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Journal of Applied Physics

Issue 3 • Date Mar 1974

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Displaying Results 1 - 25 of 88
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Dynamic dislocation behavior in ``pure'' magnesium oxide single crystals

    Page(s): 981 - 989
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    Edge- and screw-dislocation velocities in ``pure'' MgO single crystals have been measured as a function of stress, temperature, and valence state of the iron impurities in order to identify the rate-controlling drag mechanism for dislocation mobility. Edge dislocations have been observed to move faster than screw dislocations in both the valence states over the stress and the temperature regimes investigated. Both the edge and screw dislocations move faster in reduced (Fe+2) samples than in oxidized (Fe+3) samples. From the analysis of the edge- and screw-dislocation velocity data in terms of the activation parameters (activation volume, activation enthalpy, total activation enthalpy, and the stress exponent of dislocation velocity) it is suggested that the edge- and screw-dislocation mobilities in ``pure'' MgO single crystals in the reduced state are controlled by Peierls mechanism with thermally activated double-kink nucleation as the rate limiting step. The total activation barriers for edge- and screw-dislocation mobility has been found to be 11 and 17 kcal/mole, respectively. The calculated values of the Peierls stress for edge- and screw-dislocation mobilities in ``pure'' magnesium-oxide crystals in the reduced state are 0.6×108 and 1.7×108 N m-2, respectively. In oxidized MgO crystals the edge- and screw-dislocation mobilities are suggested to be governed by a mixed mode consisting of Peierls stress and the resistance due to nonsymmetric defects (FeMg.-VMg″). View full abstract»

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  • Dynamic dislocation behavior in iron‐doped magnesium oxide crystals

    Page(s): 990 - 995
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    Edge- and screw-dislocation velocities in iron-doped magnesium-oxide single crystals containing 150 ppm Fe+3 have been measured as a function of stress and temperature in order to elucidate the rate-controlling drag mechanism for dislocation mobility. Edge dislocations have been found to move faster than the screw dislocations over the stress and temperature regimes investigated. From the analysis of the edge- and screw-dislocation velocity data in terms of the activation parameters (activation volume, activation enthalpy, total activation enthalpy, and the stress exponent of dislocation velocity), it is suggested that the edge- and screw-dislocation mobilities in MgO single crystals containing 150-ppm Fe+3 dopants are controlled by the interaction of dislocations with the nonsymmetric distortions due to (FeMg.-VMg″) defects. The strain ΔЄ owing to such defects has been calculated and is related to the observed hardening of ion-doped (Fe+3) MgO single crystals. View full abstract»

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  • Generation of thickness‐twist modes in a piezoceramic plate

    Page(s): 996 - 1000
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    In the present paper we investigate theoretically the generation of thickness‐twist modes in a plate of piezoceramic material. The poling axis is chosen parallel to the plane boundaries of the plate. On one of the faces of the plate a finite number of cylindrical strip electrodes of vanishing thickness is present. If an electric generator is connected to the electrodes, piezoelectric thickness‐twist modes are generated. Our problem is to calculate the amplitudes of the different modes and the input impedance of the transducer. To this aim we employ our integral equation formulation of piezoelectric diffraction problems that has been presented in an earlier paper. Once the resulting system of integral equations has been solved, the field distribution on the electrodes is obtained. Then the input impedance of the transducer can be calculated, and with the aid of appropriate integral representations the amplitudes of the different modes are obtained. View full abstract»

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  • Dipole reorientation in polyvinylidene fluoride

    Page(s): 1001 - 1008
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    The thermally stimulated current (TSC) from polarized polyvinylidene fluoride is studied below room temperature. The experimental results indicate that the maximum of the TSC observed at ∼ -50°C is due to reorientation of dipoles in a process associated with the glass transition. The TSC peak is inhomogeneously broadened by a distribution in relaxation frequencies. The results are analyzed in terms of both Arrhenius, and Williams‐Landel‐Ferry descriptions of the temperature dependence of the relaxation processes and the distribution function for the relaxation frequencies is calculated from the temperature dependence of the TSC. It is shown that a distribution in preexponential factors or in activation energies can account for the observed width of the TSC peak. For the latter case a distribution varying exponentially with activation energy seems most likely. From the data we obtain (3.6±0.4)×104 °K for the apparent activation energy and ∼2×10-3 sec-1 for the relaxation frequency of the dominant realignment process. The glass transition temperature is determined as Tg ∼ -51°C. View full abstract»

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  • Infrared absorption of mixed silicon isotope pairs in gallium arsenide

    Page(s): 1009 - 1012
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    The infrared absorption of GaAs doped with 28Si, 30Si, or 28Si + 30Si and compensated by 6Li diffusion or electron irradiation is reported. Isotopic shifts close to those predicted from local‐mode theory are observed for all the silicon defect bands in 30Si‐doped GaAs from frequencies previously reported for 28Si‐doped material. a new band is observed at 456 cm-1 for the sample containing both 28Si and 30Si, and is attributed to (28Si30Si) pairs. The frequency of the new band is in accord with simple theory, and its presence confirms the observation of the nearest‐neighbor silicon pairs. The results indicate, however, that the indentification of one of the three absorption bands previously attributed to the 28Si pairs is questionable. The experimental result also indicates that an absorption band at 369 cm-1 previously observed in electron‐irradiated samples in indeed due to a silicon‐related defect. View full abstract»

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  • Photoplastic effect in alkali halides

    Page(s): 1013 - 1022
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    The photoplastic effect first reported by Nadeau has been extensively investigated in colored crystals of NaCl, KCl, KBr, and KI. Detailed data on its dependence on strain level, F‐center concentration, strain rate, light intensity, and light wavelength have been obtained. The excitation spectrum of the photoplastic effect follows closely the shape of the F absorption band at room temperature as well as liquid‐nitrogen temperature. On the other hand, the magnitude Δτ of the effect fits the law Δτ = C1(1 + C2v/I)-1, v being the average dislocation speed, I the light intensity, and C1 and C2 constants. A theoretical model which takes into account the light‐induced formation of an electron cloud around charged moving dislocations is proposed. Quantitative expressions for the dependence of the effect on light intensity and wavelength have been obtained which are in accordance with experimental data. Other implications of this work on light‐induced dislocation pinning and dislocation‐induced photoconductivity are briefly analyzed. View full abstract»

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  • Computer simulations of vacancy and interstitial interactions with the (a/2) 〈110〉 edge dislocation in copper

    Page(s): 1023 - 1040
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    All simulations are performed with a single interatomic potential, the general features of which are outlined in a paper by Johnson. Analyses of a vacancy, an interstitial, and a stable (a/2) 〈110〉 edge dislocation in copper are presented, along with calculations each describing a vacancy and an interstitial in static equilibrium at the edge of the dislocation. Vacancy and interstitial formation energies and associated strain patterns are calculated. The 〈100〉 split interstitial configuration is stable with a formation energy of 3.060 eV. The vacancy formation energy is 1.165 eV. The strain patterns agree well with those obtained by others. The (a/2) 〈110〉 edge dislocation on the {111} plane is positioned in the lattice according to a previously devised procedure which results in complete agreement between atomistic and continuum treatments in regions of small strain. Atomic displacements parallel to the dislocation line are analyzed and their variation with distance from the line is shown to be oscillatory and to damp out within about 9 Å of the line. The over‐all significance of such displacements to dislocation core simulation is discussed. The core radius and energy are calculated to be 4.8 Å and 0.278 eV per (112) plane, respectively, and the core configuration is shown to be consistent with the short‐range character of the potential. A lattice with 4080 atoms on 24 (112) planes is used to analyze the point‐defect‐dislocation interactions. With regard to a vacancy or an interstitial at the edge of the dislocation, each is bound to the dislocation having binding energies 0.247 and 0.800 eV, respectively. The atomic configuration and strain pattern associated with each bound defect are presented. View full abstract»

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  • The mechanics of elastic contact with film‐covered surfaces

    Page(s): 1041 - 1043
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    Solutions to the Hertz problem, which predict the contact area between cylindrical or spherical bodies elastically loaded against one another, have frequently been applied to situations in which one of the bodies is coated with a thin film of different material, notably in the analysis of bearings lubricated with thin solid films. In reality the film may often exert a profound influence on the contact area and the Hertzian assumption will be inappropriate. The present work offers approximate analytical solutions for film‐coated cylindrical and spherical contacts, that are valid provided the contact dimensions are large compared to the film thickness and provided also that the Young's modulus of the film material is less than that of the surfaces with which it interacts. It is hoped that the expressions derived here will prove to be particularly useful in the study of lubricant films deposited by such processes as sputtering and ion plating, where a knowledge of the true area of contact is a crucial factor in the understanding of the mechanics involved. View full abstract»

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  • Electrical conductivity of disordered layers in GaAs crystal produced by ion implantation

    Page(s): 1044 - 1049
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    The electrical conductivity of disordered layers in GaAs produced by ion implantation has been studied as a function of ion species, dose level, energy of implanted ions, and anneal temperature. The resistivity of the implanted layer, ρ, at room temperature can be expressed by a single relation, ρ=const×NDD-3, even for different masses and energies of implanted ions, where NDD is the total number of displacements of host atoms per unit volume due to nuclear collisions with implanted ions. At a temperature above 180 K the resistivity is proportional to exp(B/T) and below 180 K it changes as exp(B/T1/4). The conduction mechanism of the implanted layers is discussed based upon the hopping conduction in disordered or amorphous semiconductors. The annealing behavior of the implanted layers was also studied. The activation energy for recovery of the resistivity ρ was about 0.35 eV, which is quite small compared with the migration energies of stray atoms in ordered crystals. These results indicate that the implanted layer is in a disordered state rather than in a crystalline state containing the point defects. View full abstract»

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  • Defect centers in oxygen‐deficient rf‐sputtered SiO2 films. I. Electron spin resonance

    Page(s): 1050 - 1059
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    Two new defect centers have been observed by electron spin resonance (ESR) in rf‐sputtered SiO2 films with low metallic impurity content. At 77°K, as‐sputtered films have three ESR centers, two HX centers, and an HY center. The HY center, a hole center, has g = 2.008–2.009. The HX center has two components, the HXa center with axial symmetry and with ga = 2.022 and ga = 2.037; the HXb center with gb = 1.984 which is split by hyperfine interaction with hydrogen. The hydrogen hyperfine interaction has axial symmetry, Ab = 30.2 G and Ab = 63.6 G. Both the HX and HY centers show hyperfine splitting due to interaction with Si29. Annealing of as‐sputtered films in hydrogen‐containing atmospheres at 350°C eliminates the HY center, leaving the HX center. Annealing in N2 or O2 at 550°C also eliminates the HY center; the resulting HX resonance is identical to that obtained after hydrogen anneal. The activation energy for the appearance of the HX center is 0.036 eV when samples are cooled to 77°K. From similarities in hyperfine interactions, activation energies, and g values, it is suggested that the HY center is the silicon analog of the Al center in SiO2. It occurs in oxygen‐deficient SiO2 and is due to removal of a nonbonding electron from an oxygen which bonds Si+3 to Si+4. The HY center is converted to the HX center by bonding with hydrogen which can be provided by H2 from the annealing ambient or by the H atom in SiOH incorporated in SiO2 films. View full abstract»

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  • Defect centers in oxygen‐deficient rf‐sputtered SiO2 films. II. Thermoluminescence

    Page(s): 1060 - 1070
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    Thermoluminescent (TL) glow curves of rf‐sputtered SiO2 films deposited on silicon have been measured and correlated with two new defect centers detected by electron spin resonance (ESR) of the films, the HX and HY centers. As‐sputtered films have low optical absorption and ESR absorption is dominated by the HY center. TL intensity is low after x irradiation. Annealing at 400°C in hydrogen, or at 550°C in nitrogen or oxygen, converts the HY center to the HX centers. TL intensity increases with annealing and goes through a maximum after annealing at 550°C in hydrogen or 650°C in nitrogen or oxygen. A characteristic TL glow curve pattern is associated with the HX centers. Trapping centers with energies of 0.74, 0.96, 1.04, and 1.20 eV are found. The complexity of TL glow curves is due primarily to variations in s, the frequency factor, rather than to a range of trap energies. It is proposed that trapping centers are associated with oxygen vacancies, and with SiH bonds, in oxygen‐deficient SiO2 films, while the recombination center is associated with bonding oxygens. View full abstract»

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  • Effect of OH- on the low‐frequency dielectric constant of vitreous silica

    Page(s): 1071 - 1074
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    The 1000‐Hz 300°K dielectric constant, ϵs, of 24 kinds of commercially available vitreous silica has been measured to an accuracy of 0.01% and a precision of about 1 part in 300 000 by the method of substitution (two‐fluid technique). The observed dielectric constant ranges from 3.8073 to 3.8304. These results are correlated with hydroxyl ion content and other imperfections. It is found that ϵs=3.8073+2.72×10-22 N where N is the hydroxyl concentration in ions/cm3, and observed deviations from this rule are attributed to metallic impurities and inclusions. From the results it appears that 3.8073 closely approximates the low‐frequency dielectric constant of pure vitreous silica. View full abstract»

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  • Conversion of Si to epitaxial SiC by reaction with C2H2

    Page(s): 1075 - 1084
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    The growth of β‐SiC films on Si by reaction of a Si single crystal with C2H2 has been studied for the conditions 10-7 ≤PC2H2≤5×10-4 Torr, 800≤T≤1100°C, in both high‐ and ultrahigh‐vacuum chambers. At C2H2 pressures below approximately 10-5 Torr, linear growth kinetics were observed over the temperature range investigated and the reaction probability was determined as 0.02–0.03. In this pressure range growth occurs by the diffusion of Si through porous defects incorporated in the growing film. We have studied in detail the structure of defected films formed under various growth conditions by scanning electron microscopy, scanning transmission electron microscopy, and transmission electron microscopy. We conclude that the occurrence of defects is intrinsic to the mechanism of film growth. The predominant defect type consists of a shallow (∼ 2000 Å) pit in the Si substrate, over which the growing SiC assumes a porous polycrystalline morphology. The number and areal densities of these defects are proportional to the C2H2 partial pressure and the SiC film thickness, respectively. The defects act as sources of Si for reaction, and film growth occurs via diffusion of Si from the substrate through the porous overgrowth to the epitaxial SiC/vacuum interface, where reaction occurs. For C2H2 pressures exceeding approximately 10-5 Torr the porous defects are sealed off at an early stage in the growth and further reaction is virtually arrested due to the extremely small bulk and/or grain boundary diffusivity for Si in SiC over the experimental temperature range. No significant effect on growth rate due to the type of vacuum system used was found. View full abstract»

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  • Identification of interstitial‐ and vacancy‐type dislocation loops in ion‐implanted silicon

    Page(s): 1085 - 1090
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    A quick method of distinguishing between vacancy‐type and interstitial‐type dislocation loops is described which is applicable to foils near ≪111≫ orientation and loops in the size range which gives rise to double‐arc contrast. This method utilizes the Kikuchi line pattern and some general rules concerning electron diffraction contrast from small loops. With this method, small prismatic loops in As+‐implanted silicon have been shown to be of interstitial type. View full abstract»

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  • Continuum descriptions of dislocations under stress reversals

    Page(s): 1091 - 1096
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    A general continuum theory of dislocation motion is used to investigate the response of crystalline solids to cyclic straining in uniaxial tension and compression. For macroscopically homogeneous deformation under uniaxial stress a simple one‐dimensional equation suffices to relate the plastic strain rate to dislocation flux. The material is characterized by evolutionary equations for multiplication of dislocations and for immobilization of moving dislocations. Some simple example materials are considered and it is shown by numerical calculation that these exhibit respectively a Bauschinger effect, isotropic hardening, and isotropic softening when subjected to a program of alternating strains at a constant rate. View full abstract»

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  • Minimization of conductor surface heating by a pulsed magnetic field

    Page(s): 1097 - 1099
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    The heat deposition on the surface of a semi‐infinite conductor is obtained for a magnetic field pulse of arbitrary time dependence but finite duration. Given a specified ``flat‐top'' period for the magnetic field strength at the surface, the rise and decay of the field pulse for minimal surface heating are derived. View full abstract»

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  • Radiation‐limited model for a plasma conduction layer in magnetic flux compression systems

    Page(s): 1100 - 1104
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    The nature of a high‐temperature plasma layer adjacent to a vaporizing conductor surface in multimegagauss flux compression systems is of interest in terms of the maximum field levels attainable and the extent to which high‐Z conductor impurities will contaminate plasmas confined by ultrahigh magnetic fields. A model has been developed for such a conductor plasma layer, based on the assumption of a steady balance between resistive heating and radiation loss at any location within the plasma layer. A general analytical solution is found for the magnetic field distribution through the layer in terms of plasma and conductor properties and a nondimensionalized profile integral. Criteria are derived emphasizing the need for proper dynamic operation if plasma conduction layers are to have any importance in high‐field flux compression systems. View full abstract»

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  • Solutions of the classical Boltzmann equation for He and Ne gas breakdown

    Page(s): 1105 - 1111
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    A theoretical study of gas breakdown induced by intensive CO2 laser radiation is given. The basic assumption is that the gas breakdown is due to the process of cascade ionization. The Boltzmann equation for the electron energy distribution function is solved. Details of the numerical method and breakdown thresholds for He and Ne gases are given. The results are in reasonable agreement with the experimental results and are rather sensitive to the gas pressure. View full abstract»

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  • Preflashover phenomena and electron‐stimulated desorption in high electric fields

    Page(s): 1112 - 1114
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    The effect of high electric fields on the electron‐stimulated desorption (ESD) of positive ions from metal surfaces has been studied at fields between 103 and 105 V/cm for electron energies between 1 and 20 kV. Adsorbed gases characteristic of the residual vacuum (10-9 Torr) were detected under all conditions, but ions characteristic of the substrate were only detected for fields approaching 105 V/cm. These observations confirm that previously reported preflashover anode metal ion species in an ultrahigh‐vacuum diode originate at anode protrusions by a field evaporation process and that only residual gas species are produced prior to flashover by ESD. It is suggested that, if field emission processes at the cathode could be completely suppressed, electrical flashover would still occur, initiated and sustained by field‐evaporated anode ions. View full abstract»

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  • Multiple scattering from finite inhomogeneous media

    Page(s): 1115 - 1126
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    By utilizing the characteristic information on the apparent phase constant difference between the electric and magnetic fields propagating in an inhomogeneous medium, a theoretical analysis on the multiple scattering of electromagnetic waves in finite inhomogeneous media is presented. The solution is obtained by first approximating the coefficients of a pair of exact coupled first‐order differential equations and then solving the equations by first‐order iteration. The present first‐order approximate solution with multiple scattering considerations is shown to be more accurate than the WKB solution. Methods to improve the accuracy of the first‐order solution further are discussed. Application of the solution to slowly varying finite media with periodic properties demonstrates the validity of the solution. The same approach can be extended to frequencies in the optical region by retaining additional terms in the coefficients of the coupled differential equations. Further investigations are required to treat the case of oblique incidence in proper perspectives. View full abstract»

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  • Transverse heating of a cold dense helium plasma by a pulsed CO2 laser beam

    Page(s): 1127 - 1134
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    We present experimental evidence for the transverse heating of a dense (3.2 × 1017 cm-3) cold (≃4 eV) helium θ‐pinch plasma by the focused beam of a TEA CO2 laser having a pulse duration of 180 nsec and a peak power of approximately 5 MW. The laser light was incident on the plasma during the first pinch compression, when streak photographs taken with a high‐speed camera indicate a stable quiescent plasma lasting about 1.5 μsec. Time‐resolved spectroscopic measurements were made to determine the plasma density and temperature before and after irradiation by the CO2 laser. Maximum temperature increases of 0.8 eV and density increases of 0.5 × 1017 cm-3 were observed for a laser energy of 0.7 J incident on the plasma. The theoretical description of the interaction considers the quasistatic temporal response of the plasma to the absorption of laser energy by inverse bremsstrahlung, and includes deviations from local thermodynamic equilibrium (LTE) before, during, and after irradiation. The absorbed energy is consumed in expansion, heating, and further ionization of the plasma. Highly excited atomic or ionic states are assumed to be in Saha equilibrium with each other and with the ionization continuum, whereas the ground states of successive ionization stages are assumed to be in coronal equilibrium. Thermal conduction losses are negligible. The theory correctly predicts the observed temperature increases but not the observed density changes, since inertial effects are neglected in order to render the model tractable. View full abstract»

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  • Electrogasdynamic generation using solid‐gas suspension in turbulent pipe flow

    Page(s): 1135 - 1143
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    The paper describes a study of the charge transfer of a solid‐gas suspension in turbulent pipe flow. Using hollow glass spheres as the particulate phase, nitrogen and saturated air respectively as the gaseous phase, experiments were performed at flow rates of Reynolds number 5000–16000. Experimental results reveal that along a dielectric pipe there is strong electrification of the suspension, with particle electrification per pipe‐diameter displacement of the order of ‐ 10-5 C/kg, while along a conductor pipe the charge decay of the electrified suspension is of an empirical form (q/m)0 exp(-αl1/2), where l is the suspension displacement from the pipe entrance and α is a constant. In each case the pipe length was approximately 1 m, and the internal diameter approximately 1 cm. The process of charge transfer through particle‐pipe impact is discussed, and an experimental EGD generator setup is described. View full abstract»

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  • Electrohydrodynamic capillary source of ions and charged droplets

    Page(s): 1144 - 1146
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    A semiquantitative treatment predicts that when an electrohydrodynamic capillary source produces metal droplets along with the ions that are generally observed, the charge‐to‐mass ratio will reach a maximum and the radius a minimum at about the radius at which the limit of stability against breakup into smaller drops (Rayleigh limit) becomes equal to the limit of stability against the field evaporation of ions. The maximum charge‐to‐mass ratio was found to be [inverted lazy s] 17 000 C/kg for a eutectic mixture of lead and bismuth. The semiquantitative treatment, which is supported by this experimental result, predicts that the ions should be emitted from a liquid tip having a radius of about 10 Å. It is suggested that if the wobble of the tip is not too great, this type of source should have applications in ion microprobes. View full abstract»

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  • Study of the x‐ray production mechanism of a dense plasma focus

    Page(s): 1147 - 1153
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    The x‐ray emission from a 375‐kJ plasma focus is reported as measured on a time‐resolved basis with Ross filters and silicon diode detectors. Thick‐target electron beam spectra are calculated with a Monte Carlo electron beam transport program and fit to the experimental time‐integrated x‐ray spectra. A good fit is obtained with a 2‐MA E-2 power law electron beam, with cutoff energies at 8 and 200 keV, incident normal to a thick tungsten target. The source of the beam is judged to be electrons which are accelerated under the influence of strong electric fields. A 20‐nsec Q‐switched ruby laser pulse injected tungsten ions via laser ablation prior to the initial dense pinch, and the x‐ray emission below 4 keV was enhanced and that above 10 keV was reduced. The enhanced low‐energy x‐ray emission is in agreement with calculated radiation for collisional M‐shell excitation of highly stripped tungsten in a 1.5‐keV thermal plasma. A 900‐ μsec ruby laser pulse injected sufficient tungsten ions to degrade greatly the initial dense plasma pinch and reduce the beam target x‐ray emission. The time‐resolved x‐ray emission from this configuration appeared as a smooth Gaussian function in time with FWHM∼200 nsec. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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P. James Viccaro
Argonne National Laboratory