Showing papers in "IEEE Transactions on Plasma Science in 1982"
TL;DR: In this paper, a review of ion-acoustic solitons is presented, together with a modified Korteweg-deVries (KdV) equation and numerical results.
Abstract: Experiments on ion-acoustic solitons are reviewed. Theories and numerical simulations which are relevant to experimental results are also presented. The measured velocity and width of planar solitons are compared with the predictions of the Korteweg-deVries (KdV) equation which includes a finite ion temperature. The spatial evolution of compressive or rarefactive pulses is discussed. Cylindrical and spherical solitons are introduced together with a modified KdV equation and numerical results. Oblique collisions and their evolution, including overtaking and head-on collisions of two planar, cylindrical, or spherical solitons are described. Reflection, diffraction, and other topics related with ion-acoustic solitons are presented.
119 citations
TL;DR: In this paper, the high frequency response characteristics of differentiating and self-integrating Rogowski coils have been calculated for arbitrary values of the coil terminating resistance assuming Ampere's law to be valid.
Abstract: The high frequency response characteristics of differentiating and self-integrating Rogowski coils have been calculated for arbitrary values of the coil terminating resistance assuming Ampere's law to be valid. Effects due to a reactive terminating impedance are also discussed. When the displacement current is taken into account in the measurement of the current of a charged particle beam, it is found that an effective rise time is introduced into the self-integrating coil response on the order of a/??, where a is the major radius of the coil, ? is the velocity of the beam, and ? = (1 -?2/c2)-1/2.
65 citations
TL;DR: In this article, the results of a model experiment to investigate the dielectric recovery of an axially blown sulphur hexafluoride (SF6) arc after current zero are presented.
Abstract: The results are presented of a model experiment to investigate the dielectric recovery of an axially blown sulphur hexafluoride (SF6) arc after current zero With the aid of Schlieren pictures and interferometry, the temperature decay after current zero is observed up to the point of complete recovery of the gap The dielectric recovery is directly measured by applying voltage pulses across the gap which causes breakdown at different times after current zero Residual charges, which play a role in the early recovery phases, are detected using a specialiy developed technique Variations of the shape of the voltage pulses and the geometry cause characteristic changes of the recovery, which support the interpretation of the experimental data
54 citations
TL;DR: In this paper, a review of the literature on vacuum-arc phenomena and the effect of low-pressure gaseous ambients on electrode phenomena in the transition to atmospheric pressure arcs is presented.
Abstract: This paper reviews vacuum-arc phenomena, and the effect of low-pressure gaseous ambients on electrode phenomena in the transition to atmospheric pressure arcs. The 5 main areas addressed are cathode-spot phenomena, anode-spot phenomena, the properties of the interelectrode plasma for both diffuse arcs and columnar arcs, the interaction of vacuum arcs with axial and transverse magnetic fields, and finally, the transition to atmospheric pressure arcs. The current levels range from 50 A to 50 kA. For each of these 5 main areas, features of the vacuum arc which can be reasonably established from the literature are filrst described, followed by a discussion of parameters requiring additional experimental and theoretical study. For example, the current densities, microstructure, and theoretical description of the cathode spot remain the subject of much debate. There is also a need for additional experimental observations of the anode ion flux and ion energies in order to clarify the overall anode-spot mechanism. With respect to high-current columnar arcs, here there is uncertainty concerning the pressure in the arc column and the mechanism of the grossly evaporating cathode spot. It is firmly established that these high-current columnar arcs can be avoided by applying an axial magnetic field parallel to the arcing axis, but a detailed understanding of the magnetic field/arc interaction remains to be established. The review concludes with a discussion of experimental investigations of electrode phenomena in the presence of low ambient gas pressures.
42 citations
TL;DR: The Air Force Weapon Laboratory has investigated and developed inductive pulse compression techniques with fuse opening switches for driving high speed plasma implosions Experiments have demonstrated the delivery of 75 MA to a 5-nH load in < 200 ns from an initial 19-MJ 2-?s capacitor bank via induction pulse compression Circuit considerations dictate the overall energy efficiency while MHD considerations dictate overall implosion stability and thermalization time as discussed by the authors.
Abstract: The Air Force Weapon Laboratory has investigated and developed inductive pulse compression techniques with fuse opening switches for driving high speed plasma implosions Experiments have demonstrated the delivery of 75 MA to a 5-nH load in < 200 ns from an initial 19-MJ 2-?s capacitor bank via inductive pulse compression Circuit considerations dictate the overall energy efficiency while MHD considerations dictate overall implosion stability and thermalization time Theoretical considerations along with initial experiment results are presented in this paper
41 citations
TL;DR: In this paper, the authors used a low-divergence (100,?rad) KrF laser to trigger 2.8-MV gas switches for lage pulsed-power systems.
Abstract: We are investigating the use of a low-divergence (100, ?rad) KrF laser to trigger 2.8-MV gas switches for lage pulsed-power systems. Using less than 0.1 J of laser energy, we have demonstrated subnanosecond-jitter triggering (1?) of these switches, which are insulated with pure SF6, at voltages between 75-90 percent of the self-breakdown voltage of the switch. The time delay between the laser pulse and the switch closure is relatively insensitive to variations in voltage, with delay changing by as little as 1.5 ns between 80-90 percent of the self-breakdown voltage. We also present parametric studies of laser triggering using lenses with different focal lengths at various input laser energies.
37 citations
TL;DR: Optical control of diffuse discharges is discussed as opening mechanism for rep-rated switches in this article, which can be sustained or terminated by making use of optogalvanic effects, that means resonant interaction of laser radiation with diffuse plasma.
Abstract: Optical control of diffuse discharges is discussed as opening mechanism for rep-rated switches. Diffuse discharges can be sustained or terminated by making use of optogalvanic effects, that means resonant interaction of laser radiation with diffuse plasma. Independent of control mechanisms, the performance of diffuse discharge opening switches is strongly affected by such fill gas properties as attachment and electron mobility.
36 citations
TL;DR: In this paper, a theoretical solution for the turbulence onset and for the radial temperature profile at current zero is derived based on experimental results for the turbulent onset and the radial profile at the current zero, which is compared with various measured data, e.g., the radius of the hot-gas channel as a function of time and the dielectric recovery characteristics.
Abstract: A detailed comparison between experiment and theory is made on the basis of the results of Parts I and II. As a first step, a theoretical solution is derived which is based on experimental results for the turbulence onset and for the radial temperature profile at current zero. This solution is compared with the various measured data, e. g., the radius of the hot-gas channel as a function of time and the dielectric recovery characteristics. The influence of space-charge effects on the recovery are shown to depend on the time after current zero and the shape of the applied voltage. Recommendations for further research are made.
35 citations
TL;DR: In this paper, the turn-on times of a triggered vacuum gap were determined as a function of main gap voltage and trigger and main gap polarities, where the trigger pin protruding through one electrode was used as a tungsten trigger pin.
Abstract: Measurements have been conducted to determine the turn-on times of a triggered vacuum gap as a function of main gap voltage and trigger and main gap polarities. The triggered vacuum gap consisted of a pair of molybdenum electrodes mounted in a low-inductance (20 nH) stainless-steel chamber. Triggering was accomplished by supplying a 10-kV pulse from a charged 12.5-? cable circuit to a tungsten trigger pin protruding through one electrode. The main gap voltage was supplied by a 4-? charged cable circuit. Minimum wait times (the time from application of the trigger pulse to the beginning of main gap voltage coliapse) of 50 ns were observed when a negative pulse was applied to the trigger located in the cathode. A minimum value of voltage collapse time of 10 ns was observed when a positive pulse was applied to the anode located trigger. The switch could be triggered for all main gap voltages in the range 50 V-75 kV, with minimum delay times occurring at 500 V.
31 citations
TL;DR: In this paper, a series of theoretical calculations were performed in order to identify the electron transport and other gas properties which optimize the performance of e-beam switches, and determine the laws which predict the scaling properties of ebeam switches.
Abstract: An electron beam (e-beam) controlled switch makes use of the low-energy secondary electrons in a diffuse e-beam sustained discharge as the conducting medium which carries the switched current. The conductivity of the gas in the switch is negligible before the e-beam is turned on because the circuit parameters are chosen so that the open circuit voltage which appears across the switch electrodes is well below the static breakdown voltage of the gas in the switch gap. The e-beam switch can interrupt direct current because the density of the electrons in the switch decays by recombination and attachment when the e-beam is turned off and the switch conductivity decreases. In typical circuits, this decay in conductivity causes the switch voltage to rise and the switch current to fall, i.e., the switch "turns off." This paper presents the results of a series of theoretical calculations which were performed in order to: 1) identify the electron transport and other gas properties which optimize the performance of e-beam switches, 2) evaluate the performance of several real gases for use in e-beam switches, and 3) determine the laws which predict the scaling properties of e-beam switches. Results are presented for N2, Ar, a N2:Ar = 1:9 mixture, and CH4. These results show that CH4 provides the best e-beam switch performance. Comparison of experimental results and theoretical predictions for CH4 supports both the theory and the predicted good e-beam switch performance for CH4.
30 citations
TL;DR: In this article, a self-consistent optimization procedure, free from reliance on comparison with a trial source function, for optimizing the configuration of these chords is described and used to demonstrate that an asymmetric arrangement usually leads to greater reconstruction accuracy than a regular array.
Abstract: Matrix inversion and least squares fitting have been used to recover two dimensional distribution functions from a small number of line integrals taken along chords across them. A self-consistent optimization procedure, free from reliance on comparison with a trial source function, for optimizing the configuration of these chords is described and used to demonstrate that an asymmetric arrangement usually leads to greater reconstruction accuracy than a regular array. Smoothing is incorporated by imposing auxiliary conditions relating to the second derivative ?2f of the source function f, and its effect on reconstruction accuracy and resolution is investigated. These methods are applied to the ten-channel far-infrared interferometer being prepared for use on JET. Electron denisty contour shapes can be identified rather sensitively if the source function contours belong to a predetermined family.
TL;DR: The results of an investigation of the statistical behavior of the observational time lag to breakdown in an overvolted sparkchamber are presented as a function of pressure (up to 1350 torr of nitrogen), electrode separation (1 and 2 cm) and percent overvoltage (upto 2800 percent) as mentioned in this paper.
Abstract: The results of an investigation of the statistical behavior of the observational time lag to breakdown in an overvolted sparkchamber are presented as a function of pressure (up to 1350 torr of nitrogen), electrode separation (1 and 2 cm) and percent overvoltage (up to 2800 percent). Rogowski contoured, graphite, brass, and aluminum electrodes have been investigated. Automated diagnostic equipment has allowed the reduction of large amounts of data. The results indicate: 1) the shapes of the distributions are strong functions of pressure, 2) the electron emission rate associated with graphite is an order of magnitude greater than that associated with aluminum and brass, 3) the cathode emission rate is much higher than the "apparent" rate determined from a simple stochastic model, and 4) the formative time (taken as the minimum observed time lag) is an order of magnitude greater than that predicted by the streamer model of breakdown.
TL;DR: In this paper, the authors show that small-scale transient luminous anode-spot activity is associated with the strong voltage noise that precedes the establishment of the conventional large anode spots.
Abstract: Coordinated high-speed movies, streak photographs, and voltage/current oscillograms have been taken for vacuum arcs on copper-based electrodes at peak currents up to 70 kA in half-cycle pulses. These results show that small-scale transient luminous anode-spot activity is associated with the strong voltage noise that precedes the establishment of the conventional large anode spots. The characteristic dimensions of the small-scale spots go below a millimeter, and may be less than 100 ?m. Unlike cathode spots of that size, these small anode spots always move in the I × B direction. This small-scale activity is especially pronounced in experimental systems initially containing surface films of volatile matter. Good correlations have been established between bursts of anode light and corresponding bursts of arc voltage noise, both of which appear to be associated with variations in the small luminous structures. The practical importance of the small transient luminous anode activity reported here is in its clear tendency to advance the formation of electrode jets, particularly under experimental conditions favoring the evolution of gas or vapor from anode surfaces. It has theoretical significance as a precursor to the formation of the usual large anode spots and jets, and as a possible source of structure within large anode spots.
TL;DR: In this article, a simple model, which utilizes the electron continuity equation, provides a description of the formative period as well as the current buildup during the resistive phase, was investigated in the context of a transmission-line pulse system.
Abstract: The development of cufrent in gaseous spark gaps has been investigated in the context of a transmission-line pulse system. A simple model, which utilizes the electron continuity equation, provides a description of the formative period as well as the current buildup during the resistive phase. The E-field in the gap is assumed to be spatially uniform and dependent on time through temporal variations in the applied field. We have employed this simple model in analyzing the dependence of the formative time on the initial parameters of the discharge. At the end of the breakdown formation process, space-charge and secondary ionization effects become important. A two-dimensional time dependent model has been developed to include these effects. Current waveforms obtained from both models have been compared with experimental waveforms. Experimental measurements were performed in a 50-? pulse transmission-line system. Incident voltage waveforms of approximately rectangular shape were applied between large electrodes in a nitrogen filled test gap. Incident voltage and transmitted current waveforms were monitored with capacitive dividers and recorded by a fast transient digitizer.
Abstract: The chemical interactions and physical processes occurring in a high energy spark gap with different combinations of gases, electrodes, and insulators were studied. The electrodes studied were graphite and a tungsten-copper composite; the insulators were Lexan and Blue Nylon; and the gases were N2 and SF6. The gas composition was monitored with a mass spectrometer. Spectroscopic techniques were used to observe the arc channel. The electrode surfaces were studied with several surface analysis techniques, including scanning electron microscopy, electron spectroscopy for chemical analysis, Auger electron spectroscopy, and X-ray fluorescence. The breakdown voltage distribution was examined for different material combinations. The plasma chemistry processes involving the gas, electrode, and insulator materials were found to affect the voltage self-breakdown distribution. The detailed surface analysis gave information about the nature of the chemical processes. The presence of Blue Nylon seemed to have a more adverse effect than Lexan and graphite seemed to have a narrower voltage distribution than the tungsten-copper composite.
TL;DR: In this paper, two surface wave plasma columns, generated by microwave power in argon at gas pressures of 0.05 torr to 330 torr, interact in the same discharge tube to form standing surface waves.
Abstract: Two surface wave plasma columns, generated by microwave power in argon at gas pressures of 0.05 torr to 330 torr, interact in the same discharge tube to form standing surface waves. Radial electric field Er and azimuthal magnetic field H? outside the discharge tube are measured to be 90° out of phase with respect to axial position and to decay exponentially with radial distance from the tube axis. Maximum light emission occurs at the position of maximum H?, and minimum Er. Electron temperature and density are measured at low pressures with double probes inserted into the plasma at a null of Er. Measured electron densities compare well with those predicted by Gould-Trivelpiece (GT) surface wave theory. Measured electron temperatures are the same order of magnitude as temperatures predicted by positive column theory.
TL;DR: In this paper, an analysis of the relativistic electron motion at electron cyclotron resonance (ECR) condition in a magnetic field which is gradually growing in time is accomplished.
Abstract: An analysis of the relativistic electron motion at electron cyclotron resonance (ECR) condition in a magnetic field which is gradually growing in time is accomplished. The results show the existence of a strong mechanism (basically nonrelativistic) which automatically maintains the phase stability during the gyro-resonant acceleration. The conditions in which the gyro-resonant acceleration (up to arbitrarily high energies) is possible are established. The conceptual design of a gyro-resonant accelerator (Gyrac) is proposed. The parameters of possible Gyrac devices for the energies of 5 GeV, 1 GeV, 100 MeV, and 10 MeV with peak powers of accelerated electron bunches (e-vortex) correspondingly 2.5 TW, 0.5 TW, 25 GW, and 0.4 GW are given.
TL;DR: In this paper, the authors present a review of the theory and experimental data for a volume discharge relevant to potential applications for high power switching, and suggest that an optimum balance between the contradictory requirements of low resistivity and short opening time may be realized by proper choice of gas mixture.
Abstract: When an electron beam (e-beam) is injected into a gas located between two electrodes, a volume discharge, which turns on and off in association with the beam, can be generated. We present a review of the theory and new experimental data for such a discharge relevant to potential applications for high-power switching. The data suggest that an optimum balance between the contradictory requirements of low resistivity and short opening time may be realized by proper choice of gas mixture.
TL;DR: In this article, the authors present an analysis of the plasma occurring during the steady-state phase in a hydrogen thyratron and show that the plasminarity of this plasma is positively correlated with the density of the hydrogen atoms.
Abstract: This paper presents an analysis of the plasma occurring during the steady-state phase in a hydrogen thyratron.
TL;DR: In this article, a two-pulse method is used to determine how fast and to what degree a small spark gap can recover its voltage holdoff capability after breaking down, and the experimental setup, pulse circuits, and data collection methods are described.
Abstract: A two-pulse method is used to determine how fast and to what degree a small spark gap can recover its voltage holdoff capability after breaking down. The first pulse is used to overvolt and break down the gap. The second pulse is used, after a time delay, to determine the voltage recovery of the gap. By varying the time delay to the second pulse, a recovery voltage versus time plot can be obtained. Time delays from 10 ?s to 100 ms have been recorded. The spark gap discharges millijoules of energy with a gap spacing of less than 1 mm. Recovery has been measured at breakdown voltages of up to 10 kV in argon, hydrogen, and a mixture of the 2 gases. The experimental setup, pulse circuits, and data collection methods are described. Percent voltage recovery versus time plots for various parameters (gas species, gap spacing, and pressure) are discussed.
TL;DR: In this article, the strong compression TFTR discharge has been segmented into regions where linear dynamics can approximate the plasma's interaction with the OH and EF power supply systems, and the dynamic equations for these regions are utilized within the linear optimal control theory framework to provide active feedback gains to control the plasma position and current.
Abstract: The strong compression TFTR discharge has been segmented into regions where linear dynamics can approximate the plasma's interaction with the OH and EF power supply systems. The dynamic equations for these regions are utilized within the linear optimal control theory framework to provide active feedback gains to control the plasma position and current. Methods are developed to analyze and quantitatively evaluate the quality of control in a nonlinear, more realistic simulation. Tests are made of optimal control theory's assumptions and requirements, and the feasibility of this method for TFTR is assessed.
TL;DR: In this paper, the dual channel triggering of a spark gap switch by fiberoptic transported ruby laser radiation is discussed, and the correlation of this behavior with the space charge build up in the slightly over-volted gap is discussed.
Abstract: The dual channel triggering of a spark gap switch by fiberoptic transported ruby laser radiation is discussed. The spark gap is the output switch of a 20-ns water dielectric Blumlein generator. The Blumlein generator is pulse charged in approximately 250 ns by a three-stage Marx bank to 150 kV. The spark gap is operated at a pressure of 2540 torr with a mixture of Ar and N2 gas and an electrode separation of 2 cm. Two 1-mm diameter quartz optical fibers are used to transport 2 2-MW laser beams into the spark gap onto points 6 cm apart on the target electrode. The two beams are obtained by optical splitting of the output of a single laser. Under appropriate conditions, two arc channels are initiated by the laser beams along their paths. A small improvement in current rise time for dual channel events over single channel events is observed. Moreover, the number of successful dual channel events is observed to depend on the time of laser entry with reference to the beginning of the charging pulse, and not the gap polarity. The correlation of this behavior with the space charge build up in the slightly over-volted gap is discussed.
TL;DR: In this paper, the optogalvanic effects of the He 2.058-?m line (21P-21S) from He lamps illuminating a weak dc He discharge (current density?10?A/cm2, field/pressure ~25 V/cm - torr) are reported.
Abstract: The optogalvanic effects of the He 2.058-?m line (21P-21S) from He lamps illuminating a weak dc He discharge (current density ?10 ?A/cm2, field/pressure ~25 V/cm - torr) are reported. For illumination at the positive column, we have made quantitative measurements of the decreases in the discharge current, electron density, and metastable densities, as weli as the increase in the electric field in the positive column, as the intensity of illumination increases. We have also observed that for sufficiently strong illumination (using He lamps only), the optogalvanic effect is catastrophic, i.e., the discharge is switched off; this clearly shows that a sufficiently large metastable density (which is reduced by the illumination) is necessary to maintain a weak He discharge. For illumination at the cathode regions, the optogalvanic effects are "anomalous": the discharge current is strongly suppressed by illumination at the cathode dark space next to the cathode, but is enhanced by iumination at the adjacent negtive glow region.
TL;DR: In this article, a theoretical investigation of high-pressure discharges ionized by an external electron beam (e-beam) was conducted, where the secondary emission from the cathode and electron-impact ionization of metastable states were included in the analysis.
Abstract: A theoretical investigation of high-pressure discharges ionized by an external electron beam (e-beam) was conducted. Only when secondary emission from the cathode and electron-impact ionization of metastable states were included in the analysis did calculated current-voltage (I-V) characteristics for argon and methane discharges compare well with experimental data. The I-V characteristics obtained reveal a sharp rise in the current at a certain threshold voltage. This threshold voltage and the entire I-V characteristic are shifted to lower voltages when metastable ionization is significant. Below the threshold voltage and at low external ionization source strengths, a region of negative differential conductivity is obtained. In the high-current region, the I-V slope is controlled by the secondary emission coefficient. The additional cathode sheath ionization from secondary emission and ionization from metastable states significantly reduces the discharge voltage. This important effect can be used to reduce e-beam switch losses and increase lifetime through judicious gas mixture selection and proper cathode conditioning.
TL;DR: In this paper, a theoretical model for the behavior of emitting sites on the cathode surface is proposed to explain arc duration and related erosion occuring in telecommunication relays and circuit breakers.
Abstract: This paper presents a study of instabilities and of spontaneous extinctions which occur in low current dc arcs between metal electrodes. A theoretical model for the behavior of emitting sites on the cathode surface is proposed. This model explains experimental results obtained in arc duration measurements and arc noise correlation. The model yields figures for site life time and elementary current of emitting sites. These values are compared with those given by other authors. The proposed model can be applied to explain arc duration and related erosion occuring in telecommunication relays and circuit breakers.
TL;DR: In this paper, the authors measured statistical times as a function of overvoltage and gap conditioning in small (0.127 mm) flowing-gas spark gaps, and found that statistical time increased with pressure in air-filled spark gaps.
Abstract: Statistical times were measured as a function of overvoltage and gap conditioning in small (0.127 mm) flowing-gas spark gaps. Results for air, nitrogen, oxygen, and helium are reported here. Statistical time was determined by averaging 60 measurements of the time between application of a step voltage to the gap and breakdown of the gap. These times, ranging from 100 ns to over 100 ?s, were measured with 10-ns resolution. Conditioning was done by breaking down the spark gap 40 times per second until the desired number of pulses was obtained (5000, 50 000, 500 000). Conditioning increased the breakdown voltage of gaps filled with air, nitrogen, and oxygen, but had little effect when helium was used. The functional dependence of the statistical time on electric-field strength was not changed by conditioning. Limited results showed statistical time increased with pressure in air-filled spark gaps.
TL;DR: In this article, an experimental investigation of airblast arcs in nozzles under clogged conditions has been carried out using a suitable computer model of the air supply system and by the use of approximately flat current pulses of sufficiently long duration of nearly 18 ms.
Abstract: This paper describes an experimental investigation of airblast arcs in nozzles under clogged conditions. From a suitable computer model of the air supply system and by the use of approximately flat current pulses of sufficiently long duration of nearly 18 ms, the clogging current as well as the reversed rate of flow energy from the nozzle to the upstream chamber under overclogged conditions have been determined. Theoretical scaling law for the clogging current [2] has been verified for upstream pressures in the range of 5-13 bar using three-nozzle geometries.
TL;DR: In this article, the fundamental processes occurring in hydrogen thyratrons are discussed, and the presence of both molecular and atomic species affecting recovery and voltage reerection is discussed.
Abstract: The purpose of this paper is to provide a discussion of the fundamental processes occurring in hydrogen thyratrons. Recent experimental data pertaining to electron densities, energies, and excitation processes occurring in devices during their normal operation are presented. Electron densities are observed to be lower than 2 × 1014 cm-3, corresponding to current densities of approximately 100 A/cm2. The presence of both molecular and atomic species affecting recovery and voltage reerection is reported, and mechanisms for this are discussed. Streak camera data showing a delay in breakdown of the gridanode relative to the grid-cathode region are also presented.
TL;DR: In this article, an experiment to measure the radiation of ion-acoustic waves from a quadrupole antenna is described, which consists of four hemispherical grids located at the corners of a square structure.
Abstract: An experiment to measure the radiation of ion-acoustic waves from a quadrupole antenna is described. The quadrupole consists of 4 hemispherical grids located at the corners of a square structure. The results are contrasted with those obtained from an antenna with the 4 hemispheres excited in phase and compared with a fluid model prediction. Electrostatically coupled excitation of ion-acoustic waves from 3 hemispheres when only the fourth is excited is also observed in this experiment.