Double Layers In Plasma Research Articles

Characteristics and transformations of dust acoustic double-layers in plasmas with adiabatically trapped-nonextensive ions using Tsallis-Gurevich distribution

The investigation focuses on examining the characteristics of dust acoustic double-layers (DA-DLs) in the presence of adiabatically trapped-nonextensive ions featuring Tsallis-Gurevich distribution. Indeed, the ion-density and pseudo-potential expressions are formulated in terms of transcendental functions, allowing for a detailed analysis of Dust Acoustic Double Layers associated with complex plasmas in the presence of non-extensive adiabatically trapped ions. The study then delves into the impact of background ion nonextensivity on key DA-DLs properties. The findings reveal that our plasma model can exhibits both compressive and rarefactive DA-DLs, depending on the nonextensive parameter q. Also, the results indicate that in both sub-sonic and supra-sonic scenarios, the amplitude of the DA-DLs structure rises as the nonextensive parameter decreases. Additionally, it is observed that, for a constant value of the nonextensive parameter q, the amplitude of the DA-DLs structure increases with higher Mach numbers. This investigation, prompted by observations in space and laboratory plasmas containing non-Maxwellian particles alongside trapped particles, has the potential to complement and offer fresh insights into previous works on solitary waves in plasma.

Wideband radar cross-section reduction by a double-layer-plasma-based metasurface

Reduction of the radar cross-section (RCS) is the key to stealth technology. To improve the RCS reduction effect of the designed checkerboard metasurface and overcome the limitation of thin-layer plasma in RCS reduction technology, a double-layer-plasma-based metasurface—composed of a checkerboard metasurface, a double-layer plasma and an air gap between them—was investigated. Based on the principle of backscattering cancellation, we designed a checkerboard metasurface composed of different artificial magnetic conductor units; the checkerboard metasurface can reflect vertically incident electromagnetic (EM) waves in four different inclined directions to reduce the RCS. Full-wave simulations confirm that the double-layer-plasma-based metasurface can improve the RCS reduction effect of the metasurface and the plasma. This is because in a band lower than the working band of the metasurface, the RCS reduction effect is mainly improved by the plasma layer. In the working band of the metasurface, impedance mismatching between the air gap and first plasma layer and between first and second plasma layers cause the scattered waves to become more dispersed, so the propagation path of the EM waves in the plasma becomes longer, increasing the absorption of the EM waves by the plasma. Thus, the RCS reduction effect is enhanced. The double-layer-plasma-based metasurface can be insensitive to the polarization of the incoming EM waves, and can also maintain a satisfactory RCS reduction band when the incident waves are oblique.

Reconfigurable Plasma Composite Absorber Coupled With Pixelated Frequency Selective Surface Generated by FD-CGAN

Conventional plasma absorbers are challenging to obtain high electron density and sizeable spatial scale for effective absorption while meeting the applied requirements of low profile and low power consumption. Although the frequency selective surface (FSS) has proved to realize a lower profile of plasma absorber with some empirical patterns adequately, the issue of the FSS design matching the dispersion distribution of complicated plasmas is still in suspense. A reverse prediction method referenced as the forecast and design Conditional Generative Adversarial Network (FD-CGAN) is proposed to generate a pixelated FSS between double-layer plasma periodic arrays. The reflection attenuation characteristics examined by experiments show that the addition of the FSS makes the coupling absorption effect surpass that of either pixelated FSS or plasma solely. Measurements in reconfigurable working modes and array arrangements demonstrate that the proposed configuration maximizes absorption effectiveness in the same profile, accompanied by the simulation. An interfacial void model is proposed to assist the design of the composite absorbing structure, together with an equivalent circuit for the hybrid absorber including periodic patterns with stochastic distribution characteristics, which analyze the absorption effect of the composite structure. The study provides a new approach for various microwave applications, including multilayer radar-absorbing structures, plasma-based stealth technology, and reconfigurable filters.

Surface plasma wave excited by laser pulse obliquely incident on a double-layer plasma target and ts application

Surface plasma wave (SPW) will significantly affect the subsequent mutual coupling between laser and plasma, so there are many important applications such as particle acceleration driven by laser pulses and transmission enhancement. In this work, the properties of the SPW produced by an ultra-short and ultra-intensity laser pulse incident on a double-layer plasma target are studied by using the all-electromagnetic large-scale two-dimensional particle in cell (PIC) simulations. It is shown that the high-intensity laser incident with a large angle, <i>θ</i> =75°, can drive the electrons of the low-density layer to form a transportable periodic structure with the propagation speed close to light speed, and excite electrostatic wave whose wavelength is similar to that of the incident laser and is numerically close to the theoretical result according to previous theory. In order to excite the SPW, the laser intensity needs to reach a certain threshold. Besides, the ratio of the surface wave intensity to the incident laser intensity in the double-layer target case obviously deviates from the theoretical result of the single-layer target case, showing a nonlinear relationship. In the second part of the simulation, it is found that the SPW can significantly enhance the transmission of subsequent laser pulse, allowing the subsequent laser to break through the "black barrier" due to the dense plasma. A pre-laser irradiates the double-layer plasma target at <i>θ</i> = 75°, and then the subsequent laser is normally incident after a delay of Δ<i>t</i> = 23<i>T</i>. As a result, an obvious electromagnetic wave with the same direction as the sub-laser can be observed behind the target, which indicates that the sub-laser absolutely transmits the dense plasma. In comparison, when a single laser is normally incident on the target without pre-laser while other conditions keep unchanged, no obvious wave can be distinguished behind the target, that is, the field is nearly zero. Another simulation where a single-layer target is injected by pre-laser and sub-laser in order but the wave behind the target is also unobservable, proves that it is SPW that plays the main role in transmission enhancement instead of accelerated hot electrons on the target which can also transport the laser energy.

Development of computer-controlled atmospheric pressure plasma structuring for 2D/3D pattern on fused silica

Fused silica with structured and continuous patterns is increasingly demanded in advanced imaging and illumination fields because of its excellent properties and functional performance. Atmospheric pressure plasma, based on pure chemical etching under atmospheric pressure, is developed as a promising fabrication technique for fused silica due to its deterministic high material removal rate, controllable removal imprint and no mechanical load. The stable and controllable Gaussian-shape removal function makes computer-controlled plasma tool potential to generate complex structures with high accuracy, efficiency and flexibility. In the paper, computer-controlled atmospheric pressure plasma structuring (APPS) is proposed to fabricate 2D/3D patterns on fused silica optics. The capacitively coupled APPS system with a double-layer plasma torch and its discharge characteristics are firstly developed. By means of multi-physics simulation and process investigation, the stable and controllable Gaussian-shape removal function can be achieved. Two different structuring modes, including discrete and continuous APPS, are explored for 2D/3D patterns. A series of structuring experiments show that different kinds of 2D patterns (including square lens array, hexagon lens array and groove array) as well as complex 3D phase plate patterns have been successfully fabricated, which validates the effectiveness of the proposed APPS of 2D/3D patterns on fused silica optics.

Arbitrary amplitude ion acoustic double layer in plasma with k-distributed electrons and negative ions

In this paper we have discussed the consequence of superthermal electrons and negative ion concentration on the arbitrary amplitude ion-acoustic double layers (IA-DLs) for plasma comprising the hot negative and positive ions with kappa distribution electrons. The energy equation is deduced for ion acoustic waves using Pseudo potential technique. We have investigated different parametric regimes for the existence of rarefactive and compressive ion acoustic DLs. The existence of double layers in term of minimum and maximum Mach number has calculated numerically. The effect of spectral index k on the amplitude of DLs and depth of Sagdeev potential has been discussed in detail. From numerical analysis, it is found that the compressive DLs exist at low values of α and rarefactive double layer exist at higher values of α. On the other hand, the effect of ionic temperature ratio (σ 1 and σ 2) plays significant role for the formation of double layer. Our analytical work also shows that the system supports coexistence of compressive and rarefactive DLs. It is also observed that the mass ratio affect the basic properties of DLs. We expect that the present results may be used to explain the ion-acoustic double layer in space plasma, where two ionic species and superthermal electrons are observed NO52.35g.

Effects of nonthermal electrons and ion beams on ion-acoustic double layers in warm ion plasma

The effects of nonthermal electrons and ion beams on the ion acoustic double layers in warm ion plasma have been studied using the pseudopotential technique. Sagdeev potential of ion-acoustic wave in the plasma has been derived and the solution of ion acoustic double layers has been obtained. The critical value of nonthermal parameter of electrons for existence of double layers is obtained and discussed. The profiles of double layers in the plasma are drawn taking different values of density and temperature of ion beams, and the nonthermal parameter of electrons obeying the critical condition. It has been shown that both compressive and rarefactive double layers are excited in the plasma depending on the values of nonthermal electrons and ion beam parameters. The width of double layers is also graphically discussed. The results are new and may be useful in understanding the acceleration processes of charged particles in space plasma.

Proton acceleration from laser interaction with a complex double-layer plasma target

Target-normal sheath acceleration (TNSA) of protons from a solid-density plasma target consisting of a thin foil, with a thin hydrogen layer behind it and a plasma-filled tube with a parabolic density profile at its front, is investigated using two-dimensional particle-in-cell simulation. It is found that the targetback sheath field induced by the laser driven hot electrons is double peaked, so that the protons are additionally accelerated. The hot sheath electrons, and thus the TNSA protons, depend strongly on the tube plasma, which unlike the preplasma caused by the laser prepulse can be easily controlled. It is also found that the most energetic and best collimated TNSA protons are produced when the tube plasma is of near-critical density.

A local meshless method for solving multi-dimensional Vlasov–Poisson and Vlasov–Poisson–Fokker–Planck systems arising in plasma physics

In this paper, we use a linear combination of the shape functions of reproducing kernel particle method (RKPM) and RBFs for achieving the unknown weights into each stencil. We obtain an error bound for the new shape function. Also, in this paper, we investigate a numerical procedure based on the presented technique for solving the Vlasov---Poisson and Vlasov---Poisson---Fokker---Planck systems. The Vlasov equation is a differential equation describing time evolution of the distribution function of plasma. The Vlasov---Poisson equations are used to describe various phenomena in plasma, in particular Landau damping and the distributions in a double layer plasma. We use the RKPM/RBF-FD technique for discretization of space direction and employ the method of lines to achieve a high-order accuracy in temporal direction. Numerical examples are reported which demonstrate the theoretical results and the efficiency of proposed scheme.

W-type ion-acoustic solitary waves in plasma consisting of cold ions and nonthermal electrons

Sagdeev potential approach is used for the study of nonlinear propagation of ion-acoustic waves in plasma consisting of cold positive ions and nonthermal electrons. The nonlinear equation so derived are analysed with the help of Bogoliubov–Mitropolosky method. The profiles of Sagdeev potential solitary waves are evaluated in first-, second- and third- order which are depicted for different values of nonthermal parameter of electrons. It is seen that nonthermal electrons has considerable impact on the shape of ion-acoustic solitary waves in each order. The plasma consisting of cold positive ions and no negative ions can support the formation of compressive as well as W-type solitary waves in second- and third- order for certain value of nonthermal parameter of electrons. The results are new because W-type ion-acoustic solitary wave is found by earlier authors in plasma in presence of negative ions only. The ion-acoustic solitary waves near critical value of nonthermal parameter and arbitrary amplitude solitary waves in presence of nonthermal electrons have also been studied in the paper. Moreover, the solution for ion-acoustic double layers in plasma consisting of nonthermal electrons is obtained. Our results in the paper would be useful to understand the nonlinear wave processes in ionospheric and magnetospheric multicomponent plasma having nonthermal electrons.

Ion Acceleration by Ultra-intense Laser Pulse Interacting with Double-layer Near-critical Density Plasma

A collimated ion beam is generated through the interaction between ultra-intense laser pulse and a double layer plasma. The maximum energy is above 1GeV and the total charge of high energy protons is about several tens of nC/μm. The double layer plasma is combined with an underdense plasma and a thin overdense one. The wakefield traps and accelerates a bunch of electrons to high energy in the first underdense slab. When the well collimated electron beam accelerated by the wakefield penetrates through the second overdense slab, it enhances target normal sheath acceleration (TNSA) and breakout after-burner (BOA) regimes. The mechanism is simulated and analyzed by 2.5 dimensional Particle-in-cell code. Compared with single target TNSA or BOA, both the acceleration gradient and energy transfer efficiency are higher in the double layer regime.

On the generation of double layers from ion- and electron-acoustic instabilities

A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric field structures traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs—electron acoustic DLs—generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e., the hypothetical electron acoustic DLs cannot be formed in a way similar to ion acoustic DLs. Linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric field structures that propagate at the electron thermal speed, suggesting another potential explanation for the observations.

Observation of warm, higher energy electrons transiting a double layer in a helicon plasma

Measurements of an inductive RF helicon argon plasma double layer with two temperature electron distributions including a fast (>80 eV) tail are observed at 0.17 mTorr Ar pressure. The fast, untrapped electrons observed downstream of the double layer have a higher temperature (13 eV) than the trapped (Te = 4 eV) electrons. The reduction of plasma potential and density observed in the double layer region would require an upstream temperature ten times the measured 4 eV if occurring via Boltzmann ambipolar expansion. The experimental observation in Madison helicon experiment indicates that fast electrons with substantial density fractions can be created at low helicon operating pressures.

Foil-less plasma-filled diode for HPM generator

Plasma-filled diode regarded as perspective source of electron beam feeding HPM generator of GW power level, comparing to conventional explosive emission vacuum diode. Electron beam generation occurs in plasma double layer, where plasma boundary plays as an anode. It allows cancelling the usage of anode foils or grids in HPM generators with the virtual cathode, which could limit its life time to few shots. The presence of ions in the e-beam drift space could raise the limiting current for a drift space, but it could affect to microwave generation also. Sectioned plasma-filled diode with beam current of about 100 kA, electron beam energy of about 0.5 MV and beam current density of 1-10 kA/cm2 was realized. Cylindrical transport channel with the diameter of 200 mm and the length of about 30 cm was attached to the diode. Beam current measurements in a drift space were performed. Computer simulations of electron beam transport with the presence of ions were carried out with the 2.5D axisymmetric version of PiC-code KARAT. Obtained results would help optimizing electrodynamic system of HPM generator subjected to the presence of ions.

Enhancement of proton acceleration field in laser double-layer target interaction

A mechanism is proposed to enhance a proton acceleration field in laser plasma interaction. A double-layer plasma with different densities is illuminated by an intense short pulse. Electrons are accelerated to a high energy in the first layer by the wakefield. The electrons accelerated by the laser wakefield induce the enhanced target normal sheath (TNSA) and breakout afterburner (BOA) accelerations through the second layer. The maximum proton energy reaches about 1 GeV, and the total charge with an energy higher than 100 MeV is about several tens of μC/μm. Both the acceleration gradient and laser energy transfer efficiency are higher than those in single-target-based TNSA or BOA. The model has been verified by 2.5D-PIC simulations.

Gardner Solitons and Double Layers in a Multi-Ion Plasma With Degenerate Electrons

A precise theoretical investigation is made on ion-acoustic (IA) solitary waves (SWs) and double layers (DLs) in a degenerate multi-ion plasma (composed of inertial positive and negative ions and degenerate electrons). The standard reductive perturbation method is employed to derive the Korteweg-de Vries (K-dV), the mixed K-dV (mK-dV), and the Gardner (GE) equations. The GE admits SW and DL solutions for $\mu$ around its critical value $\mu_{c}$ (where $\mu_{c}$ is the value of $\mu$ corresponding to the vanishing of the nonlinear coefficient of the K-dV equation). The basic features of IA SWs and DLs are analyzed. It is found that the characteristics of IA SWs found from GE are different from those of the K-dV solitons and mK-dV solitons. The implications of our results to different space and laboratory plasma situations, where opposite polarity ions are observed, are briefly discussed.

Endpoint Detection Using Principle Component Analysis and Local Outlier Factor in the Double Layer Plasma Etching

.In plasma etch process, the optical emission spectroscope (OES) is widely used to detect plasma etch endpoint. The OES gathers the intensity of the wavelength from the radicals in the plasma chamber. In addition, the OES is very sensitive to the external elements or a particles, which means that there are diverse noise in OES data. Therefore, it is necessary to choose meaningful data, reduce noise, and reduce the quantity of data. In this paper, a new method to detect endpoint of double layer plasma etching is proposed. This algorithm uses data from OES and utilizing principle component analysis (PCA) and local outlier factor (LOF).

Dielectronic satellite lines and double layers in solar flares

Context. Particle acceleration during solar flares results in departures of the distribution of particle energies from the Maxwellian distribution. Apart from the high-energy tail, the bulk of the distribution was recently also found to be significantly affected, due, e.g., to the presence of double layers. Aims. We investigate the influence of several proposed non-Maxwellian distribution functions on the X-ray flare line spectra. The distribution functions considered are sharply peaked and include the n-distribution, the moving Maxwellian distribution, and the distribution formed in strong double layers in the flaring plasma. Methods. Synthetic Si xiid‐Si xiv spectra involving allowed and dielectronic transitions at 5−6 A are calculated numerically. The parameters chosen for the calculations correspond to the impulsive phase of solar flares, as inferred by previous authors. Results. The Si xiid λ5.56/Si xiii λ5.68 and Si xiid λ5.82/Si xiii λ5.68 ratios depend on the relative number of electrons at energies corresponding to the formation of the Si xiid lines. Therefore, these ratios increase with the increasing narrowness of the peak of the electron distribution function. The highest ratios are achieved for the distribution formed in double layers, while the moving Maxwellian distribution is less likely to reproduce the observed enhancement of Si xiid intensities. However, the ratio of the allowed Si xiv λ5.22/Si xiii λ5.68 transitions depends on the ionization equilibrium. This ratio is very small for the double-layer distribution. Combination of the double-layer distribution with a Maxwellian distribution with the same mean energy significantly enhances this ratio, while keeping the Si xiid intensities sufficiently increased to explain the characteristics of the observed spectra. Conclusions. These results support the presence of double layers in the plasma during impulsive phase of solar flares.

Two-dimensional double layer in plasma in a diverging magnetic field

Plasma created by an inductive RF discharge is allowed to expand along a diverging magnetic field. Measurement of the axial plasma potential profile reveals the formation of an electric double layer near the throat of the expansion chamber. An accelerated ion beam has been detected in the downstream region, confirming the presence of the double layer. The 2-D nature of the ion energy distribution function of the downstream plasma has been studied by a movable ion energy analyser, which shows that the beam radius increases along the axial distance. The 2-D structure of the plasma potential has been studied by a movable emissive probe. The existence of a secondary lobe in the contour plot of plasma equipotential is a new observation. It is also an interesting observation that the most diverging magnetic field line not intercepting the junction of the discharge tube and the expansion chamber has an electric field aligned with it.

Large amplitude double-layers in a dusty plasma with a q-nonextensive electron velocity distribution and two-temperature isothermal ions

Arbitrary amplitude dust-acoustic (DA) double-layers in a plasma with nonextensive electrons, two-temperature thermal ions, and warm drifting dust grains are addressed. It is shown that DA double-layer structures, the onset of which depends sensitively on the plasma parameters, can exist. In particular, it may be noted that the electron nonextensivity may affect drastically the existence of these localized structures. In view of recent observation, our results should assist in the interpretation of the nonlinear double-layers observed in the downward current region of the aurora.