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Unscreened (ungated) plasmons in large-area grating-gate AlGaN/GaN heterostructures were studied experimentally by Fourier-transform spectroscopy. Special attention was paid to the recently discovered THz plasmonic crystal modes observed at totally depleted gated regions when plasma oscillations were localized only in ungated parts of the grating-gate structures. The frequency of these modes is still gate voltage-dependent in the limited range due to the depletion of the ungated parts located close to the gate edges. Double gate structures with an additional bottom gate were fabricated and studied to improve the gate voltage tunability of the unscreened plasmons. Since this gate is located deep below the channel, the plasmons behaved as ungated ones, but their frequency still could be tuned by this bottom gate. We show that the combined effect of the top and bottom gates allows the efficient tuning of terahertz frequencies of unscreened modes in the grating-gate AlGaN/GaN plasmonic crystals. [ABSTRACT FROM AUTHOR]

Current–voltage characteristics, space- and time-resolved optical emission spectroscopy, and 1D fluid modeling are used to examine the effect of dual-frequency sheath oscillations on the ion and electron transport in dielectric barrier discharges sustained by a combination of low frequency (LF, 50 kHz, 650 V) and radiofrequency (RF, 5.3 MHz, 195 V) voltages, exhibiting the α-to-γ mode transition. On one hand, when polarities of the LF and RF voltages are opposite, an electric field near the LF cathode (due to LF cathode sheath) drives the secondary electrons to the plasma bulk and an opposite electric field between the sheath edge and the LF anode attracts the electrons toward the LF cathode (to maintain quasi-neutrality in the plasma bulk). At the sheath edge, electrons become trapped and ions drift toward the cathode and the anode simultaneously according to their position in the gap. On the other hand, when the RF voltage has the same polarity as the LF voltage, the total applied voltage increases and this yields to enhanced production of electrons and ions in the sheath. To maintain quasi-neutrality in the bulk, the electric field along the gap exhibits the same polarity as the one in the sheath, allowing electrons created in the sheath to be evacuated toward the LF anode. The behavior of the LF cathode is, therefore, controlled by the LF sheath, and, thus, by the LF voltage amplitude, while the behavior in the bulk and at the anode alternates on the time scale of the RF voltage. [ABSTRACT FROM AUTHOR]

Hollow cathodes are an integral part of ion, and Hall thrusters are used for electric propulsion in deep space missions and in commercial communications satellites. Hollow cathodes are known to operate in a quiescent "spot mode" and in a noisy "plume mode" in which plasma instabilities generate erosive energetic ions. The onset of the plume mode in hollow cathodes has been defined historically as when the keeper voltage oscillation values exceed 5 Vpp (peak-to-peak). Using a LaB6 hollow cathode in a vacuum chamber setup that simulates operation in ion and Hall thrusters, a set of emissive and Langmuir probes have been used to investigate the plasma properties associated with plume mode onset as a function of discharge current and gas flow rate. We find that the plume mode onset occurs at even less than 2 Vpp of the keeper voltage for the 5–75 A hollow cathode investigated here and starts at higher gas flow rates than expected from the traditional 5 Vpp metric used by those in the field. Mode competition and coupling between three different instabilities observed in the near-cathode plume affect the overall plasma oscillation levels that are correlated to energetic ion production. We find that the plasma oscillation levels measured by in situ plasma diagnostics are more indicative of the presence of oscillations and the generation of energetic ions than indirect keeper voltage measurements. [ABSTRACT FROM AUTHOR]

An analysis of plasma density distributions at arbitrary ion–atom collisionality for one-dimensional axially symmetrical cylindrical and annular plasmas is presented. Perturbations of plasma densities caused by a cylindrical probe are studied for arbitrary ion–atom collisionality. Analytical expressions for the plasma characteristics near the probe for low collisionality have been obtained. The plasma was modeled by the hydrodynamic neutral plasma equations, taking into account ionization, ion inertia, and a non-linear ion frictional force, which dominates the plasma transport at low gas pressures. Significant plasma density depletion around the probe has been observed for a wide range of ion–atom collisionality. The presented results predict underestimation of plasma density obtained from the classical Langmuir probe procedure and should provide a better understanding of electrostatic, magnetic, and microwave probes inserted into plasmas at low gas pressure. [ABSTRACT FROM AUTHOR]

Introduction: The process of laser-induced breakdown of amorphous and crystalline selenium nanoparticles (Se NPs) of various shapes during nanosecond laser fragmentation of aqueous colloidal solutions of nanoparticles with different concentrations has been studied. Methods: The methods of studying the characteristics of plasma and acoustic oscillations induced by optical breakdown are applied. The methods of assessing the concentration of hydrogen peroxide and hydroxyl radicals, the amount of long-lived reactive species of protein and 8-oxoguanine are applied. Results: It has been established that in the process of laser fragmentation of selenium nanoparticles at a wavelength of 532 nm, corresponding to the maximum absorption of selenium, the highest probability of breakdown, the number of plasma flashes, their luminosity and the amplitude of acoustic signals are achieved at concentrations of the order of 109 NPs/mL. It has been shown that the use of selenium nanoparticles of various shapes and structures leads to a change in the photoacoustic signal during laser-induced breakdown. When crystalline selenium nanoparticles are irradiated, the intensity of the photoacoustic response during breakdown turns out to be greater (1.5 times for flash luminosity and 3 times for acoustics) than when amorphous particles are irradiated at the same concentration. It has been shown that selenium nanoparticles exhibit significant antioxidant properties. Selenium nanoparticles effectively prevent the formation of reactive oxygen species (ROS) during water radiolysis, eliminate radiation-induced long-lived reactive species of protein, and reduce the radiation-chemical yield of a key marker of oxidative DNA damage 8-oxoguanine. Discussion: In general, the intensity of processes occurring during laser fragmentation of amorphous and crystalline selenium nanoparticles differs significantly. The antioxidant properties are more pronounced in amorphous selenium nanoparticles compared to crystalline selenium nanoparticles. [ABSTRACT FROM AUTHOR]

Highlights Epsilon‐negative materials (ENM) at radio frequency, usually designed based on percolation theory, recently drew much attention because of their potential applications in capacitors, transistors, and antennas. However, randomly distributed conductive functional materials cannot achieve directional long‐range electron transportation within the material, resulting in decreased utilization efficiency. The morphology design of the substrate material can change the distribution state and electron transfer pathway of conductive fillers. By controlling the size of the polystyrene (PS) and the content of multi‐walled carbon nanotubes (MWCNTs), PS/MWCNTs composites with random structures and segregated structures were designed, both of which exhibited negative permittivity with increasing MWCNTs content. Further investigation revealed that negative permittivity behavior is due to the establishment of the conductive network and the plasma oscillation of free electrons. Moreover, components with segregated structures have lower percolation thresholds, as directional electron transport is achieved and conductive fillers are efficiently utilized. This work provides a new method for guiding the electron transport pathway and effectively changing the distribution state of conductive fillers in ENM. Negative permittivity is achieved by plasma oscillation at radio frequency. The segregated structure leads to a decrease in the percolation threshold. Epsilon‐negative materials have good prospects in inductive components. [ABSTRACT FROM AUTHOR]

We study the influence of the friction term on the radially symmetric solutions of the repulsive Euler–Poisson equations with a non‐zero background, corresponding to cold plasma oscillations in multiple spatial dimensions. It is shown that for any arbitrarily small non‐negative constant friction coefficient, there exists a neighborhood of the zero equilibrium in the C1$$ {C}^1 $$ norm such that the solution of the Cauchy problem with initial data belonging to this neighborhood remains globally smooth in time. Moreover, this solution converges to zero as t→∞$$ t\to \infty $$. This result contrasts with the situation of zero friction, where any small deviation from the zero equilibrium generally leads to a blow‐up. Our method allows us to estimate the lifetime of smooth solutions. Further, we prove that for any initial data, one can find such a coefficient of friction that the respective solution to the Cauchy problem keeps smoothness for all t>0$$ t>0 $$ and converges to zero. We also present the results of numerical experiments for physically reasonable situations, which allows us to estimate the value of the friction coefficient, which makes it possible to suppress the formation of singularities of solutions. [ABSTRACT FROM AUTHOR]

In this paper, the dust acoustic wave is studied in conditions where the dust temperature is not constant. This model includes negatively charged dust particles and thermal ions. The reductive perturbation technique is used and the new point in this study is the nonuniformity of the plasma temperature. The nonconstancy of the temperature is entered as a first-order perturbation in the calculations, and finally the modified Korteweg–de Vries (mKdV) equation is derived. The solution of the modified KdV equation clarifies the change in soliton shape of the wave when it moves in the perturbation plasma. We show how the soliton wave undergoes deformation and amplitude reduction during propagation when it encounters a region with a different temperature. The output of this research can be effective to better understand the wave behavior in a real plasma with nonuniform temperature. [ABSTRACT FROM AUTHOR]

An implicit MacCormack-type scheme is constructed for a kinetic plasma model based on the Vlasov–Ampère equations. As compared with the explicit scheme, it has a weaker stability restriction, but preserves computational efficiency, i.e., it does not involve inner iterations. The error of the total energy corresponds to a second-order accurate algorithm, and the total charge (number of particles) is preserved at the grid level. The formation of plasma waves excited by a short intense laser pulse is modeled as an example. [ABSTRACT FROM AUTHOR]

In this paper, a study of surface plasma wave excitation from a magnetized metallic surface using two co-propagating lasers is conducted. Two lasers propagating in the same direction with frequency difference of plasmon frequency of the metal excite plasma oscillations on the metallic surface, which generate surface plasma waves. The transverse components of the field associated with these surface plasma wave lead to excite transverse current at terahertz frequency. We report a systematic theoretical model for this study and subsequent numerical results are presented for THz field estimation. [ABSTRACT FROM AUTHOR]

The paper reports the results of study of composition, emission, and optical properties of polycrystalline W and Mo samples implanted with Ba+ ions and coated with submonolayer Ba atoms by applying Auger electron spectroscopy, secondary electron emission coefficient s technique, as well as the photoelectron quantum yield Y. The experimental part was carried out by using the instrumentation and under vacuum Р ≈ 10-6 Pa. It is shown that during the implantation of Ba ions in the surface layers of refractory metals, a mechanical mixture of the W + Ba and Mo-Ba types is formed. It has been established that the values of the coefficient of secondary electron emission s and the quantum yield of photoelectrons Y at the same value of the work function еφ in the case of implantation of Ba+ ions are much larger than in the case of deposition of atoms. The obtained experimental results are substantiated by theoretical calculations.

The Schrödinger equation and Bloch theorem are applied to examine a system of protons confined within a periodic potential, accounting for deviations from ideal harmonic behavior due to real-world conditions like truncated and non-quadratic potentials, in both one-dimensional and three-dimensional scenarios. Numerical computation of the energy spectrum of bound eigenfunctions in both cases reveals intriguing structures, including bound states with degeneracy matching the site number Nw, reminiscent of a finite harmonic oscillator spectrum. In contrast to electronic energy bands, the proton system displays a greater number of possible bound states due to the significant mass of protons. Extending previous research, this study rigorously determines the constraints on the energy gap and oscillation amplitude of the previously identified coherent states. The deviations in energy level spacing identified in the computed spectrum, leading to the minor splitting of electromagnetic modes, are analyzed and found not to hinder the onset of coherence. Finally, a more precise value of the energy gap is determined for the proton coherent states, ensuring their stability against thermal decoherence up to the melting temperature of the hosting metal.

The plasma density is one of the most fundamental quantities of any plasma yet measuring it in space is exceptionally difficult when the density is low. Measurements from particle detectors are contaminated by spacecraft photoelectrons and methods using plasma wave emissions are hampered by natural plasma instabilities which dominate the wave spectrum. Here we present a new method which calculates the density from magnetosonic waves near the lower hybrid resonance frequency. The method works most effectively when the ratio of the plasma to cyclotron frequency is fpe/fce < 3.5. The method provides a lower bound on the plasma density. Using the new method we show that wave acceleration of electrons to relativistic energies is increased by orders of magnitude. The method enables years of satellite data to be re‐analyzed for the Earth and the effectiveness of wave acceleration at the Earth, Jupiter and Saturn to be re‐assessed. Plain Language Summary: The electron plasma density is a fundamental quantity of any plasma, but it is very difficult to measure in space using satellites. Satellites charge to different potentials with repel or attract electrons making the true measurement very difficult. The plasma density can be determined from wave oscillations at the plasma frequency, but the waves are difficult to identify as the wave spectrum is often dominated by other much stronger waves. Here we analyze satellite data and show that magnetosonic waves near the lower hybrid resonance frequency can be used to calculate the plasma density. This method provides a lower bound on the density. We show that this lower density leads to much faster electron acceleration by wave‐particle interactions, accelerates electrons to much higher energies and increases the electron flux at one MeV by two orders of magnitude or more. The method enables the importance of electron acceleration at the Earth, Jupiter and Saturn to be re‐evaluated. Key Points: New method to calculate plasma density from magnetosonic waves near the lower hybrid resonance frequencyMethod enables low densities to be measured near the magnetic equatorLow density increases wave acceleration of electrons by orders of magnitude [ABSTRACT FROM AUTHOR]

In this paper, kapok-derived carbon/fly ash (KDC/FA) ceramic metacomposites were fabricated by vacuum hot-press sintering with FA and kapok fiber as raw materials, and their conductivity, dielectric properties, and impedance response were researched. The composition and microstructure of the metacomposites had a significantly impact on the electrical characteristics. With the increase of KDC content, a 3D conductive network was formed inside the composite, accompanied by a shift in the conductive mechanism. The tunable plasma-type negative permittivity behavior was observed. The absolute value of negative permittivity and the plasma oscillation frequency became larger as the KDC contents increased, which were consistent with the analytical results of the Drude model. This study designed and prepared a new environmental metacomposite with adjustable negative permittivity using biomass materials (kapok fibers) and solid waste (FA), which had a great significance for development of metamaterials in the future. [ABSTRACT FROM AUTHOR]

In this work the phenomenon of the quasi-coherent mode of plasma fluctuations in purely ohmic plasmas of the T-10 tokamak is investigated. The plasma magnetic fluctuation spectra along with spectra of relative electron density oscillations and plasma potential fluctuation spectra were studied. The presence of both electrostatic and magnetic components of the quasi-coherent mode has been established in the core and as well at the edge regions of the plasma column. This fact allows one to consider the quasi-coherent mode as one of the types of electromagnetic turbulence of fusion plasma. [ABSTRACT FROM AUTHOR]

The two-parameter Mittag–Leffler function E α , β is of fundamental importance in fractional calculus, and it appears frequently in the solutions of fractional differential and integral equations. However, the expense of calculating this function often prompts efforts to devise accurate approximations that are more cost-effective. When α > 1 , the monotonicity property is largely lost, resulting in the emergence of roots and oscillations. As a result, current rational approximants constructed mainly for α ∈ (0 , 1) often fail to capture this oscillatory behavior. In this paper, we develop computationally efficient rational approximants for E α , β (− t) , t ≥ 0 , with α ∈ (1 , 2) . This process involves decomposing the Mittag–Leffler function with real roots into a weighted root-free Mittag–Leffler function and a polynomial. This provides approximants valid over extended intervals. These approximants are then extended to the matrix Mittag–Leffler function, and different implementation strategies are discussed, including using partial fraction decomposition. Numerical experiments are conducted to illustrate the performance of the proposed approximants. [ABSTRACT FROM AUTHOR]

The two-fluid and two-temperature diffusion-drift model of gas-discharge plasma is used to study numerically the structure of the Penning discharge in a cylindrical discharge chamber at the molecular hydrogen pressure of 1 mTorr, the voltage between the electrodes of 500–1000 V, and the axial magnetic field induction of 0.001–0.2 T. Two regimes of existence of the Penning discharge are obtained in the calculations. These regimes differ qualitatively in the electrodynamic structure of the charged-particle flows of gas-discharge plasma, as well as there exist transient and extinction regimes in the weak and strong magnetic fields. The conditions under which the oscillatory motion of electron and ion flows develops in the paraxial regions are found. It is shown that the results of numerical simulation with the use of the diffusion-drift model make it possible to obtain consistent data in comparison with experiment, and at the same time to get an insight about the formation of the structure of flows of electric-discharge plasma particles. This makes it possible to explain the observed experimental data. [ABSTRACT FROM AUTHOR]

We consider the operation of a digital linear ion trap with resonant radial ejection. A sequence of rectangular voltage pulses with a dipole resonance signal is applied to the trap electrodes. The periodic waveform is piecewise constant, has zero mean, and is determined by an asymmetry parameter d$$ d $$: one value is taken on interval 0dT$$ \left(0, dT\right) $$ and another on dTT$$ \left(dT,T\right) $$, where T$$ T $$ is the RF period. Ion mass scanning is performed by varying the asymmetry parameter d$$ d $$ and amplitude of the negative pulse part with time. The ion oscillation frequencies and acceptance of the linear trap are calculated. The dependence of the ion mass to charge ratio m/z$$ m/z $$ on the parameter d$$ d $$ is m/z~d2$$ m/z\sim {d}^2 $$. The maximum value is about m/z=30$$ m/z=30 $$ kDa for typical parameters of the linear trap: frequency 0.5 MHz, rod radius 4 mm, and negative pulse amplitude 1 kV. The dipolar excitation frequency is 0.125 MHz at which the LIT acceptance is maximal. [ABSTRACT FROM AUTHOR]

The Schrödinger equation and Bloch theorem are applied to examine a system of protons confined within a periodic potential, accounting for deviations from ideal harmonic behavior due to real-world conditions like truncated and non-quadratic potentials, in both one-dimensional and three-dimensional scenarios. Numerical computation of the energy spectrum of bound eigenfunctions in both cases reveals intriguing structures, including bound states with degeneracy matching the site number N w , reminiscent of a finite harmonic oscillator spectrum. In contrast to electronic energy bands, the proton system displays a greater number of possible bound states due to the significant mass of protons. Extending previous research, this study rigorously determines the constraints on the energy gap and oscillation amplitude of the previously identified coherent states. The deviations in energy level spacing identified in the computed spectrum, leading to the minor splitting of electromagnetic modes, are analyzed and found not to hinder the onset of coherence. Finally, a more precise value of the energy gap is determined for the proton coherent states, ensuring their stability against thermal decoherence up to the melting temperature of the hosting metal. [ABSTRACT FROM AUTHOR]

In this paper, the Penning ion sources (PIS) characteristics are studied applied to their use in an inertial electrostatic confinement (IEC) system based on a two-electrode spherical chamber. In the IEC chamber with deuterium filling, due to multiple oscillations of ion beams through a gas-plasma target inside the central electrode, a beam-target mechanism for generating neutron radiation is realized. Based on the method for the neutron yield calculating of IEC systems, the requirements for a PIS are formulated to ensure the neutron yield (2.5 MeV) in the range of 106–107 neutr./s. A computational and experimental study of the discharge combustion regimes in the PIS has been carried out depending on the configuration of the external magnetic field and comparison of the currents in the PIS and the currents through the central electrode of the IEC chamber in the pressure range from 0.1 to 10 mTorr. The optimal number of PIS in the considered spherical chamber of the IEC justified. [ABSTRACT FROM AUTHOR]

The paper reports the results of study of composition, emission, and optical properties of polycrystalline W and Mo samples implanted with Ba+ ions and coated with submonolayer Ba atoms by applying Auger electron spectroscopy, secondary electron emission coefficient σ technique, as well as the photoelectron quantum yield Y. The experimental part was carried out by using the instrumentation and under vacuum Р ≈ 10-6 Pa. It is shown that during the implantation of Ba ions in the surface layers of refractory metals, a mechanical mixture of the W + Ba and Mo-Ba types is formed. It has been established that the values of the coefficient of secondary electron emission σ and the quantum yield of photoelectrons Y at the same value of the work function еφ in the case of implantation of Ba+ ions are much larger than in the case of deposition of atoms. The obtained experimental results are substantiated by theoretical calculations. [ABSTRACT FROM AUTHOR]

An experimental method to measure the electric fields existing in a plasma wake produced by a ∼0.24 GW, ∼0.5 ns, 9.5 GHz microwave pulse traversing a plasma-filled waveguide is presented. The intensity of the second harmonic of a 30 fs 800 nm laser generated inside a gas-filled dielectric tube placed inside the waveguide is used to characterize the wakefield parameters. Three distinct decaying oscillations of the plasma wakefield, with peak amplitude of ∼20 kV/cm, were observed. The experimental results were confirmed by 3D large-scale plasma particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

The influence of atmospheric planetary waves on the occurrence of irregularities in the low latitude ionosphere is investigated using Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X) simulations and Global Observations of the Limb and Disk (GOLD) observations. GOLD observations of equatorial plasma bubbles (EPBs) exhibit a ~6-8 day periodicity during January-February 2021. Analysis of WACCM-X simulations, which are constrained to reproduce realistic weather variability in the lower atmosphere, reveals that this coincides with an amplification of the westward propagating wavenumber-1 quasi-six day wave (Q6DW) in the mesosphere and lower thermosphere (MLT). The WACCM-X simulated Rayleigh-Taylor (R-T) instability growth rate, considered as a proxy of EPB occurrence, is found to exhibit a ~6-day periodicity that is coincident with the enhanced Q6DW in the MLT. Additional WACCM-X simulations performed with fixed solar and geomagnetic activity demonstrate that the ~6-day periodicity in the R-T instability growth rate is related to the forcing from the lower atmosphere. The simulations suggest that the Q6DW influences the day-to-day formation of EPBs through interaction with the migrating semidiurnal tide. This leads to periodic oscillations in the zonal winds, resulting in periodic variability in the strength of the prereversal enhancement, which influences the R-T instability growth rate and EPBs. The results demonstrate that atmospheric planetary waves, and their interaction with atmospheric tides, can have a significant impact on the day-to-day variability of EPBs. [ABSTRACT FROM AUTHOR]

The paper presents the results of solving a boundary value problem for a system of two integro-differential equations that simulate the action of an external electric field on a plasma layer. This system is an implication of the Boltzmann–Maxwell equations, and the physical meaning of the sought functions is the strength of a self-consistent electric field and perturbation of the electron distribution density. The solution of the problem is constructed using the theories of Fourier transform of generalized functions and singular integral equations with the Cauchy kernel. The dependence of the solution on the frequency of the external field is studied. [ABSTRACT FROM AUTHOR]

This paper reports on the generation of a directed flux of electromagnetic radiation with an energy content of 10 J in the frequency range of 0.2–0.3 THz at a microsecond pulse duration in a beam–plasma system. The flux is generated when a relativistic electron beam (REB) pumps electron plasma waves in a magnetized plasma column. In the described experiments, this fundamentally new approach to generate terahertz radiation was carried out at the GOL-PET facility in the conditions of varying the beam current density and the plasma density in the appropriate ranges of 1–2 kA/cm2 and 1014–1015 cm–3. From the comparison of the flux energy spectrum measured experimentally in the frequency range 0.15–0.45 THz with the calculated one obtained using the previously proposed model of radiation generation in a beam–plasma system it was shown that this process occurs through resonant pumping by REB of precisely the branch of upper-hybrid plasma waves. Mastering this new method to generate terahertz radiation opens the prospect of its use to obtain multi-megawatt radiation fluxes in the frequency range up to 1 terahertz and higher. For such a development approach the most promising beam for pumping plasma oscillations seems to be a kiloampere REB generated in a linear induction accelerator. [ABSTRACT FROM AUTHOR]

Calculations of the spectrum of eigen oscillations of an inhomogeneous ultracold plasma are presented both in the absence and in the presence of charge imbalance. The collective modes of these plasma oscillations are recorded in experiments as absorption resonances of a radio frequency electric field. It is shown that in the presence of friction of the electronic component, a discrete spectrum of plasma eigen oscillations is formed. The dependence of the frequency of these resonances on the plasma expansion time in the presence of a charge imbalance is obtained. There is good agreement with the experiments of different authors. [ABSTRACT FROM AUTHOR]

In this study, we investigate the generation of electromagnetic emission near the second harmonic of the plasma frequency induced by pairs of counter-propagating electron beams. Such systems can naturally occur in cosmic plasmas when particle acceleration regions are closely spaced, and they can also be implemented in a laboratory device. We specifically focus on the regime where the oblique beam–plasma instability dominates. The emission mechanism relies on the coalescence of counter-propagating plasma waves with different transverse structures. It has been demonstrated that the parameters of the system necessary for efficient radiation generation can be determined using the exact linear theory of beam–plasma instability. Through particle-in-cell numerical simulations, we show that a high beam-to-radiation conversion efficiency can be achieved when the beams excite small-scale oblique plasma oscillations. Importantly, we find that the efficiency and spectral characteristics of the radiation are not dependent on the thickness of the beams. We explore two scenarios involving pairs of symmetric beams: one with relativistic beams having a directed velocity of v b = 0.9 c and another with sub-relativistic beams at v b = 0.7 c. Additionally, we consider the injection of two beams with different velocities. In all cases considered, the beam-to-radiation power conversion efficiency reaches a level of a few percent, a sufficiently high value for beam–plasma systems. [ABSTRACT FROM AUTHOR]

Hall thrusters are plasma-based devices that have established themselves as one of the most attractive and mature electric propulsion technologies for space applications. These devices often operate in a regime characterized by low frequency, large amplitude oscillations of the discharge current, which is commonly referred to as the 'breathing mode'. The intensity of these oscillations depends on the thruster's design and operating conditions and can reach values of the order of the average discharge current, posing issues for the thruster's performance and for coupling with the driving electronics. A 0D model of the thruster discharge was developed to investigate the core physical mechanisms leading to the onset and sustenance of the breathing mode. The model was found to be capable of reproducing oscillations with characteristics in line with those observed in the breathing mode. In this work, we extend the use of the 0D model to investigate the effect of the magnetic field intensity and of different propellants on the system stability. [ABSTRACT FROM AUTHOR]

The dynamic responses of magnetic reconnection to localized three-dimensional (3D) magnetic field perturbations imposed by a pair of figure-8-shaped coils are investigated in the Magnetic Reconnection Experiment (MRX) device. Both the magnetic field geometry and current sheet profiles are altered by external perturbations. For the case when the inductive electric field associated with these perturbations aligns with the preexisting reconnection electric field, O-type magnetic structures appear within an elongated current sheet. When these magnetic structures are ejected downstream at the speed close to the ion outflow velocity, the inductive electric field is enhanced considerably. Despite that the imposed perturbation amplitude is larger than 30% of the original reconnecting magnetic field, the overall reconnection process remains robust without current sheet disruptions. This technique to form O-type magnetic structures can serve as an additional experimental knob for future systematic laboratory investigations of 3D magnetic reconnection and related instabilities without disrupting two-dimensional current sheet. [ABSTRACT FROM AUTHOR]

A propagation of ultrawideband electromagnetic pulses (UWB EMPs) through magnetized plasma has been experimentally studied using a "gigantic" coaxial line, which has been developed at IAP RAS for laboratory modeling of ionospheric effects. This coaxial line is 1.4 m in diameter and 10 m in length and is installed inside the chamber of the large-scale Krot plasma device. The line can be filled with rf inductively coupled plasma, magnetized or not. It allows one to explore the propagation of UWB EMPs in plasma along a long path without refraction and divergence and obtain a physical picture of EMP transformation. Under conditions where the duration of the UWB EMP is comparable to the period of electron plasma oscillations (fp−1), the period of cyclotron rotation of electrons (fc−1), or even significantly shorter, a complex of effects of transformation of the waveform and frequency spectrum of the pulse occurs. Without ambient magnetic field, a UWB EMP is distorted due to the effects of the cutoff and frequency dispersion. In dense magnetized plasma, i.e., when fp >> fc, the UWB EMP breaks into two wave packets, the high-frequency one (f > fp) and low-frequency one (f < fc). In rare magnetized plasma (fp << fc), the cyclotron absorption produces a long train of damped oscillations at a frequency close to the cyclotron frequency fc following the UWB EMP. [ABSTRACT FROM AUTHOR]

The paper presents an investigation of the plasma fluctuation in the SMOLA helical mirror, which is suspected to be responsible for anomalous scattering. The helical mirror confinement is effective when the ion mean free path is equal to the helix pitch length. This condition can be satisfied in hot collisionless plasma only by anomalous scattering. The wave, which scatters the passing ions, is considered to receive energy from the trapped ions. The oscillations of the electric field in the helically symmetric plasma were observed in experiment. The oscillations have both regular highly correlated and chaotic components. The dependency of the regular component frequency on the Alfvén velocity is linear for $V_{\rm A} and constant for higher values. It is shown experimentally that the condition for the wave to be in phase resonance with the trapped ions is satisfied in a specific region of the plasma column for the highly correlated component. The amplitude of the chaotic component (up to $3\ \text {V}\ \text {cm}^{-1}$) is higher than the estimated electric field required for the ion scattering. [ABSTRACT FROM AUTHOR]

As a continuity of our previous work with an emphasis mainly on temporal variations, this research aims to statistically investigate the temporal-spatial characteristics on seismo-ionospheric influence associated with strong earthquakes. Firstly, the latest electron density and ion density data measured by the CSES satellite for more than three years have been utilized to globally search ionospheric disturbances by limiting spatial scale 140–2,100 km (in-situ measurement time t = 20–300 s if the satellite velocity 7 km/s is considered) and without limit on amplitude (A). At the same time, 3,577 strong earthquakes with a magnitude equal to or > 5.0 occurring during this period and three-hourly averaged Kp index have also been collected. It has shown that ionospheric variations with large scale (t > 200 s) and large amplitude (| A | > 100%) majorly reveal the major large-scale ionosphere structures, such as EIA, WN3/4, WSA, MIT, and so on, as well as strengthened varieties globally induced by strong solar activities especially on daytime, although electron density and ion density vary with different properties. Secondly, by large ionospheric perturbations eliminated, the sensitivity of nighttime plasma variations (here, | A | < 100% and t < 200 s) to different group strong earthquakes with respect to several aspects has been tentatively testified. Kp index is kept < 3 during this period to avoid its global effect from solar activities. The results have demonstrated that the seismic activities are more sensitive to ionospheric anomalies predominantly appearing 7 days before and with the spatial size < 120 s. Finally, nighttime plasma perturbations with various sizes and amplitudes have been further applied to a worldwide correlation in space and time with total 3,577 strong earthquakes happening within 1,500 km and 15 day's delay. The statistical results show that seismo-electron influence subtracted by an averaged variation significantly occurs 5 days prior to events and shifts 500–700 km away instead of right above the epicenters, which highly complies theoretically with the physical seismoionospheric model based on zonal electric field propagating along magnetic lines. While seismo-ion effect shows a specified temporal feature but without a confirmed spatial distribution and further work on validation and reliability of ion data is needed. [ABSTRACT FROM AUTHOR]

Plasma parameter profiles along the effective minor radius of flux surfaces are modeled for the conditions with neon impurity puffing and external resonant magnetic perturbations at the plasma edge in the large helical device. For the electron cyclotron heating scenario, calculations qualitatively reproduce stable steady states with plasma detached from divertor target plates and radiation losses exceeding 90% of the heating power. It is unlikely with neutral beam injection heating that the plasma collapses if the radiation approaches a critical level noticeably below 100%. The latter is explained by the dependence of neutral beam attenuation on the plasma ion effective charge. [ABSTRACT FROM AUTHOR]

Introduction: Oscillations are frequently observed on plasma dilution curves during intravenous fluid therapy. This study aimed to examine how common these oscillations are and what they represent. Methods: Fourier transforms were used to analyze the residuals obtained during fitting of a volume kinetic model to 269 plasma dilution curves. Oscillating patterns were identified in two-thirds of the fluid infusion experiments. Results: The wave frequency usually had a dominating frequency of 1 h or multiples thereof. The wave amplitudes varied between 1% and 4% of the plasma volume. The "peak-to-peak" amplitudes were then twice as large, which corresponded to blood volume changes of 60–240 mL. A population kinetic analysis of the distribution of infused fluid between body fluid compartments was then applied to search for clues that could explain the oscillations. This analysis showed that amplitudes >1.5% were associated with doubled turnover of fluid in a fast-exchange interstitial fluid compartment and, together with data on plasma albumin, suggested that oscillations might represent bursts of efferent lymph. Conclusions: Oscillations with very low frequency were often observed on plasma dilution-time curves obtained during fluid therapy. They were associated with fast turnover of interstitial fluid and can possibly have resulted from accelerated lymphatic flow. [ABSTRACT FROM AUTHOR]

Plasma oscillations below 100 kHz in a high-power, magnetically shielded Hall-effect thruster are characterized experimentally. A time-resolved laser-induced fluorescence diagnostic was used to measure the evolution of the axial ion velocity distribution along the discharge channel centerline. A method was developed to correct for artificial broadening of the distribution due to finite spatial resolution, enabling accurate ion temperature measurements in the acceleration region. Time-dependent ion heating behavior is revealed, which varies with axial location. Electrostatic, collisionless particle-pushing calculations were employed to simulate the effects of a shifting acceleration front on ion motion. It is found that ions exchange energy with these oscillations, which accounts for a portion of the ion velocity fluctuations observed in the thruster plume. Phasing relationships between ion dynamics and discharge current oscillations are discussed in the context of prior Hall thruster experiments. [ABSTRACT FROM AUTHOR]

Information on the ionization of propellant gases is invaluable for Hall thruster plasma studies because the ion beam is the source of thrust generation. This study proposes a new method that identifies the ionization location of Xe+ ions in Hall thruster plasmas by combining the laser-induced fluorescence spectroscopy and floating emissive probe measurements in annular and cylindrical Hall thrusters. In an annular Hall thruster, this method indicated that ionization became the largest at a few millimeters upstream of the maximum radial magnetic field, whose result agreed with a one-dimensional hybrid fluid/particle-in-cell (PIC) simulation result. On the other hand, the ionization region in a cylindrical Hall thruster was located deeper inside the discharge cavity than that of the annular thruster. In addition, a large upstream shift of the ionization region was observed with the decreasing fraction of the radial magnetic field in the cylindrical Hall thruster. [ABSTRACT FROM AUTHOR]

The influence of the effects of thermal conduction and heating/radiative losses on the propagation of acoustic waves in a rarefied high-temperature plasma is studied. A constant heating function is chosen, and an interpolation is used for the radiative-loss function, which is based on the values found by the CHIANTI 10 code. Waves are analyzed in a linear approximation based on the dispersion relation. The input parameters in the problem are the plasma temperature and density and the output parameters are the period of oscillations and their damping time. Conversely, having observational data on compression waves, one can pose the problem of finding the parameters of the coronal plasma from the oscillation parameters. The situations in which the effect of the misbalance between heating and losses can, along with thermal conductivity, play a significant role in wave damping are shown. The temperature ranges at which instability and aperiodic damping of acoustic oscillations are possible are determined. [ABSTRACT FROM AUTHOR]

From August to October 2018, a series of strong earthquake (EQ) events occurred in southeast Asia and northern Oceania (22°S to 0°N, 115°E to 170°E) within 50 days. In this paper, we analyze the features of ionospheric plasma perturbations, recorded by the Plasma Analyzer Package (PAP) and Langmuir probe (LAP) onboard the China Seismo-Electromagnetic Satellite (CSES-01), before four EQs with magnitudes of Ms 6.9 to Ms 7.4. The ion parameters such as the oxygen ion density (No+), the ion drift velocity in the vertical direction (Vz) under the conditions of geomagnetic storms, and strong EQs are compared. The results show that within 1 to 15 days before the strong EQs, the No+ and the electron density (Ne) increased while the electron temperature (Te) decreased synchronously. Meanwhile, the Vz significantly increased along the ground-to-space direction. The relative variation of No+ and Vz before the strong EQs is more prominent, and the Vz is not easily influenced by the geomagnetic storm but is susceptible to the seismic activities. Our results suggest that the anomaly of ionospheric plasma perturbations occurring in this area is possibly related to the pre-EQ signatures. [ABSTRACT FROM AUTHOR]

We consider electron–positron plasma in strong electric field capable of creating electron–positron pairs. The dynamics of pair creation and plasma oscillations depends on pair distribution function. Assuming Fermi–Dirac distribution we found that for small temperatures pair creation is suppressed, while for small chemical potentials it is enhanced, with respect to the case when plasma degeneracy is neglected. Astrophysical settings where such conditions may occur are discussed. [ABSTRACT FROM AUTHOR]

Metacomposites with extraordinary electromagnetic (EM) parameters recently offered a brand-new strategy for EM shielding, but still suffered from the unclear paradigm and regulation mechanism for ε′ -negative and ε′ -near-zero response. Herein, we presented an effective paradigm of binary composites consisting of CaCu 3 Ti 4 O 12 (CCTO) and graphitized-multiwall carbon nanotube (g-MWCNT) which was designed by percolation theory. The ε′ switched from positive to negative with increasing frequency was obtained in g-MWCNT/CCTO composites, which could be explained by electrical dipole resonance of interconnected g-MWCNT clusters. Once the percolated g-MWCNT network is formed, Drude-type ε′ -negative response would be obtained due to the low-frequency plasma oscillation. Epsilon-near-zero effect (at ∼385 MHz and ∼135 MHz) were tuned by adjusting g-MWCNT content, which respectively corresponds to the loss peaks. The EM medium of CCTO/g-MWCNT composites with ε′ -negative or ε′ -near-zero response showed great EM shielding performance at specific frequency region. The g-MWCNT/CCTO metacomposites provide a classical paradigm of ceramic matrix composites for ε′ -negative and ε′ -near-zero response which will guide the practical application of metacomposites in dielectric ceramics and metamaterials, and promote the next steps in EM shielding field. [ABSTRACT FROM AUTHOR]

Ceramic composites made up of well-selected components have enriched the varieties of the metamaterials with negative electromagnetic parameters. In this work, TiN/BaTiO 3 ceramic composites were prepared with a simple dry-pressing and pressureless sintering process. Percolation was eventually determined to be the key inducements which caused the permittivity of the ceramic composites changing from positive to negative. Essentially, negative permittivity was closely related to the plasma oscillations of free electrons in percolation networks. Meanwhile, conduction mechanism of the composites varied owing to the changes in microstructure, where the percolation networks brought out pathways for electron migration and achieved high conductivity. In addition, ac impedance behavior with changes of the sign for reactance were also discussed, thus the transition from electrical capacitive to inductive for the percolative ceramic composites has been demonstrated. This work clarified the influence of percolation on the conductivity, impedance, and permittivity of ceramic composites altogether. The obtained negative permittivity composites have enormous potential in various electronic devices and electromagnetic apparatus. [ABSTRACT FROM AUTHOR]

The metabolites in the plasma serve as potential biomarkers of disease. We previously established an early-onset diabetes mouse model, Ins2 +/Q104del Kuma mice, under a severe immune-deficient (Rag-2 / Jak3 double-deficient in BALB/c) background. Here, we revealed the differences in plasma amino acid profiles between Kuma and the wild-type mice. We observed an early reduction in glucogenic and ketogenic amino acids, a late increase in branched-chain amino acids (BCAAs) and succinyl CoA-related amino acids, and a trend of increasing ketogenic amino acids in Kuma mice than in the wild-type mice. Kuma mice exhibited hyperglucagonemia at high blood glucose, leading to perturbations in plasma amino acid profiles. The reversal of blood glucose by islet transplantation normalized the increases of the BCAAs and several aspects of the altered metabolic profiles in Kuma mice. Our results indicate that the Kuma mice are a unique animal model to study the link between plasma amino acid profile and the progression of diabetes for monitoring the therapeutic effects. • The diabetic Ins2 +/Q104del Kuma mice showed characteristic plasma amino acid profiles. • Kuma mice showed an early reduction in glucogenic and ketogenic amino acids. • A late increase in branched-chain amino acids (BCAAs) was observed in the Kuma mice. • Islet transplantation corrected blood glucose and metabolic profile to some extent. • Increases in plasma glucagon in Kuma mice may explain the elevated BCAAs. [ABSTRACT FROM AUTHOR]

A new method was proposed to generate high-power narrow-band terahertz radiation in the process of nonlinear interaction of counterpropagating laser wake waves, the potential profiles of which are modulated in the transverse direction and do not coincide locally with each other. It was shown that, to achieve a high efficiency of radiation at the doubled plasma frequency, the period of such modulation should coincide with the length of the generated electromagnetic wave. Each of the plasma waves with such a small-scale transverse structure was proposed to be created by a pair of interfering laser pulses propagating at a small angle to each other. Numerical simulation by the particle-in-cell method confirmed such a scheme can provide a narrow (2%) spectral emission line and a high energy conversion efficiency at a level of 1%. With the XCELS design parameters, the proposed method opens the way to achieving a record terawatt radiation power in the THz frequency range. [ABSTRACT FROM AUTHOR]

We investigate a nonlinear response of the physical vacuum by the example of the third harmonic in radiation of the electron–positron–photon plasma excited by a strong time dependent electric field at the focus spot of counterpropagating laser pulses. The investigation was developed within the framework of the Bogoliubov–Born–Green–Kirkwood–Yvon kinetic theory nonperturbatively describing vacuum creation of the quasiparticle electron–positron plasma (EPP) and different channels of its interaction with the photon subsystem in the single-photon approximation that are opened in the presence of a strong semiclassical field. We investigate the radiation of EPP in the annihilation channel on the basis of the well known approximations and compare the obtained result with the semiclassical radiation of the plasma oscillations. In the high-frequency range for large adiabaticity parameter the quantum radiation dominates in comparison with the semiclassical one. [ABSTRACT FROM AUTHOR]

The need for a model able to provide the dynamic evolution of the intrinsic magnetic error fields amplitude in tokamaks is of a significant importance in order to develop strategies to correct its destabilizing effect. The present paper specifically aims to deliver this kind of model and adjacent code. A previously built direct perturbations interpretative model (Miron (JET Contributors) 2021 Nucl. Fusion 61 106016) is used to calculate the plasma instabilities amplitude and frequency aiming to match the same quantities provided by the device diagnostics data analysis specific code for various discharges at JET. The mentioned good match ensures our model validity against the experimental results. Based on its proven structural validity, our model considering the error field quantities is inverted. This time the initial direct model output results, namely the plasma perturbations amplitude and frequency, become input data for our inverse model aiming to solve the corresponding error field modes system of equations searched as unknowns. The error fields basically satisfy the same outer plasma perturbed equations as the plasma perturbations do (vacuum/wall/plasma column external structures). Obviously they do not satisfy the perturbed plasma equations. A clear and explicit dynamic error field solution is finally provided. It has been demonstrated that whenever the error fields are responsible for the mode locking effect and plasma rotation damping, the calculated error fields shows its expected disruptive resonant behavior during various discharges at JET. [ABSTRACT FROM AUTHOR]

A comprehensive lipid profile was analyzed in patients with non-small cell lung cancer (NSCLC) using nanoflow ultrahigh-performance liquid chromatography–electrospray ionization–tandem mass spectrometry. This study investigated 297 and 202 lipids in saliva and plasma samples, respectively, comparing NSCLC patients to healthy controls. Lipids with significant changes (>2-fold, p < 0.05) were further analyzed in each sample type. Both saliva and plasma exhibited similar lipid alteration patterns in NSCLC, but saliva showed more pronounced changes. Total triglycerides (TGs) increased (>2–3-fold) in plasma and saliva samples. Three specific TGs (50:2, 52:5, and 54:6) were significantly increased in NSCLC for both sample types. A common ceramide species (d18:1/24:0) and phosphatidylinositol 38:4 decreased in both plasma and saliva by approximately two-fold. Phosphatidylserine 36:1 was selectively detected in saliva and showed a subsequent decrease, making it a potential biomarker for predicting lung cancer. We identified 27 salivary and 10 plasma lipids as candidate markers for NSCLC through statistical evaluations. Moreover, this study highlights the potential of saliva in understanding changes in lipid metabolism associated with NSCLC. [ABSTRACT FROM AUTHOR]

Spatiotemporal signal analysis is essential in investigating magnetic fluctuations of tokamak plasmas. Signal analysis of Mirnov coils through biorthogonal decomposition (BD) can reveal the spatial structure and time evolution of magnetohy-drodynamic (MHD) instabilities in a tokamak. This technique is comparable to singular value decomposition in terms of formulation. The present study calculates the probability of instability modes’ presence and identifies the dominant modes using the method above. Moreover, the relationship between the singular value entropy as a signal characteristic and magnetic field oscillations of Mirnov coils in the IR-T1 tokamak is investigated. This study evaluated the presence of active modes with and without applying a resonant helical field. The results indicate that when L = 2 and L = 3 are applied independently, the probability of m = 2 and 3 active modes is greater than when the resonant helical field is absent. In contrast, by combining these two, the likelihood of the presence of these modes is reduced. [ABSTRACT FROM AUTHOR]

The electron–positron oscillations (EPOs) around fixed massive ions in cold electron–positron–ion (EPI) plasmas mix up in phase and break at arbitrarily small amplitudes (C Maity, Phys. Plasmas21, 072317 (2014)). In the present paper, we report the collisional effects on the process of phase mixing of EPOs in such plasmas. For our purpose, we assume that the electrons and positrons suffer collisions with the static ions. A perturbation treatment of the basic equations is carried out to derive an expression for phase-mixing time. The phase-mixing time depends on the equilibrium ion to electron density ratio, the perturbation amplitude and the rate of collisions. The collisional effects are found to delay the overall phase mixing process of EPOs. [ABSTRACT FROM AUTHOR]

Our paper considers the possibility of the emergence and control of non-equilibrium states of a quasi-homogenous condensed medium with energy and particle flows in the phase space, which, first of all, manifest themselves in the explosive development of the asymmetry in the initially symmetric equilibrium system. This symmetry breaking and the appearance of non-equilibrium in the system are controlled by the coherent acceleration of the system. Dependencies of thermodynamic parameters of a strong nonequilibrium system on the indices of disequilibrium in coherently correlated states are given, and the estimates of the dielectric permittivity in a non-equilibrium system and modes of plasma acoustic oscillations are made. An estimate of the superconducting transition temperature under nonequilibrium conditions has been made. It is demonstrated that the superconducting transition temperature can approach the limiting value, corresponding to a quantum with its plasma frequency of the medium. [ABSTRACT FROM AUTHOR]