Search

Accompanying a reduction in process temperature from 400 $^{\circ}$ C to 300 $^{\circ}$ C, the channel current of an elevated-metal metal-oxide (EMMO) thin-film transistor (TFT) is found to change from one insensitive to the size of the conductive source/drain (S/D) regions to one suppressed with decreasing size of the regions. The different behavior is attributed to the distinct donor-species responsible for the formation of the thermally induced S/D regions at the two process temperatures. Such sensitivity, often undesirable, can be reduced by completing a donor drive-in thermal treatment before the patterning of the S/D electrodes. This alternative process flow with drive-in pretreatment allows the construction at 300 $^{\circ}$ C of an EMMO TFT with a significantly reduced footprint while still exhibiting a relatively low S/D resistance. IEEE

p-channel GaN field-effect transistors (FETs) with a SiNx/GaON gate stack have been demonstrated with enhanced stability within a wide range of voltage bias and temperature. In this letter, the gate leakage characteristics and reliability of this unconventional staggered gate stack is investigated. At relatively low gate voltages, the gate current is suppressed owing to the buried-channel structure and the presence of GaON that presents an effective hole barrier. With more negative gate biases, the gate leakage was found to be dominated by the transport of holes that spillover from the p-channel through the SiNx via Poole-Frenkel emission. Based on this gate leakage mechanism at large gate bias, √ model was used for gate lifetime prediction. The maximum applicable ON-state gate voltage of -7.3 V is obtained for a 10-year lifetime with a 1% gate failure rate. IEEE

Low-temperature deposited PE-CVD SiCN has been comprehensively investigated towards the dielectric layer of Die-to-Wafer hybrid bonding. The PECVD SiCN was deposited at room temperature. The characterization of the deposited film and the impact of the plasma activation on the surface has been analyzed.

Low-temperature deposited PE-CVD SiCN has been comprehensively investigated towards the dielectric layer of Die-to-Wafer hybrid bonding. The PECVD SiCN was deposited at room temperature. The characterization of the deposited film and the impact of the plasma activation on the surface has been analyzed.

The proposed study compares the electrical, thermal and mechanical performances of thermally aged cellulose pressboard material impregnated in mineral oil, synthetic ester fluid and mixed oil. The electrical insulation characteristics of oil-impregnated pressboard (OIP) are studied by means of surface discharge inception voltage (SDIV) using an ultra-high frequency technique and surface potential measurement analysis. It indicates that OIP aged in mineral oil has higher surface potential due to higher charge trap density compared to that of the mixed oil and synthetic ester fluid. Mechanical and thermal characteristics of the aged OIP are studied by means of tensile strength measurement and thermo-gravimetric analysis, respectively. The change in the chemical composition of OIP is studied by means of laser-induced breakdown spectroscopy, which indicates lower plasma temperature with mineral oil-based OIP indicating higher degradation state. To further understand the microscopic structure of the thermally aged OIP in different oils, scanning electron microscopy and X-ray diffraction studies have been performed. The pressboard thermally aged in synthetic ester fluid and the mixed oil has better electrical, thermal and mechanical properties as compared with the pressboard aged in mineral oil., QC 20210503

Slag is foamed in electric arc furnace during steelmaking to reduce the amount of energy emitted to the furnace walls. The behavior of the electric arc plasma during slag foaming is not very well understood, since it is very hard to obtain empirical data about arc plasma from industrial furnaces. In this work the effect of foaming on the arc plasma is studied by generating electric arc plasma over a foaming slag in laboratory scale. The arc was generated on top of the slag with a system modified from a welding power supply and the foaming of slag was induced by blowing oxygen gas into the slag. The electric arcs were monitored with two cameras filtered to measure different wavelengths and three spectrometers measuring different spectral regions with varying spectral resolution. The first camera was able to detect only the light emitted directly from the arc plasma while the second can detect the high temperature slag surrounding the submerged arc. By comparing the two images, it was possible to differentiate between arc burning inside the foaming slag and free burning arc. The use of plasma diagnostics with optical emission spectrometry provided information about electron temperature and density of the arc plasma. The plasma diagnostics and camera pixel intensities indicate that the arc burning inside foaming slag is constricted and has high plasma temperature. Comparing the free-burning arc on top of the foaming slag and non-foaming slag show that the CO bubbles cause the plasma temperature to fluctuate significantly., QC 20210927

In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer-leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others.

In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer-leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others.

In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer-leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others.

A process aimed at fabricating proximity x-ray lithography masks is presented. In this technique, the Ta absorber layer is deposited and patterned on the back side of the membrane and nonspin-coated electron sensitive layers were used in order to achieve high resolution patterning of this absorber. The advantages gained by this approach include a reduction of the membrane temperature during the plasma etching step of the absorber patterns without using any cooling gas. This temperature reduction results from the direct contact of the membrane with a cooling plate. This approach also allows increased protection of the absorber patterns from contamination during exposure of the mask. A third advantage is that the smooth surface of the mask exposed to the wafer in the x-ray lithography stepper may also make it possible to reduce the gap between wafer and mask, thus achieving increased resolution with the x-ray lithography process.

In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer-leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others.

A process aimed at fabricating proximity x-ray lithography masks is presented. In this technique, the Ta absorber layer is deposited and patterned on the back side of the membrane and nonspin-coated electron sensitive layers were used in order to achieve high resolution patterning of this absorber. The advantages gained by this approach include a reduction of the membrane temperature during the plasma etching step of the absorber patterns without using any cooling gas. This temperature reduction results from the direct contact of the membrane with a cooling plate. This approach also allows increased protection of the absorber patterns from contamination during exposure of the mask. A third advantage is that the smooth surface of the mask exposed to the wafer in the x-ray lithography stepper may also make it possible to reduce the gap between wafer and mask, thus achieving increased resolution with the x-ray lithography process.

In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer-leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others.

The propagation of intense picosecond laser pulses in air in the presence of strong nonlinear self-action effects and air ionization is investigated experimentally and numerically. The model used for numerical analysis is based on the nonlinear propagator for the optical field coupled to the rate equations for the production of various ionic species and plasma temperature. Our results show that the phenomenon of plasma-driven intensity clamping, which has been paramount in femtosecond laser filamentation, holds for picosecond pulses. Furthermore, the temporal pulse distortions in the picosecond regime are limited and the pulse fluence is also clamped. In focused propagation geometry, a unique feature of picosecond filamentation is the production of a broad, fully ionized air channel, continuous both longitudinally and transversely, which may be instrumental for many applications including laser-guided electrical breakdown of air, channeling microwave beams and air lasing.

The thermomagnetic hysteresis loops of a NiMnInCo Heusler-type alloy exhibiting inverse magnetocaloric effect were studied with the help of first-order reversal curves (FORC). These have been measured using two different protocols (either upon heating or cooling the sample) and using different applied magnetic fields. For proper comparison, FORC distributions were shifted according to the field dependent center of the M(T) hysteresis loop, which follows a linear trend. The qualitative behavior of FORC distributions remains the same, allowing their use for fingerprinting the transition, while there is a shift of their maxima along the hysteretic temperature axis and their distributions also get broader along the interaction temperature axis with increasing magnetic field. This was evidence that FORC distributions are dependent on the intensive variables temperature and field. As a consequence, it is necessary to obtain them for different temperatures and fields in order to accurately model the transition.

Fine particle plasma is a kind of one component plasmas and strongly coupled plasmas and is predicted to have the critical point. The experimental verification of existence of such a kind of interesting phenomena is now planning to be performed under microgravity condition by the collaboration between German and Japanese research groups.

Following a successful deployment in 1999 and predictions of further Leonid storms in 2001 and 2002, a new set of two airborne missions was prepared in the Leonid Multi-Instrument Aircraft Campaign. Geopolitical circumstances affected the scope of the 2001 mission more than usual. The NKC-135 FISTA aircraft executed a CONUS single-plane deployment with 19 US citizen researchers onboard out of Edwards AFB, CA. The researchers traveled to Alabama and, after 08:50 UT, slowly returned back to base on a westward trajectory at an altitude of 37,000 ft. Non US citizen participants observed from various ground sites. The 1767-dust trail of comet 55P/Tempel-Tuttle was well observed. Key results were: 1) measurements of meteor flux to discriminate among meteor storm prediction models; 2) high resolution optical spectra that set a strong lower limit to the CN abundance in meteor plasma and measured plasma temperatures as a function of meteoroid mass; 3) further mid-IR detections of meteors with simultaneous optical imaging; 4) HDTV recorded low-resolution optical spectra for studies of compositional anomalies in large cometary meteoroids; 5) the surprising detection of persistent train emission in a slow and not-so-bright Taurid fireball, as well as 6) the observation of an elve at the peak of the storm. Results from ground-based efforts included flux measurements of the 1866 storm peak in Australia, the first high frame-rate images of meteors showing a shock-like feature, and the detection of recombination lines, the UV OH A-X band, and unidentified near-IR emission in meteor persistent emissions. This paper gives a brief overview of the airborne effort and puts the new results in the context of prior work.

The build-up of plasma parameters following the H-mode transition in JET has been analysed in view of its consequences for the alpha power evolution in the access to burning plasma conditions in ITER. JET experiments show that the build-up of plasma temperature both at the plasma core and the plasma edge occurs in timescales comparable to the energy confinement time. In contrast, the evolution of the edge and core densities differs strongly depending on the level of plasma current in the discharge and of the associated NBI penetration. For higher plasma current H-mode discharges (I-p > 2.0-2.5 MA, depending on plasma shape), with naturally higher plasma densities for which NBI penetration is poorer, the core density evolves in much longer timescales than the edge density leading to the formation of rather hollow density profiles. These hollow density profiles persist for timescales of several energy confinement times until they are usually terminated by a sawtooth. Modelling of the JET experiments with JETTO shows that the density build-up following the H-mode transition can be described with a purely diffusive model, despite the low collisionalities of high current H-mode plasmas at JET. The consequences of these JET experimental/modelling findings for the access to burning plasma conditions in the ITER Q(DT) = 10 scenario are presented., QC 20130920

Two different methods have been employed to determine the plasma temperature in a laser-cluster fusion experiment on the Texas Petawatt laser. In the first, the temperature was derived from time-of-flight data of deuterium ions ejected from exploding D2 or CD4 clusters. In the second, the temperature was measured from the ratio of the rates of two different nuclear fusion reactions occurring in the plasma at the same time: D(d,He3)n and He3(d,p)He4. The temperatures determined by these two methods agree well, which indicates that (i) the ion energy distribution is not significantly distorted when ions travel in the disassembling plasma; (ii) the kinetic energy of deuterium ions, especially the "hottest part" responsible for nuclear fusion, is well described by a near-Maxwellian distribution. © 2013 American Physical Society.

Nonrelativistic electrostatic unmagnetized shocks are frequently observed in laboratory plasmas and they are likely to exist in astrophysical plasmas. Their maximum speed, expressed in units of the ion acoustic speed far upstream of the shock, depends only on the electron-to-ion temperature ratio if binary collisions are absent. The formation and evolution of such shocks is examined here for a wide range of shock speeds with particle-in-cell simulations. The initial temperatures of the electrons and the 400 times heavier ions are equal. Shocks form on electron time scales at Mach numbers between 1.7 and 2.2. Shocks with Mach numbers up to 2.5 form after tens of inverse ion plasma frequencies. The density of the shock-reflected ion beam increases and the number of ions crossing the shock thus decreases with an increasing Mach number, causing a slower expansion of the downstream region in its rest frame. The interval occupied by this ion beam is on a positive potential relative to the far upstream. This potential pre-heats the electrons ahead of the shock even in the absence of beam instabilities and decouples the electron temperature in the foreshock ahead of the shock from the one in the far upstream plasma. The effective Mach number of the shock is reduced by this electron heating. This effect can potentially stabilize nonrelativistic electrostatic shocks moving as fast as supernova remnant shocks.

Two-dimensional axisymmetric particle-in-cell simulations with Monte Carlo collision calculations (PIC-MCC) have been conducted to investigate argon microplasma characteristics of a miniature inductively coupled plasma source with a 5-mm-diameter planar coil, where the radius and length are 5 mm and 6 mm, respectively. Coupling the rf-electromagnetic fields to the plasma is carried out based on a collisional model and a kinetic model. The former employs the cold-electron approximation and the latter incorporates warm-electron effects. The numerical analysis has been performed for pressures in the range 370–770 mTorr and at 450 MHz rf powers below 3.5 W, and then the PIC-MCC results are compared with available experimental data and fluid simulation results. The results show that a considerably thick sheath structure can be seen compared with the plasma reactor size and the electron energy distribution is non-Maxwellian over the entire plasma region. As a result, the distribution of the electron temperature is quite different from that obtained in the fluid model. The electron temperature as a function of rf power is in a reasonable agreement with experimental data. The pressure dependence of the plasma density shows different tendency between the collisional and kinetic model, implying noncollisional effects even at high pressures due to the high rf frequency, where the electron collision frequency is less than the rf driving frequency.

type:text, We present here analysis of electron energy of a micro dielectric barrier discharge (micro-DBD) for alternating-current plasma display panel (ac-PDP) with Ne/Xe gas mixture by using the optical emission spectroscopy (OES). The OES method is quite useful to evaluate a variety of electron energy in a high pressure DBD ignited in a PDP small cell. Experiment shows that the ratio of Ne emission intensity (I-Ne) relative to Xe emission intensity (I-Xe) drastically decreases with time. This temporal profile is well consistent with dynamic behavior of electron temperature in a micro-DBD, calculated in one-dimensional fluid model. I-Ne/I-Xe also decreases with an increase in Xe gas pressure and a decrease in applied voltage especially in the initial stage of discharge, and these reflect the basic features of electron temperature in a micro-DBD. The influences of plasma parameters such as electron temperature on luminous efficacy are also theoretically analyzed using one-dimensional fluid model. The low electron temperature, which is attained at high Xe gas pressure, realizes the efficient Xe excitation for vacuum ultraviolet radiation. The high Xe-pressure condition also induces the rapid growth of discharge and consequent high plasma density, resulting in high electron heating efficiency.

We present here analysis of electron energy of a micro dielectric barrier discharge (micro-DBD) for alternating-current plasma display panel (ac-PDP) with Ne/Xe gas mixture by using the optical emission spectroscopy (OES). The OES method is quite useful to evaluate a variety of electron energy in a high pressure DBD ignited in a PDP small cell. Experiment shows that the ratio of Ne emission intensity (I-Ne) relative to Xe emission intensity (I-Xe) drastically decreases with time. This temporal profile is well consistent with dynamic behavior of electron temperature in a micro-DBD, calculated in one-dimensional fluid model. I-Ne/I-Xe also decreases with an increase in Xe gas pressure and a decrease in applied voltage especially in the initial stage of discharge, and these reflect the basic features of electron temperature in a micro-DBD. The influences of plasma parameters such as electron temperature on luminous efficacy are also theoretically analyzed using one-dimensional fluid model. The low electron temperature, which is attained at high Xe gas pressure, realizes the efficient Xe excitation for vacuum ultraviolet radiation. The high Xe-pressure condition also induces the rapid growth of discharge and consequent high plasma density, resulting in high electron heating efficiency.

We present here analysis of electron energy of a micro dielectric barrier discharge (micro-DBD) for alternating-current plasma display panel (ac-PDP) with Ne/Xe gas mixture by using the optical emission spectroscopy (OES). The OES method is quite useful to evaluate a variety of electron energy in a high pressure DBD ignited in a PDP small cell. Experiment shows that the ratio of Ne emission intensity (I-Ne) relative to Xe emission intensity (I-Xe) drastically decreases with time. This temporal profile is well consistent with dynamic behavior of electron temperature in a micro-DBD, calculated in one-dimensional fluid model. I-Ne/I-Xe also decreases with an increase in Xe gas pressure and a decrease in applied voltage especially in the initial stage of discharge, and these reflect the basic features of electron temperature in a micro-DBD. The influences of plasma parameters such as electron temperature on luminous efficacy are also theoretically analyzed using one-dimensional fluid model. The low electron temperature, which is attained at high Xe gas pressure, realizes the efficient Xe excitation for vacuum ultraviolet radiation. The high Xe-pressure condition also induces the rapid growth of discharge and consequent high plasma density, resulting in high electron heating efficiency.

Open questions concerning structures and dynamics of diffusion regions and electron acceleration in collisionless magnetic reconnection are addressed based on data from the four-spacecraft mission Cluster and particle-in-cell simulations. Using time series of electron distribution functions measured by the four spacecraft, distinct electron regions around a reconnection layer are mapped out to set the framework for studying diffusion regions. A spatially extended electron current sheet (ecs), a series of magnetic islands, and bursts of energetic electrons within islands are identified during magnetotail reconnection with no appreciable guide field. The ecs is collocated with a layer of electron-scale electric fields normal to the ecs and pointing toward the ecs center plane. Both the observed electron and ion densities vary by more than a factor of 2 within one ion skin depth north and south of the ecs, and from the ecs into magnetic islands. Within each of the identified islands, there is a burst of suprathermal electrons whose fluxes peak at density compression sites [L.-J. Chen , Nat. Phys. 4, 19 (2008)] and whose energy spectra exhibit power laws with indices ranging from 6 to 7.3. These results indicate that the in-plane electric field normal to the ecs can be of the electron scale at certain phases of reconnection, electrons and ions are highly compressible within the ion diffusion region, and for reconnection involving magnetic islands, primary electron acceleration occurs within the islands.

Asimulation study of the magnetic electron drift vortex (MEDV) modeturbulence in a magnetoplasma in the presence of inhomogeneities inthe plasma temperature and density, as well as in theexternal magnetic field, is presented. The study shows that theinfluence of the magnetic field inhomogeneity is to suppress streamerlikestructures observed in previous simulation studies without background magnetic fields.The MEDV mode turbulence exhibits nonuniversal (non-Kolmogorov-type) spectra for differentsets of the plasma parameters. In the presence of aninhomogeneous magnetic field, the spectrum changes to a 7/3 powerlaw, which is flatter than without magnetic field gradients. Therelevance of this work to laser-produced plasmas in the laboratoryis briefly mentioned.

The nonlinear wave modulation of planar and nonplanar (cylindrical and spherical) ion-acoustic envelope solitons in a collisionless unmagnetized electron-positron-ion plasma with two-electron temperature distributions has been studied. The reductive perturbative technique is used to obtain a modified nonlinear Schrodinger equation, which includes a damping term that accounts for the geometrical effect. The critical wave number threshold K(c), which indicates where the modulational instability sets in, has been determined for various regimes. It is found that an increase in the positron concentration (alpha) leads to a decrease in the critical wave number (K(c)) until alpha approaches certain value alpha(c) (critical positron concentration), then further increase in alpha beyond alpha(c) increases the value of K(c). Also, it is found that there is a modulation instability period for the cylindrical and spherical wave modulation, which does not exist in the one-dimensional case.

Peripheral magnetic field lines extending from the plasma source into the diffusion chamber are found to separate two regions of Maxwellian electron energy probability functions: the central, ion-beam containing region with an electron temperature of 5 eV, and region near the chamber walls with electrons at 3 eV. Along the peripheral field lines a bi-Maxwellian population with a hot tail at 9 eV is shown to both originate from electrons in the source traveling downstream across the double layer and correspond to a local maximum in ion and electron densities.

The line integrated line emission measured by neutron spectrometers at JET along sight lines in the vertical and horizontal planes has been simulated in Monte Carlo calculations to determine the relationship between the measured (effective) ion temperature (T-eff) relative to the peak value of the profile (T-0). The general sight line dependence of (T-eff) was expressed analytically for circular plasmas which was used to explain the simulated results for the actual JET sight lines. The analytical model with parametrization of sight lines and plasma profiles is described and the results are used to discuss dual sight line measurements that can be tested at JET and its forward implications for study burning (nearly thermal) plasmas of ITER., Conference Information: 17th Topical Conference on High-Temperature Plasma Diagnostics Albuquerque, NM, 2008

The geosynchronous environment is the most important region in the magnetosphere for spacecraft charging because the plasma temperature can be very high; the plasma density is sometimes very low, and most communications satellites are there. It is now well understood that, for a given surface material, there exists a critical plasma temperature above which spacecraft charging to negative potentials occurs. High energy (MeVs) electrons and ions penetrate into material to different depth. At energies below 100 MeV, electrons penetrate deeper than ions, and may remain in a deep layer, causing a high electric field. High energy "killer electrons" can cause deep dielectric charging and spacecraft anomalies. Studies of correlations of coronal mass Ejections, and exo-events, when a satellite gets outside of the magnetosphere are needed. Spacecraft used for planetary studies can also be affected. More study is also needed to determine whether surface charging or deep dielectric charging is more damaging to satellites., The original document contains color images. Published in the Proceedings of the 38th AIAA Plasmadynamics and Lasers Conference, held in Miami, FL on 25-28 Jun 2007.

The properties of the coupled trapped electron and toroidal ion temperature gradient modes are investigated using the standard reactive fluid model and taking rigorously into account the effects attributed to the ion polarization drift and to the drifts associated with the lowest-order finite ion Larmor radius effects. In the flat density regime, where the coupling between the modes is relatively weak, the properties of the unstable modes are slightly modified through these effects. For the peak density regions, where the coupling of the modes is rather strong, these second-order drifts determine the spectra of the unstable modes near the marginal conditions.

The measurement of the electron mean kinetic energy by identifying the electron temperature and the excitation temperature obtained by optical emission spectroscopy is theoretically studied for two temperature argon plasmas at atmospheric pressure. Using a 32-level collisional radiative model in which both electron impact and argon-impact inelastic collisions are taken into account, it has been found that under certain conditions the argon inelastic collisions may cause a decrease of the argon excitation temperature so that the relation Te>Texc>T0 is satisfied. This inequality also appears when electron losses due to diffusion are important and the electron density is lower than its equilibrium value.

Results are presented from a multi-instrument study of the spatial distribution of the summertime, polar ionospheric electron density under conditions of relatively stable IMF Bz

An atmospheric pressure glow discharge was generated using a needle-array electrode in nitrogen, and the voltage–current characteristics of the glow discharge were obtained in a range from 1 mA to 60 A. A pulsed high voltage with short rise time under 10 ns was employed to generate streamer discharges simultaneously at all needle tips. The large number of streamer discharges prevented the glow-to-arc transition caused by inhomogeneous thermalization. Semiconductor opening switch diodes were employed as an opening switch to shorten the rise time. The glow voltage was almost constant until the discharge current became 0.3 A, whereas the voltage increased with the current higher than 0.3 A. Electron density and temperature in a positive column of the glow discharge at 60 A were obtained to 1.4×1012 cm−3 and 1.3 eV from calculation based on nitrogen swarm data.

A complex low-pressure argon discharge plasma containing dust grains is studied using a Boltzmann equation for the electrons and fluid equations for the ions. Local effects, such as the spatial distribution of the dust density and external electric field, are included, and their effect on the electron energy distribution, the electron and ion number densities, the electron temperature, and the dust charge are investigated. It is found that dust particles can strongly affect the plasma parameters by modifying the electron energy distribution, the electron temperature, the creation and loss of plasma particles, as well as the spatial distributions of the electrons and ions. In particular, for sufficiently high grain density and/or size, in a low-pressure argon glow discharge, the Druyvesteyn-like electron distribution in pristine plasmas can become nearly Maxwellian. Electron collection by the dust grains is the main cause for the change in the electron distribution function.

The nanopowder management and control of plasma parameters in electronegative SiH4 plasmas were discussed. The spatial profiles of electron and positive/negative ion number densities, electron temperature and charge of the fine particles were obtained. It was found that management of powder charge distribution is also possible through control of the external parameters.

The temperature of the propellant's bed may play a role in the burn rates under plasma injection. In this report, a set of experiments was first conducted on the plasma-flow field to determine the spatial and temporal distribution of the plasma temperature, pressure, number density, and velocity. The experiments revealed a decreasing plasma pressure, plasma temperature, and plasma number density as plasma is leaving the capillary source and expands in air. The plasma jet velocity 2 inches from the source exit was found to be about 1300 m/s. Following characterization of the plasma-flow field, a set of experiments was conducted on JA-2 solid propellant with controlled bed temperature. Experiments, with proposed models, revealed a functional form that includes the bed temperature. Increased burn rates were observed with increased bed temperature, which appears to follow a power law. A model for the burn rate is proposed, which includes the bed temperature and has the burn rate equals A P(a) (T/T ambient)(b). Further investigation of plasma parameters helped to modify the proposed model to include plasma radiative heat flux and plasma number density. (6 tables, 19 figures, 29 refs.)

A novel electron-beam characterization technique called Charge Contrast Imaging has been used to identify the type and spatial extent of doping and electrically active defects in MWIR reactive-ion etched (RIE) HgCdTe n-on-p photodiodes. In this technique, improved electro-morphological sensitivity to the material is observed. Quantitative characterization of the beam effects upon the junction properties is modelled upon experimental results using Laser Beam Induced Current Techniques (LBIC).

Operation regimes, plasma parameters, and applications of the low-frequency (∼500 kHz) inductively coupled plasma (ICP) sources with a planar external coil are investigated. It is shown that highly uniform, high-density (ne∼9×1012 cm-3) plasmas can be produced in low-pressure argon discharges with moderate rf powers. The low-frequency ICP sources operate in either electrostatic (E) or electromagnetic (H) regimes in a wide pressure range without any Faraday shield or an external multipolar magnetic confinement, and exhibit high power transfer efficiency, and low circuit loss. In the H mode, the ICP features high level of uniformity over large processing areas and volumes, low electron temperatures, and plasma potentials. The low-density, highly uniform over the cross-section, plasmas with high electron temperatures and plasma and sheath potentials are characteristic to the electrostatic regime. Both operation regimes offer great potential for various plasma processing applications. As examples, the efficiency of the low-frequency ICP for steel nitriding and plasma-enhanced chemical vapor deposition of hydrogenated diamond-like carbon (DLC) films, is demonstrated. It appears possible to achieve very high nitriding rates and dramatically increase micro-hardness and wear resistance of the AISI 304 stainless steel. It is also shown that the deposition rates and mechanical properties of the DLC films can be efficiently controlled by selecting the discharge operating regime.

The performance of the 500 KHz planar-coil inductively coupled plasma source was studied. The global electrical characteristics of the discharge, distributions of the induced electromagnetic fields, plasma density, potential, and electron temperature were investigated. Achieved high plasma density and low electron temperature implied that the studied plasma source was promising for industrial applications.

We report the first soft gamma-ray observation by the OSSE experiment onboard the CGRO of the optically selected Seyfert II galaxy, NGC 4507. The source was observed on two separate weeks in 1993 and detected between 50 and 200 keV at a confidence level of 7 . There is no evidence of flux variability within or between the two observation periods which sample timescales from days to months. The source spectrum obtained from combining the two sets of data is best described by spectral forms including some exponential cutoff. The observed shape is steeper than the one observed by GINGA in the X-ray band in 1990. The joint GINGA/OSSE spectrum is best described by an absorbed power law exponentially cutoff at high energies and having an iron K alpha emission line. Comparison between NGC 4507 and other Seyfert galaxies indicate that although at low energies a difference between type I and II objects is possible (but still weak in this specific case) at high energies the observed shapes are indeed similar. We interpret this as evidence that the primary source emission (i.e. not reprocessed by material in the source) is the same for both types; this finding is in agreement with the unified scheme of Seyfert galaxies. Apart from its own interest, the OSSE detection of hard X-ray emission from a Seyfert II galaxy is also important for the implications it has on the contribution of Seyfert galaxies of both types to the cosmic diffuse background, as type II objects are expected to outnumber type I sources., Prepared in collaboration with the Centre National de la Recherche Scientifique, Toulouse, France and the E.O. Hulburt Center for Space Research, Naval Research Laboratory, Washington, DC. Preprint. Accepted for publication in the Astrophysical Journal; published Astrophysical Journal, Part 2-Letters, v444, n2, pL73-L76, May 1995.

QC 20120528

QC 20120528

QC 20120528

QC 20120528

QC 20120528

A three-year study was made of physical phenomena underlying operation of the plasma-arc welding (PAW) process. Experimental methods were developed to measure plasma spectral intensities during welding, a mathematical method was perfected to compute plasma temperature distributions from the spectral data, and statistical methods were used to extract maximum information from the data and to infer improved values for four ARII transition probabilities. Welds in mild and stainless steels and in Ti-6Al-4V up to 12.7 mm thick were evaluated by metallography and/or by cyclic fatigue studies. At low stress concentration levels PAW was found to reduce cyclic crack growth rates in the weld metal compared to the parent metal. There appears to be evidence that plasma spectroscopy can aid in selection and control of welding parameters. The plasma temperature measurements clarify the mechanism whereby use of auxiliary ports in the PAW torch orifice cup reduces the width of a weld nugget. Simple plasmadynamic models were used to relate orifice geometry to plasma temperature and electrical resistance, and to weld quality, thus accounting for the observation that a convergent orifice enhances weld penetration, reduces weld width, and improves weld nugget geometry without causing double-arcing, while a divergent orifice (which simulates an eroded orifice cup) has the opposite, deleterious, effects. Nine documents are cited in which these results were reported and complete preprints of four journal articles not yet published are included as appendices. (Author)