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Magnetic flux ropes are pivotal structures and building blocks in astrophysical and laboratory plasmas, and various equilibrium models have thus been studied in the past. However, flux ropes in general form at non-equilibrium, and their pathway from formation to relaxation is a crucial process that determines their eventual properties. Here we show that any localized current parallel to a background magnetic field will evolve into a flux rope via non-equilibrium processes. The detailed kinetic dynamics are exhaustively explained through single-particle and Vlasov analyses and verified through particle-in-cell simulations. This process is consistent with many proposed mechanisms of flux rope generation such as magnetic reconnection. A spacecraft observation of an example flux rope is also presented; by invoking the non-equilibrium process, its structure and properties can be explicated down to all six components of the temperature tensor. Flux ropes are fundamental structures that govern much of the dynamics in astrophysical and space plasmas. The authors show how out-of-equilibrium processes can form small-scale flux ropes and compare them to simulations and spacecraft observations. [ABSTRACT FROM AUTHOR]

The dynamics of Langmuir modes, waves (LW), and shear Langmuir vortices (SLV) are studied in kinematically complex astrophysical plasma flows. It is found that they exhibit several peculiar, velocity shear-induced, asymptotically persistent phenomena, including efficient energy exchange with the background flow and various kinds of instabilities, leading to their exponential growth and echoing solutions with persistent wave-vortex-wave conversions. There is a remarkable similarity between these phenomena and those happening with compressible acoustic modes. The relevance and possible importance of these phenomena for different types of astrophysical plasma flow patterns with kinematic complexity are discussed. In particular, we argue that these physical processes may account for the persistent appearance of plasma oscillations in the heliosphere and interstellar plasma flows. In particular, we believe that the kinematically complex motion of plasma may naturally lead to the asymptotically persistent appearance of Langmuir modes that are born, grown, fed, sustained and maintained by these flows. [ABSTRACT FROM AUTHOR]

The hydrodynamic instability of a magnetized, self-gravitating rotating anisotropic plasma is analyzed in the collisionless approximation and considering the heat flux vector based on the modified Chu–Goldberger–Low equations. A dispersion relation is obtained, on the basis of which simplified cases of propagation of low-amplitude disturbance waves and the derivation of modified criteria for hydrodynamic instability are discussed. Using the obtained dispersion relation, three simple cases are treated when the disturbance wave propagates across, along, and obliquely to the magnetic field vector. It is shown that the anisotropy of pressure and heat flow not only changes the classical criterion of the Jeans instability, but also leads to the appearance of new wave modes and causes the appearance of new unstable domains. It has been found that the presence of uniform rotation of the plasma reduces the critical wave number and has a stabilizing effect on the criterion of gravitational instability when the disturbance wave propagates transversely, without having an effect in the case of longitudinal propagation. These results are important for developing evolutionary magnetohydrodynamic models of astrophysical collisionless plasma. [ABSTRACT FROM AUTHOR]

Incompressible vortex flow are observed in a large variety of astrophysical plasmas such as the convection zone and the atmosphere of stars, in astrophysical jets in stellar winds and in planetary magnetospheres. More specifically, magnetohydrodynamic (MHD) simulations have shown that two large scale interlaced Alfvénic vortices structure the magnetic tail of Uranus at solstice time. Assuming identical vortices, we compute the general linear structure of the flow near their centers within the frame of ideal MHD. We then use the analytic results to interpret and qualify the vortices observed in a 3D MHD simulation of a fast rotating Uranus-type planet. [ABSTRACT FROM AUTHOR]

A neural network is employed to address a non-binary classification problem of plasma instabilities in astrophysical jets, calculated with the Legolas code. The trained models exhibit reliable performance in the identification of the two instability types supported by these jets. We also discuss the generation of artificial data and refinement of predictions in general eigenfunction classification problems. [ABSTRACT FROM AUTHOR]

Astrophysical jets play crucial roles in star formation and transporting angular momentum away from accretion discs, however, their collimation mechanism is still a subject of much debate due to the limitations of astronomical observational techniques and facilities. Here, a quasi-static toroidal magnetic field is generated through the interaction between lasers and a four-post nickel target, and our all-optical laboratory experiments reveal that a wide-angle plasma plume can be collimated in the presence of toroidal magnetic fields. Besides the confinement effects, the experiments show the jet can also be accelerated by the enhanced thermal pressure due to the toroidal magnetic fields compressing the flow. These findings are verified by radiation magneto-hydrodynamic simulations. The experimental results suggest certain astrophysical narrow plasma flows may be produced by the confinement of wide-angle winds through toroidal fields. Astrophysical jets are pivotal in the process of star formation, yet the mechanism responsible for their collimation remains a topic of intense debate, largely due to the constraints imposed by astronomical observational techniques and facilities. In this study, the authors demonstrate that a wide-angle plasma plume can undergo collimation and acceleration when subjected to toroidal magnetic fields, as evidenced by all-optical laboratory experiments. [ABSTRACT FROM AUTHOR]

The dynamic evolution of a coronal mass ejection (CME) in the interplanetary space generates a highly turbulent, compressed, and heated shock-sheath. This region provides an exceptional setting for investigating the intricate fluctuations occurring at small scales and offers a valuable opportunity to unravel the underlying physical processes responsible for turbulence dissipation and plasma heating. Understanding the role of turbulence in controlling the energy transport process in a magnetized plasma, within space and astrophysics, remains an enticing challenge of the twenty-first century. In this article, we study sheath regions observed by the Wind spacecraft from 1995 to 2021. We find 80 sheath events out of the studied 384 events that show a significant Alfvénic nature (≈21%). These fluctuations are interpreted as Alfvénic wave packets propagating either parallel or antiparallel to the background magnetic field, quantified by the normalized crosshelicity ( σ C ). We find 47 sheath events with outward-propagating Alfvénic fluctuations and 33 events with inward Alfvénic characteristics. The Alfvénic sheaths had a mean value of σ C = 0.46 ± 0.03 and − 0.43 ± 0.02 for outward- and inward-directed Alfvénic sheaths, respectively. Furthermore, we compare the average interplanetary parameter values of both the Alfvénic sheaths and the ambient solar wind. The study has strong implications in the domain of interplanetary space plasmas, its interaction with planetary plasmas, and astrophysical plasmas. [ABSTRACT FROM AUTHOR]

A quantum hydrodynamic model formalism is semi-analytically offered to explore the propagatory and dispersive nature of heavy nucleus-acoustic waves (NAWs) in the completely degenerate (CD) oxygen–neon (ONe) and CO white dwarf (WD) cores. It includes their surrounding nearly degenerate (ND) transition regions. It has classical light nuclear species (LNS), heavy nuclear species (HNS) and quantum electrons in a spherically symmetric geometry. The electronic equation of state here considers the temperature degeneracy, interaction of electrons with the surrounding electrons and nuclei, exchange interaction and correlation interaction effects collectively. A methodical application of normal spherical mode analysis yields a generalised linear sextic dispersion relation of a unique mathematical type. A numerical illustrative platform shows the NAW propagatory and dispersive behaviours of current interest elaborately. It is interesting to find that the NAW is composed of multiple-frequency acoustic wave-spectral components. It is seen that both the CD core of the ONe WD and the ND region around the core are more sensitive to the temperature than the CO WD case. We finally indicate the tentative applicability of the investigated results with a special mention of compact astronomic situations. [ABSTRACT FROM AUTHOR]

The problem of self-gravitational instability of an astrophysical rotating plasma in a strong magnetic field with an anisotropic pressure tensor is studied on the basis of the Chew–Goldberger–Low (CGL) quasi-hydrodynamic equations modified by generalized polytropic laws. Using the general form of a dispersion relation obtained by the normal-mode perturbation method, a discussion is provided of the propagation of small-amplitude perturbation waves in an infinite homogeneous plasma medium for transverse, longitudinal, and oblique directions with respect to the magnetic field vector. It is shown that different polytropic indices and anisotropic pressures not only change the classical Jeans instability condition but also cause the appearance of new unstable regions. Modified Jeans instability criteria are obtained for isotropic MHD equations and anisotropic CGL equations owing to the influence of the polytropic indices on gravitational and firehose instabilities for astrophysical plasma. It is shown that in the case of a longitudinal mode of perturbation wave propagation, the Jeans instability criterion does not depend on uniform rotation. In the case of the transverse propagation regime, the presence of rotation reduces the critical wave number and exerts a stabilizing effect on the growth rate of the unstable regime. [ABSTRACT FROM AUTHOR]

The cross sections and rate coefficients for dielectronic recombination (DR) and electron-impact excitation processes of helium-like isoelectronic sequence are systematically investigated using the relativistic distorted-wave approach. The detailed DR resonance energies, resonance strengths, cross sections, and plasma rate coefficients are presented for the twelve abundant astrophysical elements including C4+, O6+, Ne8+, Mg10+, Si12+, S14+, Ar16+, Ca18+, Ti20+, Cr22+, Fe24+, and Ni26+ ions, encompassing the DR processes due to K-shell 1s → 2l (∆n = 1), 1s → 3l (∆n = 2), and 1s → 4l (∆n = 3) excitations. The theoretical results are compared with the existing experimental measurements, excellent agreements are obtained. With the same approach, the direct and resonant electron-impact excitation cross sections associated with 1s → nl core excitations are also calculated for the helium-like C4+ to Ni26+ ions mentioned above. It is found that the resonant contribution is significant. The present results are suitable for modeling of astrophysical and fusion plasma. [ABSTRACT FROM AUTHOR]

A method for the numerical solution of a nonlinear equation describing the diffusion transfer of radiation energy has been developed. According to the method, the second time derivative with a small parameter is introduced into the parabolic equation and an explicit difference scheme is applied. The explicit approximation of the initial equation makes it possible to implement on its basis an algorithm that is effectively adapted to the architecture of high-performance computing systems. In comparison with the original scheme, the new one allows for a larger time integration step and a sufficiently high resolution of the solution structure, providing the second order of accuracy. A heuristic algorithm for choosing the parameters of the three-level difference scheme is proposed. A promising field of application of the method can be problems in plasma physics and astrophysics. [ABSTRACT FROM AUTHOR]

Cylindrical three dimensional dust–ion–acoustic (DIA) solitary waves (SWs) in a complex plasma medium consisting of nonthermal electrons, adiabatically warm ions, and immobile positively charged dust (PCD) species are studied. The reductive perturbation method, which is valid for small but finite amplitude waves, is used to derive the (3 + 1)-dimensional cylindrical Kadomstev–Petviashvili (cKP) equation (also known as cylindrical Korteweg–de Vries equation). The parametric regimes for the existence of solitary structures are shown. The plasma model under consideration supports both the positive and negative DIA SWs. Moreover, the effects of the physical plasma parameters (the ratio of the dust to ion number density, the nonthermal parameter, etc.) on the basic features (amplitude, width, and speed, etc.) of DIA SWs are discussed. Depending on the plasma parameters (the PCD and ion number density ratio, nonthermality of electron, and temperature ratio of ion and electron) the solitary pulses change their polarity. The present investigation may be helpful to the understanding of the properties of the DIA SWs in different astrophysical plasma environments as well as in laboratory devices. [ABSTRACT FROM AUTHOR]

Multiple statistical and event studies based on in situ observations have shown that the solar wind contains mesoscale (∼ 100 – 10,000 Mm) periodic structures in the proton number density. Remote observations of such structures and event studies of concurrent variations in composition have demonstrated that they can form in the solar atmosphere and be preserved while advecting outwards through the heliosphere. Viall, Kepko, and Spence (J. Geophys. Res. (Space Phys.)113, A07101, 2008; J. Geophys. Res. (Space Phys.)114, A01201, 2009) and Kepko, Viall, and Wolfinger (J. Geophys. Res. (Space Phys.)125(8), e28037, 2020) have reported that periodic proton density structures preferentially occur at specific radial length scales and have published their distributions from Wind measurements near L1. Here, we conduct a statistical study of 14 years (1998 – 2011) of 12-minute composition data measured by the Solar Wind Ion Composition Spectrometer instrument aboard the Advanced Composition Explorer spacecraft. We found that the elemental and ionic composition also contain statistically significant mesoscale periodic structures and, for the first time, present occurrence distributions for elemental abundance ratios with low, intermediate, and high first ionization potentials as well as for key solar wind charge states. These distributions set important constraints on solar wind formation in general and the formation of periodic mesoscale solar wind structures specifically, as the elemental and ionic composition are known to be determined at the Sun and to not evolve during advection. [ABSTRACT FROM AUTHOR]

Photoionization cross-section results for the ground state 2p63s (2S1/2) along with the lowest four excited states 2p63p (2Po1/2, 3/2) and 2p63d (2D5/2, 3/2) of Na-like Si IV are reported by employing the close-coupling Breit–Pauli R-matrix (BPRM) method. The target state wavefunctions of Si V ion have been obtained using the configuration interaction method (CIV3) in the LSJ-coupling scheme. Relativistic effects and all key physical effects such as short-range correlations, exchange and channel coupling are considered in the computations. Our evaluated target state energies of the Si V core ion show close agreement with the NIST database. Quigley and Berrington (QB) technique is applied to determine resonance positions (Er) and autoionization line widths (Γ) with quantum defects caused by the removal of the 2p electron from 2s22p63s2S1/2, the ground state of Si IV. To the best of our understanding, the study presented here details thorough relativistic photoionization calculations for this system for the first time. We hope that our results will be valuable to astrophysical and laboratory plasma modeling and diagnosis. Photoionization cross-sections (σ) for the ground state 2p63s (2S1/2) of Si IV. [ABSTRACT FROM AUTHOR]

A brief review of recent studies on dusty plasma above the lunar surface at the Space Research Institute, Russian Academy of Sciences is presented. The research is related to the future Luna-25 and Luna-27 missions, which will study the properties of dust and dusty plasma above the lunar surface. The problems of formation of dusty plasma over the illuminated part of the Moon, in the region of the lunar terminator, the influence of magnetic fields on the circumlunar dusty plasma, and the influence on the results of measurements of the spacecraft landing module are considered. Unsolved problems concerning the study of the near-lunar dusty plasma are formulated. [ABSTRACT FROM AUTHOR]

In this paper, a computational-theoretical analysis of the possibilities of using the method of phase-contrast X-ray radiography for the study of low-contrast turbulent flows in laser plasma in experiments with astrophysical similarity is carried out. By modeling the passage of hard coherent X-ray radiation through test objects, we studied the parameters of a laboratory experiment that affect the contrast and resolution of the resulting phase-contrast images. The limiting scale for measuring the frequency-spatial spectrum of image power was determined, on which the manifestation of artifacts from the superimposition of diffraction effects from neighboring objects is not yet critical for the correct interpretation of the results. Optimal object-detector distances are found that provide resolution of the power spectrum of a turbulent flow on micron scales. These results are relevant for future laboratory experiments on the development of instabilities in plasma with astrophysical similarity up to the stage of energy dissipation. [ABSTRACT FROM AUTHOR]

A technique is described for achieving high accuracy (relative error up to ≈0.001%) for measuring the absolute wavelengths of the spectral lines of multiply charged ions with an average (Z = 17–25) by the nuclear charge, the spectra of which can be used for plasma diagnostics in laboratory astrophysics experiments. It is based on irradiation with subnanosecond laser pulses with an intensity of 1015–1016 W/cm2 targets with a multicomponent chemical composition, including atoms with both medium and low Z. The presence of the latter ensures the presence in the emission spectrum of the resulting laser plasma of lines of hydrogen-like ions used as references. An atomic-kinetic code was created, and the intensities of possible reference and investigated spectral lines were calculated. The principles of selecting the target material, the features of the implementation of the technique on the example of a focusing spectrometer with spatial resolution based on spherically curved mica and α-quartz crystals are considered, and specific parameters of spectrometer circuits and types of targets for precision measurement of the wavelengths of spectral lines of helium- and lithium-like ions with nuclear charges are given. Z = 13–25. The results obtained in this work will be used in the planning of fundamental X-ray spectral studies at the ELF laser facility being developed at MEPhI. [ABSTRACT FROM AUTHOR]

The primary scientific goal of ICARUS (Investigation of Coronal AcceleRation and heating of solar wind Up to the Sun), a mother-daughter satellite mission, proposed in response to the ESA "Voyage 2050" Call, will be to determine how the magnetic field and plasma dynamics in the outer solar atmosphere give rise to the corona, the solar wind, and the entire heliosphere. Reaching this goal will be a Rosetta Stone step, with results that are broadly applicable within the fields of space plasma physics and astrophysics. Within ESA's Cosmic Vision roadmap, these science goals address Theme 2: "How does the Solar System work?" by investigating basic processes occurring "From the Sun to the edge of the Solar System". ICARUS will not only advance our understanding of the plasma environment around our Sun, but also of the numerous magnetically active stars with hot plasma coronae. ICARUS I will perform the first direct in situ measurements of electromagnetic fields, particle acceleration, wave activity, energy distribution, and flows directly in the regions in which the solar wind emerges from the coronal plasma. ICARUS I will have a perihelion altitude of 1 solar radius and will cross the region where the major energy deposition occurs. The polar orbit of ICARUS I will enable crossing the regions where both the fast and slow winds are generated. It will probe the local characteristics of the plasma and provide unique information about the physical processes involved in the creation of the solar wind. ICARUS II will observe this region using remote-sensing instruments, providing simultaneous, contextual information about regions crossed by ICARUS I and the solar atmosphere below as observed by solar telescopes. It will thus provide bridges for understanding the magnetic links between the heliosphere and the solar atmosphere. Such information is crucial to our understanding of the plasma physics and electrodynamics of the solar atmosphere. ICARUS II will also play a very important relay role, enabling the radio-link with ICARUS I. It will receive, collect, and store information transmitted from ICARUS I during its closest approach to the Sun. It will also perform preliminary data processing before transmitting it to Earth. Performing such unique in situ observations in the area where presumably hazardous solar energetic particles are energized, ICARUS will provide fundamental advances in our capabilities to monitor and forecast the space radiation environment. Therefore, the results from the ICARUS mission will be extremely crucial for future space explorations, especially for long-term crewed space missions. [ABSTRACT FROM AUTHOR]

The smallest characteristic scales, at which electron dynamics determines the plasma behaviour, are the next frontier in space and astrophysical plasma research. The analysis of astrophysical processes at these scales lies at the heart of the research theme of electron-astrophysics. Electron scales are the ultimate bottleneck for dissipation of plasma turbulence, which is a fundamental process not understood in the electron-kinetic regime. In addition, plasma electrons often play an important role for the spatial transfer of thermal energy due to the high heat flux associated with their velocity distribution. The regulation of this electron heat flux is likewise not understood. By focussing on these and other fundamental electron processes, the research theme of electron-astrophysics links outstanding science questions of great importance to the fields of space physics, astrophysics, and laboratory plasma physics. In this White Paper, submitted to ESA in response to the Voyage 2050 call, we review a selection of these outstanding questions, discuss their importance, and present a roadmap for answering them through novel space-mission concepts. [ABSTRACT FROM AUTHOR]

Notably, solitary waves that emerge from the nonlinear properties of plasmas are the main focus of many current studies of localized disturbances in both laboratory and astrophysical plasmas. By applying the reductive perturbation method, we derive the nonlinear homogeneous quantum Zakharov–Kuznetsov (QZK) equation in three-component collisionless quantum plasma consisting of electrons, positrons, and ions in the presence of an external static magnetic field. The solitary wave structures are dependent on the Bohm potential, magnetic field, obliqueness, species Fermi temperatures, and densities. The soliton's electric field and energy are also derived and investigated, which were found to be reduced as the magnetic field increases. The instability growth rate is also derived by using the small-k perturbation expansion method. The previous parameters affect the instability growth rate as well. A comparison of the energy and instability growth rate behaviour against system parameters is carried out. Large energy and large instability growth rate occur at large values of positron density or lower values of ion density. At zero or small rotation angle, both decrease as the magnetic field increases. Our findings could help us understand the dynamics of magnetic white dwarfs, pulsar magnetospheres, semiconductor plasma, and high-intensity laser-solid matter interaction experiments where e-p-i plasma exists. [ABSTRACT FROM AUTHOR]

Identifying how energy transfer proceeds from macroscales down to microscales in collisionless plasmas is at the forefront of astrophysics and space physics. It provides information on the evolution of involved plasma systems and the generation of high-energy particles in the universe. Here we report two cross-scale energy-transfer events observed by NASA's Magnetospheric Multiscale spacecraft in Earth's magnetosphere. In these events, hot ions simultaneously undergo interactions with macroscale (~ 10 5 km) ultra-low-frequency waves and microscale (~ 10 3 km) electromagnetic-ion-cyclotron (EMIC) waves. The cross-scale interactions cause energy to directly transfer from macroscales to microscales, and finally dissipate at microscales via EMIC-wave-induced ion energization. The direct measurements of the energy transfer rate in the second event confirm the efficiency of this cross-scale transfer process, whose timescale is estimated to be roughly ten EMIC-wave periods about (1 min). Therefore, these observations experimentally demonstrate that simultaneous macroscale and microscale wave-ion interactions provide an efficient mechanism for cross-scale energy transfer and plasma energization in astrophysical and space plasmas. Cross-scale energy transfers in collisionless plasmas help understanding involved mechanisms. Here, the authors show simultaneous macro- and micro-scale wave-ion interactions provide an efficient mechanism for cross-scale energy transfer and plasma energization in astrophysical and space plasmas. [ABSTRACT FROM AUTHOR]

In this paper, gravitational field within a spherically symmetric star overwhelmed through dynamical de Sitter space is obtained. Indeed, closer situation to reality manifesting effects of the dark energy on the properties of astronomical compact objects is considered. It seems the cosmological constant does not play an outstanding role in astronomical scales, however I showed that mass of a typcal star does vary with time in a way that depends upon the polytropic index of the star. In addition, some of astrophysical limits such as the Buchdahl limit may depend on time. The Oppenheimer–Volkoff mass limit also obeys this rule and although the cosmological constant is too small, the value of the Oppenheimer–Volkoff limit shall be halved after 560 million years under some special conditions. [ABSTRACT FROM AUTHOR]

The relativistic energy corrections for the spherically confined hydrogen with penetrable wall are calculated for various orbitals as a function of pressure and confinement radius. The relativistic corrections at high pressures of the order of 108–109 atm are found to be more than thousand times higher than the corresponding values for the free atom. For calculating the energy eigenvalues, the efficient Numerov method is adopted. The partition function and other thermodynamic properties are also calculated for temperature range 104 K to 1010 K at low (0–10 atm) and high pressures (104–108 atm). We investigate the behaviour of partition function and thermodynamic parameters graphically with pressure and temperature. We discuss the effect of high temperature and reduction of confinement radius on these parameters. The present study will be useful in Industrial applications like development of hydrogen fuel and in various physics branches such as in fusion and astrophysical plasma, condensed matter, statistical mechanics and also in other research areas where we encounter atoms which are subjected to high pressures. [ABSTRACT FROM AUTHOR]

The formation and main features of the fully nonlinear structure in a six-component dusty plasma system have been investigated using Sagdeev potential approach. By means of pseudo-potential technique, the fluid equations describing the plasma system were diminished into a single nonlinear differential equation, called energy equation modified by presenting the parameters of addition plasma components. For certain values of the configurationally plasma parameters, our findings show that in addition to the solitary waves, double-layers and super-solitons exist and propagate in this plasma system. The main features of these waves have been studied by investigating the associated phase-portrait trajectories and potential curves as well and are found to be very sensitive to the variation of these parameters. The obtained results are mainly relevant to the cometary plasma and it may also provide better and helpful understanding of the nonlinear nature of space, astrophysical and cometary plasmas. The formation and main features of the fully nonlinear structure in a six-component dusty plasma system have been investigated using Sagdeev potential approach. By means of pseudo-potential technique, the fluid equations describing the plasma system were diminished into a single nonlinear differential equation, called energy equation modified by presenting the parameters of addition plasma components. For certain values of the configurationally plasma parameters, our findings show that in addition to the solitary waves, double-layers and super-solitons exist and propagate in this plasma system. The main features of these waves have been studied by investigating the associated phase-portrait trajectories and potential curves as well and are found to be very sensitive to the variation of these parameters. [ABSTRACT FROM AUTHOR]

Coulomb collisions provide plasma resistivity and diffusion but in many low-density astrophysical plasmas such collisions between particles are extremely rare. Scattering of particles by electromagnetic waves can lower the plasma conductivity. Such anomalous resistivity due to wave-particle interactions could be crucial to many processes, including magnetic reconnection. It has been suggested that waves provide both diffusion and resistivity, which can support the reconnection electric field, but this requires direct observation to confirm. Here, we directly quantify anomalous resistivity, viscosity, and cross-field electron diffusion associated with lower hybrid waves using measurements from the four Magnetospheric Multiscale (MMS) spacecraft. We show that anomalous resistivity is approximately balanced by anomalous viscosity, and thus the waves do not contribute to the reconnection electric field. However, the waves do produce an anomalous electron drift and diffusion across the current layer associated with magnetic reconnection. This leads to relaxation of density gradients at timescales of order the ion cyclotron period, and hence modifies the reconnection process. It is suggested that waves can provide both diffusion and resistivity that can potentially support the reconnection electric field in low-density astrophysical plasmas. Here, the authors show, using direct spacecraft measurements, that the waves contribute to anomalous diffusion but do not contribute to the reconnection electric field. [ABSTRACT FROM AUTHOR]

The rate of magnetic reconnection is of the utmost importance in a variety of processes because it controls, for example, the rate energy is released in solar flares, the speed of the Dungey convection cycle in Earth's magnetosphere, and the energy release rate in harmful geomagnetic substorms. It is known from numerical simulations and satellite observations that the rate is approximately 0.1 in normalized units, but despite years of effort, a full theoretical prediction has not been obtained. Here, we present a first-principles theory for the reconnection rate in non-relativistic electron-ion collisionless plasmas, and show that the same prediction explains why Sweet-Parker reconnection is considerably slower. The key consideration of this analysis is the pressure at the reconnection site (i.e., the x-line). We show that the Hall electromagnetic fields in antiparallel reconnection cause an energy void, equivalently a pressure depletion, at the x-line, so the reconnection exhaust opens out, enabling the fast rate of 0.1. If the energy can reach the x-line to replenish the pressure, the exhaust does not open out. In addition to heliospheric applications, these results are expected to impact reconnection studies in planetary magnetospheres, magnetically confined fusion devices, and astrophysical plasmas. Different models exist to characterize magnetic reconnection, a process that converts magnetic energy into plasma thermal and kinetic energy, but a quantitative theoretical predictive model of how rapidly it proceeds has been lacking. Here, a self-consistent theory of the reconnection rate derived from first principles, and confirmed with numerical simulations, provides a new understanding of reconnection in solar flares and geomagnetic substorms. [ABSTRACT FROM AUTHOR]

Various types of electric fields contained in the laboratory and astrophysical plasma cause a Stark broadening of spectral lines in plasma. Therefore, a large number of spectroscopic diagnostics of laboratory and astrophysical plasma are based on experimental and theoretical studies of Stark broadening of spectral lines in plasma. The topic of the present investigation is the Stark broadening caused by free electrons in plasma and its dependence on certain atomic parameters using a new method based on the machine learning (ML) approach. Analysis of empirical data on atomic parameters was done by ML algorithms with more success that it was previously done by classical methods of data analysis. The correlation parameter obtained by artificial intelligence (AI) is slightly better than the one obtained by classical methods, but the scope of application is much wider. AI conclusions are applicable to any physical system while conclusions made by classical analysis are applicable only to a small portion of these systems. ML algorithms successfully identified quantum nature by analyzing atomic parameters. The biggest issue of classical analysis, which is infinite spectral line broadening for high ionization stages, was resolved by AI with a saturation tendency. [ABSTRACT FROM AUTHOR]

We have performed atomic structure calculations of Be-like C, N, O and Ne ions using systematically enlarged multiconfiguration Dirac–Fock wavefunctions. Present calculations are fully relativistic in nature with Breit interaction and quantum electrodynamic (QED) corrections such as vacuum polarization and self-energy correction to obtain low lying energy levels, transition probability, oscillator strength and line strength. Selective radiative data for electric dipole, magnetic quadrupole and fine structure data in terms of hyperfine coupling constants and isotopic shift parameters are also reported. Comparisons are made with the existing available results and a good agreement has been found. Additionally, an attempt is made to study the impact of relativistic and QED corrections on forbidden and allowed transitions. We have also used the above-computed transition probabilities here to provide the line intensity ratio and plasma parameters of optically thin and moderately dense plasma. We believe that the detailed atomic data computed here will be further helpful in line identification and plasma modeling studies for laboratory plasma devices like ITER and astrophysical plasma work related to elemental abundance calculations from solar corona to active galactic nuclei. [ABSTRACT FROM AUTHOR]

Shocks are one of nature's most powerful particle accelerators and have been connected to relativistic electron acceleration and cosmic rays. Upstream shock observations include wave generation, wave-particle interactions and magnetic compressive structures, while at the shock and downstream, particle acceleration, magnetic reconnection and plasma jets can be observed. Here, using Magnetospheric Multiscale (MMS) we show in-situ evidence of high-speed downstream flows (jets) generated at the Earth's bow shock as a direct consequence of shock reformation. Jets are observed downstream due to a combined effect of upstream plasma wave evolution and an ongoing reformation cycle of the bow shock. This generation process can also be applicable to planetary and astrophysical plasmas where collisionless shocks are commonly found. Several mechanisms exist for formation of jets observed in Earth's magnetosheath. Here, the authors show evidence of high-speed downstream flows generated at the Earth's bow shock as a direct consequence of shock reformation, which is different than the proposed mechanisms. [ABSTRACT FROM AUTHOR]

Shocks are one of nature's most powerful particle accelerators and have been connected to relativistic electron acceleration and cosmic rays. Upstream shock observations include wave generation, wave-particle interactions and magnetic compressive structures, while at the shock and downstream, particle acceleration, magnetic reconnection and plasma jets can be observed. Here, using Magnetospheric Multiscale (MMS) we show in-situ evidence of high-speed downstream flows (jets) generated at the Earth's bow shock as a direct consequence of shock reformation. Jets are observed downstream due to a combined effect of upstream plasma wave evolution and an ongoing reformation cycle of the bow shock. This generation process can also be applicable to planetary and astrophysical plasmas where collisionless shocks are commonly found. Several mechanisms exist for formation of jets observed in Earth's magnetosheath. Here, the authors show evidence of high-speed downstream flows generated at the Earth's bow shock as a direct consequence of shock reformation, which is different than the proposed mechanisms. [ABSTRACT FROM AUTHOR]

We have shown the simultaneous generation of macroscale fast flows and strong magnetic fields in the two-temperature relativistic electron–ion plasmas of astrophysical objects due to the Unified Reverse Dynamo/Dynamo mechanism. The resulting dynamical magnetic-field amplification and/or flow acceleration is directly proportional to the initial turbulent kinetic/magnetic (magnetic) energy; the process is very sensitive to the relativistically hot electron–ion fraction temperature and the magnetofluid coupling. It is shown that for realistic physical parameters of White Dwarfs accreting hot astrophysical flow /Binary systems there always exists such a real solution of the dispersion relation for which the formation of dispersive strong super-Alfvénic macroscale flow/outflow with Alfvén–Mach number > 10 6 and/or generation of superstrong magnetic fields is guaranteed. [ABSTRACT FROM AUTHOR]

In this work, we investigated the propagation of ion acoustic shock waves IAShWs in an ultra-relativistic degenerate plasma composed of positrons, electrons and ions in the presence of an external magnetic field. We have derived the KdV-B equation using the reductive perturbation technique and analyzed its solution graphically. The impact of the different plasma parameters (positron concentration, kinematic viscosity, strength of the magnetic field, obliqueness, relativistic effects, etc.) on the basic features of the IAShWs have been rigorously examined. It has been found that shock waves co-propagate with solitons in the ultra-relativistic case, whereas in the non-relativistic case, monotonic shock waves are in favor. Moreover, to highlight the relevance of our research in astrophysical environments, we have applied the plasma model to the surface of magnetic neutron stars where the plasma components are ultra-relativistic and degenerate. We have discerned that the parameters taken into account have significant effects on the nature and amplitude of the ion acoustic structures. [ABSTRACT FROM AUTHOR]

The numerical simulation of hot and low density plasmas using the Vlasov–Poisson model is necessary for many practical applications such as the characterization of laboratory and astrophysical plasmas. The numerical treatment of the Vlasov equation is addressed using Eulerian methods when high precision and low noise are required. Among these methods, we highlight those based on finite-volumes without splitting, which have shown to be a good option for capturing small structures in phase space with low dissipation while preserving positivity. The problem is that kinetic simulations usually require the discretization of 3–6-dimensional phase-spaces which results in a huge number of ordinary differential equations (ODEs). This stands out the importance of using efficient schemes for the time integration. In this article, linear multistep methods are implemented for the time stepping of the resulting equations, and compared against traditional Runge–Kutta ones. Schemes with built-in error estimation are also implemented in an attempt to perform adaptive stepsize control. Their accuracy, stability and computational cost are compared through the simulation of classical benchmark problems for the two-dimensional Vlasov–Poisson system. [ABSTRACT FROM AUTHOR]

Surface waves process the turbulent disturbances which drive dynamics in many space, astrophysical and laboratory plasma systems, with the outer boundary of Earth's magnetosphere, the magnetopause, providing an accessible environment to study them. Like waves on water, magnetopause surface waves are thought to travel in the direction of the driving solar wind, hence a paradigm in global magnetospheric dynamics of tailward propagation has been well-established. Here we show through multi-spacecraft observations, global simulations, and analytic theory that the lowest-frequency impulsively-excited magnetopause surface waves, with standing structure along the terrestrial magnetic field, propagate against the flow outside the boundary. Across a wide local time range (09–15h) the waves' Poynting flux exactly balances the flow's advective effect, leading to no net energy flux and thus stationary structure across the field also. Further down the equatorial flanks, however, advection dominates hence the waves travel downtail, seeding fluctuations at the resonant frequency which subsequently grow in amplitude via the Kelvin-Helmholtz instability and couple to magnetospheric body waves. This global response, contrary to the accepted paradigm, has implications on radiation belt, ionospheric, and auroral dynamics and potential applications to other dynamical systems. The magnetopause surface waves (SW) that drive global plasma dynamics are thought, like waves on water, to travel with the driving solar wind. Here, the authors show that impulsively-excited SW, with standing structure along the geomagnetic field, are stationary by propagating against this flow. [ABSTRACT FROM AUTHOR]

The Particle-In-Cell (PIC) method has been developed by Oscar Buneman, Charles Birdsall, Roger W. Hockney, and John Dawson in the 1950s and, with the advances of computing power, has been further developed for several fields such as astrophysical, magnetospheric as well as solar plasmas and recently also for atmospheric and laser-plasma physics. Currently more than 15 semi-public PIC codes are available which we discuss in this review. Its applications have grown extensively with increasing computing power available on high performance computing facilities around the world. These systems allow the study of various topics of astrophysical plasmas, such as magnetic reconnection, pulsars and black hole magnetosphere, non-relativistic and relativistic shocks, relativistic jets, and laser-plasma physics. We review a plethora of astrophysical phenomena such as relativistic jets, instabilities, magnetic reconnection, pulsars, as well as PIC simulations of laser-plasma physics (until 2021) emphasizing the physics involved in the simulations. Finally, we give an outlook of the future simulations of jets associated to neutron stars, black holes and their merging and discuss the future of PIC simulations in the light of petascale and exascale computing. [ABSTRACT FROM AUTHOR]

Multistability and dynamical properties of ion-acoustic flow are studied in a quantum plasma containing positive beam ions, positive ions and electrons. A four dimensional conservative dynamical system has been proposed for the considered plasma system and is analyzed by considering effects of Mach number and quantum diffraction parameter. Coexistences of multiple chaotic trajectories, chaotic with quasiperiodic and multiperiodic trajectories and chaotic with quasi-periodic and periodic trajectories for ion-acoustic waves are established. The results are suitable for application in comprehending the beam-plasma interaction and studying dynamics of coexisting features in extreme astrophysical plasmas, such as, neutron stars. [ABSTRACT FROM AUTHOR]

Electron impact excitation collision strengths for the transitions among the lowest twelve fine structure levels belonging to 2 p 6 nl ( n = 3 , 4 , l = 0 - 3 ) configurations of Cu XIX ion are presented using the close-coupling Breit–Pauli R-matrix method. Target state wavefunctions have been constructed using the AUTOSTRUCTURE. The collision strengths are also tabulated at selected energies above the excitation thresholds in the range 50–300 Ryd. For assessing the accuracy and reliability of our collision strength values, an independent calculation has been carried out using the relativistic distorted wave method. The effective collision strengths are obtained over a wide electron temperature range of 1.0 × 10 5 - 4.0 × 10 7 K by averaging over a Maxwellian distribution of velocities. We believe that our present results will be beneficial in the modelling of astrophysical and fusion plasmas. [ABSTRACT FROM AUTHOR]

In a recent paper Bouziane and Annou (Astrophys. Space Sci. 366:121, 2021) investigate the propagation of shock waves in a specific plasma model through the Korteweg-de Vries-Burgers equation, find its solutions and analyze those graphically. Unfortunately, the analysis is not correct, as a comparison with earlier papers on the tanh method for the KdVB equation shows, and the proposed solution does not annul the KdVB equation. Consequently, the graphics shown are also deficient. [ABSTRACT FROM AUTHOR]

Dynamics of the positron acoustic waves (PAWs) in magnetoplasmas following Cairns non-thermal distribution is studied on the frameworks of the Korteweg–de Vries (KdV) and modified Korteweg–de Vries (mKdV) equations. The reductive perturbation technique is used to derive the KdV and mKdV equations. Bifurcations of positron acoustic traveling waves of these equations are addressed by employing the bifurcation theory of planar dynamical systems. It is found that the KdV equation supports compressive positron acoustic solitary waves (PASWs), while the mKdV equation supports both compressive and rarefactive PASWs. Using numerical simulations, effect of the nonthermal parameter (β ), temperature ratio of hot electron to hot positron (σ ), magnetic field ( ω c 1 ), ratio of hot electron to cold positron concentration ( μ e ), and ratio of hot to cold positron concentration ( μ p ) are discussed on the PASWs solutions of the KdV and mKdV equations. The criterion of chaos for these perturbed equations under the external periodic perturbation are obtained through quasi-periodic route to chaos. It is in fact shown that transition to chaos in our system depends on the frequency ω and the strength of the external periodic perturbation f 0 . These parameters control the dynamic behavior of the PAWs. The relevance of this work may be useful to understand the qualitative changes in the dynamics of perturbed PAWs appearing in auroral acceleration region as well as the astrophysical and laboratory plasma, where static external magnetic field and nonthermal parameter are present. [ABSTRACT FROM AUTHOR]

In this work, fully relativistic multi-configuration Dirac–Hartree–Fock approach for calculating atomic structure parameters has been presented and compared to other approaches such as Hartree–Fock pseudo-Relativistic (HFR) method. As an example of application, results of fully relativistic calculations for the ion Ca XV have been obtained and compared to Hartree–Fock pseudo-relativistic calculations and to NIST database values.This example is important for plasma diagnostic and astrophysical studies because Ca XV atomic data of high accuracy are still very scarce. [ABSTRACT FROM AUTHOR]

The studies of close-orbit gaseous exoplanets—hot Jupiters and warm Neptunes—are reviewed. Transit spectral observations of the Hubble Space Telescope stimulated the numerical modeling of these objects. The supersonic outflow of the upper atmosphere of hot exoplanets and its interaction with the stellar plasma flow is a newly-discovered phenomenon in plasma physics and astrophysics that pools photo- and plasma-chemistry, collision-induced gas-dynamics, and collisionless space plasma. Starting from 2003, the modeling of physical processes in this field has considerably developed from simple quasi-empiric analytical formulas to global three-dimensional magnetic hydrodynamic (3D MHD) codes. The attained level makes it possible to interpret the in-transit measurements in absorption lines of different elements and estimate the parameters of both the planetary atmospheres and the stellar plasma wind. [ABSTRACT FROM AUTHOR]

The wave processes in a rotating layer of compressible astrophysical plasma with a stable stratification and a linear entropy profile are studied theoretically. The compressibility is taken into account in the anelastic approximation. In this approximation the acoustic waves are filtered out, the system contains terms with a potential temperature (entropy), and the continuity equation contains an initial stratified density profile. The Coriolis force in the magnetohydrodynamic equations for a compressible astrophysical plasma is considered in four different approximations: a traditional f-plane, a nontraditional f-plane (given the horizontal component of the Coriolis force), a traditional β-plane, and a nontraditional β-plane. Linear and nonlinear theories of wave processes have been developed for each Coriolis force approximation under consideration. New types of waves have been found, with the rotation, magnetic field, gravity, and compressibility serving as their restoring mechanisms. The compressibility effects are represented in the new dispersion equations by the Brunt–Väisälä frequency for compressible stratified flows dependent on both initial density and pressure profiles. All of the realizable types of three-wave interactions have been revealed through a qualitative analysis of the dispersion curves. A system of equations for the amplitudes of interacting waves and the growth rates of parametric instabilities have been derived by the multiscale expansion method. [ABSTRACT FROM AUTHOR]

Methods of description of ion–acoustic shock waves in dusty plasma are presented. A new type of dust ion–acoustic shock waves related to anomalous dissipation is described. The main dissipative processes related to charging of dust particles, absorption of ions by dust particles, Coulomb collisions between ions and dust particles, and Landau damping are analyzed. Proposed methods of theoretical analysis enable explaining all major specific features of dust ion–acoustic shock waves observed in the laboratory experiments. The shock waves of this type are present in the near-Earth plasma and the universe. Their investigation is possible in active ionospheric experiments of the Fluxus type. Important astrophysical problems in which the appearance of shock waves under consideration should be taken into consideration are the shock waves of supernovas, evolution of Local Interstellar medium, etc. [ABSTRACT FROM AUTHOR]

The one-dimensional nonlinear dynamical wave interactions in a system of quasineutral two-fluid plasma in a constant magnetic field are investigated. The existence of the travelling wave solutions is discussed. The modulation stability of linear waves and the modulation instability of weakly nonlinear waves are presented. Both suggest that the Korteweg-de Vries (KdV) system is modulationally stable. Besides, the wave interactions including the periodic wave interaction and the solitary wave interaction are captured and presented. It is shown that these interacting waves alternately exchange their energy during propagation. The Fourier spectrum analysis is used to depict the energy transformation between the primary and harmonic waves. It is known that the wave interactions in magnetized plasma play an important role in various processes of heating and energy transportation in space and astrophysical plasma. However, few researchers have considered such magnetohydrodynamic (MHD) wave interactions in plasma. It is expected that this work can provide additional insight into understanding of behaviors of MHD wave interactions. [ABSTRACT FROM AUTHOR]

Rotating magnetohydrodynamic flows of a thin stratified plasma layer in a gravitational field with a free boundary in an external vertical magnetic field were investigated. Magnetohydrodynamic equations were obtained in the two-layer shallow-water approximation in an external magnetic field when plasma is divided into two layers of different densities. A system of shallow-water equations for rotating stratified plasma in an external magnetic field was obtained in the beta-plane approximation. A linear theory was developed, and solutions in the form of magnetic Rossby waves, along with corrections that describe the effects of stratification, were obtained for stationary solutions in the form of vertical or horizontal magnetic field. Qualitative analysis of dispersion curves reveals the presence of three-wave nonlinear interactions of magnetic Rossby waves for each of the stationary states. The existence of parametric instabilities was demonstrated and their increments were found. [ABSTRACT FROM AUTHOR]

Modulation instability, bright envelope soliton, and rogue waves of ion acoustic waves in dense plasma consisting of ultra-relativistic degenerate electrons and positrons, cold and mobile inertial ions, and negatively charged static dust particles have been investigated using Fried and Ichikawa method. Nonlinear Schrödinger equation has been derived and the growth rate of modulationally unstable ion acoustic wave in such plasma are discussed. It has been found that ion acoustic wave will be always modulationally unstable for all possible values of density of positrons, electrons, and charged dust particle. The solutions of envelope solitons and rogue waves are obtained from the nonlinear Schrödinger equation. The theoretical results have been analyzed numerically and graphically for different values of plasma parameters. It is found that only bright envelope soliton would be excited in the ultra-relativistic degenerate plasma. Our results are new and may be applicable for the study of nonlinear wave processes in relativistic degenerate dense plasmas of astrophysical objects, namely, in white dwarfs and neutron stars. [ABSTRACT FROM AUTHOR]

Abstract: Two systems of magnetohydrodynamic equations in the shallow water approximation are proposed as a basis for studies in the field of plasma astrophysics: the system of equations with a full allowance for the Coriolis force and the system of equations on the β-plane in which the changes of the Coriolis parameter are linear in coordinate. Both systems of equations take into account such fundamentally important phenomena in plasma astrophysics as the compressibility and external magnetic field effects, increasing significantly the potential for applying these equations to study astrophysical objects. Compressibility in plasma astrophysics is shown to change significantly the dispersion laws for magneto-Poincare, magnetostrophic, and magneto-Rossby waves. The same nonlinear interactions as those in the absence of compressibility have been found to be realized in the case of a compressible rotating plasma. Three-wave equations in the weak nonlinearity approximation, in which the interaction coefficients depend on plasma large-scale compressibility and thermodynamic characteristics, have been derived by the method of multiscale expansions. Expressions for the growth rates of the parametric instabilities of three-wave interactions with large-scale compressibility have been derived. [ABSTRACT FROM AUTHOR]

Space and astrophysical plasmas often develop into a turbulent state and exhibit nearly random and stochastic motions. While earlier studies emphasize more on understanding the energy spectrum of turbulence in the one-dimensional context (either in the frequency or the wavenumber domain), recent achievements in plasma turbulence studies provide an increasing amount of evidence that plasma turbulence is essentially a spatially and temporally evolving phenomenon. This review presents various models for the space-time structure and anisotropy of the turbulent fields in space plasmas, or equivalently the energy spectra in the wavenumber-frequency domain for the space-time structures and that in the wavevector domain for the anisotropies. The turbulence energy spectra are evaluated in different one-dimensional spectral domains; one speaks of the frequency spectra in the spacecraft observations and the wavenumber spectra in the numerical simulation studies. The notion of the wavenumber-frequency spectrum offers a more comprehensive picture of the turbulent fields, and good models can explain the one-dimensional spectra in the both domains at the same time. To achieve this goal, the Doppler shift, the Doppler broadening, linear-mode dispersion relations, and sideband waves are reviewed. The energy spectra are then extended to the wavevector domain spanning the directions parallel and perpendicular to the large-scale magnetic field. By doing so, the change in the spectral index at different projections onto the one-dimensional spectral domain can be explained in a simpler way. [ABSTRACT FROM AUTHOR]

We have studied rotating magnetohydrodynamic flows of a thin layer of astrophysical plasma with a free boundary in the β-plane. Nonlinear interactions of the Rossby waves have been analyzed in the shallow-water approximation based on the averaging of the initial equations of the magnetic fluid dynamics of the plasma over the depth. The shallow-water magnetohydrodynamic equations have been generalized to the case of a plasma layer in an external vertical magnetic field. We have considered two types of the flow, viz., the flow in an external vertical magnetic field and the flow in the presence of a horizontal magnetic field. Qualitative analysis of the dispersion curves shows the presence of three-wave nonlinear interactions of the magnetic Rossby waves in both cases. In the particular case of zero external magnetic field, the wave dynamics in the layer of a plasma is analogous to the wave dynamics in a neutral fluid. The asymptotic method of multiscale expansions has been used for deriving the nonlinear equations of interaction in an external vertical magnetic field for slowly varying amplitudes, which describe three-wave interactions in a vertical external magnetic field as well as three-wave interactions of waves in a horizontal magnetic field. It is shown that decay instabilities and parametric wave amplification mechanisms exist in each case under investigation. The instability increments and the parametric gain coefficients have been determined for the relevant processes. [ABSTRACT FROM AUTHOR]