Search

Atmospheric-pressure plasma jets operated in noble gases with an oxygen admixture have high application potential in industry and medicine. In this paper, we report on an extension of the well-studied RF-driven plasma jet from the European Cooperation in Science and Technology (COST-Jet), which has shown to deliver stable and reproducible discharge conditions but is limited to the α -discharge mode at low input powers. The so-called capillary-jet features the same discharge geometry as the COST-Jet, but the plasma is ignited inside a capillary with a square cross section acting as a dielectric in front of the electrodes. This prevents a glow-to-arc-transition at high input powers and allows stable operation in the γ -mode. We performed a set of measurements on the capillary-jet in the α - and γ -mode and compared the α -mode results to data obtained for the COST-Jet showing that the discharges are indeed similar and that the capillary-jet extends the accessible parameter range to high input powers. The presented results include power characteristics, temperature measurements, atomic oxygen densities from helium state enhanced actinometry, and molecular beam mass spectrometry (MBMS) as well as ozone densities from MBMS as functions of input power and molecular oxygen admixture. The results are summarized into an energy balance with most of the power dissipated into heating of the plasma feed gas. [ABSTRACT FROM AUTHOR]

This paper comprehensively investigates the oblique propagation of ion-acoustic solitary waves (IASWs) with arbitrary amplitude in a magnetoplasma consisting of inertialess non-Maxwellian (nonthermal) electrons, inertialess Maxwellian positrons, and inertial adiabatically heated ions. It is postulated that the positive ions demonstrate adiabatic behavior that is distinguished by anisotropic thermal pressure. The study utilizes Sagdeev's pseudopotential theory to analyze the fluid equations of the plasma model and reduce them to the energy equation. Different plasma configuration factors, such as nonthermal parameters, positron concentration, and parallel and perpendicular ion pressure, are being studied to see how they affect the properties of solitary waves with large amplitudes. The findings demonstrate the simultaneous coexistence of compressive and rarefactive IASWs, significantly influenced by positrons and nonthermal electron parameters. The study provides valuable insights into wave phenomena in magnetized plasmas and presents possible applications in both Space and laboratory plasma environments. [ABSTRACT FROM AUTHOR]

Accurate radiative properties data are required for the further calculations of radiative transfer in thermodynamic nonequilibrium plasmas produced by Earth entry. However, most of the published radiative properties were determined using the outdated spectroscopic constants, transition probabilities, and partition functions, some of which are less accurate and may deviate from the experimental results. In this paper, the spectral emission and absorption coefficients of diatomic molecules in air plasmas are thoroughly calculated based upon the exact line by line approach. In this scheme, the accurate spectroscopic constants and Franck–Condon factors were selected from the recent publications to reconstruct the rotational structure of spectral lines. Moreover, the level populations were determined by means of our newly reported two-temperature partition functions. The required thermodynamic parameters of each species were obtained by simulating a hypersonic flow field of the RAMC II vehicle. The calculated radiative properties were verified by the experimental and numerical equilibrium radiative source strength and the results show good consistency with measured and theoretical values in the available literature. Based upon the obtained flow field parameters, we finally predicted the distributions of nonequilibrium source strength along the stagnation line. Estimates and analysis were also made for the contributions of each transition system of the diatomic molecule to the total source strength. [ABSTRACT FROM AUTHOR]

Recently, the catalytic conversion of greenhouse gases by plasma technology has attracted more and more attention. In this paper, a two-dimensional fluid model is developed to study the reaction mechanism of plasma CO2 hydrogenation in atmospheric-pressure dielectric barrier discharge (DBD). The effect of varying volume ratio of CO2/H2 on reaction mechanism of CO2 hydrogenation is studied carefully, such as temporal and spatial density distributions of main radicals and ions, dynamics of streamer propagation, and generation and loss pathways of H, CO, and CH3OH. It is found that H, O, and CO are the three most abundant species, and lower hydrogen content in gas mixture promotes streamer propagation and the formation of conduction current in plasma column. Besides, H is mainly produced by electron-impact dissociation of H2 (e + H2 ⇒ e + 2H); O and CO are dominantly produced by electron-impact dissociation of CO2 (e + CO2 ⇒ e + CO + O). Interestingly, H addition reaction to the intermediate species CH3O (CH3O + H⇒ CH3OH) is found to be the main reaction pathway for methanol formation. Finally, a schematic overview of dominant reaction pathways for plasma CO2 hydrogenation in atmospheric DBD is presented, which ultimately leads to a better understanding of the intrinsic reaction mechanism. [ABSTRACT FROM AUTHOR]

In this paper, the effect of mixing of argon and oxygen gas on the mode transition and negative ion production in the helicon discharge is investigated. In the source chamber of the experimental setup, argon–oxygen gas mixture plasma is produced by applying RF power from 100 W to 2000 W at an applied magnetic field of 0.03 T. In this experiment, the total flow rate is kept at 200 SCCM, corresponding to the working pressure of 4–5 × 10−1 Pa. The mode transition to helicon discharge is investigated by varying the concentration of these two gases. To the best of our knowledge, the literature survey indicates this to be the first study of the influence of the mixing of oxygen–argon gas on the mode transition from the inductive to the helicon mode. It is observed that an increase in the concentration of oxygen gas in the discharge shifts mode transition toward higher RF power values, indicating the influence of the nature of the working gas on the transition to the inductive as well as to the helicon mode. The variation of the electron density and temperature is explained in terms of particle and power balance equation. In the source and in the downstream expansion chamber, the effect of the concentration of argon gas on the negative ion production in oxygen discharge is also studied, and the results are explained in terms of various reactions involved in the production and loss of negative ions. [ABSTRACT FROM AUTHOR]

Fluid mechanics is seen as the study on the underlying mechanisms of liquids, gases and plasmas, and the forces on them. In this paper, we investigate a (2 + 1)-dimensional generalized nonlinear system in fluid mechanics and plasma physics. By virtue of the Pfaffian technique, the Nth-order Pfaffian solutions are derived and proved, where N is a positive integer. Based on the Nth-order Pfaffian solutions, the first- and second-order breather solutions are obtained. In addition, Y-type and X-type breather solutions are constructed. Furthermore, we investigate the influence of the coefficients in the system on those breathers as follows: The locations and periods of those breathers are related to δ1, δ2, δ3, δ4, and δ5, where δc's (c = 1 , 2 , 3 , 4 , 5) are the constant coefficients in the system. Moreover, hybrid solutions composed of the breathers and solitons are derived. Interactions between the Y/X-type breather and Y-type soliton are illustrated graphically, respectively. Then, we show the influence of the coefficients in the system on the interactions between the Y/X-type breather and Y-type soliton. [ABSTRACT FROM AUTHOR]

The problem of interaction of microwaves with plasma is complicated and has garnered considerable interest. Parameters of plasma density, collision frequency, and plasma size have been shown to exert substantial impacts on microwave transmission in plasma. The respective influences of plasma parameters can be evaluated relatively easily; however, plasma must also be considered integrally as it is an electrically neutral medium. In this paper, using a designed plasma-metal model, we assess how plasma parameters influence the interaction of microwaves in plasma, revealing a nonmonotonic and complex relationship. Using parameter optimization, we obtain plasma parameters for plasma device design that meet the requirements of microwave transmission in plasma; the findings should prove useful in applications of electromagnetic waves in plasma. [ABSTRACT FROM AUTHOR]

This paper reports on a trilayer Ba0.85Ca0.15Zr0.1Ti0.9O3/La0.67Ca0.33MnO3/Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT/LCMO/BCZT) laminated composite fabricated using plasma-activated sintering. The interfacial structure and the electrical, ferromagnetic, and magnetoelectric properties of the laminated composite are characterized in detail. The laminated composite is found to be highly dense with high-quality interfacial bonding, and its dielectric properties are superior to those of BCZT. The characteristics of the ferroelectric and ferromagnetic properties demonstrate the multiferroic nature of the laminated composite, which exhibits a maximum magnetoelectric coefficient of 1.07 mV/cm Oe. [ABSTRACT FROM AUTHOR]

In this paper, attention is drawn to the importance of accounting for osmotic pressure when analyzing physiological effects on cellular structures in plasma medicine. Interaction of a weakly ionized plasma jet with a saline solution leads to detectable changes in the saline's ion-molecular composition and hence changes in the osmotic pressure. This, in turn, leads to a stretching or compression of the membrane, depending on the difference of total external and internal pressures. The selective effect of plasma on cells, observed in experiments, is associated with the change in the mechanical properties of membranes (and thereby, a weakening of their protective properties). Corresponding estimates are given in the article. [ABSTRACT FROM AUTHOR]

We study the effects of deuterium irradiation on D-uptake by simultaneously boronized, lithiated, oxidized, and deuterated carbon surfaces. We present analysis of the bonding chemistry of D for various concentrations of boron, lithium, oxygen, and deuterium on carbon surfaces using molecular dynamics with reactive force field potentials, which are here adapted to include the interaction of boron and lithium. We calculate D retention and sputtering yields of each constituent of the Li-C-B-O mixture and discuss the role of oxygen in these processes. The extent of the qualitative agreement between new experimental data for B-C-O-D obtained in this paper and computational data is provided. As in the case of the Li-C-O system, comparative studies where experimental and computational data complement each other (in this case on the B-Li-C-O system) provide deeper insights into the mechanisms behind the role that O plays in the retention of D, a relevant issue in fusion machines. [ABSTRACT FROM AUTHOR]

In this paper, we present the electron bunches extracted from a dense plasma produced by the interaction of a ns laser at an intensity of 1013W cm-2 with a solid target, when this plasma expands in an electric field. The plasma expansion dynamics measured in the previous works [M. Comet et al., J. Appl. Phys. 119, 013301 (2016)] is used to determine the electron charge density profile at different instants after the laser shot. When applying the electric field, a few 1013 electrons are extracted with continuous energy distributions. Particle-In-Cell simulations are run to understand the extraction process and reproduce the measured energy distributions, with the electron charge density profiles used as inputs. These simulations show that the electron extraction proceeds from the plasma front edge throughout the plasma expansion. [ABSTRACT FROM AUTHOR]

The paper presents results of numerical investigation of a large-volume plasma source based on a DC discharge with gridded anode. Geometry and configuration of the electrodes were chosen so as to ensure the formation of a cathode sheath, which would accelerate electrons up to high energies and inject them into the post-anode space and create plasma. Simulations were carried out using a hybrid model, and distributions of the main discharge parameters were obtained in a wide range of currents. At low currents, cathode sheath occupies whole interelectrode gap while plasma is formed in the post-anode space. It is shown that ions moving through the anode grid into the interelectrode gap cause reduction of discharge voltage when compared to the case of classical obstructed discharge with virtually closed anode grid. At higher currents, however, plasma is formed within the interlectrode gap as well, and ions moving from plasma in the post-anode space become trapped by reversed electric field. This essentially nullifies influence of the post-anode plasma on discharge properties. [ABSTRACT FROM AUTHOR]

This paper reports a previously unreported anomaly that occurs when attempting to perform deep, highly anisotropic etches into fused silica using an Inductively-Coupled Plasma (ICP) etch process. Specifically, it was observed that the top portion of the etched features exhibited a substantially different angle compared to the vertical sidewalls that would be expected in a typical highly anisotropic etch process. This anomaly has been termed as “faceting.” A possible explanation of the mechanism that causes this effect and a method to eradicate it has been developed. Additionally, the method to eliminate the faceting is demonstrated. It is theorized that this faceting is a result of the interaction of the electro-potential electrical fields that surround the patterned nickel layers used as a hard mask and the electrical fields directing the high-energy ions from the plasma to the substrate surface. Based on this theory, an equation for calculating the minimum hard mask thickness required for a desired etch depth into fused silica to avoid faceting was derived. As validation, test samples were fabricated employing hard masks of thicknesses calculated based on the derived equation, and it was found that no faceting was observed on these samples, thereby demonstrating that the solution performed as predicted. Deep highly anisotropic etching of fused silica, as well as other forms of silicon dioxide, including crystalline quartz, using plasma etching, has an important application in the fabrication of several MEMS, NEMS, microelectronic, and photonic devices. Therefore, a method to eliminate faceting is an important development for the accurate control of the dimensions of deep and anisotropic etched features of these devices using ICP etch technology. [ABSTRACT FROM AUTHOR]

This paper presents a simple but quite accurate numerical model for analyzing electrical explosion of copper wires in water. The numerical model solves a circuit equation coupled with one-dimensional magneto-hydrodynamic (MHD) equations with the help of appropriate wide-range equation of state (EOS) and electrical conductivity for copper. The MHD equations are formulated in a Lagrangian form to identify the interface between the wire and surrounding water clearly. A quotidian EOS (QEOS) that is known as the simplest form of EOS is utilized to build wide-range EOS for copper. In the QEOS, we consider the liquid-vapor phase transition, which is critical in analyzing the wire explosion system. For the electrical conductivity of copper, a semi-empirical set of equations covering from solid state to partially ionized plasma state are employed. Experimental validation has been performed with copper wires of various diameters, which are exploded by a microsecond timescale pulsed capacitive discharge. The simulation results show excellent agreements with the experimental results in terms of temporal motions of a plasma channel boundary and a shock front as well as current and voltage waveforms. It is found that the wire explodes (vaporizes) along the liquid branch of a binodal curve irrespective of wire dimension and operating voltage. After the explosion, the wire becomes a plasma state right away or after the current pause (dwell), depending on the operating conditions. It is worth noting that such a peculiar characteristic of wire explosion, i.e., current pause and restrike, is well simulated with the present numerical model. In particular, it is shown that the wire cools down along the vapor branch of the binodal curve during the current dwell, due to a significant difference of thermodynamic characteristics across the binodal curve. The influence of radiation for studying nonideal plasmas with a wire explosion technique and a physical process for shock wave formation by an exploding wire is discussed as well. [ABSTRACT FROM AUTHOR]

This paper is Part I of an integrated experimental/modeling investigation of a procedure to coat nanofibers and core-clad nanostructures with thin-film materials using plasma-enhanced physical vapor deposition. In the experimental effort, electrospun polymer nanofibers are coated with aluminum under varying operating conditions to observe changes in the coating morphology. This procedure begins with the sputtering of the coating material from a target. This paper focuses on the sputtering process and transport of the sputtered material through the reactor. The interrelationships among the processing factors for the sputtering and transport are investigated from a detailed modeling approach that describes the salient physical and chemical phenomena. Solution strategies that couple continuum and atomistic models are used. At the continuum scale, the sheath region and the reactor dynamics near the target surface are described. At the atomic level, molecular-dynamics (MD) simulations are used to study the sputtering and deposition mechanisms. Ion kinetic energies and fluxes are passed from the continuum sheath model to the MD simulations. These simulations calculate sputtering and sticking probabilities that in turn are used to calculate parameters for the continuum reactor model. The reactor model determines the concentration field of the coating material. [ABSTRACT FROM AUTHOR]

This paper is concerned with modeling the formation of beryllium (Be) layers deposited from a Be-seeded deuterium (D) plasma. In recent experiments at the PISCES-B divertor simulator [Y. Hirooka et al., J. Vac. Sci. Technol. A 8, 1790 (1990)] at UC-San Diego, C targets biased at -50 V were exposed to a Be-seeded D plasma in the temperature range from 500 to 1280 K and Be plasma concentrations in the range from 0.01% to 0.4%. It was found in [K. Schmid, M. Baldwin, R. Doetner, and A. Wiltner, Nucl. Fusion 44, 815 (2004)] that even at these low Be concentrations the C samples become covered with a shielding Be layer which almost eliminates chemical and physical erosions of the C sample in the observed target temperature range. Three different approaches were used to model these experimental results: the well-established binary collision Monte Carlo code TRIDYN [W. Möller, W. E. Und, and J. P. Biersack, Comput. Phys. Commun. 51, 355 (1988)], the recently developed plasma surface interaction code GWAR, and analytical expressions were compared. The paper explains the details of the developed models and how their results compare to the experiment. [ABSTRACT FROM AUTHOR]

In laser ablation, nanosecond to femtosecond lasers with a wide range of laser power densities are used. During ablation, the result of collisions between two plasmas is of interest to many researchers in inertial confinement fusion and nuclear astrophysics. In this paper, the collisions of two seed plasmas ablated from planar target surfaces of different target materials (Al, Cu, and W) were studied with temporal-spatially resolved imaging and spectroscopy. The initial relative velocities and densities of the seed plasmas were measured, and then the collisional parameters were calculated to evaluate the degree of the collisions. In addition, spatially resolved spectra were analyzed to study the influences of materials on the temporal-spatial distribution of atom or ions. The results indicated that under the same laser intensity, the high atomic number (Z) material had a small value of collisionality parameter, mostly because of its heavy ion mass. Higher laser intensity would increase the initial relative velocity of seed plasmas, resulting in a lower collision frequency. In addition, the distribution of the ions from seed plasmas was influenced by the stagnation layer plasmas. [ABSTRACT FROM AUTHOR]

The typical yttria-stabilized zirconia material for making the thermal barrier coatings (TBCs) is intrinsically semitransparent to thermal radiation, and the unique disordered microstructures in TBCs make them surprisingly highly scattering. To quantitatively understand the influence of disordered microstructures, this paper presents a quantitative prediction on the radiative properties, especially the transport scattering coefficient of plasma sprayed TBC based on microstructure analysis and rigorous electromagnetic theory. The impact of the porosity, shape, size, and orientation of different types of voids on transport scattering coefficient is comprehensively investigated under the discrete dipole approximation. An inverse model integrating these factors together is then proposed to quantitatively connect transport scattering coefficient with microstructural information, which is also validated by available experimental data. Afterwards, an optimization procedure is carried out based on this model to obtain the optimal size and orientation distribution of the microscale voids to achieve the maximal radiation insulation performance at different operating temperatures, providing guidelines for practical coating design and fabrication. This work suggests that the current model is effective and also efficient for connecting scattering properties to microstructures and can be implemented as a quantitative tool for further studies like non-destructive infrared imaging as well as micro/nanoscale thermal design of TBCs. [ABSTRACT FROM AUTHOR]

Microscopic jets of cryogenic substances such as liquid nitrogen are important regenerative high-density targets for high-repetition rate, high-brightness laser-plasma soft x-ray sources. When operated in vacuum such liquid jets exhibit several non-classical instabilities that negatively influence the x-ray source's spatial and temporal stability, yield, and brightness, parameters that all are important for applications such as water-window microscopy. In the present paper, we investigate liquid-nitrogen jets with a flash-illumination imaging system that allows for a quantitative stability analysis with high spatial and temporal resolution. Direct and indirect consequences of evaporation are identified as the key reasons for the observed instabilities. Operating the jets in an approximately 100 mbar ambient atmosphere counteracts the effects of evaporation and produces highly stable liquid nitrogen jets. For operation in vacuum, which is necessary for the laser plasmas, we improve the stability by introducing an external radiative heating element. The method significantly extends the distance from the nozzle that can be used for liquid-jet laser plasmas, which is of importance for high-average-power applications. Finally, we show that laser-plasma operation with the heating-element-stabilized jet shows improved short-term and long-term temporal stability in its water-window x-ray emission. [ABSTRACT FROM AUTHOR]

The year 2008 marked the 50th Anniversary of the Division of Plasma Physics (DPP) of the American Physical Society. This Special Issue presents many of the Review, Tutorial, and Invited papers that were presented at the 2008 Annual Meeting of the DPP, which was held 17–21 November, in Dallas, Texas. We are very pleased that many of the speakers have submitted an archival-quality version of their presentation for peer review and publication in Physics of Plasmas. [ABSTRACT FROM AUTHOR]

The article informs about the papers from the 46th Annual Meeting of the APS Division of Plasma Physics (DPP) held Savannah, Georgia in the year 2004. The full program of the Savannah meeting included a presentation by the 2004 Maxwell Prize recipients, Valery Godyak and Noah Hershkowitz. The meeting facilitated numerous topical satellite meetings, as well as the highly successful Teacher's Day and Plasma Physics Expo involving teachers and students from area schools. Like the DPP meeting itself, this Special Issue contains exciting research advances and reflects the central themes in today's plasma physics.

The introduction of 3D printing has enabled fabrication of photonic crystal devices with complex crystal structures that would be challenging to construct using other fabrication methods. In this paper, we construct and characterize a photonic crystal consisting of two 4 × 8 × 8 cubic lattices composed of spherical silicon nitride elements straddling a layer of 8 plasma discharge tubes, creating a 3D hybrid plasma photonic crystal device. Integrating under-dense gaseous plasma elements provides a unique coupling dynamic between the dielectric spheres and the cylindrical plasma discharges, creating a monolithic hybrid photonic crystal with solid state and reconfigurable elements. The device has resonant modes that have attenuation peaks that are either switchable, tunable in amplitude, or tunable in frequency with variations in plasma density. The response of these bands seen with varying plasma density is confirmed through simulations when effects due to the heating of the photonic crystal from the gaseous plasma elements are accounted for in the experiments. We discuss how this reconfigurable device may be used and expanded upon for applications in photonic artificial neural networks and optical computing systems. [ABSTRACT FROM AUTHOR]

Microscopic instability and the macroscopic flow pattern resulting from colliding plasmas are studied analytically in support of laboratory experiments. The plasma flows are assumed to stream radially from two separate centers. In a quasi-planar (2D) geometry, they may arise from an Ohmic explosion of two parallel wires, but similar configurations emerge from other outflows, e.g., colliding winds in binary star systems. One objective of this paper is to characterize the flow instabilities developing near the flow stagnation line. An exact solution for the Buneman-type dispersion equation is obtained without conventional simplifications. The unstable wave characteristics are key to anomalous resistivity that determines the reconnection rate of opposite magnetic fields transported with each flow toward the stagnation zone. The second objective of this paper is to calculate the stream function of the plasma shocked upon collision. We addressed this task by mapping the flow region to a hodograph plane and solving a Dirichlet problem for the stream function. By providing the instability growth rate, responsible for anomalous transport coefficients, and the overall flow configuration, these studies lay the ground for the next step. From there, we will examine the field reconnection scenarios and emerging mesoscopic structures, such as radial striata observed in the experiments. [ABSTRACT FROM AUTHOR]

A hybrid model is used to investigate the fragmentation of C4F8 inductive discharges. Indeed, the resulting reactive species are crucial for the optimization of the Si-based etching process, since they determine the mechanisms of fluorination, polymerization, and sputtering. In this paper, we present the dissociation degree, the density ratio of F vs. CxFy (i.e., fluorocarbon (fc) neutrals), the neutral vs. positive ion density ratio, details on the neutral and ion components, and fractions of various fc neutrals (or ions) in the total fc neutral (or ion) density in a C4F8 inductively coupled plasma source, as well as the effect of pressure and power on these results. To analyze the fragmentation behavior, the electron density and temperature and electron energy probability function (EEPF) are investigated. Moreover, the main electron-impact generation sources for all considered neutrals and ions are determined from the complicated C4F8 reaction set used in the model. The C4F8 plasma fragmentation is explained, taking into account many factors, such as the EEPF characteristics, the dominance of primary and secondary processes, and the thresholds of dissociation and ionization. The simulation results are compared with experiments from literature, and reasonable agreement is obtained. Some discrepancies are observed, which can probably be attributed to the simplified polymer surface kinetics assumed in the model. [ABSTRACT FROM AUTHOR]

Low-temperature (≤200 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasmaenhanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems not only from the growth conditions but also from unintentional contamination of the reactor. Based on our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material. [ABSTRACT FROM AUTHOR]

A foreword to "Physics of Plasmas," is presented.

A foreword to "Physics of Plasmas" is presented.

A foreword to "Physics of Plasma" is presented.

A relativistic electron beam propagating through plasma induces a return electron current in the system. Such a system of interpenetrating forward and return electron current is susceptible to a host of instabilities. The physics of such instabilities underlies the conversion of the flow kinetic energy to the electromagnetic field energy. Keeping this in view, an energy principle analysis has been enunciated in this paper. Such analyses have been widely utilized earlier in the context of conducting fluids described by MHD model [I. B. Bernstein et al., Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 244(1236), 17–40 (1958)]. Lately, such an approach has been employed for the electrostatic two stream instability for the electron beam plasma system [C. N. Lashmore-Davies, Physics of Plasmas 14(9), 092101 (2007)]. In contrast, it has been shown here that even purely growing mode like Weibel/current filamentation instability for the electron beam plasma system is amenable to such a treatment. The treatment provides an understanding of the energetics associated with the growing mode. The growth rate expression has also been obtained from it. Furthermore, it has been conclusively demonstrated in this paper that for identical values of S 4 = ∑ α n 0 α v 0 α 2 / n 0 γ 0 α , the growth rate is higher when the counterstreaming beams are symmetric (i.e. S3 = ∑αn0α v 0α/n0γ0α = 0) compared to the case when the two beams are asymmetric (i.e. when S3 is finite). Here, v 0α, n0α and γ0α are the equilibrium velocity, electron density and the relativistic factor for the electron species ‘α’ respectively and n0 = ∑αn0α is the total electron density. Particle - In - Cell simulations have been employed to show that the saturated amplitude of the field energy is also higher in the symmetric case. [ABSTRACT FROM AUTHOR]

In a pair of linked articles (called Papers I and II, respectively), we apply the concept of Lagrangian Coherent Structures borrowed from the study of Dynamical Systems to chaotic magnetic field configurations in order to separate regions where field lines have different kinds of behavior. In the present article, Paper II, by means of a numerical procedure, we investigate the Lagrangian Coherent Structures in the case of a two-dimensional magnetic configuration with two island chains that are generated by magnetic reconnection and evolve nonlinearly in time. The comparison with previous results, obtained by assuming a fixed magnetic field configuration, allows us to explore the dependence of transport barriers on the particle velocity. [ABSTRACT FROM AUTHOR]

In a pair of linked articles (called Papers I and II, respectively), we apply the concept of Lagrangian Coherent Structures (LCSs) borrowed from the study of dynamical systems to magnetic field configurations in order to separate regions where field lines have a different kind of behaviour. In the present article, Paper I, after recalling the definition and the properties of the LCSs, we show how this conceptual framework can be applied to the study of particle transport in a magnetized plasma. Furthermore, we introduce a simplified model that allows us to consider explicitly the case where the magnetic configuration evolves in time on time scales comparable to the particle transit time through the configuration. In contrast with previous works on this topic, this analysis requires that a system that is aperiodic in time be investigated. [ABSTRACT FROM AUTHOR]

This paper describes numerical magnetohydrodynamic (MHD) calculation of heat plasma used in heating and welding processes. Most of the calculation models have been two dimensional and static. Since physical phenomena are three dimensional and nonstatic, three dimensional, dynamic MHD calculation of heat plasma is developed in this paper. Since local heat balance is assumed, the heat plasma is considered as a conductive fluid dynamic material such as molten metal. However, heat plasma's material constants such as density, heat transfer coefficient, specific heat, and electrical conductivity are strong functions of the temperature. Temperature is governed by heat plasma material transfer and heat transfer. Material transfer is driven by the electromagnetic force. Turbulent flow is modeled by the large eddy simulator including heat transfer. The electrical phenomenon is modeled using the Poisson equation in a dc magnetic field. It is assumed that the static electrical force may be ignored. Calculations show that the heat plasma concentrates at the center. The center area is of low density and high electrical conductivity. To verify the usefulness of this 3D dynamic MHD method, a conventional model, which is 2D and static is compared to a k-ε model. Comparison of velocity distributions shows good agreement. [ABSTRACT FROM AUTHOR]

Transistors operating well above the frequencies at which they have gain can still rectify terahertz currents and voltages, and have attracted interest as room-temperature terahertz detectors. We show that such rectifying field-effect transistors may still be treated as a lumped element device in the limit where plasma resonances of the electron gas do not occur. We derive analytic formulas for important transistor parameters, such as effective rectification length and device impedance using a transmission-line model. We draw conclusions for plasma-resonant detection where possible. We derive the THz response of a field-effect transistor with a two-dimensional electron-gas channel by a Taylor expansion of the drain-source bias. We connect circuit theory to the existing theories that describe the bias in the gated region by differential equations. Parasitic effects, such as the access resistance, are included. With the approach presented in this paper, we derive the responsivity for a novel field detector that mixes a (THz) signal applied between gate and source with another signal applied between drain and source in homodyne or heterodyne operation mode. We further derive expressions for the expected noise-equivalent power (NEP) in direct detection and mixing mode, including parasitic effects, and find that sub-[formula] should be achievable for realistic device and material parameters for direct detection and less than 900 K noise temperature for mixing at 10 μW local oscillator power. [ABSTRACT FROM AUTHOR]

In this paper, we examine the electromagnetic (EM) wave tunneling and filtering characteristics of multi-layer structures composed of an arbitrary number of &eh;-negative (Epsilon-negative or ENG) metamaterial layers sandwiched by very thin double-positive (DPS) layers with high dielectric constant values. We explain the phenomenon of EM wave tunneling through this propagation barrier by drawing an analogy between this problem and a generalized coupled resonator system. Using this analogy, we demonstrate that a multi-layer structure composed of N DPS layers (N ≥ 2 is an integer number) that sandwich N-1 ENG layers can not only be made transparent in a frequency range where the ENG layers are normally opaque but also be designed to provide a desired spectral filtering characteristics. Furthermore, we present an analytical method for synthesizing such multi-layer spectral filters from the characteristics of their desired responses. The proposed synthesis procedure can be used to develop spatial filters operating throughout the microwave and mm-wave frequency bands as well as multi-layer metallo-dielectric filters at optical wavelengths. We demonstrate the validity of the proposed analytical synthesis method using full-wave numerical electromagnetic simulations. Finally, using the duality principle, we expand these analytical results to the problem of EM wave tunneling through multiple μ-negative layers surrounded by thin DPS layers with high relative permeability values. [ABSTRACT FROM AUTHOR]

We put forward an approximate method to locate the fluid-solid (freezing) phase transition in systems of classical particles interacting via a wide range of Lennard-Jones-type potentials. This method is based on the constancy of the properly normalized second derivative of the interaction potential (freezing indicator) along the freezing curve. As demonstrated recently it yields remarkably good agreement with previous numerical simulation studies of the conventional 12-6 Lennard-Jones (LJ) fluid [S.A.Khrapak, M.Chaudhuri, G.E.Morfill, Phys. Rev. B 134, 052101 (2010)]. In this paper, we test this approach using a wide range of the LJ-type potentials, including LJ n-6 and exp-6 models, and find that it remains sufficiently accurate and reliable in reproducing the corresponding freezing curves, down to the triple-point temperatures. One of the possible application of the method-estimation of the freezing conditions in complex (dusty) plasmas with 'tunable' interactions-is briefly discussed. [ABSTRACT FROM AUTHOR]

Since plasma parameters are altered by dust particles, studying how plasma parameters are related to dust particle growth is an important research issue in dusty plasma. In this paper, the correlation between plasma parameters (electron temperature and ion flux) and particle parameters (particle radius and density) is investigated in silane plasma both experimentally using a floating probe and theoretically by solving balance equations including an additional electron and ion loss to the dust. The results reveal that while the ion flux shows two peak values in the early discharge phase and at the end of coagulation phase, the electron temperature shows a sudden increase in the coagulation step and a gradual decrease in the molecular accretion step. Moreover, the calculated results with the secondary electron emission taken into account produce the best fit with the experimental results. Thus the study confirms that the secondary electron emission plays a crucial role in the coagulation of the dust particles. [ABSTRACT FROM AUTHOR]

Modeling the chemical erosion of carbon materials due to low-energy H+ impact is of paramount importance for the prediction of the behavior of carbon-based plasma-facing components in nuclear fusion devices. In this paper a simple general model describing both energy and temperature dependence of carbon-based chemical erosion is presented. Enlightened by Hopf's model {Hopf et al., [J. Appl. Phys. 94, 2373 (2003)}, the chemical erosion is separated into the contributions from three mechanisms: thermal chemical erosion, energetic chemical sputtering, and ion-enhanced chemical erosion. Using input from the Monte Carlo code TRIDYN, this model is able to reproduce experimental data well. [ABSTRACT FROM AUTHOR]

Capacitively coupled plasmas (CCPs) generated using high frequency (3-30 MHz) and very high frequency (30-300 MHz) radio-frequency (rf) sources are used for many plasma processing applications including thin film etching and deposition. When chamber dimensions become commensurate with the effective rf wavelength in the plasma, electromagnetic wave effects impose a significant influence on plasma behavior. Because the effective rf wavelength in plasma depends upon both rf and plasma process conditions (e.g., rf power and gas pressure), a self-consistent model including both the rf power delivery system and the plasma discharge is highly desirable to capture a more complete physical picture of the plasma behavior. A three-dimensional model for self-consistently studying both electrodynamic and plasma dynamic behavior of large-area (Gen 10, >8 m2) CCP is described in this paper. This model includes Maxwell's equations and transport equations for charged and neutral species, which are coupled and solved in the time domain. The complete rf plasma discharge chamber including the rf power delivery subsystem, rf feed, electrodes, and the plasma domain is modeled as an integrated system. Based on this full-wave solution model, important limitations for processing uniformity imposed by electromagnetic wave propagation effects in a large-area CCP (3.05×2.85 m2 electrode size) are studied. The behavior of H2 plasmas in such a reactor is examined from 13.56 to 200 MHz. It is shown that various rectangular harmonics of electromagnetic fields can be excited in a large-area rectangular reactor as the rf or power is increased. The rectangular harmonics can create not only center-high plasma distribution but also high plasma density at the corners and along the edges of the reactor. [ABSTRACT FROM AUTHOR]

In this paper, an experimental study on generation of nanoparticle various sizes using Ti:sapphire laser pulses, is reported. Nanoparticle formation in plasma plumes of metals like silver and copper, expanding in vacuum, has been studied using stretched pulses of 300 ps duration [subnanoseconds (sub-ns)] from a Ti:sapphire laser. It has been compared with the nanoparticle formation (of the same materials) when compressed pulses of 45 fs duration were used under similar focusing conditions. Nanoparticle formation is observed at intensities as high as 2×1016 W/cm2. The structural analysis of the nanoparticle deposition on a silicon substrate showed that, using 45 fs pulses, smaller nanoparticles of average size ∼20 nm were generated, whereas on using the sub-ns pulses, larger particles were produced. Also, the visible light transmission and reflection from the nanoparticle film of Ag on glass substrate showed surface plasmon resonance (SPR). The SPR curves of the films of nanoparticles deposited by femtosecond pulses were always broader and reflection/transmission was always smaller when compared with the films formed using the sub-ns pulses, indicating smaller size particle formation by ultrashort pulses. Thus, it has been demonstrated that variation in the laser pulse duration of laser offers a simple tool for varying the size of the nanoparticles generated in plasma plumes. [ABSTRACT FROM AUTHOR]

The properties of kinetic ablation models are considered in this paper. The widely used kinetic ablation model (model-K) only considers monatomic vapor. A revised model (model-Z) was introduced by taking into account the polyatomic vapor’s internal degrees of freedom, as well as the temperature dependence of the average particle mass. In this work, both temperature and pressure dependence of average particle mass and the specific heat ratio γ are taken into account, producing an improved version of model-Z (denoted model-Z*). Ablation data calculated by model-K and model-Z* for two typical capillary materials are presented. Compared to model-K, model-Z* predicts an increased ablation rate at lower plasma temperature and higher plasma density, and a decreased rate for the opposite conditions. Finally, based on the plasma parameters in a typical discharge cycle, all three models are used to calculate the time-dependent ablation rate and the integrated ablated mass. It is found that the main difference between their results arises because of the different average particle masses near the wall surface, and model-Z* is the most accurate for the discharge cycle considered. Further, it is found that the ablation parameters are highly sensitive to the pressure, in particular, through the pressure dependence of average particle mass. [ABSTRACT FROM AUTHOR]

The fundamental of the generation and propagation of the atmospheric pressure nonequilibrium plasma jets has recently attracted significant interests. In this paper, investigations on the effects of the parameters of the pulsed dc voltages on the optical emission intensity of the plasma jet and the bullet propagation behavior are carried out based on the temporal-spatial resolved optical emission spectroscopy measurements and the high-speed photography. It is found that, with the increase in the applied voltage, the bullet propagates out from the nozzle earlier and accelerates to higher peak-velocities. The increase in the pulse frequency exerts no significant influences on the optical emission of the plasma jet and the bullet propagation velocity. But it can induce the bullet propagates out from the nozzle earlier. Besides, it is interesting to notice that, with the increase in the pulse width in the beginning, the bullet propagates out from the nozzle with longer delay time. However, when the pulse width is increased to be more than 100 μs, the delay time of the bullet propagating out from the nozzle becomes much shorter. On the other hand, with the increase in the pulse width, the optical emission intensity of the plasma jet drops and the maximum bullet velocity decreases too. Detailed analysis shows that it may be due to the accumulation of the charges and radicals, which can shorten the prebreakdown of the discharge inside the syringe and result in the bullet propagating out earlier from the nozzle. [ABSTRACT FROM AUTHOR]

The development of new alternative routes for production of second generation ethanol from sugarcane biomass poses a challenge to the scientific community. Current research in this field addresses the use of a plasma-based pretreatment of the lignocellulosic raw material. With the aim to provide a theoretical background for this experimental technique we investigate the role of low-energy electrons from the plasma in the rupture of the matrix of cellulosic chains. In this paper, we report calculated cross sections for elastic scattering of low-energy electrons by the α- and β-D-glucose monomers. The calculations employed the Schwinger multichannel method with pseudopotentials and were carried out at the static-exchange and static-exchange plus polarization levels of approximation. Through the comparison of the results obtained with inclusion of polarization effects we discuss the influence of the different conformations of the hydroxyl group linked to the anomeric carbon on the resonance spectra of these molecules. Resonant structures appearing at different energies for α- and β-glucose at the low-energy regime of impact energies can be understood as a fingerprint of an “isomeric effect” and suggest that distinct fragmentation mechanisms proceeding via σ* shape resonances may become operative depending on the glucose anomer under consideration. For energies above 15 eV the integral elastic cross sections are very similar for both monomers. Differential cross sections for the glucopyranose anomers considered in this work are typically dominated by a strong forward scattering due to the molecules’ large electric dipole moments and, for energies close to the resonances’ positions, they display particular features at the intermediate angular region, notably a pronounced f-wave scattering pattern, that are probably associated with the presence of those structures. [ABSTRACT FROM AUTHOR]

Cold plasmas have recently received great attention. In this paper, optical and electrical diagnostics are carried out on a reliable and user-friendly plasma plume. A simple electrical model is used to simulate the electrical characteristics of the device. The plasma is represented by a resistor connected in parallel with a capacitor, an inductor, and another resistor, which are connected in series. The simulated current-voltage waveforms have very good agreement with experimental measurements. Besides, the emission spectra of the plasma are also studied. It shows that, when Ar is used as working gas, there is strong OH (hydroxyl radical) emission and the emission intensities of the N2 emission bands are more than three times higher than that of He. On the contrary, when He is used as working gas, the emission intensities of N2+ band are much stronger. Detail analyses on these observations are presented. [ABSTRACT FROM AUTHOR]

One of the general challenges for the evaluation and interpretation of optical emission spectroscopy measurements is the occurrence of radiation trapping, which is also named self-absorption or opacity. A convenient technique to treat radiation trapping is the introduction of a parameter, which is called escape factor and gives a measure for the amount of radiation trapping. In this paper evaluations on the concept of escape factors are presented for an inductively coupled plasma in argon. Especially, the strong argon line at 811.53 nm, which arises from the transition of 2p9-1s5, is under consideration. To estimate escape factors for this line, a particular method is proposed and presented here. First experimental results are obtained under the restrictive assumptions that transitions into the resonant levels 1s2 and 1s4 are sufficiently optically thin and ratios of population densities are constant. [ABSTRACT FROM AUTHOR]