnormal inverted form.     

Kinetic approach on the DIA wave propagation in a non-extensive distributed dusty plasma

The Landau damping of the dust ion-acoustic wave (DIAW) in a dusty plasma with non-extensive distributed components is analysed relying on the kinetic approach. The electron, ion, and dust particles are effectively modelled by the non-extensive distribution function of the Tsallis statistics. For a collisionless plasma with different values of plasma components indices, the general dispersion relation is achieved, and the non-extensivity effects on the frequency, as well as the Landau damping of the DIAW, are studied. We show that for , the preliminary results of the Maxwellian plasma are obtained. The decrease of wave damping is achieved by increasing the coefficient q index and the ion-to-electron density ratio. The damping rate also increases with an increasing ion-to-electron temperature ratio.     

Multipole cross sections for collisional excitation of highly charged ions by isotropic electrons

The relativistic distorted-wave program of the flexible atomic code for calculating the cross sections for electron-impact excitation of ions between fine-structure levels is extended to get the multipole components of cross sections in the case of excitation by isotropic electrons. These components may be needed for interpreting the intensity and polarization of line emissions from thermal plasmas exposed to anisotropic radiations, such as the solar corona under photosphere irradiation. Illustrative numerical results are given for excitation of Si-like Fe¹²⁺ between the , and levels. These results can be useful in the analysis of infrared forbidden lines emitted from the solar corona. A comparison is made with the only published work based on the semi-relativistic distorted-wave approximation, showing some agreement for the excitation and discrepancies for the weak transition .     

Population of the states in collisions of mixed-state (1s21S,1s2s3S) B3+ and C4+ ion beams with He and H2 targets

Auger KLn lines are observed in high-resolution electron spectra obtained in collisions of mixed-state (1s²¹S,1s2s³S) He-like beams of 4 MeV B³⁺ with H₂ and 6 MeV C⁴⁺ with He targets. Supporting atomic structure calculations show these lines to correspond to doubly excited states, which can be readily populated by electron transfer to the component of the mixed-state beam. They thus provide indirect evidence for the existence of the corresponding KLn quartet states, similarly produced, even though their weak Auger decay does not allow for their direct observation in the electron spectra. These KLn quartet states mostly decay in a cascade chain of strong radiative E1 transitions, eventually terminating at the state, which is thus additionally enhanced. An upper limit on the state population due to cascades is obtained by assuming a statistical production of KLn quartet to doublet states followed by a 100% cascade feeding of the state. Our estimated upper limit is supported by our absolute cross section measurements and corresponding three-electron atomic orbital close coupling calculations in progress. Results to date are presented and discussed.     

The effect of the plasma density gradient on current filamentation instability

The filamentation instability is one of the basic beam-plasma instabilities that play a significant role in the energy deposition mechanism of the relativistic electrons generated by the laser-plasma interaction in the fast ignition scenario. In this paper, the effect of the density gradient into plasma on the filamentation instability was investigated in the Weibel unstable plasma, where the plasma temperature anisotropy can play an important role. Results indicated that the density gradient enhances the instability growth rate so that decreasing the density gradient from the critical surface to the core of fuel leads to instability for longer regions in k space. Also, investigations in the region close to the critical surface showed that for decreasing the beam number density n_b ≤ 0.01n₀, the instability occurs for while this can be different for higher values. Increasing the beam relativistic factor causes a decreasing peak of instability growth rate because of a reduction in beam current, whereas the initial thermal spread of plasma amplifies the filamentation instability.     

Determination of binary systems based on light elements by the ratio of the Compton and Rayleigh scattering intensities

A generalization of the Compton method for determining elements with a low atomic number Z from 1 (H) to 9 (F) by the ratio of the intensities of incoherent (Compton) and coherent (Rayleigh) scattering is proposed. The generalization takes into account not only the dependence of this ratio on the effective atomic number of the scatterer material but also the momentum transfer variable x = . The new method is based on the application of calibration function of obtained by measuring scattering spectra at two values of x₁= 0.831 Å⁻¹ and x₂= 1.297 Å⁻¹ with a WDXRF spectrometer. The elemental atomic numbers and their concentrations of binary compounds with unknown compositions are determined by the solution of a system of linear equations. Coefficients of the equations are calculated from the measured ratios for the test sample and the regularization solution for the corresponding calibration. The experiments have been carried out for standard samples of single-component, binary and triple stoichiometric compounds based on H, Li, Be, B, C, O and F. The identification of these elements was found to be possible in the absence of a relationship between the positions of scattering peaks and the composition of the sample, and a qualitative and quantitative analysis of the composition of the material was carried out as part of the solution of a single inverse problem.     

Dynamics of ion-acoustic rogue waves in electron-positron-ion magneto-plasmas

A more general and realistic four-component magnetized plasma medium consisting of opposite polarity ions and nonthermal distributed positrons and electrons is considered to investigate the stable/unstable frequency regimes of modulated ion-acoustic waves (IAWs) in the D-F regions of Earth's ionosphere. A (3 + 1) -dimensional nonlinear Schrödinger equation, which leads to the modulation instability (MI) of IAWs, is derived. The parametric regimes for the existence of the MI, first- and second-order rogue waves, and also their basic features (viz., amplitude, width, and speed) are found to be significantly modified by the effect of physical plasma parameters and external magnetic field. It is found that the nonlinearity of the different types of electronegative plasma system depends on the positive to negative ion mass ratio. It is also shown that the presence of nonthermal distributed electrons and positrons modifies the nature of the MI of the modulated IAWs. The implication of our results for the laboratory plasma [e.g., (Ar⁺, F⁻ ) electronegative plasma] and space plasma [e.g., (H⁺, H⁻ ), () electronegative plasma in D-F regions of Earth's ionosphere] are briefly discussed.     

Observation of 1D−1S forbidden optical emission of atomic oxygen in atmospheric-pressure N2/O2 plasma jet

We observed green optical emission from an atmospheric-pressure N₂/O₂ plasma jet. The green optical emission was composed of a line emission at λ = 557.71 ± 0.03 nm and a broadband component at 530 ≤ λ ≤ 560 nm . The line emission was assigned to the ¹D−¹S forbidden transition of atomic oxygen, whereas the broadband emission was due to the formation of O(¹S)N₂ excimer. We measured the absolute densities of O(¹S) and O(¹S)N₂ using a spectrograph with the absolute sensitivity calibration, and we discussed the kinetics in the green plasma jet on the basis of the absolute O(¹S) and O(¹S)N₂ densities. According to the rate coefficients and the transition probabilities reported in literature, the present experimental results are explained if the densities of and O(³P) are 9 × 10¹³ and 3 × 10¹³cm⁻³ , respectively.     

Rogue waves in multi‐pair plasma medium

The non‐linear propagation of ion acoustic (IA) waves, which is governed by the non‐linear Schrödinger equation, in multi‐pair plasmas (MPPs) containing adiabatic positive and negative ion fluids as well as non‐extensive (q‐distributed) electrons and positrons is theoretically investigated. It is observed that the MPP under consideration supports two types of modes, namely fast and slow IA modes, and the modulationally stable and unstable parametric regimes for the fast and slow IA modes are determined by the sign of the ratio of the dispersive coefficient to the non‐linear one. It is also found that the modulationally unstable regime generates highly energetic IA rogue waves (IARWs), and the amplitude as well as the width of the IARWs decreases with increase in the value of q (for both q > 0 and q < 0 limits). These new striking features of the IARWs are found to be applicable in the space (i.e., D‐region [], and F‐region [H⁺, H^?] of the Earth's ionosphere) and laboratory MPPs (i.e., fullerene [C⁺, C^?]).     

Structural properties of Li atom under quantum and classical plasmas: A composite variational framework

Structural properties of 1s²nl (²L) [n = 2–5, l = 0–4; where, n and l are the principal quantum number and orbital angular momentum quantum number, respectively] states of Li atom embedded in classical weakly coupled plasma (WCP) and dense quantum plasma (DQP) have been discussed. The Debye-Hckel potential or the screened-Coulomb potential (SCP) and exponential-cosine-screened Coulomb potential (ECSCP) have been used to mimic the WCP and DQP, respectively. Li atom has been treated as a composite system with a frozen core Li⁺ ion and a chemically active valence electron. The Rayleigh-Ritz variational method with Hylleraas-type basis set has been used to estimate the energy eigenvalue of 1s² (¹S) state of Li⁺ ion core and a pure exponential basis has been considered to compute the energy of nl (²L) states of the valence electron of Li atom. The influence of ECSCP and SCP on the radial probability distribution of the valence electron of the Li atom has also been studied.     

Interaction phenomena of ion‐acoustic quasi‐solitons and classical‐solitons in three component plasma

The space–time evolution of the cnoidal‐soliton solution, characteristics of the quasi‐soliton solution of Korteweg‐de‐Vries (KdV) equation, and the interaction phenomena of ion‐acoustic waves (IAWs) are investigated in a plasma system consisting of positive and negative ions with superthermal electrons. To do this, and (Ar⁺, F^?) plasmas are considered and two‐sided KdV equations (KdVEs) are derived applying the extended Poincaré‐Lighthill‐Kuo (ePLK) method. The effects on wave structures, potential profiles, and propagation characteristics with plasma parameters of the cnoidal‐wave, quasi‐soliton solution, and head‐on collision phenomena of IAWs are presented graphically. It was found that the superthermality parameter and the mass ratio of ions play a significant role in the head‐on collision between soliton and standing cnoidal wave and reveal that the collision is elastic and both waves change their phase shifts due to collision. Moreover, the superthermality parameters are also responsible for the production of compressive and rarefactive phase shifts in overtaking collision processes between right travelling classical soliton (CS) and cnoidal wave (CW) and reduced the amplitudes of IAWs. It was also found that a new wave is created with a high amplitude in the interacting region during collision depending on the plasma parameters.     

Monitoring active species in an atmospheric pressure dielectric‐barrier discharge: Observation of the Herman‐infrared system

An electronic and spectroscopic study of dielectric‐barrier discharge transition from the Townsend to the filamentary mode is presented. The discharge is generated under pure nitrogen flow at atmospheric pressure in a reactor with parallel configuration of cylindrical electrodes covered with Al₂O₃ dielectrics, applying a frequency of 4.85 kHz. The goal of the study was to find optimal conditions for observation of the Herman‐infrared (HIR ) transition (C” → A') in a perspective to develop and test a ro‐vibrational model for this quintet band. We have focused on finding the maximum emissivity of the HIR transition in the homogeneous discharge regime as it offers a more suitable source for calibrating the HIR model. Besides the capability of generating a spatially homogeneous type of radiation, our discharge design also allowed the observation of HIR without detectable interference from the first positive system of nitrogen which is not common for atmospheric pressure discharges. In the study, a time‐resolved observation of the NO _γ system, the second positive and the HIR nitrogen systems were performed and their emissivities analysed as a function of the discharge period and power. The optimum for the observation of the HIR system was found at 2.94 W (power density of 6 W/cm³), corresponding to the Townsend discharge just before its transition to the filamentary one.     

Phase Diagrams of Periodically Driven Spin–Orbit Coupled 87Rb and 23Na Bose–Einstein Condensates

The phase boundaries of periodically driven spin–orbit coupled BECs with effective two‐body interactions are analytically calculated by using variational method. The phase diagrams of periodically driven ${}^{87}\mathrm{Rb}$ and ${}^{23}\mathrm{Na}$ systems present distinguished features from undriven systems, respectively. For the ${}^{87}\mathrm{Rb}$ BECs, the critical density $n_c$ (density at quantum tricritical point) will be dramatically reduced in some parameter regions, and the prospect of observing this intriguing quantum tricritical point is greatly enlarged. Moreover, a series of quantum tricritical points emerge quasi‐periodically when increasing the Raman coupling strength with fixed ${}^{87}\mathrm{Rb}$ density. In the ${}^{23}\mathrm{Na}$ BECs, two hyperfine states of ${}^{23}\mathrm{Na}$ atoms can be miscible within the suitable regions of driving parameter space. As a result, ${}^{23}\mathrm{Na}$ systems will stay in the stripe phase with small Raman frequency at typical density, which expands the region of stripe phase in the phase diagram. In addition, an absence of quantum tricritical point in such ${}^{23}\mathrm{Na}$ system is observed, which is very unlike ${}^{87}\mathrm{Rb}$ systems.     

Three‐dimensional ultra‐broadband integrated tapered mode multiplexers

The demonstration of a three‐dimensional tapered mode‐selective coupler in a photonic chip is reported. This waveguide‐based, ultra‐broadband mode multiplexer was fabricated using the femtosecond laser direct‐write technique in a boro‐aluminosilicate glass chip. A three‐core coupler has been shown to enable the multiplexing of the LP₀₁, LP and LP spatial modes of a multimode waveguide, across an extremely wide bandwidth exceeding 400 nm, with low loss, high mode extinction ratios and negligible mode crosstalk. Linear cascades of such devices on a single photonic chip have the potential to become a definitive technology in the realization of broadband mode‐division multiplexing for increasing optical fiber capacity.     

Atom‐Interferometry Measurement of the Fine Structure Constant

Using an atom interferometer to measure the quotient of the reduced Planck's constant and the mass of a cesium‐133 atom $?/m_{\mathrm{Cs}}$, the most accurate measurement of the fine structure constant $\alpha =1/137.035999046(27)$ is recorded, at an accuracy of 0.20 parts per billion (ppb). Using multiphoton interactions (Bragg diffraction and Bloch oscillations), the largest phase (12 million radians) of any Ramsey–Bordé interferometer and controlled systematic effects at a level of 0.12 ppb are demonstrated. Comparing the Penning trap measurements with the Standard Model prediction of the electron gyromagnetic anomaly $a_e$ based on the α measurement, a 2.5 $\sigma$ tension is observed, rejecting dark photons as the reason for the unexplained part of the muon's gyromagnetic moment discrepancy at a 99% confidence level according to frequentist statistics. Implications for dark‐sector candidates (e.g., scalar and pseudoscalar bosons, vector bosons, and axial‐vector bosons) may be a sign of physics beyond the Standard Model. A future upgrade of the cesium fountain atom interferometer is also proposed to increase the accuracy of $?/m_{\mathrm{Cs}}$ by 1 to 2 orders of magnitude, which would help resolve the tension.