Showing papers in "IEEE Transactions on Plasma Science in 2003"
TL;DR: In this paper, the structure of a capacitively coupled high-pressure glow (HPG) discharge in high-purity helium is investigated using a detailed one-dimensional modeling approach.
Abstract: The structure of a capacitively coupled high-pressure glow (HPG) discharge in high-purity helium is investigated using a detailed one-dimensional modeling approach. Impurity effects are modeled using trace amounts of nitrogen gas in helium. Average electron temperatures and densities for the HPG discharge are similar to their low-pressure counterpart. Helium-dimer ions dominate the discharge structure for sufficiently high-current densities, but model impurity nitrogen ions are found to be dominant for low-discharge currents. Helium dimer metastable atoms are found to be the dominant metastable species in the discharge. The high collisionality of the HPG plasma results in significant discharge potential drop across the bulk plasma region, electron Joule heating in the bulk plasma, and electron elastic collisional losses. High collisionality also results in very low ion-impact energies of order 1 eV at the electrode surfaces.
299 citations
TL;DR: In this paper, a numerical study has been carried out to understand the influences of barrier arrangements on the discharge characteristics of dielectric barrier discharge (DBD), where a 1.5-dimensional (1.5D) modeling is considered in the arrangements of bare, single-barrier, and double-Barrier electrodes while a two-dimensional approach is employed in a configuration of ferroelectric packed discharge (FPD).
Abstract: A numerical study has been carried out to understand the influences of barrier arrangements on the discharge characteristics of dielectric barrier discharge (DBD). A 1.5-dimensional (1.5-D) modeling is considered in the arrangements of bare, single-barrier, and double-barrier electrodes while a two-dimensional (2-D) approach is employed in a configuration of ferroelectric packed discharge (FPD). Numerical simulations show that the evolution of microdischarges in DBD occurs sequentially in the three distinctive phases of avalanche, streamer, and decay, and that the dielectric barriers make streamer discharges stabilized and sustained in lowered electric fields without transition to spark compared with no barrier case. Especially, the highly nonuniform strong electric field effect created by the pellets appears to be formed in FPD, which enables the flue gas cleaning to be expected to enhance the decomposition efficiency.
185 citations
TL;DR: In this paper, the magnetohydrodynamic approach is applied to the simulation of high-current diffuse columnar arcs and the anode-directed flow of plasma of diffuse arcs is decelerated and highest pressures appear in front of anode.
Abstract: Numerical simulations are presented for physical behavior and heat flux to the anode of high-current diffuse of arcs as found in vacuum interrupters. The magnetohydrodynamic approach is applied. Of importance is the consideration of energy balance. Heat flux densities to the anode are predicted in the right order of magnitude and essential physical details of the high-current vacuum arc are disclosed. Only at low or no axial magnetic field superimposed externally and low-arc currents, the anode-directed flow of plasma of diffuse arcs reveals supersonic conditions. Otherwise, subsonic conditions exist. In supersonic diffuse arcs, the anode-directed plasma flow is decelerated and highest pressures appear in front of the anode. At subsonic conditions the highest pressure prevails in the cathode region and the pressure gradient drives the flow to the anode. The transition from diffuse to diffuse columnar arc seems to occur when the evaporation rate of metal vapor from the contact surfaces approaches the emission rate of plasma from the body of cathode spots. Diffuse columnar arcs have moderate pressure variations from cathode to anode. With rising plasma density, the energy loss from the emission of electromagnetic radiation increases and can no longer be neglected.
170 citations
TL;DR: In this article, a microstrip split-ring resonator was used for low-power microwave plasma source with an ion density of 1.3/spl times/10/sup 11/ cm/sup -3/ in argon at 400 mtorr (53.3 Pa) in a relatively wide pressure range.
Abstract: Microplasma sources can be integrated into portable devices for applications such as bio-microelectromechanical system sterilization, small-scale materials processing, and microchemical analysis systems. Portable operation, however, limits the amount of power and vacuum levels that can be employed in the plasma source. This paper describes the design and initial characterization of a low-power microwave plasma source based on a microstrip split-ring resonator that is capable of operating at pressures from 0.05 torr (6.7 Pa) up to one atmosphere. The plasma source's microstrip resonator operates at 900 MHz and presents a quality factor of Q=335. Argon and air discharges can be self-started with less than 3 W in a relatively wide pressure range. An ion density of 1.3/spl times/10/sup 11/ cm/sup -3/ in argon at 400 mtorr (53.3 Pa) can be created using only 0.5 W. Atmospheric discharges can be sustained with 0.5 W in argon. This low power allows for portable air-cooled operation. Continuous operation at atmospheric pressure for 24 h in argon at 1 W shows no measurable damage to the source.
157 citations
TL;DR: In this article, the pseudoglow and glow discharge behavior of a 0.5mm metallic-dielectric electrode gap in helium under atmospheric pressure was examined as a function of ac voltage between 0.3 and 32 kHz.
Abstract: The pseudoglow and glow discharge behavior of a 0.5-mm metallic-dielectric electrode gap in helium under atmospheric pressure was examined as a function of ac voltage between 0.3 and 32 kHz. The number of discharge current pulses per half-cycle within the pseudoglow was found to diminish with rising frequency, as opposed to the increase observed with rising voltage. The reduction in the rise time and the quasi-monotonic decreases in amplitude of the successive discrete current pulses within the pseudoglow were attributed to the enhanced Penning ionization due to an increase in the number of energetic precursors (metastables and dimers) over the first quadrant in each half cycle. The interruption in the discharge pulse sequence, caused by a change in polarity of the ac field, greatly reduced the precursors' concentration and resulted in the first incipient pulse of the pseudoglow having the shortest rise time and width in the pulse sequence. The increase in frequency at constant voltage caused a gradual decrease in the number of discharge current pulses within the pseudoglow, until at ca. 10 kHz and beyond only a single pulse glow discharge took place. The influence of argon, nitrogen, hydrogen, and oxygen impurities was studied and interpreted in terms of Penning ionization and electron attachment.
153 citations
TL;DR: In this paper, the absorption, reflection, and transmission of electromagnetic waves by a non-uniform plasma slab immersed in an ambient uniform magnetic field of various strengths are studied, and the effects of the plasma parameters and magnetic field strength on the absorbed, reflected, and transmitted power are discussed.
Abstract: The absorption, reflection, and transmission of electromagnetic waves by a nonuniform plasma slab immersed in an ambient uniform magnetic field of various strengths are studied in this paper. The effects of the plasma parameters and magnetic field strength on the absorbed, reflected, and transmitted power are discussed. The magnetized nonuniform plasma slab is modeled by a series of magnetized uniform plasma subslabs. The calculation results show that the effects of the magnetic field strength and density gradient on the absorbed power, as well as the frequency band of resonant absorption, are significant. A complete analysis utilizing the scattering matrix method is also used to compare the above calculation results which neglect multiple reflections between subslab interfaces. Broadband absorption of electromagnetic waves can be achieved by changing the magnetic field strength and plasma density. More than 90% of the electromagnetic wave power can be absorbed in a magnetized nonuniform plasma slab with width of 12 cm and the absorption bandwidth can range from 1 to 20 GHz with different plasma parameters and external magnetic field strengths.
137 citations
TL;DR: In this paper, the authors present experimental results of atmospheric pressure glow discharges (APGD) in a dielectric barrier discharge reactor under varying experimental conditions (frequency f, gap length d; and electric field intensity E).
Abstract: We present experimental results of atmospheric pressure glow discharges (APGD) in a dielectric barrier discharge reactor. These are examined in different noble gases and in the N/sub 2//O/sub 2/ system (air and pure N/sub 2/), under varying experimental conditions (frequency f; gap length d; and electric field intensity E). Discharge diagnostics have been carried out using ultrahigh speed imaging, and synchronous dual-detection of light emission and current-voltage measurements, the former using a photomultiplier . The time evolutions of the discharges and of columnar patterns in regular geometric arrangements at atmospheric pressure under different experimental conditions are reported for all of the noble gases studied here. We present evidence that columnar patterns and APGD are manifestations of the same discharge physics, which is discussed with reference to recent work reported by others.
132 citations
TL;DR: In this article, a microgap dielectric barrier discharge at ambient pressure was used for the synthesis of ammonia in nitrogen-hydrogen plasma, where high energy electrons were obtained in a narrow discharge gap.
Abstract: The plasma synthesis of ammonia has been studied in nitrogen-hydrogen plasma using a microgap dielectric barrier discharge at ambient pressure. With the new technology of dielectric layers, the high-energy electrons are obtained in a narrow discharge gap; meanwhile, N/sub 2/ and H/sub 2/ molecules are ionized and dissociated and a large number of free atoms, ions, and radicals are formed in a nonequilibrium plasma after inelastic collisions. The final product was mainly ammonia, and the yield of ammonia reaches 12500 ppm (1.25%). In this way, plasma synthesis of ammonia at ambient pressure is realized and a new method is provided for inorganic synthesis.
107 citations
TL;DR: In this paper, it is argued that Kirchhoff's extension of his law to the perfect reflector is not justified based on experimental evidence, and it is emphasized that graphite is unique in its ability to act as a nearly perfect absorber.
Abstract: In this paper, Kirchhoff's law is discussed in the context of two extremes: the perfect absorber and the perfect reflector. It is argued that Kirchhoff's extension of his law to the perfect reflector is not justified based on experimental evidence. This greatly limits the universality of the formulations advanced by Kirchhoff and Planck in that blackbody radiation becomes dependent on the nature of the radiating object. In this regard, it is emphasized that graphite is unique in its ability to act as a nearly perfect absorber. The consequences are important in our analysis of all temperatures based on radiative emission.
96 citations
TL;DR: In this paper, the emission from pulsed streamer discharges in a coaxial electrode system in air at 01 MPa was observed using a high-speed gated intensified charge-coupled display camera.
Abstract: Pulsed streamer discharges have been extensively used in many applications such as control of NO/sub X/ and SO/sub 2/ from exhaust gases, treatment of dioxins, removal of volatile organic compounds, generation of ozone, and laser excitation An operation with a high energy efficiency is necessary for practical applications It is very important to know the propagation mechanism of streamer discharges in order to improve the energy efficiency of pulsed discharge systems In this paper, the emission from pulsed streamer discharges in a coaxial electrode system in air at 01 MPa was observed using a high-speed gated intensified charge-coupled display camera A concentric wire-cylinder electrodes configuration was used A positive pulsed voltage having a width of about 100 ns was applied to the central electrode The streamer discharges were initiated at the inner electrode and terminated at the outer electrode The propagation velocity of the streamer discharges was 18-33 mm/ns
87 citations
TL;DR: In this article, the mechanism of high luminous efficiency discharges with high Xe content in an AC plasma display panel was analyzed by computer simulation using a two-dimensional fluid model.
Abstract: The mechanism of high luminous efficiency discharges with high Xe content in an AC plasma display panel was analyzed by computer simulation using a two-dimensional fluid model. The model has reproduced well the experimental results. The high luminous efficiency with high Xe content is attributed to high electron heating efficiency as well as high excitation efficiency by electron. The electron heating efficiency is increased with increasing the sustaining voltage under high Xe content and this phenomenon was analyzed by investigating the cathode sheath and secondary electron emission characteristics.
TL;DR: In this article, a review of worldwide efforts trying to reveal the problems and perspectives of modern collisionless laboratory astrophysics with high-power lasers is presented, where the physics of such widely different phenomena as barium releases in Earth's magnetosphere, collisionless deceleration of supernova remnants, and related shock-wave generation in interstellar medium or possible near-Earth anti-asteroid explosions could be reproduced in the laboratory.
Abstract: Possibilities of laboratory simulation of various explosive phenomena in space and cosmic plasmas with magnetic fields are analyzed on the bases of similarity criteria, properties of collisionless interactions, and parameters of laser-produced plasmas. It is shown how the physics of such widely different phenomena as barium releases in Earth's magnetosphere, collisionless deceleration of supernova remnants, and related shock-wave generation in interstellar medium or possible near-Earth anti-asteroid explosions could be reproduced in the laboratory. This review of worldwide efforts tries to reveal the problems and perspectives of modern collisionless laboratory astrophysics with high-power lasers.
TL;DR: In this article, the authors considered four waveforms of the plasma-generating voltage, namely, sinusoidal, peak-levelled, peak levelled and tail-trimmed, and pulsed with a Gaussian-shaped tail, at the same repetition frequency of 10 kHz.
Abstract: Diffuse nonthermal gas discharges generated at atmospheric pressure have found increasing applications in many key materials processing areas such as etching, deposition, and structural modification of polymeric surfaces. To facilitate tailored and improved applications of these novel gas plasmas, we consider their pulsed generation based on one-dimensional numerical simulation of helium-nitrogen discharges. We consider four waveforms of the plasma-generating voltage, namely: 1) sinusoidal; 2) peak-levelled sinusoidal; 3) peak-levelled and tail-trimmed sinusoidal; and 4) pulsed with a Gaussian-shaped tail, all at the same repetition frequency of 10 kHz. For each case, voltage and current characteristics are calculated and then used to assess whether the generated plasma is diffuse and nonthermal. Densities of electrons, ions, and metastables are calculated, together with the dissipated electric power in the plasma bulk. It is found that plasma pulsing can significantly reduce the electric power needed to sustain diffuse nonthermal atmospheric plasmas. Specifically by choosing appropriate pulse shape, the plasma-sustaining power can be reduced by more than 50% without reducing densities of electrons, ions, and metastables. On the other hand, electron density can be enhanced by 68% with the same input electric power if the pulsewidth is suitably narrowed.
TL;DR: In this paper, the speed of a high-current vacuum arc by radial magnetic fields (RMF) forcing the constricted arc to move has been investigated for long time in the design of vacuum interrupters.
Abstract: The principle of controlling a high-current vacuum arc by radial magnetic fields (RMF) forcing the constricted arc to move has been utilized for long time in the design of vacuum interrupters. Detailed electrical and optical measurements in conjunction with finite-element method (FEM)-calculations have provided a better physical understanding of the function of RMF contacts. By balancing the processes of surface heating and momentum gain in the moving arc column, an expression for the speed of the arc and arc voltage is obtained. The speed varies as the 5/6 power of the short-circuit current. This result is then used to describe the number of rotations of the arc on the contact and to explain the linear scaling law of contact diameter with current. The investigations are mainly concentrated on spiral-type contact designs.
TL;DR: In this article, the distribution of the spots over the cathode of a high-current vacuum arc stabilized by an axial magnetic field (AMF) has been investigated and the complex effect of the AMF configuration on the behavior of cathode spots has been satisfactorily explained based on the Steenbeck minimum principle.
Abstract: The distribution of the spots over the cathode of a high-current vacuum arc stabilized by an axial magnetic field (AMF) has been investigated. AMF configuration has been varied from conventional "bell-shaped" to "magnetic barrier," where a substantial AMF is created on the electrode edge and virtually vanishes in the center. The complex effect of the AMF configuration on the behavior of cathode spots has been satisfactorily explained based on the Steenbeck minimum principle. It has been shown that the "magnetic barrier" represents an optimum AMF configuration, providing even current distribution and relatively low and stable arc voltage.
TL;DR: The properties and behavior of arc spots on cathodes, especially in vacuum arcs-the purest form of electrical discharges-are most surprising and very difficult to comprehend and to disclose at first glance as discussed by the authors.
Abstract: The properties and the behavior of arc spots on cathodes, especially in vacuum arcs-the purest form of electrical discharges-are most surprising and very difficult to comprehend and to disclose at first glance. Their experimental exploration and theoretical interpretation took several decades and the task is not yet completed, in spite of many efforts and much progress. It remains an exciting problem and a challenge for future physical investigations, mainly due to the highly complex nature of arc spot operation, which calls for joint endeavors of several disciplines of physics, mathematics, chemistry, and material science. The effort is justified also by the technical applications and their requirements. I point out as a personal view some of these characteristic problems in the understanding of arc spots without claim to completeness. The main issues discussed are the cathode as the decisive electrode for the existence of electrical discharges, comparison with the anode, the strange properties of vacuum arc spots, their relation to glow cathodes and high pressure arc cathodes, the necessarily limited parameter range of arc spots, the astonishing, and the miraculous interplay of very different processes in arc spots cooperating in such a way to implement all the conditions to enable vacuum arcs, the conditions within the expanding cathodic plasma cloud (only briefly discussed) and, finally, arc spots as complex thermodynamic systems and self-organizing dissipative structures.
TL;DR: In this article, a 35 GHz 45kV third-harmonic complex cavity gyrotron with a permanent magnet system was designed, constructed, and tested with a pulse output power of 147.3 kW at a beam voltage of 45 kV with beam current of 32.2 A.
Abstract: A systematic theoretical and experimental study on a 35-GHz 45-kV third-harmonic gyrotron with a permanent magnet system is presented in this paper. A complex cavity with gradual transition and a diode magnetron injection gun (MIG) are employed in the gyrotron. A self-consistent field nonlinear theoretical investigation and numerical simulation for electron beam interaction with RF fields are given. The diode MIG is simulated numerically utilizing our code in detail. The permanent magnet system provided the maximum axial magnetic field of about 4.5 kG in the cavity region of the gyrotron. The Ka band third-harmonic complex cavity gyrotron with a permanent magnet system has been designed, constructed, and tested. A pulse output power of 147.3 kW was obtained at a beam voltage of 45 kV with beam current of 32.2 A, corresponding to an efficiency of 10.2%.
TL;DR: In this paper, the state-of-the-art study of the physical processes in the cathode spot of a vacuum arc is described in terms of the ecton model.
Abstract: This paper reviews the state-of-the-art study of the physical processes in the cathode spot of a vacuum arc. The most important experimental data are explained in terms of the ecton model of a cathode spot. The finite lifetime of an ecton is responsible for the cyclic character of the processes occurring in a cathode spot. It has been shown that the arc plasma is generated by microexplosions occurring at the cathode surface heated by the Joule mechanism due to the high-explosive emission current density. Up to kiloampere currents, the charge state of the arc plasma and directed velocities of the ions are governed by the operation of a cathode spot cell-an ecton.
TL;DR: In this article, a resonant energy transfer mechanism was proposed to explain the broadening of the 656.3-nm Balmer alpha/spl line emitted from inductively and capacitively coupled radio frequency (RF), microwave, and glow-discharge plasmas.
Abstract: From the width of the 656.3-nm Balmer /spl alpha/ line emitted from inductively and capacitively coupled radio frequency (RF), microwave, and glow-discharge plasmas, it was found that inductively coupled RF helium-hydrogen and argon-hydrogen plasmas showed extraordinary broadening corresponding to an average hydrogen atom energy of 250-310 and 180-230 eV, respectively, compared to 30-40 and 50-60 eV, respectively, for the corresponding capacitively coupled plasmas. Microwave helium-hydrogen and argon-hydrogen plasmas showed significant broadening corresponding to an average hydrogen atom energy of 180-210 and 110-130 eV, respectively. The corresponding results from the glow-discharge plasmas were 33-38 and 30-35 eV, respectively, compared to /spl ap/ 4 eV for plasmas of pure hydrogen, neon-hydrogen, and xenon-hydrogen maintained in any of the sources. Similarly, the average electron temperatures T/sub e/ for helium-hydrogen and argon-hydrogen inductively coupled RF and microwave plasmas were high (43 200 /spl plusmn/ 5% K, 18 600 /spl plusmn/ 5% K, 30 500 /spl plusmn/ 5% K, and 13 700 /spl plusmn/ 5% K, respectively); compared to 9300 /spl plusmn/ 5% K, 7300 /spl plusmn/ 5% K, 8000 /spl plusmn/ 5% K, and 6700 /spl plusmn/ 5% K for the corresponding plasmas of xenon-hydrogen and hydrogen alone, respectively. Stark broadening or acceleration of charged species due to high electric fields cannot explain the inductively coupled RF and microwave results since the electron density was low and no high field was present. Rather, a resonant energy transfer mechanism is proposed.
TL;DR: In this paper, a high-power piezoelectric pulse generator was designed to maximize the output power by maximizing the product of generated voltage and output current, which was derived from the mechanical and electrical models of the generator and provided design guidelines as to the geometric dimensions of the piezel material and circuital conditions that will produce maximum power in the device.
Abstract: This investigation presents and discusses maximization techniques for a high-power piezoelectric pulse generator. Maximizing the piezoelectric generator's output power is done by maximizing the product of generated voltage and output current. The maximization methods are derived from the mechanical and electrical models of the generator and provide design guidelines as to the geometric dimensions of the piezoelectric material and circuital conditions that will produce maximum power in the device. The theoretical results show the peak stack voltage to increase with an increasing thickness to area ratio of the piezoelectric material and with increasing applied force. However, in contrast to the peak output voltage, the peak output current increases with the decreasing of thickness to area ratio of the material. In addition to the physical dimension, the peak stack current increases as the value of the antenna inductor decreases. The output power of the piezoelectric generator, which is the product of output voltage and current, linearly increases with the thickness to area ratio. This result is due to the fact that the output voltage is larger comparing to the output current. Experimental results are also given to verify the theoretical results and represent the performance of several types of piezoelectric materials with different thickness to area ratios. The experimental results show good agreement with theoretical predictions. The results also show the peak power output of the experimental generator ranging from 7 to 28 kW with a corresponding power density from 9 to 173 kW/cm/sup 3/.
TL;DR: Lower-hybrid solitary structures (LHSSs) as discussed by the authors are spatially localized structures embedded in space plasmas, which are characterized by localized electric field fluctuations at frequencies both above and below the ambient lower hybrid resonance.
Abstract: The subject of lower-hybrid solitary structures (LHSS), sometimes called lower-hybrid cavities, is reviewed. LHSS are spatially localized structures embedded in space plasmas. They are characterized by localized electric field fluctuations at frequencies both above and below the ambient lower-hybrid resonance in a density depletion of a few percent to several tens of percent. The localized fluctuations are more intense than the ambient turbulence by a factor of three to five. The LHSS are observed to have dimensions across the magnetic field of a few to many thermal ion gyroradii, usually 10-100 m in the topside auroral ionosphere. Along the magnetic field the dimensions are inferred to be several kilometers to several hundred kilometers although there exist no direct measurements. Analysis of the electric field fluctuations within LHSS using plasma wave interferometers reveals that the phase fronts rotate relative to the geomagnetic field at the center of the LHSS: right-handed at frequencies above and left-handed at frequencies below the ambient lower-hybrid resonance. Within a gyrodiameter of LHSS, ions are found to be preferentially heated perpendicular to the geomagnetic field and local transit time acceleration is the likely mechanism for energization. Two classes of theories have been applied to LHSS: linear theories that assume that the density depletions are preexisting and use the observed spatial properties of the density depletions to compute the propagation characteristics of lower-hybrid waves, and nonlinear, strongly turbulent, collapse theories which assume that the density depletion and the electric field fluctuations are directly coupled through a ponderomotive force. The linear scattering theories successfully explain the rotational and frequency spectrum of LHSS electric field fluctuations. The nonlinear theories predict relations between field strength and cavity size, cavity spatial distributions, and electric field amplitude statistical distributions. None of these nonlinear predictions are validated by observations. Most observations of LHSS have been made by sounding rockets or satellites in the auroral ionosphere. However, recent observations demonstrate that LHSS exist at much higher altitudes in the magnetosphere. Overall, this evidence suggests that LHSS are a universal feature of whistler mode turbulence.
TL;DR: In this article, the authors observed the development of drawn arcs in vacuum with an imposed axial magnetic field (AMF) measured the time required for the bridge column to evolve into the high-current diffuse mode.
Abstract: The opening of electrical contacts while passing current generates a drawn arc. In vacuum, the arc begins as a bridge of molten metal connecting the contacts, which then ruptures to form a bridge column arc. Previous work observing the development of drawn arcs in vacuum with an imposed axial magnetic field (AMF) measured the time required for the bridge column to evolve into the high-current diffuse mode. Arc visualization experiments on Cu-Cr contacts with an AMF have now determined that the transition to the fully diffuse mode has a more complicated development. With high-speed photography, we characterized the appearance of the arc modes over half-cycles of power frequency short-circuit current. The opening sequence begins with the rupturing of the molten metal bridge, forming the bridge column. This column evolves into the transition mode, and then into the fully diffuse mode. This transition mode in an AMF consists of a region of concentrated cathode spots, similar to the transition mode for butt contacts at lower currents and no AMF. Over a few milliseconds, an increasing number of individual cathode spots begin to appear outside the concentrated region, until a diffuse arc forms. The transition mode produces a transient peak in the arc voltage. Increasing the AMF strength at a particular current can shorten the duration of the transition mode and reduces the arc voltage peak. Single or multiple half-cycle operations have been performed on Cu-Cr contacts to investigate the effect of the transition mode on contact melting. The melting patterns after a single half-cycle of high current are correlated with the behavior observed in the arc movies. Anode melting is confined to one or two regions of shallow melting, while individual cathode spot tracks covered most of the cathode surface. The combination of arc visualization and post-arcing contact examinations demonstrated that the transition arc mode was a significant source of contact melting.
TL;DR: In this article, the authors used the self-consistent particle-in-cell/Monte Carlo (PIC/MC) simulation to examine the dynamic structure of dual frequency (2/60 MHz) capacitively coupled plasmas.
Abstract: The dynamic structure of dual frequency (2/60 MHz) capacitively coupled plasmas (CCPs) in Ar (25 mtorr) are examined using the self-consistent particle-in-cell/Monte Carlo (PIC/MC) simulation. At first, the dependence of the discharge structure on wafer biasing conditions were investigated using one-dimensional computation. The results show that the plasma potential oscillates with the high frequency superposed on the low frequency. The amplitude of the high-frequency oscillation is modulated by the instantaneous potential of the low frequency biasing electrode. Furthermore, the axisymmetrical two-dimensional PIC/MC simulation is performed to investigate the influence of a geometric configuration of the reactor on the plasma structure.
TL;DR: In this article, the results of hydrogen and deuterium Balmer alpha line shapes and line intensities study in an abnormal glow discharge are reported and analyzed using Doppler shifts along line wings.
Abstract: The results of hydrogen and deuterium Balmer alpha line shapes and line intensities study in an abnormal glow discharge are reported and analyzed. The Doppler shifts along line wings are used to determine energies of excited hydrogen and deuterium atoms. For 12 different cathodes, intensity and shape of line wings are examined and dependence upon cathode material is determined. Tentative explanation of line wings intensity dependence is related to the sputtering of cathode material and back-scattering coefficients of incident hydrogen or deuterium ions and atoms from cathode surface. The influence of the light reflected on a cathode surface to the line shape measurements along discharge axis is considered. In hydrogen, deuterium, and Ar+3%H/sub 2/ discharges, basic mechanisms of fast hydrogen generation and excitation are studied. The shape and intensities of the H/sub /spl alpha// line profiles in pure hydrogen and in argon-hydrogen mixture may be correlated with hydrogen atom-carrier gas collision excitation cross sections. In order to assess the importance of reflected fast hydrogen atoms back scattered from the cathode surface, for the Balmer line shape formation, a simulation program is used. The results are in a qualitative agreement with Balmer line shapes observations.
TL;DR: In this article, the position of the ion sheath and the value of the electric field at the sheath edge were found using asymptotic matching techniques for collisionless plasma-wall systems.
Abstract: The position of the sheath edge and the value of the electric field at the sheath edge are found using asymptotic matching techniques for collisionless plasma-wall systems. It is demonstrated that specifying the position of the sheath edge by the Bohm criterion or by Riemann's weak electric field is inconsistent with the asymptotic matching theory and contradicts the commonly accepted definition of the sheath as a region where ionization can be neglected. It is shown that the sheath found using the asymptotic matching theory is the ion sheath, characterized by negligible electron density, and that the value of the electric field at the sheath edge practically coincides with the value of Godyak's electric field. In addition, analytical expressions are given for the position of the wall, the sheath width, and sheath characteristics for arbitrary potentials at the wall.
TL;DR: In this article, the authors present experimental and simulation studies of the plasma in a macroscopic AC plasma display panel discharge cell operating with a large coplanar gap and find that the xenon excitation efficiency is much larger than that in the conventional, small-gap electrode configuration but with larger sustaining voltage.
Abstract: We present experimental and simulation studies of the plasma in a macroscopic AC plasma display panel discharge cell operating with a large coplanar gap. We find that the xenon excitation efficiency is much larger than that in the conventional, small-gap electrode configuration but with larger sustaining voltage. We discuss the discharge mode and efficiency in such large gap configurations, with the help of time resolved optical diagnostics and simulations.
TL;DR: In this paper, the authors describe the variation of intrinsic stress as a function of applied pulsed bias voltage (V) and pulse frequency (f) for deposition of carbon and titanium nitride films.
Abstract: The almost fully ionized cathodic arc plasma is a versatile source for the deposition of thin films. Ion energies impinging on the growth surface can easily be controlled by applying substrate bias. The natural energy of the depositing ions is moderate (tens of electron volts) and generates substantial compressive stress in most materials. In hard materials (such as tetrahedral-carbon and titanium nitride), the high-yield stress makes the problem particularly severe. Recent work has shown that stress relaxation can be achieved by pulses of high ion-energy bombardment (/spl sim/10 keV) applied to the substrate during growth. In this paper, we describe the variation of intrinsic stress as a function of applied pulsed bias voltage (V) and pulse frequency (f) for deposition of carbon and titanium nitride films. We found that stress relaxation depends on the parameter Vf, so it is possible to achieve the same level of stress relief for a range of voltages by selecting appropriate pulsing frequencies. With the right choice of parameters, it is possible to almost completely eliminate the intrinsic stress and deposit very thick coatings. Our experimental results showed correlations between intrinsic stress and film microstructures, such as the preferred orientation. This leads to the possibility of controlling microstructure with high energy ion pulsing during growth. Molecular dynamics computer simulations of isolated impacts provide insight into the atomic-scale processes at work. Using the results of such simulations, we describe a model for how stress relief might take place, based on relaxation in thermal spikes occurring around impact sites of the high-energy ions.
TL;DR: In this article, the PSpice simulation software was used to simulate the electrical characteristics of a one atmosphere uniform glow discharge plasma (OAUGDP) reactor system, where at least one electrode is covered with a dielectric, which can be modeled as a capacitor, as can the gap containing the plasma.
Abstract: The PSpice software has been used to simulate the electrical characteristics of a one atmosphere uniform glow discharge plasma (OAUGDP) reactor system. An OAUGDP reactor system normally includes a power supply, a transformer, an impedance matching network, and the plasma reactor. The principal task in simulation is to develop a comprehensive PSpice model for the plasma discharge in an OAUGDP reactor, which may consist either of two parallel electrode plates with a small gap between them, or a planar plasma layer generated by coplanar parallel electrode strips. In an OAUGDP, at least one electrode is covered with a dielectric, which can be modeled as a capacitor, as can the gap containing the plasma. The plasma discharge itself is modeled as a voltage-controlled current source that is switched on when the voltage across the gap exceeds the plasma initiation voltage. The current source and its output current follow a power law of the applied voltage, an observed phenomenological characteristic of the voltage-current behavior of normal glow discharges. Simulation results agree well with experimental data from actual reactors. It has been found that in different operating regimes, the discharge current of the OAUGDP is described by voltage power laws with different exponents, and that the capacitance of the impedance matching network affects the shape of the modeled discharge current waveform in a manner consistent with experiment.
TL;DR: In this article, the authors investigated the time-relaxation of the electron energy distribution function (EEDF) in the nitrogen afterglow of an /spl omega/2/spl pi/=433 MHz flowing discharge at p=3.3 torr, in a tube with inner radius R=1.9 cm.
Abstract: In this paper, we present an investigation of the time-relaxation of the electron energy distribution function (EEDF) in the nitrogen afterglow of an /spl omega//2/spl pi/=433 MHz flowing discharge at p=3.3 torr, in a tube with inner radius R=1.9 cm. We solve the time-dependent Boltzmann equation, including the term for creation of new electrons in associative/Penning reactions, coupled to a system of rate balance equations for the heavy-particles. The EEDFs are also obtained experimentally, from second derivatives of digitized probe characteristics measured using a triple probe technique, and compared with the calculations. It is shown that an equilibrium between the vibrational distribution function of ground-state molecules N/sub 2/(X/sup 1//spl Sigma//sub g//sup +/,v) and low-energy electrons is rapidly established, in times /spl sim/10/sup -7/ s. In these early instants of the postdischarge, a dip is formed in the EEDF around 4 eV. The EEDF finally reaches a quasi-stationary state for t/spl gsim/10/sup -6/ s, although the electron density still continues to decrease beyond this instant. Collisions of highly excited N/sub 2/(X/sup 1//spl Sigma//sub g//sup +/,v/spl gsim/35) molecules with N(/sup 4/S) atoms are in the origin of a maximum in the electron density occurring downstream from the discharge at /spl sime/2/spl times/10/sup -2/ s. These reactions create locally the metastable states N/sub 2/(A/sup 3//spl Sigma//sub u//sup +/) and N/sub 2/(a'/sup 1//spl Sigma//sub u//sup -/), which in turn ionize the gas in associative/Penning processes. Slow electrons remain for very long times in the postdischarge and can be involved in electron stepwise processes with energy thresholds smaller than /spl sim/2-3 eV.
TL;DR: In this paper, nonlinear interaction of two radio frequency (RF) sources in a magnetized Ar/C/sub 2/F/sub 6/ capacitively coupled plasma discharge was investigated using a computational model.
Abstract: Nonlinear interaction of two radio frequency (RF) sources in a magnetized Ar/C/sub 2/F/sub 6/ capacitively coupled plasma discharge is investigated using a computational model. Results show that application of a radial magnetic field enhances charged and neutral species densities in the plasma reactor due to reduction in electron loss to surfaces and trapping of secondary electron emission generated electrons. Amplitude of RF currents at electrodes also increases with magnetic field strength and source frequency for a given RF voltage. Due to nonlinear nature of plasma sheath, higher harmonics of applied frequencies and source interaction generated harmonics can be observed in electrode currents. Application of magnetic field decreases electron mobility and makes the system less nonlinear, which reduces higher harmonics relative to primary components. Magnetic field also tends to make the RF sources more isolated. Increase in source frequency moves the plasma from electrode edge to the center of the chamber, which redistributes current through the electrodes. If frequencies of the two RF sources are commensurate, nonlinear interaction of RF sources generates subharmonics of primary frequencies.