Electron Plasma Research Articles

Optimization of plasma parameters for effective attenuation of microwaves in specified frequency range

AbstractIn this article, a plasma‐metal model is studied as an electromagnetic absorber for stealth application. Epstain distribution is considered for plasma and the electromagnetic reflection of the structure is analyzed by the Green's function volume integral equation method. The attenuation of microwaves in plasma depends on microwave frequency, plasma electron density, spatial distribution of plasma, collision frequency, and plasma thickness. Using a metaheuristic optimization method, it is possible to change the parameters simultaneously in the specified domains to obtain conditions for which microwaves can be absorbed effectively in the specified frequency. In this paper, optimized plasma parameters related to ideal attenuation in desired frequency band are determined by this method. The advantage of this method is that the intervals related to the plasma parameters are selecting according to the practical conditions and in many cases prevent the production of high volume with high density plasma to achieve effective attenuation. The proposed method can be useful for designing adjustable devices in stealth applications. Proper management of power consumption in these devices is one of the results of adjustment.

Study on the Physical Characteristics of Plasma and Its Relationship with Pore Formation during Laser-Metal Active Gas Arc Hybrid Welding of 42CrMo Steel

The automobile industry puts forward higher requirements for the design and manufacture of steel pistons. However, the welding of 42CrMo steel pistons still has unsolved technical problems, especially welding defects that cannot be directly detected, such as pores, which are easily generated inside the weld. A plasma experiment of laser-metal active gas arc (MAG) hybrid welding 42CrMo steel was conducted in this paper, and plasma signals inside and outside the keyhole were detected during the laser welding, leading laser laser-MAG hybrid welding, and leading arc laser-MAG hybrid welding of 42CrMo steel. The characteristic parameters such as electron temperature and electron density were calculated and analyzed to investigate the relationship between plasma behavior and the formation of weld porosity in the welding process of 42CrMo steel. Based on the fluctuations in plasma electron temperature and electron density, the prediction of pore formation in the weld of 42CrMo steel was made, aiming to provide guidance for achieving a stable and reliable laser-MAG hybrid welding process for 42CrMo steel.

Anomalous staged hot-electron acceleration by two-plasmon decay instability in magnetized plasmas.

We present a staged hot-electron acceleration mechanism of the two-plasmon decay (TPD) instability in the transverse magnetic field under the parameters relevant to inertial confinement fusion experiments. After being accelerated by the forward electron plasma wave (FEPW) of TPD, the hot-electrons can be anomalously accelerated again by the backward electron plasma wave (BEPW) of TPD and then obtain higher energy. Moreover, the surfatron acceleration mechanism of TPD in the magnetic field is also confirmed, the electrons trapped by the TPD daughter EPWs are accelerated in the direction along the wave front. Interestingly, the velocity of electrons accelerated by surfing from the FEPW is quite easily close to the BEPW phase velocity, which markedly enhances the efficiency of the staged acceleration. The coexistence of these two acceleration mechanisms leads to a significant increase of energetic electrons generated by TPD in the magnetic field. Meanwhile the EPWs are dissipated, TPD instability is effectively suppressed, and the laser transmission increases.

Beat wave excitation of electron plasma wave by cross-focused q-Gaussian laser beams in thermal quantum plasmas

Beat wave excitation of electron plasma wave by cross-focused q-Gaussian laser beams in thermal quantum plasmas

Electronic structure and optical properties of superconducting compounds ScGa3 and LuGa3

The optical properties of bulk AuCu3-type ordered superconducting binary compounds ScGa3 and LuGa3 have been experimentally investigated for the first time in the wide spectral range and explained in terms of the band structure. First-principles calculations of electronic densities of states and optical conductivities are performed within the framework of LSDA+U method using the LMTO-ASA software package. The measured dielectric functions spectra for both materials exhibit a strong absorption region above ∼ 1[Formula: see text]eV, which are in a reasonable agreement with the calculated metal-like energy structures of compounds. Features of quantum light absorption are discussed on the basis of a comparative analysis of experimental and theoretical spectra of interband optical conductivity. Plasma and relaxation frequencies of conduction electrons are determined.

Unprecedented confinement time of electron plasmas with a purely toroidal magnetic field in SMARTEX-C

Confinement time of electron plasmas trapped using a purely toroidal magnetic field has been found to exceed {100}, hbox {s} in a small aspect ratio (R_{o}/a sim {1.59}, R_o and a are device major and minor radius, respectively), partial torus. It improves upon the previously reported confinement time by nearly two orders of magnitude. Lifetime is estimated from the frequency scaling of the linear diocotron mode launched from sections of the wall, that are also used for mode diagnostics. Confinement improves as neutral pressures are reduced to < 5 times 10^{-10} hbox{mbar} in the presence of a steady state magnetic field of 200 Gauss (sim {60}, hbox {s} with droop < 0.1%) at {100}, hbox {V} electron injection energies. With reduced pressures the role of (ion driven) instability diminishes and loss mechanisms resulting from elastic electron–neutral (e–n) and the ubiquitous electron–electron (e–e) scattering seem to play an important role which suggests low electron temperatures. The contribution to electron population resulting from the ionization of background neutral gas at these temperatures and pressures are expected to be insignificant and is corroborated in our experiments.

Applied Plasma Physics Experiments in Linear (APPEL) device for plasma surface interaction studies

The APPEL device (Applied Plasma Physics Experiments in Linear Device), recently commissioned at the Institute for Plasma Research (IPR), is an intermediate setup towards building a Plasma Material Interaction (PMI) facility. A particular application of this device is to develop and test high-density, low-pressure plasma sources that can be operated under magnetic fields; optimize the plasma sources for working under various magnetic field configurations; and perform physics experiments relevant to electron heating and plasma interactions with external electrodes. The setup consists of 16 electromagnets that provide a flexible, steady-state axial magnetic field in excess of 0.4 T over an axial distance of 3.5 m, with 2 % radial uniformity across 32.0 cm diameter. This paper gives a brief overview of the APPEL device, emphasizes on the APPEL magnet system, and presents the characteristics of a 3.5 m long, high-density (1017–1018 m−3) helium plasma column, using a hollow cathode plasma source obtained in the pressure range below i.e., p < 2.0 Pa. The corresponding ion flux is found to be in the range of 1021 -1022 m−2s−1, similar to other linear systems currently in use for plasma surface interaction studies. A qualitative discussion is given to explain the characteristics of the plasma column.

Plasmon dispersion and Landau damping in the nonlinear quantum regime.

We study the dispersion properties of electron plasma waves, or plasmons, which can be excited in quantum plasmas in the nonlinear regime. In order to describe nonlinear electron response to finite amplitude plasmons, we apply the Volkov approach to nonrelativistic electrons. For that purpose, we use the Schrödinger equationand describe the electron population of a quantum plasma as a mixture of quantum states. Within the kinetic framework that we are able to derive from the Volkov solutions, we discuss the role of the wave amplitude on the nonlinear plasma response. Finally, we focus on the quantum properties of nonlinear Landau damping and study the contributions of multiplasmon absorption and emission processes.

Ammonia Nitrogen Removal by Gas–Liquid Discharge Plasma: Investigating the Voltage Effect and Plasma Action Mechanisms

Atmospheric pressure gas–liquid discharge plasma has garnered considerable attention for its efficacy in wastewater contaminant removal. This study utilized atmospheric oxygen gas–liquid discharge plasma for the treatment of ammonia nitrogen wastewater. The effect of applied voltage on the treatment of ammonia nitrogen wastewater by gas–liquid discharge plasma was discussed, and the potential reaction mechanism was elucidated. As the applied voltage increased from 9 kV to 17 kV, the ammonia nitrogen removal efficiency rose from 49.45% to 99.04%, with an N2 selectivity of 87.72%. The mechanism of ammonia nitrogen degradation by gas–liquid discharge plasma under different applied voltages was deduced through electrical characteristic analysis, emission spectrum diagnosis, and further measurement of the concentration of active species in the gas–liquid two-phase system. The degradation of ammonia nitrogen by gas–liquid discharge plasma primarily relies on the generation of active species in the liquid phase after plasma–gas interactions, rather than direct plasma effects. Increasing the applied voltage leads to changes in discharge morphology, higher energy input, elevated electron excitation temperatures, enhanced collisions, a decrease in plasma electron density, and an increase in rotational temperatures. The change in the plasma state enhances the gas–liquid transfer process and increases the concentration of H2O2, O3, and, ⋅OH in the liquid phase. Ultimately, the efficient removal of ammonia nitrogen from wastewater is achieved.

Electron-field instability: Excitation of electron plasma waves by an electric field

Electric fields are commonplace in plasmas and affect transport by driving currents and, in some cases, instabilities. The necessary condition for instability in collisionless plasmas is commonly understood to be described by the Penrose criterion, which quantifies a sufficient relative drift between different populations of particles that must be present for wave amplification via inverse Landau damping. For example, electric fields generate drifts between electrons and ions that can excite the ion-acoustic instability. Here, we use particle-in-cell simulations and linear stability analysis to show that the electric field can drive a fundamentally different type of kinetic instability, named the electron-field instability. This instability excites electron plasma waves with wavelengths ≳30λDe, has a growth rate that is proportional to the electric field strength, and does not require a relative drift between electrons and ions. The Penrose criterion does not apply when accounting for the electric field. The large value of the observed frequency, near the electron plasma frequency, further distinguishes it from the standard ion-acoustic instability, which oscillates near the ion plasma frequency. The ubiquity of macroscopic electric fields in quasineutral plasmas suggests that this instability is possible in a host of systems, including low-temperature and space plasmas. In fact, damping from neutral collisions in such systems is often not enough to completely damp the instability, adding to the robustness of the instability across plasma conditions.

Dispersion Characteristics of Low-Frequency Electron Waves in a Magnetoactive Plasma of Arbitrary Density

The article studies waves in a collisionless magnetoactive plasma with frequencies much lower than the electron cyclotron frequency at an arbitrary ratio between the electron plasma and cyclotron frequencies. A general dispersion relation is obtained for the wave frequency as a function of the wave vector and the ratio of the plasma frequency to the cyclotron frequency. This relation is a bicubic equation with respect to frequency. Based on this equation, the existence domains of various wave modes depending on the specified parameter, their group velocity, polarization, and energy density are studied. Special attention is paid to low-frequency whistler waves in a low-density plasma, since, among the propagating wave modes existing in the specified range of parameters, whistler waves have the highest refractive index and play an important role in theresonant interaction of waves and particles.

Characterization of high-frequency waves in the Martian magnetosphere

Context. Various high-frequency waves in the vicinity of upper-hybrid and Langmuir frequencies are commonly observed in different space plasma environments. Such waves and fluctuations have been reported in the magnetosphere of the Earth, a planet with an intrinsic strong magnetic field. Mars has no intrinsic magnetic field and, instead, it possesses a weak induced magnetosphere, which is highly dynamic due to direct exposure to the solar wind. In the present paper, we investigate the presence of high-frequency plasma waves in the Martian plasma environment by making use of the high-resolution electric field data from the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft. Aims. This study aims to provide conclusive observational evidence of the occurrence of high-frequency plasma waves around the electron plasma frequency in the Martian magnetosphere. We observe two distinct wave modes with frequency below and above the electron plasma frequency. The characteristics of these high-frequency waves are quantified and presented here. We discuss the generation of possible wave modes by taking into account the ambient plasma parameters in the region of observation. Methods. We have made use of the medium frequency (100 Hz–32 kHz) burst mode-calibrated electric field data from the Langmuir Probe and Waves instrument on board NASA’s MAVEN mission. Due to the weak magnetic field strength, the electron gyro-frequency is much lower than the electron plasma frequency, which implies that the upper-hybrid and Langmuir waves have comparable frequencies. A total of 19 wave events with wave activities around electron plasma frequency were identified by examining high-resolution spectrograms of the electric field. Results. These waves were observed around 5 LT when MAVEN crossed the magnetopause boundary and entered the magnetosheath region. These waves are either a broadband- or narrowband-type with distinguishable features in the frequency domain. The narrowband-type waves have spectral peak above the electron plasma frequency. However, in the case of broadband-type waves, the spectral peak always occurred below the electron plasma frequency. The broadband waves consistently show a periodic modulation of 8–14 ms. Conclusions. The high-frequency narrowband-type waves observed above the electron plasma frequency are believed to be associated with upper-hybrid or Langmuir waves. However, the physical mechanism responsible for the generation of broadband-type waves and the associated 8–14 ms modulation remain unexplained and further investigation is required.

Electron-enhanced atomic layer deposition of Ru thin films using Ru(DMBD)(CO)3 and effect of forming gas anneal

Ruthenium (Ru) thin films were deposited utilizing electron-enhanced atomic layer deposition (EE-ALD). Sequential exposures of Ru(DMBD)(CO)3 (DMBD = 2,3-dimethylbutadiene) and low-energy electrons at ∼125 eV were used to grow the Ru films at temperatures ≤160 °C. The electrons were obtained from a hollow cathode plasma electron source that provided an electron current of ∼200 mA over a surface area of ∼4 cm2. Low-energy electrons can desorb surface ligands derived from Ru(DMBD)(CO)3, such as CO, through electron-stimulated desorption. The desorbed surface ligands leave chemically reactive sites for subsequent Ru(DMBD)(CO)3 precursor absorption. Ru EE-ALD film growth was monitored utilizing in situ spectroscopic ellipsometry (SE). The electron exposures resulted in rapid Ru film nucleation and growth. Under saturation conditions at 160 °C, the growth rate for Ru EE-ALD was 0.2 Å/cycle. The electron efficiency factor for Ru EE-ALD was ∼21 500 electrons/deposited Ru atom. There was no film growth without electron exposures. Ru growth was observed on various substrates including silicon with native oxide and titanium. Ru growth was also obtained on insulating substrates such as 400 nm thick thermal SiO2 substrates. XPS analysis measured &amp;lt;1 at. % oxygen in the deposited Ru films. XRD, x-ray reflectivity, and SE were used to characterize the Ru films before and after forming gas anneal (FGA). FGA successfully removed carbon impurities from the as-deposited Ru films. The resistivity of the Ru EE-ALD films after FGA was determined to be as low as 17 μΩ cm for a film thickness of 6.7 nm. SE measurements of the imaginary part of the pseudodielectric function, 〈ɛ2〉, were utilized to characterize the as-deposited Ru films and the high purity Ru films after FGA. The low resistivity of the Ru films after FGA was consistent with a prominent Drude absorption in the ⟨ε2⟩ spectrum at ≤1 eV. Various reactive background gases such as H2, NH3, and H2O were utilized during EE-ALD to attempt to remove the carbon from the as-deposited Ru EE-ALD films.

Measurement and reduction of Ar metastable densities by nitrogen admixing in electron beam-generated plasmas

Electron beam (e-beam) generated plasmas are useful for material processing applications such as deposition and etching because the plasmas deliver a large fluence of very low energy of ions to surfaces. Metastable species produced in the beam-region can also transport significant energy to the plasma periphery and surfaces. In this work, we have investigated the spatially resolved density of metastable Ar 1s5 species produced in an Ar and Ar/N2 e-beam generated plasma at pressures of 60–67 mTorr using laser-induced fluorescence (LIF). The experiments provide the first direct measure of absolute density and reduction of Ar 1s5 in an e-beam generated plasma when argon is diluted with nitrogen. These results are consistent with previous predictions of numerical modeling and measurements using optical emission spectroscopy. The present spatially resolved LIF measurements directly quantify the reduction of Ar 1s5 in the e-beam generated plasma by nitrogen admixing. This reduction was observed in the region of the electron beam and in the plasma periphery, where substrates are usually placed. For example, up to a threefold reduction of the density of Ar 1s5 was measured when the argon background was diluted with 15.5% nitrogen at pressure of 60 mTorr. Ar 1s5 reduction is attributed to excitation exchange with nitrogen molecules as well as the cooling of plasma electrons via inelastic collisions with nitrogen molecules.

Non-ideal classical plasma: laser pulse effects and dynamic dipole polarizabilities

The properties of a hydrogen atom inside a non-ideal classical plasma, in terms of its behavior in the presence of an applied laser pulse, are explored. The strength of the pulse is chosen such that it maintains near sphericity of the system. The pulse parameters have a strong bearing on the final state attained by the system after its interaction with the pulse. Dynamic dipole polarizability is calculated and the poles are observed to be red shifted with an increase in non-ideality as well as an increase in plasma temperature. The polarizabilities for frequencies of the field below the frequency corresponding to the first pole are found to be greater for larger values of field frequency, plasma non-ideality and electron plasma temperature.

Suppression of stimulated Brillouin and Raman scatterings using an alternating frequency laser and transverse magnetic fields

A novel scheme to suppress both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) by combining an alternating frequency (AF) laser and a transverse magnetic field is proposed. The AF laser allows the laser frequency to change discretely and alternately over time. The suppression of SBS is significant as long as the AF difference is greater than the linear growth rate of SBS or the alternating time of the laser frequency is shorter than the linear growth time of SBS. However, the AF laser proves ineffective in suppressing SRS, which usually has a much higher linear growth rate than SBS. To remedy that, a transverse magnetic field is included to suppress the SRS instability. The electrons trapped in the electron plasma waves (EPWs) of SRS can be accelerated by the surfatron mechanism in a transverse magnetic field and eventually detrapped. While continuously extracting energy from EPWs, the EPWs are dissipated and the kinetic inflation of SRS is suppressed. The one-dimensional particle-in-cell simulation results show that both SBS and SRS can be effectively suppressed by combining the AF laser with a transverse magnetic field with tens of Tesla. The total reflectivity can be dramatically reduced by more than one order of magnitude. These results provide a potential reference for controlling SBS and SRS under the related parameters of inertial confinement fusion.

A kinetic theory approach to second harmonic generation by high power laser in magnetized plasma with nonextensive distribution

The present study presents a kinetic theory approach to second-harmonic generation (SHG) through high-power laser in collisionless plasma with nonextensively-distributed electrons. The study applied a relativistic Vlasov equation to obtain nonlinear current density and second-harmonic (SH) conversion efficiency. It was observed that the power conversion efficiency (PCE) of second-harmonic generation depends on plasma and laser parameters such as dimensionless cyclotron frequency, plasma density, normalized thermal velocity, the nonextensive q-parameter, and laser intensity. Moreover, cyclotron frequency associated with plasma electrons has been found to play an important role in increasing the power conversion efficiency of SH generation.

Laser wakefield acceleration of electrons in a magnetically controlled plasma

In the present study, the laser wakefield acceleration of electrons in a magnetically-controlled plasma is investigated. The results indicate that by employing a linearly-chirped laser pulse propagating through magnetized plasma with a reversed external magnetic field, higher energy electrons are obtained than with unmagnetized plasma and/or a nonchirped laser pulse. By considering an appropriate constant chirping magnitude and an axial external magnetic field, one can obtain remarkable GeV electron energies. It is also found that the effect of the external magnetic field direction on the electron energy is not sensed much in the mildly relativistic regime, while the reversed magnetic field increases the peak of electron energy gains compared with the forward magnetic field in the highly relativistic regime. For the mildly relativistic case, a peak energy of 412 MeV and a relative energy spread of 7% is obtained. In addition, for the highly relativistic case, a peak energy of 1.55 GeV is obtained.

Nonlinear interaction of electromagnetic wave with electron acoustic wave in plasma

An analysis on the nonlinear interaction of electromagnetic waves with electron acoustic waves is performed in plasma with two different temperature electron fluids in the presence of a neutralizing static ion background. A newly structured Zakharov’s equations are derived employing two fluid two-time scale theory. These coupled Zakharov’s equations describe the weakly nonlinear interaction of em wave perturbation with electron acoustic waves while propagating through plasma. In the low frequency or adiabatic limit, these Zakharov’s equations may be unified to produce a modified NLSE. A solution of the equation, novel in the literature, is derived following the method shown by Kudryashov. In a resonant regime, the modified NLSE reduces to NLSE. Though a stable solution exists for both cases, instability analysis shows caviton instability may arise. The threshold value of the electric field, at which instability sets in, is virtually zero for the resonant region whereas, apart from that region there is a threshold value of the electric field, determined by the frequency difference of em wave and electron plasma wave. Experimental observations support these results. This study is relevant for laser-plasma interaction and astrophysical and space plasma.

Terahertz to near infrared radiation generation using two-colour counter and co-polarized laser pulses propagating in homogeneous plasma

This study deals with the generation of terahertz (THz) to near infrared (NIR) radiation fields using two-colour linearly polarized copropagating laser pulses having either counter or co-polarization state. The frequency difference between the two laser pulses is considered to be integral multiple of the plasma frequency. Perturbation technique and quasistatic approximation have been used to obtain radiation field equations. Analytical and two-dimensional particle in cell simulation studies of the proposed configuration show that the transverse and axial plasma electron velocities arising due to nonlinear coupling of the two pulses are responsible for generation of off-axis linearly polarized radiation fields which propagate through plasma into vacuum. The frequency of generated radiation is ∼40 THz (∼60 THz), when the frequency difference of the laser pulses is two (three) times the plasma frequency. Analytical results are validated using VSim particle in cell simulation code.