Showing papers on "Electric discharge published in 1985"

Plasma potentials of 13.56-MHz rf argon glow discharges in a planar system

Abstract: The plasma potential of 13.56‐MHz low‐pressure argon glow discharges has been measured for various modes of applying the rf power in a geometrically asymmetric planar system. The plasma potential is determined from the energy distribution of positive ions incident on the grounded electrode. The voltages on the excitation electrode (target electrode) are carefully measured and the capacitive sheath approximation is used to relate these measured voltages to the measured plasma potential. This approximation is successful in most of the situations encountered in this low‐pressure (20 mTorr) relatively low‐power density regime. The effects of superimposing dc voltages on the excitation electrode are discussed.

The corona discharge, its properties and specific uses

Abstract: The main properties of corona discharges are reviewed, with emphasis on the features which make them unique for use as non-equilibrium chemical reactors : Their stability and ease of operation over a wide range of gases and pressures, including atmospheric ; their sharply confined ionization regions where hot electrons interact with cold gas, inducing reactions without back reactions ; and their extended low field drift regions which act as gaseous electrolytes, inducing electrochemical reactions on surfaces. Present and future applications are discussed : Synthesis of ozone and ammonia, promotion of flames and combustion, surface treatment, and electrical insulation improvement.

Distribution of ion energies incident on electrodes in capacitively coupled rf discharges

Abstract: The energy and angular distribution of ions striking the electrodes in rf discharges are of interest with respect to the application of such discharges to the processing of semiconductor materials. The ability to fabricate small (< 1 μm) semiconductor features using the plasma etching process results, in part, from the energetic and anisotropic flux of ions which strike the semiconductor surface. In this paper the energy and angular distribution of ions striking the electrodes in low‐pressure capacitively coupled rf discharges are studied using a Monte Carlo model for ion trajectories and a parametric model for the time‐dependent electric field within the sheath. Energy and angular distributions are discussed as a function of rf frequency, ion mass, and the mean‐free path between charge exchange collisions within the sheath. The ion energy distribution is found to be characterized by a scaling parameter proportional to (rf frequency × sheath thickness)2 × ion mass/(sheath voltage); small values of this parameter yield bimodal distributions, intermediate values yield distributions peaked at the maximum sheath potential, and high values yield distributions peaked at the average sheath potential. The ion energy distribution is also examined for different values of the dc and rf components of the sheath potential and for different models for the electric field within the sheaths. When the dc component of the sheath potential is small compared to the rf amplitude, a large thermal component to the ion energy distribution results. The implication of this result and that for the angular distribution of ions incident on the electrodes is discussed with respect to the isotropy of the etch obtained during plasma etching of semiconductor materials.

Production Rates for Oxyfluorides SOF2, SO2F2, and SOF4 in SF6 Corona Discharges.

Abstract: The most abundant, long-lived stable gaseous species generated by corona discharges in SF6 gas containing trace levels of O2 and H2O are the oxyfluorides SOF2, SO2F2, and SOF4. Absolute energy and charge rates-of-production of these and the minor products SO2, OCS, and CO2 have been measured at different total gas pressures from 100 kPa to 300 kPa and for discharges of different current, power, and polarity. Oxyfluoride yields for SF6/O2 mixtures containing up to 10% O2 have also been measured. The results indicate that oxyfluoride production is not controlled by the concentrations of either O2 or H2O at levels below about 1%, and the rate controlling factor is the dissociation rate of SF6 in the discharge. The discharge current and time dependence of the production rates are discussed in terms of gas-phase mechanisms that have been proposed to explain previous observations of electrical, thermal, and laser-induced decomposition of SF6 and SF6/O2 mixtures. Upper limits on the total SF6 decomposition rate in low-current discharges have been estimated. Details of the chemical analysis procedures are given, and application of the results to the design of chemical diagnostics for SF6-insulated, high-voltage apparatus is discussed.

Electrical discharge propagation in and around space charge clouds

Abstract: The electron trapping characteristic of a solid dielectric material (polymethylmethacrylate) is exploited to study electrical discharge propagation in laboratory-scale space charge clouds. Similarities with the static and dynamic behaviors of thundercloud electricity are identified, and a combination of theoretical and empirical scaling relationships enables a rough translation of parameters from laboratory scale to thundercloud scale. Applications of the laboratory technique to specific thunderstorm situations reinforce the value of discharge structure studies in exposing the very important space charge configuration that gives rise to lightning.

Studies of the discharge mechanisms in electrochemical arc machining

Abstract: The electrochemical arc machining (ECAM) process combines features of ECM and EDM by application of a pulsed voltage between a cathode-tool and anode-workpiece in a liquid electrolyte. The new process offers rates of metal removal as much as five and fifty times greater than ECM and EDM, respectively. The study reported in this paper explores some of the fundamental processes which occur during ECAM. Experimental apparatus was constructed to enable single pulse discharges to be studied. Results are presented for 200μs pulses between 2 mm diameter silver steel electrodes in NaNO3 and NaCl electrolytes over a gap range of 10 to 90μm. Four stages of electrical phenomena were distinguished within a pulse: (a) high frequency voltage and current oscillations, (b) high rate electrochemical action, (c) low rate electrochemical action, and (d) electrodischarge action. The relative durations of the electrochemical and discharge phases, respectively, increase and decrease with increasing gap width, and vary with electrolyte type and concentration. High speed photography with an image-converter camera was used to record the occurrence of both spark and arc discharge in an electrolyte.

Electric discharge machine

Abstract: PURPOSE:To prevent the continuation of abnormal electric discharge and improve working speed by installing the electric-discharge suspension-time controllers which output signals into the suspension-time setting devices, in an electric discharge machine CONSTITUTION:The terminal for outputting the number of abnormal electric-discharge wave-forms which is installed onto an electric-discharge state discriminating apparatus 19 and the terminal for outputting the number of electric-discharge wave-forms generated when an electrode gap is contaminated are connected to the OR elements 23 of an electric-discharge suspension time controller 21, and the logic sum of each number of both wave-forms is outputted into a counter 25 The output A of the counter 25 is input into a comparator 27 for increasing the electric-discharge suspension time and a comparator 25 for reducing the electric- discharge suspension time, and the both values are compared with the standard value B for increasing the electric-discharge suspension time and the standard value C for reducing the electric-discharge suspension time, respectively, and when A is larger than B, a signal at H-level is outputted into one input terminal of an AND element 31 With such constitution, the continuation of abnormal electric discharge can be prevented, and working speed can be improved

Multidimensional modeling of transverse avalanche laser discharges: Applications to the HgBr laser

Abstract: Geometrical considerations are important with respect to the stability and efficiency of avalanche electric discharge lasers. Parameters such as the electrode contours and the distribution of preionization electrons affect excitation rates through the relative values of the local electric field, local depletion of initial species, and through the response of the discharge circuitry to spatially dependent conditions within the plasma. Constriction of the discharge and subsequent impedance mismatch of the discharge to the pulse forming line result from these spatial nonuniformities. In this paper geometrical effects in the mercury bromide electric discharge laser are examined by comparing the results from a multidimensional discharge and kinetics model with experimental observations. The code models electron and heavy particle kinetics and laser intensity in time and one spatial dimension: parallel to the electrodes and perpendicular to the optical axis. Quantities whose spatial dependence is perpendicular ...

Surface fluorination of polymers in a glow discharge plasma: photochemistry

Abstract: La fluoruration par F 2 et l'oxydation par O 2 sont exaltees par irradiation UV, a la surface de polymere

Electrodeless discharge lamp device

Abstract: PROBLEM TO BE SOLVED: To provide an electrodeless discharge lamp device in which temperature of the induction coil or magnetic core can be lowered while realizing manpower saving in the manufacturing process and which has high luminous efficiency and a long life. SOLUTION: The electrodeless discharge lamp comprises an airtight container 1 filled with a discharge gas and a power coupler 3 that is inserted in the recessed cavity 2 of the airtight container 1. The power coupler 3 comprises an induction coil 8 that makes emit light by exciting the discharge gas by generating high frequency magnetic field as a result of impression of high frequency current and a core assembly in which a magnetic core 10 and a heat conductor 11 are mutually combined and then the induction core is wound. And each of the induction coil 10 and the heat conductor 11 is provided in a state mutually contacting closely with each of the above magnetic core, and each of the induction coil 8 and heat conductor 11 is provided without contacting each other. COPYRIGHT: (C)2004,JPO

Development of a Microwave-Induced Nitrogen Discharge at Atmospheric Pressure (MINDAP)

Abstract: A microwave-induced plasma has been sustained with the use of nitrogen as the nebulizer and plasma supporting gas A concentric tube torch was constructed so the plasma could be easily ignited and maintained This new plasma emission source has a flame-like appearance and extends 10 cm beyond the cavity, at an applied power of 250 W The nitrogen plasma readily accepts aerosol samples and is compatible with sample introduced from a conventional nebulizer system The radial (side-on) optical viewing configuration was found to have lower background emission than the more commonly employed axial (end-on) configuration Optimum operating conditions were established from the effects of applied power, flow rate, and signal-to-background noise on the intensity of both atom and ion transitions A discussion of the background spectral features and the analytical potential of this new source is presented

Power source for electric discharge machining

Abstract: A power source for electric discharge machining, which performs a semi-mirror-finish machining operation with a surface roughness of 1 μm Rmax or less. The power source includes either a resonance circuit or an impedance matching circuit so that the electric discharge is carried out under the condition that resonance is caused to occur with the capacitance of an interelectrode gap between an electrode and a workpiece to be machined or the impedance-matching is effected in response to variation in interelectrode condition. With such a power source, it is possible to eliminate the effect of the stray capacitance exsiting in a current supplying line and also to eliminate the shortcoming due to variation on the interelectrode condition, and therefore a mirror-finished machining operation can be stably carried out to provide machined surfaces excellent in surface roughness.

Bubble Growth Following a Localized Electrical Discharge and its Relationship to the Breakdown of Triggered Spark Gaps in Liquids

Abstract: In order to investigate the mechanism of breakdown of the liquid-filled, triggered spark gap, a flash-illuminated, shadowgraph optical system has been used to photograph the pre-breakdown events in a triggered gap. Photographs indicate that in all cases the trigger spark is followed by the growth of a hemispherical bubble, or vapor cavity, and this bubble appears to be the precursor of the main gap breakdown. A theoretical investigation shows that the expansion and collapse of the cavity in the low-viscosity limit, follows a simple hydrodynamic model. We find that only about 1% of the circuit energy is transferred to kinetic energy of the liquid surrounding the expanding cavity. The time required for an expanding bubble to fill a 1 mm gap is of the same order as the breakdown time lag for the triggered gap. It is concluded that the bubble generated by the trigger spark clears the gap of liquid, leaving a low-density gas or vapor between the electrodes, so that the actual process of electrical breakdown takes place through the low strength gas, not through the liquid. In the case of longer gaps, of 2 mm and above, the bubble may have time to expand across the entire gap and it is suggested that an electrohydrodynamic instability may cause the bubble surface to breakup into streamers, which cross the gap and cause breakdown.

Micro-Gap Discharge Phenomena and Television Interference

Abstract: Electromagnetic Interference from power lines is found to affect amplitude modulated communication services such as radio and television. Corona and microgap discharges have been identified as sources. While a large number of studies have been devoted to investigation of corona as the source of electromagnetic noise, only a very limited amount of basic information is available on mechanisms of the microgap discharge. The present paper is intended to partially fill this gap by presenting the results of an experimental program exploring characteristics of discharge processes that take place in two well defined point-to-plane geometries, one with a spherically shaped, the other with a conically shaped active electrode. A diameter of 1.588 mm was used for the rod, and gap spacings between 0.1 and 19 mm were investigated. Behaviour under both voltage polarities was studied.

Wire-cut electric discharge machine

Abstract: PURPOSE: To keep off the disconnection of a wire electrode, by detecting an electric current flowing into each of paired current-carrying terminals sandwiching a work, and stopping a voltage impression by means of a signal corresponding to the difference. CONSTITUTION: In each of cables 14a and 14b energized to current-carrying terminals 6a and 6b, there are provided with current detectors 15a and 15b which detect an electric current flowing into each terminal. Signals out of each detector are amplified each by amplifiers 16a and 16b and inputted into a differential amplifier 17. A signal in proportion to a difference between the currents flowing into theses terminals 6a and 6b is outputted from this amplifier 17. This signal I 3 is inputted into a discharge processing circuit 18 whereby a concentrated state of discharge is detected. With output from this circuit 18, a voltage impression from a power supply 100 for electro-discharge machining is stopped. COPYRIGHT: (C)1987,JPO&Japio

Neutral heating in glow to spark transition in air and nitrogen

Abstract: The heating of the neutral molecules in the glow to spark transition in air and nitrogen has been theoretically studied. A hydrodynamic first-order model has been used for electrons (density, momentum) and a second-order model (density, momentum, temperature) for neutral molecules. The interaction between the electron dynamics and the neutral dynamics has been compared in two kinds of discharges: a fast discharge (170 ns) in an overvolted plane parallel gap in nitrogen, and a discharge of longer duration (1.15 mu s) in a positive point-to-plane gap in air. The kinetics of the discharge, which is linked to the possible feedback of the neutral gas on the electron cloud, is mainly a function of the duration of the energy injection. In the case of the fast parallel gap discharge, the background gas plays a passive role; it is an energy absorber, so its temperature increases continuously. In the case of the point-to-plane discharge, lasting longer, the dynamics of the interaction between the electron cloud and the background gas constitutes the fundamental process of the discharge. The gas heating gives rise to a neutral depopulation in the core of the discharge. This leads to an increase of the reduced electric field E/N, thus to an increase of the electron production and thus of the current. In this kind of discharge, the heterogeneity of the neutral gas leads to the breakdown, owing to a constriction of the current core induced by the depopulation mechanisms.

An analysis of the current in a point-to-plane corona discharge and the effect of a back-ionising layer on the plane

Abstract: The increase in the current that flows in a negative point-to-plane corona discharge when a porous layer is present on the plane was studied by using a fast storage oscilloscope. It was found that the current increase is due primarily to an increase in the frequency of the Trichel pulses at the cathode, and less than 0.1% can be attributed to pulsed phenomena at the anode. It is proposed that the increase in Trichel pulse frequency is caused by neutralisation of the negative ion space charge by positive ions produced by discharges in the porous layer. These positive ions are not detected in the current measured in the external circuit because of their low mobility. Breakdown in the porous layer is thus a source of positive ions, which increase the corona current by modifying the Trichel pulse frequency and not by contributing directly to the measured current.

Arc expansion in xenon flashlamps

Abstract: Plasma arcs in large diameter (d>1 cm) xenon flashlamps often do not completely fill the bore of the discharge tube. The arc is usually initiated on one side of the discharge tube, adjacent to the ground plane, and the fraction of the discharge tube filled with plasma varies as a function of axial location. A model is presented that describes, from first principles, arc expansion in xenon flashlamps. The model simultaneously solves a coupled set of one‐dimensional transport equations in different regions of the discharge tube to simulate two‐dimensional effects in hydrodynamics, electron kinetics, and radiation transport. Using this method, expansion of arcs initiated at arbitrary locations within the discharge tube can be studied. Arc filling fractions are found to decrease with increasing filling pressure of xenon, increasing diameter of the discharge tube, and decreasing stored energy in the discharge circuit. The arc filling fraction also decreases as the breakdown filament moves away from the axis of the discharge tube and towards the wall. Arc expansion is slowed and ultimately halted by a lowered E/N (electric field/gas density) in the gas exterior to the arc, rapid conversion of atomic ions to molecular ions and their subsequent recombination, and by the efficient manner in which radiation dissipates energy which might otherwise be available for thermodynamicexpansion of the arc. The asymmetric expansion of the plasma arc results in asymmetric heating of the inside wall of the discharge tube, also calculated in the model. The growth of the plasma arc is also found to be in part responsible for changes in the spectrum of radiation emitted from the arc for various angles of observation. This effect results from wavelength‐dependent absorption coefficients in the plasma.

Metal halide lamp

Abstract: PURPOSE:To obtain a metal halide lamp, which can be started with the voltage of a usual commercial power source without using neon gas or a high-voltage- pulse generating circuit, by constituting a metal halide lamp by installing an ultraviolet-ray generating source tubular bulb. CONSTITUTION:In a metal halide lamp, when the voltage of an alternating power source 15 is applied through a base 16 and a ballast 14, at first, an ultraviolet-ray generating source 3 starts to discharge ultraviolet rays. A number of free electrons develop in an emission tube 2 due to the discharged ultraviolet rays, and as a result, electric discharge develops between a main electrode 9 and an auxiliary electrode 11. Then, in a short time, electric discharge develops between main electrodes 9 and 10, and the electric discharge of the tube 2 is initiated. Here, since the value of a cerrent flowing through the ultraviolet-ray generating source 3 is sufficiently smaller than 30% (0.3 A) of a current flowing during the normal lighting condition, there is no possibility that the electric discharge of the tube 2 is suppressed.

Selective power supply for travelling wire EDM apparatus

Abstract: In a travelling wire EDM apparatus the thermal stresses of the electrode wire are substantially reduced by detecting the position of the triggering electrical discharges preceding the machining electrical discharges, and by controlling the supply of the machining electrical discharge current at one end of the machining zone, at the other end of the machining zone or at both ends of the machining zone. When a machining electrical discharge is located between one end of the machining zone and a first reference position, the machining current is applied at that end. When the electrical discharge is located between the other end of the machining zone and a second reference position, machining current is supplied at that second end. When the electrical discharge is located between the two reference positions, the machining current is applied simultaneously at both ends of the machining zone.

Surface discharges as intense photon sources in the extreme ultraviolet

Abstract: We are investigating surface discharges as XUV photon sources for in situ cleaning and preionizing of anode surfaces in light‐ion‐fusion accelerators. In these experiments the surface discharge was formed by discharging a capacitor bank across a spark gap which consisted of two copper electrodes attached to an insulator and facing each other across a 5.5‐mm gap. The surface discharge and its power feeds were constructed in a stripline configuration to minimize overall system inductance. When the surface discharge was driven by a 2.9‐μF, 45‐kV capacitor bank, the peak current thru the discharge was ∼250 kA. When driven at these levels, a single discharge radiated with a peak power of over 80 MW of 10–70 eV photons and had a total extreme ultraviolet output energy of 60 J per pulse.

Wire cut electrical discharge machining device

Abstract: PURPOSE:To prevent the accuracy of machining from lowering, by detecting variations in the electrical resistance between the electrical power supply point and electrical discharge point of a wire electrode so that a position where electrical discharge occures is detected, and as well by controlling, in accordance with the position, the mean machining current or discharge pulse energy between the electrode and a workpiece. CONSTITUTION:A wheatstone bridge is balanced so that no current runs through resistances 15, 16 when electrical discharge occurs at the mid-point of a wire electrode 2 between electrical power rollers 3, 4 in such a condition that the resistant values of resistances 13, 14 are equal together. However, when electrical discharge occurs at a point remote from the mid-point of the electrode 2, unbalanced current runs through resistances 15, 16. When an electrical discharge point detector 17 detects satisfactory electrical discharge, randomly and uniformly in the vicinity of the mid-point of the electrode 2, a control circuit controls a switching element 8 to make large the width of voltage pulses fed between the workpiece 1 and the electrode 2 or to increase discharge current or the number of pulses, thereby satisfactory machining may be made with a high degree of efficiency in the vicinity of the center section of the workpiece 1 so that any defects are prevented from occuring.

An intense and efficient source of vacuum ultraviolet radiation: Low‐ pressure Xe Townsend discharge

Abstract: An intense vacuum ultraviolet spike 0.2 μs in width is observed at the initial stage of low‐pressure Xe discharge, i.e., Xe Townsend discharge, in submillimeter tubes. The intensity of the 147 nm resonance line reaches 1.3 W/cm2, about 200 times stronger than that obtained from the steady‐state Xe positive column. Efficiency of the vacuum ultraviolet radiation exceeds 24%, or 32 lm/ W when green phosphor is excited, four times higher than that of the positive column, or more than an order of magnitude higher than that of the negative glow. This high intensity and efficiency originate from the optimized electron energy which can be adjusted externally by changing the electric field and pressure, contrary to that in the positive column or negative glow. Another important feature of the Townsend discharge is its wide dynamic range of operation, which is advantageous when driving a panel having a large number of cells with scattered discharge characteristics. Consequently, a gas discharge display panel utilizing the Townsend discharge has more than an order of magnitude higher efficiency than the positive column or negative glow panels.

Multiplex electric discharge gas laser system

Abstract: A multiple pulse electric discharge gas laser system is described in which a plurality of pulsed electric discharge gas lasers are supported in a common housing. Each laser is supplied with excitation pulses from a separate power supply. A controller, which may be a microprocessor, is connected to each power supply for controlling the application of excitation pulses to each laser so that the lasers can be fired simultaneously or in any desired sequence. The output light beams from the individual lasers may be combined or utilized independently, depending upon the desired application. The individual lasers may include multiple pairs of discharge electrodes with a separate power supply connected across each electrode pair so that multiple light output beams can be generated from a single laser tube and combined or utilized separately.

Transient processes in plasmas produced by surface waves

Abstract: The rise time of a wave electric field tau HF and the ionisation front velocity nu f are measured in a pulsed plasma produced by a surface wave. Different behaviours of tau HF and nu f are observed when the pressure is varied. The passage from a collisional to a non-collisional mode may be identified, in accordance with the electronic mean free path estimated for the discharge. The variations of nu f and tau HF with power corroborate this classification. The electron density along the plasma column is also measured for different instants ti from the beginning of the pulse. Thus the discharge stabilisation can be identified by its behaviour in analogy with the stationary plasma.

Evaluation of Microwave-Induced Air-Plasma as an Excitation Source:

Abstract: A single-electrode atmospheric pressure microwave discharge air-plasma is reported. Fundamental characteristics, such as the effects of microwave power, auxiliary air flow, and nebulizer air flow on emission intensity, detection limits, and dynamic ranges for twelve elements and several interference experiments are reported. The plasma temperature is found to be about 4700°K. This simple system can be applied to the spectrochemical analysis of solution samples. The results with the use of this system to determine calcium, sodium, and potassium in SRM-1566 (oyster tissue) and SRM-92 (low-boron glass) show excellent agreement with the NBSs certified values.

Domain control by spark ablation

Abstract: The power loss of grain oriented electrical steel can be usefully reduced by refinement of the ferromagnetic domain structure in cases where overlarge grains support widely spaced domains. Artificial grain boundaries can be produced by laying down lines of ablated spots on the steel surface to generate a stress and atomic disruption pattern which pins domain walls and leads to a smaller wall spacing. A high voltage electrical discharge from capacitors or otherwise can be used to give high enough energy rates and spatial densities to achieve suitably ablated spots on the metal surface. The method is readily adaptable to a production situation.