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In this study, we examined the potential errors in plasma-density measurements using the cutoff probe method under various structural conditions, such as tip distance and length. Our studies indicate that under conditions of thin sheath thickness, the length or distance of the metal tips on the cutoff probe has a slight effect on the plasma transmission spectrum or cutoff frequency. However, under conditions with a notably thick sheath, the structure of the probe tip can cause an error of up to 2% between the measured cutoff frequency and actual plasma frequency. Consequently, for precise measurements of plasma density using the cutoff probe method, it is imperative to maintain a probe tip distance exceeding five times the sheath width and utilize a sufficiently long probe tip length. This finding is anticipated to provide essential guidelines for the design and fabrication of effective cutoff probes and enhance the accuracy of plasma-density measurements using a cutoff probe. [ABSTRACT FROM AUTHOR]

We investigate the plasmon-mediated nonlinear dynamics and the optics of a laser emission of random nanoemitters (NEs) embedded in a two-dimensional (2D) lattice of conducting nanorings (NRs) enhanced by plasmon–polariton (PP) excitations. The interaction of quantum NEs with the PP field in the NRs perturbs the dynamics of the electronic populations in NEs, leading to a significant dependence of laser generation (dynamics) on the plasma frequency ωp of PP. This results in a strong coupling of NE field emission with the PP field and sharp variations of the average current in the NR lattice. The phase transition in the system was found when the macroscopic structures of PP fields are excited simultaneously in different regions of the system if ωp (control parameter) reaches critical value ωc. We have established the analytical dependence of the PP current I = I(ωp/ωc) on the plasma frequency, which is in excellent agreement with the results of numerical simulations. This effect may allow the design of new types of PP active devices with the use of conducting NRs in modern nanoelectronics. [ABSTRACT FROM AUTHOR]

Electromagnetic shielding is a critical function in various technologies, which is ideally achieved using a metal that reflects all incident radiation below its plasma frequency. Using high-resolution finite difference frequency domain simulations at microwave/RF frequencies, we show that the same efficacy can be achieved using a disordered collection of metal nanoparticles embedded in a flexible material. The mechanism underlying the reflection in the composite material is wave localization, disallowing the propagation of radiation up to the plasma frequency of the metal that constitutes the particles. We realize such a biopolymer composite using DNA–CTMA (deoxyribonucleic acid–cetyltrimethylammonium complex) as a support structure for Ag nanoparticles. This biopolymer composite exhibits an extremely high shielding effectiveness, close to that of a metal slab, because of Anderson localization of the electromagnetic waves. [ABSTRACT FROM AUTHOR]

Fluorescent emitters are quenched near the surfaces of metals via rapid energy transfer to the metal, via surface plasmons, waveguide modes, and absorption. Commonly, this quenching is reduced by introducing a polymeric or dielectric spacer but requires large distances, at least a fraction of the wavelength, between the metal and chromophore. Using the classical theory for a dipole above a metal/dielectric substrate, we investigate the fluorescent yield for emitters above a wide range of metals and spacers. For metals with low loss and low plasma frequencies, a high index spacer is shown to be advantageous for obtaining higher fluorescent yield in an "island of emission" at finely tuned spacer thickness just 20–30 nm from the metal surface. For such metal–dielectric combinations, fluorophores can be placed surprisingly close to the metal surface while remaining significantly emissive. [ABSTRACT FROM AUTHOR]

Screened plasmon properties of graphene near a perfect electric conductor (PEC) are investigated taking into account the retardation effects. A detailed discussion of the dispersion relation of the mentioned screened plasmonic waves is presented and illustrated graphically using classical electrodynamics and a linearized hydrodynamic model that includes Fermi correction. The result indicates that for realistic wavenumbers, the dispersion relation of plasmonic waves of isolated graphene is almost unaffected by the Fermi correction, while this correction is an important factor for the screened plasmons of graphene near a PEC, where it increases the frequency of surface waves. The results show that near the graphene neutrality point, the surface wave has linear dispersion with a universal speed close to v F / 2. Such linear dispersion for surface waves (also known as energy waves) appears to be a common occurrence when splitting of plasma frequencies occurs, e.g., in the electron–hole plasma of graphene [Zhao et al., Nature 614, 688 (2023)]. Furthermore, analytical expressions for the energy parameters (the power flow, energy density, and energy velocity) of screened plasmons of the system are derived. Also, the analytical expressions are derived and analyzed for the damping function and surface plasmon and electromagnetic field strength functions of surface waves of the system with small intrinsic damping. [ABSTRACT FROM AUTHOR]

This report demonstrates tunable carrier densities in CdO thin films through local ion irradiation, providing lateral control of mid‐IR optical properties. Ion‐solid interactions produce donor‐like defects that boost electron concentrations from the practical minimum of 2.5 × 1019 cm−3 to a maximum of 2.5 × 1020 cm−3 by metered ion exposure. This range is achieved using He, N, Ar, or Au ions at 1–2.8 MeV; when normalized by displacements per atom, all ion species produce comparable results. Since CdO is well‐described by the Drude model, irradiation‐tuned carrier densities directly alter the infrared dielectric function, and in turn, mid‐infrared optical properties. Further, it is demonstrated that by combining irradiation with traditional lithography, CdO films expose to ions in the presence of 3‐µm thick, patterned photoresist exhibit lateral carrier density profiles with ≈400‐nm resolution. Scanning near‐field optical microscopy reveals sharp optical interfaces with almost no companion contrast in surface morphology, microstructure, or crystallinity. Finally, CdO lateral homostructures supporting surface plasmon polaritons (SPPs) are demonstrated whose dispersion relation can be tuned through periodic patterning in a monolithic platform by simple nanofabrication. Numerical simulations show these polaritons result from strong coupling between excitations at CdO plasma frequencies and SPPs supported by the platinum substrate. [ABSTRACT FROM AUTHOR]

The detailed analysis of the effect of light and heavy holes on the generation of terahertz (THz) radiation in GaAs in a magnetic field is given. It is shown that taking into account the motion of light holes leads to a relative increase in the field strength of the THz pulse by several times. Such an increase manifests itself at times comparable to or greater than the inverse plasma frequency of electrons and is accompanied by a relative increase in the spectral density of radiation at low frequencies. In the frequency range from 0.1 to 10 THz, the affect of heavy holes is weak and resulted in a small change in the spectral energy density at frequencies slightly higher than 0.1 THz, which leads to a relative increase in the THz field strength at the last stage of generation. [ABSTRACT FROM AUTHOR]

The formation and dynamics of vertical dust chains in the radio frequency discharge plasma sheath have been investigated. The spatiotemporal evolution diagram allows the visualization of the dust chain formation process as well as the oscillation phenomenon. A clear stratification was observed, and spatially nonuniform self‐organizing behavior of the dust chains, such as fractures and reconnections, was also observed, showing that the lower layers of the large‐grained chains are less restricted, softer, and more prone to rearrangement. The spatial distribution characteristics of the charged particles in the sheath and the modified two‐particle model, which takes into account the interparticle attraction, partially explain the mechanisms of the fracture and reorganization behavior of the dust chains. [ABSTRACT FROM AUTHOR]

The Particle-in-Cell (PIC) method, a cornerstone in plasma modeling, is widely employed for its ability to simulate kinetic phenomena in device-scale domains. Part of what makes this possible is that computational macroparticles represent many physical particles. It converges under certain constraints, including a grid spacing that resolves the Debye length and a time step small enough to respect the Courant–Friedrichs–Lewy condition and plasma frequency stability limit. Here, we introduce a new constraint necessary to avoid Artificial Correlation Heating (ACH). This requires that the macroparticle coupling strength be smaller than one, Γ w < 1 , where Γ w ≡ Γ w 2 / 3 , Γ = Z 2 e 2 / (4 π ε o a k B T) is the physical coupling strength, and w is the macroparticle weight. This is particularly relevant to 3D simulations of dense plasmas, which are becoming common with modern computing power. If this condition is violated, the finite macroparticle weight artificially enhances the coupling strength and causes the plasma to heat until the macroparticle coupling strength is near unity, depending on the grid resolution. A comprehensive model of ACH is developed that incorporates electron density, temperature, macroparticle weight, and grid resolution. It is then tested using PIC simulations, delineating the boundaries of the method's applicability and offering a predictive framework for ACH. Moreover, the research explores a runaway heating process induced by ACH in the presence of ionization, which can lead to numerical instability. A conclusion of this study is that the onset of ACH can impose a more stringent constraint on the macroparticle weight and average number of macroparticles per cell than what is typically expected, particularly in 3D simulations of dense plasmas. [ABSTRACT FROM AUTHOR]

Quantitative spectroscopy of molecular hydrogen has generated substantial demand, leading to the accumulation of diverse elementary process data encompassing radiative transitions, electron-impact transitions, predissociations, and quenching. However, their rates currently available are still sparse, and there are inconsistencies among those proposed by different authors. In this study, we demonstrate an experimental validation of such a molecular dataset by composing a collisional-radiative model (CRM) for molecular hydrogen and comparing experimentally obtained vibronic populations across multiple levels. From the population kinetics of molecular hydrogen, the importance of each elementary process in various parameter space is studied. In low-density plasmas (electron density n e ≲ 10 17 m − 3 ) the excitation rates from the ground states and radiative decay rates, both of which have been reported previously, determine the excited state population. The inconsistency in the excitation rates affects the population distribution the most significantly in this parameter space. However, in higher density plasmas ( n e ≳ 10 18 m − 3 ), the excitation rates from excited states become important, which have never been reported in the literature, and may need to be approximated in some way. In order to validate these molecular datasets and approximated rates, we carried out experimental observations for two different hydrogen plasmas; a low-density radio frequency heated plasma ( n e ≈ 10 16 m − 3 ) and the Large Helical Device (LHD) divertor plasma ( n e ≳ 10 18 m − 3 ). The visible emission lines from EF 1 Σ g + , H H ¯ 1 Σ g + , D 1 Π u ± , GK 1 Σ g + , I 1 Π g ± , J 1 Δ g ± , h 3 Σ g + , e 3 Σ u + , d 3 Π u ± , g 3 Σ g + , i 3 Π g ± , and j 3 Δ g ± states were observed simultaneously and their population distributions were obtained from their intensities. We compared the observed population distributions with the CRM prediction, in particular the CRM with the rates compiled by Janev et al., Miles et al., and those calculated with the molecular convergent close-coupling (MCCC) method. The MCCC prediction gives the best agreement with the experiment, particularly for the emission from the low-density plasma. However, the population distribution in the LHD divertor shows a worse agreement with the CRM than those from low-density plasma, indicating the necessity of the precise excitation rates from excited states. We also found that the rates for the electron attachment is inconsistent with experimental results. This requires further investigation. [ABSTRACT FROM AUTHOR]

The energy deposition of laser-accelerated proton beams in solid-density plasmas with different ion charge numbers is studied with detailed one-dimensional particle-in-cell simulations. In the plasma with a high ion charge number, in which the plasma collision frequency approaches electron oscillation frequency, the beam protons are strongly decelerated by the electric field induced by the plasma return current. The energy deposition is further enhanced as the beam travel distance increases due to beam density self-steeping, which is also confirmed by multi-dimensional particle-in-cell simulation. A simple analytical model is proposed to estimate the characteristic travel distance for significant density self-steeping, showing agreement with the simulation results. While in the plasma with a low ion charge number, in which the plasma collision frequency is much smaller than the electron oscillation frequency, the proton beam is modulated significantly by the excited two-stream instability. [ABSTRACT FROM AUTHOR]

The dynamic local field correction (LFC) of the classical one component plasma is studied with molecular dynamics simulations and analytical theory. Simulation results are obtained for a wide range of frequencies and wavenumbers in the strongly coupled regime. The dynamic LFC generally differs significantly from both the zero and high-frequency limits. The latter is attained at increasingly lower frequencies as the coupling grows. In the long wavelength limit, the frequency dependence of the LFC is studied in detail. Pronounced structure is observed in the vicinity of the plasma frequency and its first harmonic. The results provide access to the plasmon dispersion and are used to test the accuracy of various theoretical approaches. In the low-frequency limit, the simulation data are compared with the predictions of hydrodynamics, which connects the LFC with thermodynamic and transport coefficients. While a direct comparison is typically hindered by the finite size of the simulations, good agreement is found at strong coupling for a relation that connects the imaginary part of the LFC with the viscosity. [ABSTRACT FROM AUTHOR]

Spatiotemporal evolution of large amplitude upper-hybrid oscillations in a cold homogeneous plasma in the presence of an inhomogeneous magnetic field is studied analytically and numerically using the Dawson sheet model [J. Dawson, Phys. Fluids 5, 445–459 (1962)]. It is observed that the inhomogeneity in magnetic field, which causes the upper-hybrid frequency to acquire a spatial dependence, results in phase mixing and subsequent breaking of the upper-hybrid oscillations at arbitrarily low amplitudes. This result is in sharp contrast to the usual upper-hybrid oscillations in a homogeneous magnetic field, where the oscillations break within a fraction of a period when the amplitude exceeds a certain critical value [R. C. Davidson, Methods in Nonlinear Plasma Theory (Academic, New York, 1972)]. Our perturbative calculations show that the phase mixing (wave breaking) time scales inversely with the amplitude of magnetic field inhomogeneity (Δ) and amplitude of imposed density perturbation (δ) and scales directly with the ratio of magnetic field inhomogeneity scale length to imposed density perturbation scale length [ (α / k L) − 1 ] as ω p e τ mix ∼ (1 + β 2) 3 / 2 k L / (β 2 δ Δ α) , where β is the ratio of electron cyclotron frequency to electron plasma frequency. Further phase mixing time measured in simulations, performed using a 1–1/2 D code based on the Dawson sheet model [J. Dawson, Phys. Fluids 5, 445–459 (1962)], shows good agreement with the above-mentioned scaling. This result may be of relevance to plasma based particle acceleration experiments in the presence of a transverse inhomogeneous magnetic field. [ABSTRACT FROM AUTHOR]

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We demonstrate similarity rules for inductively coupled plasmas with thermohydrodynamic coupling effects using two-dimensional fluid simulations and theoretical analyses of the gas flow and heat transfer equations. The results confirm the validity of conventional similarity laws, e.g., the similarity relation for electron density, which can be violated by the nonlinear gas heating effects from exothermic and endothermic reactions. The nonlinear gas heating can obviously perturb the invariance of spatial distributions of the gas flow velocity, resulting in the electron density decreasing nonproportionally with different scaling factors. Adding an external heat source can mitigate the violation of the gas temperature scaling law, thus maintaining the validity of similarity relations to some extent. In addition, two kinds of scaling relations for excited-state argon atoms are identified with and without the consideration of nonlinear collisions. [ABSTRACT FROM AUTHOR]

We investigated the effect of the sheath around the probe tips on the transmission spectrum of a cutoff probe using an electromagnetic simulation and a circuit model. Our results show that the width of the sheath can change the transmission spectrum, which can affect the absolute value of the electron density. In a real-world cutoff probe structure, this effect may become apparent in a low-density plasma or when a high bias voltage is applied to the plasma. The key factor is capacitance, which contains the sheath component. In the case of a low-density plasma, the change in the sheath capacitance of the sheath region contributes to the shift in the resonant frequency. For thick sheath widths, at least a 5% discrepancy can occur between the actual plasma frequency and the measurement owing to variations in the capacitance, particularly the sheath components surrounding the probe. We expect that this study will facilitate reduction in the measurement error and uncertainty in microwave cutoff probe measurements, particularly when applied to low-density plasma measurements. [ABSTRACT FROM AUTHOR]

A flat-cutoff sensor installed on the chamber wall or chuck allows precise measurement of the plasma density in real time, even with a wafer placed on the sensor. However, a few studies have been conducted on the measurement characteristics in an environment where a wafer containing a metal layer is placed on a sensor. In this study, we investigated the effect of wafers containing metal layers on flat-cutoff sensor measurements using circuit models and experiments. The metal layer in the wafer shifts the cutoff frequency up to four times higher, and the degree of shift depends on the plasma density. The relationship between the shift in the cutoff frequency and plasma density can be interpreted as the ratio of the plasma inductance to that of the metal layer from the circuit model of the flat-cutoff sensor. The calculation results were verified experimentally using wafers containing Al and Ti metal layers. As a result, measurement was found to be possible even when a wafer containing a metal layer was placed on a flat-cutoff sensor, and these results can improve the measurement accuracy of the flat-cutoff sensor for the real-time plasma measurement. [ABSTRACT FROM AUTHOR]

Background: Around 10% of people with HIV (PWH) exhibit a low-level viremia (LLV) under antiretroviral therapy (ART). However, its origin and clinical significance are largely unknown, particularly at viremias between 50 and 200 copies/mL and under modern ART based on integrase strand transfer inhibitors (INSTIs). Our aim was to characterize their poor immune response against HIV in comparison to individuals with suppressed viremia (SV) and non-HIV controls (NHC). Methods: Transversal observational study in 81 matched participants: 27 PWH with LLV, 27 PWH with SV, and 27 NHC. Activation (CD25, HLA-DR, and CD38) and senescence [CD57, PD1, and HAVCR2 (TIM3)] were characterized in peripheral T-cell subsets by spectral flow cytometry. 45 soluble biomarkers of systemic inflammation were evaluated by immunoassays. Differences in cell frequencies and plasma biomarkers among groups were evaluated by a generalized additive model for location, scale, and shape (GAMLSS) and generalized linear model (GLM) respectively, adjusted by age, sex at birth, and ART regimen. Results: The median age was 53 years and 77.8% were male. Compared to NHC, PWH showed a lower CD4+/CD8+ ratio and increased activation, senescence, and inflammation, highlighting IL-13 in LLV. In addition, LLV showed a downtrend in the frequency of CD8+ naive and effector memory (EM) type 1 compared to SV, along with higher activation and senescence in CD4+ and CD8+ EM and terminally differentiated effector memory RA+ (TEMRA) subpopulations. No significant differences in systemic inflammation were observed between PWH groups. Conclusion: LLV between 50 and 200 copies/mL leads to reduced cytotoxic activity and T-cell dysfunction that could affect cytokine production, being unable to control and eliminate infected cells. The increase in senescence markers suggests a progressive loss of immunological memory and a reduction in the proliferative capacity of immune cells. This accelerated immune aging could lead to an increased risk of developing future comorbidities. These findings strongly advocate for heightened surveillance of these PWH to promptly identify potential future complications. [ABSTRACT FROM AUTHOR]

Selection of dust particles in three-dimensional plasma–dust trap in the electrodeless radio frequency inductive discharge in neon was studied for the first time. The discharge conditions and the discharge chamber design were chosen so that the dust structures of polydisperse quartz particles are created in the resulting dust trap. The structure lengths were of up to 1.5 cm and the number of particles in them was of up to 4000. Statistical analysis of the sizes of trapped particles has shown that under the conditions chosen the average particle size is close to 4 μm, and in a wide range from 0.25 to 1.0 Torr, it weakly depends on neon pressure. It was found that in the three-dimensional dust structure formed, the longitudinal interparticle distance changes in anomalously wide range, as compared to the dust structures formed in plasma of glow discharge. The characteristic size of the trapped particles was estimated based on the vertical balance of forces acting on dust particle. It was shown that, in terms of a number of parameters, the method of particle selection in radio frequency inductive discharge is preferable, as compared to similar method used in glow discharges in strata, and the dust trap applied can be used for studying three-dimensional dusty plasmas in the magnetic field. [ABSTRACT FROM AUTHOR]

This study presents the development of a ferrite core inductively coupled plasma (ICP) radio frequency (RF) ion source designed to improve the lifetime of ion sources in commercial ion implanters. Unlike existing DC methods, this novel approach aims to enhance the performance and lifetime of the ion source. We constructed a high-vacuum evaluation chamber to thoroughly examine RF ion source characteristics using a Langmuir probe. Comparative experiments assessed the extraction current of two upgraded ferrite core RF ion sources in a commercial ion implanter setting. Additionally, we tested the plasma lifetime of the ICP source and took temperature measurements of various components to verify the operational stability and efficiency of the innovative design. This study confirmed that the ICP RF ion source operated effectively under a high vacuum of 10−5 torr and in a high-voltage environment of 30 kV. We observed that the extraction current increased linearly with RF power. We also confirmed that BF3 gas, which presents challenging conditions, was stably ionized in the ICP RF ion sources. [ABSTRACT FROM AUTHOR]

In detecting hypersonic vehicles, the radar echo signal is coupled with an intra-pulse Doppler frequency (I-D frequency) component caused by relative motion of a plasma sheath (PSh) and the vehicle, which can induce the phenomenon of a ghost target in a one-dimensional range profile. In order to investigate the I-D frequency generated by the relative motion of a PSh, this study transforms a linear frequency modulated (LFM) signal into a single carrier frequency signal based on echo signal equivalent time delay-dechirp processing and realizes high resolution and fast extraction of the I-D frequency coupled with the frequency-domain echo signal. Furthermore, by relying on the computation of the surface flow field of the RAMC-II Blunt Cone Reentry Vehicle, the coupled I-D frequency in the radar echo signal of a PSh-enveloped target under circumstances of typical altitudes and carrier frequencies is extracted and further investigated, revealing the variation law of I-D frequency. The key findings of this study provide a novel approach for suppressing anomalies in radar detection of PSh-enveloped targets as well as effective detecting and as robust target tracking. [ABSTRACT FROM AUTHOR]

Validated and accurate edge profiles (temperature, density, etc.) are vitally important to the Mega Ampere Spherical Tokamak Upgrade (MAST-U) divertor and confinement effort. Density profile reflectometry has the potential to significantly add to the measurement capabilities currently available on MAST-U (e.g., Thomson scattering and Langmuir probes). This work presents the diagnostic requirements, problems, and solutions facing profile reflectometry in spherical tokamaks and MAST-U in particular. Requirements include density measurements near zero electron density in the scrape off layer region, coverage for a broad range of MAST-U plasma parameters, high time (≤10 microseconds) and spatial resolutions (≤1 cm), reliability, and identification of the plasma start frequency. [ABSTRACT FROM AUTHOR]

The diagnostic of magnetized radio frequency complex plasma via probing techniques and spectroscopy is challenging. However, a self-excited dust ion acoustic waves (DIAWs) have been observed employing laser scattering. Inspired by the current high enthusiasm for the theoretical description of complex plasma, we study the propagation of DIAWs in a three-dimensional collisional and magnetized dusty plasma medium. We consider the fluid model for dust and ion particles, while we neglect the inertia of electrons considering the Boltzmann distribution. A linear dispersion relation is obtained and a nonlinear modified Zakharov–Kuznetsov equation is derived utilizing the reductive perturbation technique. The effects of ion-neutral and dust-neutral collisions on the dynamics of the nonlinear DIAWs are considered. The phase portrait analysis and numerical illustration of a rarefactive DIA cnoidal waves and solitons are also presented. Our findings agree with experimental observations by Choudhary M, Bergert R, Mitic S, and Thomas MH. [Influence of external magnetic field on dust acoustic waves in a capacitive rf discharge. Contrib Plasma Phys. 2020;60:e201900115] as the growth of nonlinear periodic waves is recorded when the magnetic field is roughly 0.05 T and vanishes when the magnetic field is close to 0.1 T. Moreover, the model reveals that the electrostatic cnoidal and soliton waves propagate with low frequencies up to 140 Hz. [ABSTRACT FROM AUTHOR]

The Vlasov equations are used to determine the transverse and longitudinal dielectric permeabilities of a hot, rarefied ultrarelativistic electron-positron plasma. The Fermi distribution is used as the unperturbed distribution function of the electrons and positrons. It is shown that, owing to the abundant production of electron-positron pairs, the plasma frequency of the ultrarelativistic plasma increases linearly with rising temperature. Here the ratio of the frequency at which the spectral density of the equilibrium emission is maximal to the plasma frequency remains fixed and equals 28. It is shown that in this sort of plasma, in particular in the matter of the early universe in the ultrarelativistic electronpositron epoch, the spectrum of the radiation differs very little from black-body radiation. [ABSTRACT FROM AUTHOR]

This study investigates magnetosonic shock waves in a spin-polarized three-component quantum plasma using the quantum magnetic hydrodynamic model. We explore the influence of spin effects, specifically spin magnetization current and spin pressure, on shock wave behavior. Numerical analysis of the linear dispersion relation under varying parameters such as positron imbalance, spin polarization ratio, plasma beta, quantum diffraction, and magnetic diffusivity reveals differential impacts, with diffusion exerting significant influence on the plasma frequency. Our findings highlight the sensitivity discrepancy between the real and imaginary parts of the dispersion relation. Furthermore, nonlinear behavior of magnetosonic shock waves is examined via the Korteweg–de Vries–Burgers equation, showcasing transitions between oscillatory and monotonic wave patterns based on changes in dimensionless parameters. Notably, we observe the combined effects of spin-up and spin-down positrons with spin-up and spin-down electrons on shock wave dynamics, contributing to a deeper understanding of spin-plasma interactions with implications across various fields. [ABSTRACT FROM AUTHOR]

In this paper, a planar OAM reconfigurable plasma reflective metasurface with size 30 × 30 cm2 is designed. It consists of the reconfigurable plasma metasurface reflector and a feed horn antenna. The phase distribution of the plasma reflective metasurface combines the OAM phase distribution and the beam focusing required phase distribution. The required phase shifting range is 360° which obtained by adjusting the plasma frequency with changing the applied DC biasing voltage for the argon gas. The advantages of the design are high gain 22.4 dBi, narrow divergence angle 5°, high purity, good stability, planar structure, and easy fabrication. Beam scanning using the reflective metasurface for l = 1 at (θ = φ = 0°), (θ = 10°, φ = 0°), (θ = 20°, φ = 0°) and (θ = 30°, φ = 0°) is demonstrated. [ABSTRACT FROM AUTHOR]

In collisionless plasma, the function of an externally imposed static electric field has been investigated for facilitating the generation of high-power terahertz (THz) radiation. A nonlinear transient current density occurs at THz radiation frequency due to the optical rectification of high-power laser pulse having secant hyperbolic temporal intensity profile. This transient current driving a THz radiation is found to be strongly depended on the pulse width of laser, electron plasma frequency, and externally applied electric field. The effect of mismatched phase between the generated THz wave and laser has also been studied. Numerical simulations show that the strength of THz amplitude initially increases with propagation distance and then decreases. [ABSTRACT FROM AUTHOR]

Two kinds of fluorides are proposed innovatively to modulate the dielectric property of the plasma by reducing the electron density. There is a maximum of 74.41% electron density reduction after the fluorides are injected into the plasma at a magnitude of 1019 m−3, and the corresponding plasma frequency reduction is 49.42%. The fluorides proposed in this paper exhibit a wider modulation range, a faster modulation speed, and a longer maintenance time compared with SF6. The electromagnetic (EM) wave transmission characteristics in plasma are modulated correspondingly. The attenuation of S21 is reduced by 15.11–20.11 dB in 6–18 GHz, and an enhancement in the whole experimental frequency range is observed compared with SF6. The results of the paper can be applied in the mitigation of reentry vehicle's EM wave attenuation induced by the over-dense plasma sheath covering the vehicle. In addition, it also has a potential in broad applications of EM wave and plasma interactions. [ABSTRACT FROM AUTHOR]

Plasma-assisted reforming shows great promise for making ammonia compatible with current engine technology, with minimal modifications required. This study examines the impact of various discharge, flow, and composition parameters on ammonia conversion into hydrogen using a new well-stirred homogeneous plasma reactor. Gas chromatography was used to measure hydrogen and oxygen, while ICCD imaging evaluated plasma homogeneity. Initial mixture composition significantly influences the response to plasma conditions. Relative to the initial ammonia composition, the conversion of pure ammonia yields a lower hydrogen percentage when compared to air-diluted mixtures. Introducing air changes the relationship between pulsed energy deposition and hydrogen production, resulting in a more substantial increase in conversion. Efficiency calculations demonstrate that high ammonia content and high pulse frequencies improve yields, while longer residence times in the reactor result in higher temperatures, also increasing yields. These findings provide insights into the underlying mechanisms of ammonia cracking and reforming in a discharge, and will serve to promote further investigation into plasma reforming strategies. • Enhanced hydrogen production from plasma-assisted reforming of ammonia influenced by initial mixture composition. • Optimal hydrogen yields achieved with high ammonia content and high pulse repetition frequency of plasma discharges. • Effective reforming strategies demonstrated for longer residence times in reactor due to gas heating. [ABSTRACT FROM AUTHOR]

The investigation of tuneable and energy-efficient terahertz (THz) generation has become a prominent field of study due to its significant ramifications in various disciplines, including chemical analysis and medical research. This study selects two co-propagating Hermite-cosh-Gaussian (HchG) laser beams with positively chirped frequencies for analysis. The laser beam exhibits interaction with a collisionless underdense plasma in the presence of a static transverse magnetic field. The interaction between laser and plasma exhibits nonlinear characteristics, leading to the creation of THz radiation with high energy efficiency. The primary objective of this study is to conduct an analytical examination of the correlation between THz conversion efficiency, normalised transverse distance, and plasma frequency. Additionally, the analysis will consider various laser parameters, including the Hermite polynomial mode index (s), decentred parameter (a), and frequency chirp (b). The results show that in off-resonant condition THz conversion efficiency quickly decreases and approaches to zero for normalised THz frequencies. The observed phenomenon entails an augmentation in the normalized amplitude of terahertz (THz) waves, accompanied by a displacement of the peak towards greater normalized transverse distance values. This occurrence is contingent upon the variation of the Hermite polynomial mode index within the range of 0 t o 2. As the chirp parameter (b) is increased from 0.0011 t o 0.0099 , the normalised terahertz (THz) amplitude exhibits an increase with respect to the normalised transverse distance for values of s equal to 0,1 a n d 2. The proposed methodology demonstrates significant use in generating high-intensity, adjustable, and energy-efficient terahertz (THz) radiation sources through the manipulation of the decentred parameter and Hermite polynomial mode index values. [ABSTRACT FROM AUTHOR]

Earlier, a conventional grill launcher-based LHCD system has been developed to drive plasma current non-inductively in tokamaks at IPR (ADITYA and SST1) at a frequency (fo = ωo/2π) of 3.7 GHz, which has the ability to launch pure spectrum with high directivity. Grill having large number of sub-waveguides launches a sharp spectrum, which drive LH current more efficiently and therefore was preferred for carrying out plasma physics studies in a controlled manner. An over-dense plasma near the mouth of the launcher provides good coupling of LHWs with plasma and therefore the grill launcher needs to be placed close to the last close flux surface (LCFS). The grill launcher at IPR allows to launch LHWs having a parallel refractive index (N||) from 1.5 to 4.0 by varying the phase difference between adjacent sub-waveguides from 60° to 160°. For ADITYA tokamak, owing to space constraints, the grill launcher with eight sub-waveguides (arranged in two rows, each having four sub-waveguides) could be developed to launch of power up to 120 kW, and therefore, the topology of the ADITYA LHCD was not very complex. However, for the 1 MW LHCD system for SST1 tokamak, the grill launcher with sixty-four sub-waveguides (arranged in two rows, each having thirty-two sub-waveguides) was developed and the SST1 LHCD system, thus conceived, was huge and very complex offering tremendous engineering design challenges. For reactor-grade plasmas, where rf power of a few tens of MW would be launched in to the plasmas, a more compact and reactor-relevant LH launcher, often known as passive–active multijunction (PAM) is foreseen. The PAM launcher offers very good coupling with low reflection co-efficient (∼2–5%) when the plasma density near the mouth of the launcher is near cutoff densities for a given frequency (ωo = ωpe, the electron plasma frequency), and thus allowing it to be placed far away from the LCFS of the plasma, thereby minimizing deleterious effects on launcher due to hostile edge plasma conditions and makes this launcher relevant for reactor-grade plasmas. Further, the space behind the passive waveguide can be utilized for neutron shielding and efficient thermal management. On the contrary, it offers reduced directivity and the spectrum can be varied over a narrow range. Further, the network of transmission lines feeding this launcher is relatively simpler and offers less technological challenges. Thus, 250-kW PAM launcher (comprising of two modules)-based LHCD system for ADITYA-U tokamak has been designed and developed. The launched N|| may be varied over a narrow range (2.25 ± 0.375) by varying the phase difference between adjacent modules over 180° ± 90°. The physics requirements, design philosophy, engineering challenges/solutions, the key outcome and achievements as we embark on to PAM launcher are presented and discussed. Based on our experience of PAM launcher, for ADITYA-U tokamak, conceptual design of the PAM launcher for SST1 is also presented. [ABSTRACT FROM AUTHOR]

This research scrutinizes the impact of external magnetic field strength variations on plasma jet parameters to enhance its performance and flexibility. Plasma jets are widely used for their high thermal and kinetic energy in both medical and industrial fields. The study employs optical emission spectroscopy to measure electron temperature, electron density, and plasma frequency in a plasma jet subjected to varying magnetic field strengths (25, 50, 100, 150, and 250 mT). The results indicate that a stronger magnetic field results in higher electron temperature (1.485 to 1.991 eV), electron density (5.405 × 1017 to 7.095 × 1017), and plasma frequency 7.382 × 1012 to 8.253 × 1012 Hz. As well as the research investigates the influence of gas flow rate on gas temperature in the plasma jet. It is observed that gas temperature gradually drops with a growth in the flow rate of argon gas. The voltage and current waves have a sinusoidal waveform without elevation lines and with decaying waveforms. The existence of a strong magnetic field generates magnetohydrodynamic instability, leading to the plasma jet flame splitting. Understanding the effects of changing the strength of the external magnetic field on the plasma properties provides the ability to control the plasma Permart to make it suitable for many applications. [ABSTRACT FROM AUTHOR]

The aim of this article is to improve the performance of DBD excimer lamps systems for UV production. Within this framework, our approach considers two distinct directions: the geometric dimensions of the double-barrier lamp bulb and the characteristics of the power supply. To explore these directions, a sampling of 19 bulbs of different geometries is considered, and a specially designed power supply is used, capable of controlling the shape (duration and magnitude) and frequency of current pulses injected into the plasma. A dedicated test bench, including a supervisory program that drives the power supply and collects system performance data, is used to perform parametric sweeps and guarantee measurement repeatability: the set of electrical parameters is fully explored for each lamp, and each experiment is characterized by UV emission performance and electrical generator operating conditions. Multiquadric response surfaces, used to format the results of this multi-variable exploration, reveal the most efficient directions for system optimization: increasing gas volume and, at a given operating frequency, providing the shortest possible current pulses with high amplitude can increase both UV emission and conversion efficiency. [ABSTRACT FROM AUTHOR]

Insulating ceramics are widely used in power systems, but their high polarity makes them prone to wet and pollution flashover. In this paper, an Ar/polydimethylsiloxane dielectric barrier discharge excited by a parametric nanosecond-pulse power source is utilized for plasma polymerization to enhance ceramic surface insulating performance. Diagnosis of the discharge characteristics and surface physiochemical properties is conducted at different repetition frequencies to investigate the mechanism associated with the relationship between repetition frequency and the plasma polymerization process. The results indicate that a superhydrophobic surface can be achieved at repetition frequencies above 2 kHz. This transformation brings about multiple effects, including a decrease in surface polarity, an increase in charge dissipation, and an improvement in surface dry and wet flashover voltages. It is discovered that the discharge mode shifts from homogeneous to filamentary due to the memory effect of high repetition frequencies. Additionally, several filaments are generated simultaneously during a single pulse, facilitating the polymerization reactions. For high repetition frequencies, a low-polarity silicon-containing film with micro-nanometer structures is deposited on the ceramic surface, while scattered polymer fragments are generated on the surface without a cross-linked film for repetition frequencies below 2 kHz, despite longer treatment durations. [ABSTRACT FROM AUTHOR]

Three-phase gliding arc discharge reactors are devices in which it is difficult to maintain stable plasma parameters, be it electrically, physically, or chemically. The main cause of plasma instability is the source, which is freely burning arcs in a three-phase system. In addition, these arcs burn at low currents and are intensively cooled, further increasing their instability. These instabilities translate into the electrical characteristics of the plasma reactor. The analysis for the four gases nitrogen, argon, helium, and air shows that the type of plasma-generating gas and its physical parameters have a strong influence on the operational characteristics of the plasma reactor. Current–voltage, power and frequency characteristics of the plasma reactor were plotted experimentally. Characteristics obtained in this way make it possible to determine the areas of effective operation of the plasma reactor, and to estimate the quality of the generated plasma. Based on the characteristics obtained, a method of controlling the plasma parameters can be developed. [ABSTRACT FROM AUTHOR]

In this work, the surface of the telescope’s mirror is cleaned using an atmospheric-pressure radio frequency plasma jet (APRFPJ), which is generated by Argon gas between two coaxial metal electrodes. The RF power supply is set to 2 MHz frequencies with three different power levels: 20, 50, and 80 W. Carbon, that has adhered to the surface, can be effectively removed using the plasma cleaning technique, which also modifies any residual bonds. The cleaned surface was clearly distinguished using an optical emission spectroscopy (OES) technique and a water contact angle (WCA) analyzer for the activation property on their surfaces. The sample showed a super hydrophilic surface at an angle of 1° after 2.5 minutes of plasma treatment, as determined by the WCA technique, and an analysis of its optical properties showed that its reflectance had increased from 75% before cleaning to 98% after cleaning. Using the OES technique, the RF plasma jet's spectrum can be observed to contain the ArI, ArII, and NI lines. [ABSTRACT FROM AUTHOR]

A two-dimensional symmetric fluid model is established to study the influence of radio frequency (RF) wave driving frequency on the capacitively coupled plasma discharge. The relationship between the driving frequency and electron density is obtained by solving the electron energy balance equation. The calculation results show that the average electron density first increases rapidly with the increase in driving frequency and then gradually tends to saturation at a threshold frequency. A fluid simulation is also carried out, which provides similar results. Physical studies on this phenomenon are conducted, revealing that the essence of this phenomenon is due to the inability of electrons to quickly respond to potential changes within the boundary sheath when the driving frequency of RF exceeds the plasma frequency. In addition, it is also found that increasing gas pressure can enhance the electron density and the type of gas can also affect the electron density. [ABSTRACT FROM AUTHOR]

A new experimental method for creating void-free complex (dusty) plasmas under microgravity conditions is presented. The method is based on a pulsed operation mode of a four-channel radio frequency generator for plasma sustainment. A dust cloud of micrometer-sized particles can be immersed in the bulk of a low temperature plasma under microgravity conditions. It typically contains a central volume depleted of particles—the void—that prevents the generation of large, continuous clouds. Experiments performed at different neutral gas pressures and discharge volumes during the microgravity phase of a parabolic flight show that the central void is closed completely once the pulsed operation mode is applied. The particle cloud shape and the density distribution within the cloud are practically independent of the pulse period within the investigated parameter range and mainly depend on the overall discharge parameters neutral gas pressure and discharge volume. This indicates that the pulsed operation of the plasma source does not introduce new physical effects on the particles aside from the void closure. The proposed method has great potential for future application in experimental facilities dedicated to fundamental studies of large three-dimensional, homogeneous complex plasma systems in microgravity. [ABSTRACT FROM AUTHOR]

Quantum electrodynamic (QED) plasmas, describing the intricate interplay of strong-field QED and collective pair plasma effects, play pivotal roles in astrophysical settings like those near black holes or magnetars. However, the creation of observable QED plasmas in laboratory conditions was thought to require ultra-intense lasers beyond the capabilities of existing technologies, hindering experimental verification of QED plasma theories. This paper provides a comprehensive review of recent studies outlining a viable approach to create and detect observable QED plasmas by combining existing electron beam facilities with state-of-the-art lasers. The collision between a high-density 30 GeV electron beam and a 3 PW laser initiates a QED cascade, resulting in a pair plasma with increasing density and decreasing energy. These conditions contribute to a higher plasma frequency, enabling the observation of ∼ 0.2 % laser frequency upshift. This solution of the joint production-observation problem should facilitate the near-term construction of ultra-intense laser facilities both to access and to observe the realm of strong-field QED plasmas. [ABSTRACT FROM AUTHOR]

The transmission of electromagnetic radiation through a silicon substrate with a square metallic grid deposited on one side has been studied experimentally. It has been established that the electrodynamic response of the structure is equivalent to the excitation of a transverse electromagnetic plasma mode in it with the plasma frequency determined by the geometric parameters of the grating, as well as by the thickness and relative permittivity of the substrate. A theoretical model has been developed to qualitatively describe the experimental results obtained. [ABSTRACT FROM AUTHOR]

With the continuous evolution of additive manufacturing technology, the production of spherical powders has become increasingly vital. Various studies suggest that factors such as the preparation process, powder materials, and sphericity are crucial in determining product performance. This paper provides a comprehensive review of the principles, advantages, and disadvantages of three widely used preparation technologies for spherical powders: gas atomization (GA), plasma rotating electrode process (PREP), and radio frequency plasma (RFP). Next, we identify the current research gaps in the preparation process for spherical powders and analyze the techniques for controlling particle size, sphericity, and purity during powder production. Finally, we proposed the development trend of spherical powder preparation technology, which provides crucial insights for optimizing the preparation process. [ABSTRACT FROM AUTHOR]

High-order harmonic generation in laser-induced plasmas is analyzed from the point of view of presence of either molecular or atomic components. Comparison of boron carbide, carbon, and boron plasmas demonstrates the worsened characteristics of coherent extreme ultraviolet radiation in the case of B4C (smaller conversion efficiency, lower cutoff of generated harmonics, worsened stability). Similar features, alongside the disappearance of resonance-induced enhancement of harmonics and weakened quasi-phase-matching conditions, were observed in other molecular plasmas (Ag2S, GaAs, Cr3C2) compared with plasmas comprising atomic components (Ag, As, Cr). We discuss the reasons of worsening conditions in the case of high-order harmonic generation in few-atomic molecular species compared to the single-atomic ones. [ABSTRACT FROM AUTHOR]

Spatial confinement effects offered by a blocker on the laser-induced plasma parameters of titanium (Ti) are evaluated using the Optical Emission Spectroscopy technique. Nd:YAG (1064 nm, 10 ns) laser is used as an irradiation source. To observe the spatial confinement effects, an Al blocker at different distances of 4, 6, and 8 mm from the target is placed along the plume path. All the measurements are performed under the Ar environment at different pressures. It is observed that with increasing laser irradiance plasma parameters such as excitation temperature (Te) and electron number density (ne) increase, whereas it is vice versa true for increasing blocker distances. Without the blocker, the maximum values of Te and ne are about 7000 K and 1.4 × 1018 cm−3, respectively, at an Ar pressure of 50 Torr. A significant increase in emission intensity along with Te ≈ 9810 K and ne ≈ 2.2 × 1018 cm−3 is achieved in the presence of blocker. The results show that spatial confinement is responsible for the enhancement of Te and ne, which is attributed to the increased collisional frequency of plasma species after compression by shockwaves. The ablation pressure and shock pressure are also analytically evaluated and vary from 0.15 to 0.25 GPa and from 0.1 to 0.2 GPa, respectively, with increasing laser irradiance. With increasing blocker distances from 4 to 8 mm, the work done by reflected shockwaves to compress the plume varies from 0.02 to 0.002 mJ. [ABSTRACT FROM AUTHOR]

A plasma impedance probe (PIP) is a type of in situ, radio frequency (RF) probe that is traditionally used to measure plasma properties (e.g., density) in low-density environments such as the Earth's ionosphere. We believe that PIPs are underrepresented in laboratory settings, in part because PIP operation and analysis have not been optimized for signal-to-noise ratio (SNR), reducing the probe's accuracy, upper density limit, and acquisition rate. This work presents our efforts in streamlining and simplifying the PIP design, circuit-based-model, calibration, and analysis for unmagnetized laboratory plasmas, in both continuous and pulsed PIP operation. The focus of this work is a Monte Carlo uncertainty analysis, which identifies operational and analysis procedures that improve SNR by multiple orders of magnitude. Additionally, this analysis provides evidence that the sheath resonance (and not the plasma frequency as previously believed) sets the PIP's upper density limit, which likely provides an additional method for extending the PIP's density limit. [ABSTRACT FROM AUTHOR]

Fabry–Pérot (F–P) cavity and metal hole array are classic photonic devices. Integrating F–P cavity with holey metal typically enhances interfacial reflection and dampens wave transmission. In this work, a hybrid bound surface state is found within rectangular metal holes on a silicon substrate by merging an extraordinary optical transmission (EOT) mode and a high-order F–P cavity mode both spatially and spectrally. Transmission, Q-factor, and bandwidth can be enhanced significantly with respect to the classical EOT and F–P interference by simply sweeping the cavity length. This state can provide EOT properties and ten times broader EOT bandwidth well below the effective plasma frequency of the periodic metal holes, where the metal holes typically show evanescent properties and do not support EOT in theory. Furthermore, a large modulation range of 25 % and 39 % is demonstrated with various graphene patterns for the transmittance of this hybrid state at 500 and 582 GHz, respectively. [ABSTRACT FROM AUTHOR]

Most in situ plasma diagnostics are only reliable for low-pressure systems, e.g., systems where the collision frequency, ν e n , is small compared to the plasma frequency, ω p e . In this article, we describe a novel diagnostic technique for simultaneous measurement of the plasma density, n e ; electron temperature, T e ; and ν e n in systems in which ν e n approaches ω p e . We illustrate the operational setup of our probe system along with an analytical framework for ascertaining n e , T e , and ν e n . Furthermore, we show experimental results from argon capacitively coupled plasma operating in the 0.5–1 Torr pressure range. [ABSTRACT FROM AUTHOR]

In this work, we present a study of the structural, optical, elastic, thermoelectric and thermodynamic properties of iridium manganese (IrMn) using the code "WIEN2k" with the full potential linearized augmented plane wave (FP-LAPW) method. The lattice constants of the IrMn compound are calculated by the generalized gradient approximation with Perdew–Burke–Ernzerhof (GGA-PBE). Indeed, we have studied the magnetism exhibited by the compound IrMn. We found that the antiferromagnetic phase of this material is the most stable phase. The magnetic moment, plasma frequency, bandgap, elastic constants, and electronic and magnetic properties of this material are deduced and discussed. We have shown that the antiferromagnetic phase is the most stable with a minimum energy value of around −1034947.477 eV. We optimized the c ∕ a ratio and found that its value is approximately c ∕ a ≈ 0.923133. On the other hand, the absorption and reflectivity coefficients, the optical conductivity and the dielectric tensor are studied. In addition, the thermo-electric and thermodynamic properties have been illustrated. The IrMn compound could be useful for different applications of spintronics. [ABSTRACT FROM AUTHOR]

This work used spectroscopic plasma emission analysis to investigate the parameters of ZnTi plasma formed in the atmosphere by a Q-switched Nd:YAG nanosecond laser system emitting infrared (1064 nm) laser light with an energy output spanning 200-500 mJ. The spectrometer was used to examine and record the emission spectrum profiles of (ZnTi), which helped to extract crucial plasma characteristics (i.e., T e and n e). The electron density was measured using the Stark broadening, and the plasma temperature was calculated using the Boltzmann plot technique. The electron temperature was between 2.04 and 2.15 eV, and the electron density was between (15.72 and 18.99) × 10 1 6 cm − 3 . The Debye length (l) , the number of particles in the Debye sphere ( N d) , and the plasma frequency ( f p) can all be estimated from the electron temperature ( T e) and the electron density ( n e) ( f p). [ABSTRACT FROM AUTHOR]

The solar type J radio burst is a variant of type III bursts, which are a probe for understanding solar energetic electrons and local electron density. This study investigates a type J burst event on 2017 September 9. We have combined the data from the extreme-ultraviolet (EUV) imaging and the EUV Imaging Spectrometer (EIS) to analyze the event. Within 4 minutes several type J bursts with similar morphology occur. Two of them, with clear fundamental and second harmonic bands, are studied in detail. We find a delay of 2 ± 0.5 s between their different harmonic bands. During type J bursts, only one coronal loop brightens significantly at its northern footpoint, in correlation with the continuous injection of erupting jets into the loop. The EUV intensity of the brightening footpoint is correlated with the radio flux at 245 and 410 MHz, with correlation coefficients of 0.2 and 0.4, respectively. These observations suggest that the type J bursts should originate from this coronal loop. By analyzing the electron number density distribution along the coronal loop diagnosed from the EIS data and the time evolution of the plasma frequency calculated from the type J burst, we determine that the velocities of the energetic electrons exciting the two type Js are 0.10 ± 0.02 c and 0.12 ± 0.02 c. Our results confirm previous studies on type J bursts. [ABSTRACT FROM AUTHOR]