Showing papers on "Electric discharge published in 1986"
TL;DR: In this paper, a model of direct current (dc) and 13.56-MHz radiofrequency (RF) discharges in a parallel-plate configuration is presented, consisting of equations for electron and ion continuity, Poisson's equation for the self-consistent electric field, and an equation for electron energy.
Abstract: A continuum model of direct current (dc) and 13.56-MHz radio-frequency (RF) discharges in a parallel-plate configuration is presented. The model consists of equations for electron and ion continuity, Poisson's equation for the self-consistent electric field, and an equation for electron energy. The equations are solved for a single set of conditions and a comparison is made between the structure of a dc and a 13.56-MHz RF discharge. One of the major structural differences is the emergence, under RF conditions, of large electron conduction currents in the quasi-neutral region. This results in substantially higher electron heating in the quasi-neutral region and a consequent shift in the peak ionization rate from the cathode sheath to the quasineutral region. In addition, the RF solutions suggest that equivalent circuit models and ambipolar diffusion models are promising ways to simplify predictions of discharge physics. The ultimate goal of this work is to provide an adequate description of the discharge physics so that discharge chemistry can be understood. The latter is essential in predicting the behavior of plasma film etching and deposition reactors used extensively in electronics materials processing.
324 citations
TL;DR: In this paper, the results of both theoretical and experimental study of a steady E-type RF discharge, in which ionization is controlled by fast electrons generated in RF sheaths near the electrodes (y regime), are presented.
Abstract: The results of both theoretical and experimental study of a steady E-type RF discharge, in which ionization is controlled by fast electrons generated in RF sheaths near the electrodes (y regime), are presented. It is shown that the transition of an RF discharge into the ? regime is of a threshold nature and is accompanied by a sharp increase in plasma density and a decrease in electron temperature. The suggested theoretical model of an RF discharge in the ? regime satisfactorily describes experiments carried out in a wide range of frequencies, RF voltages, and gas pressures.
167 citations
TL;DR: In this article, the positions between the plane-parallel electrodes were probed by pulsed laser light scattering at several wavelengths and the particle nucleation and growth kinetics were very well demonstrated over this range of discharge parameters.
Abstract: We report laser diagnostic studies of capacitively coupled RF discharges containing 0.05-0.45-percent silane in argon. We probed positions between the plane-parallel electrodes by pulsed laser light scattering at several wavelengths. These spatial scans had a resolution of 0.25 mm and they showed unusual particle distributions which varied with silane mole fraction and gas-flow rates. Particle nucleation and growth kinetics were very well demonstrated over this range of discharge parameters. We also studied particle photophysics and demonstrated that ultraviolet pulsed lasers (251.4 and 266 nm) can form silicon atoms from laser-particle interactions. Atoms were formed in both ground and excited states with a concentration that depended linearly on laser energy. However, atoms were not formed by 354- or 532-nm excitation. Particle excitation by 354 nm at energies > 0.5 mJ created a long-time (>0.1 s) perturbation of the discharge chemistry which linearly increased the steady-state (10 Hz) light scattering with increasing 354-nm energy.
166 citations
TL;DR: In this article, the authors discuss the method of power deposition by electrons and the spatial dependence of electron-impact excitation rates in low-pressure capacitively coupled RF discharges with results from a Monte Carlo plasma simulation code.
Abstract: In low-pressure capacitively coupled parallel-plate radiofrequency (RF) discharges, such as those used in plasma processing of semiconductor materials, power deposition and the rate of electron-impact excitation collisions depend upon time during the RF cycle and position in the discharge. Power is coupled into the discharge in at least two ways: by way of a high-energy "e-beam" component of the electron distribution resulting from electrons falling through or being accelerated by the oscillating sheaths, and by "joule heating" in the body of plasma. This paper will discuss the method of power deposition by electrons and the spatial dependence of electron-impact excitation rates in low-pressure capacitively coupled RF discharges with results from a Monte Carlo plasma simulation code. Mixtures of argon and silane will be examined as typical examples of discharges used for the plasma deposition of amorphous silicon.
144 citations
TL;DR: In this paper, a detailed study of the temporal and spatial characteristics of the preionization of a XeCl rare-gas halide laser is presented, where high-resolution framing camera photographs have been used to investigate the growth of discharge instabilities.
Abstract: This paper presents a complete study of the temporal and spatial characteristics of the preionization of a XeCl rare-gas halide laser. The detailed study was made possible using the technique of laser-induced preionization which utilizes the uv radiation from a KrF laser to preionize a second rare-gas halide laser. In addition to the preionization study, high spatial and temporal resolution framing camera photographs have been used to investigate the growth of discharge instabilities which can lead to the premature termination of the XeCl optical pulse. The roles played by HCl, Xe, the buffer gas as well as the discharge energy loading in the development of discharge instabilities have been determined experimentally.
141 citations
TL;DR: In this article, the formation of decomposition by-products produced by electrical spark discharges in SF6 has been investigated by quadrupole mass spectrometry and the amount of SF4 formed was measured by "in situ" detection, utilizing a threshold technique for monitoring the SF4 ion (SF+3) in an SF6 background.
Abstract: The formation of decomposition by-products produced by electrical spark discharges in SF6 has been investigated by quadrupole mass spectrometry. The by-product SF4 was found to be a precursor to many of the long-lived decomposition by-products identified (SOF2, HF, SO2, and SiF4). The amount of SF4 formed was measured by "in situ" detection, utilizing a "threshold" technique for monitoring the SF4 ion (SF+3) in an SF6 background. The rate constant for the hydrolysis of SF4 was measured (at 350 K) and found to be ~2×10-19 cm3s-1. In addition to moisture, the effects of SiO2 and electrode material have been briefly examined. Quantification of the amounts of long-lived by-products of spark discharge in SF6 yielded the following ranking: SOF2 > SOF4 > SiF4 > S02F2 > SO2. The energy and pressure dependences in the ranges of 0.5 to 14.5 J/spark and 40 to 233 kPa respectively, of the amounts of the various by - products were examined.
128 citations
Patent•
28 Jul 1986TL;DR: In this paper, a high intensity gaseous discharge lamp employs a discharge medium which emits radiation at multiple, narrow line wavelengths which combine to produce white light, and coatings are applied to the arc tube to prevent emission of certain ultraviolet and infrared wavelengths, and a cylindrical barrier blocks certain long wavelength infrared radiation from being emitted by the lamp.
Abstract: A high intensity gaseous discharge lamp employs a discharge medium which emits radiation at multiple, narrow line wavelengths which combine to produce white light. Coatings are applied to the arc tube to prevent emission of certain ultraviolet and infrared wavelengths, and a cylindrical barrier blocks certain long wavelength infrared radiation from being emitted by the lamp.
127 citations
TL;DR: In this paper, a model was constructed to describe the electrical characteristics of the central bulk plasma region in a 13.56-MHz parallel-plate discharge in chlorine at pressures of about 1 torr.
Abstract: A model has been constructed to describe the electrical characteristics of the central bulk plasma region in a 13.56-MHz parallel-plate discharge in chlorine at pressures of about 1 torr. This region is modeled as a volume-controlled plasma with the electron balance dominated by single-step electron-impact ionization and attachment and with the electron energy distribution function in equilibrium with the local instantaneous electric field. Relationships between the ionization frequency, the attachment frequency, the electron drift velocity, and the electric field are provided by solutions of the Boltzmann equation for mixtures of Cl2 and Cl which result from Cl2 dissociation. From a measured current waveform and Cl2/Cl density ratio, the model generates the local electric-field waveform, the time-varying electron density, and the power density in the central portion of the bulk plasma. The calculated time-averaged power input per unit discharge length compares well with experimentally determined values.
112 citations
TL;DR: In this article, the measurement and interpretation of ion bombardment energies in rf discharges of SF6, CF3Cl, and CF3Br from 0.2 to 1.0 Torr, are discussed.
Abstract: The measurement and interpretation of ion bombardment energies in rf discharges of SF6, CF3Cl, and CF3Br from 0.2 to 1.0 Torr, are discussed. Errors in ion sampling due to disturbances of the electric field and neutral density around the sampling orifice are shown to be most important at higher pressures and with larger orifices. The dependence of the ion bombardment energy distribution on the electric‐field‐to‐pressure ratio is reviewed. Combining this relation with a simple electrical model of a plasma gives estimates of the ion bombardment energies in collisional sheaths. The bombardment energy is proportional to (rf current)/(electrode area×frequency ×pressure) with the proportionality constant for a particular system depending on the collision cross sections and relative ion‐to‐netural mass ratio. The constants found for the three gases studied experimentally are close to theoretical estimates.
100 citations
TL;DR: In this paper, a low pressure glow discharge switch that has a number of features that are desirable for high power applications is described, and the switch has achieved high stand-off voltage and peak current, has potential for very fast current rate of rise, and operates near the glow-to-arc transition in hydrogen or helium.
Abstract: A low pressure glow discharge switch that has a number of features that are desirable for high power applications is described. The switch has achieved high stand‐off voltage and peak current, has potential for very fast current rate of rise, and operates near the glow‐to‐arc transition in hydrogen or helium. Closure is initiated by light incident on the back of the cathode, and it is observed that surface damage within the area of illumination is less than surrounding areas. Several aspects of the switch are similar to thyratrons and pseudosparks.
82 citations
TL;DR: In this paper, the authors developed theoretical arguments supporting the concept that halogen donor depletion during the discharge pulse is the principal cause of discharge collapse and termination of lasing, and the theoretical prediction that the duration of the glow phase should vary as the inverse square of the initial halogen concentration is verified by experimental results furnished by a resistively stabilized long-pulse xenon chloride laser.
Abstract: Instability mechanisms discussed to date are unable to account for the behavior of long‐pulse self‐sustained discharge‐pumped XeCl devices. We develop theoretical arguments supporting the concept that halogen donor depletion during the discharge pulse is the principal cause of discharge collapse and the termination of lasing. The theoretical prediction that the duration of the glow phase should vary as the inverse square of the initial halogen donor concentration is verified by experimental results furnished by a study of a resistively stabilized long‐pulse xenon chloride laser.
TL;DR: In this article, an investigation of the electrical, gas-dynamic, and radiative properties of surface discharges intended as intense optical pump sources for lasers was performed, which demonstrated the importance of proper source-driver impedance matching to short-pulse operation and efficient electrical-to-optical energy conversion.
Abstract: An investigation was undertaken of the electrical, gasdynamic, and radiative properties of surface discharges intended as intense optical pump sources for lasers. Large‐area (≂20–300 cm2), short‐pulse (∼1 μs) planar surface discharges were produced across various ceramic and polymer substrates and operated in all of the rare gases, N2, and air at absolute pressures up to 4 atm. Parametric studies of the electrical circuitry and discharge dimensions demonstrate the importance of proper source‐driver impedance matching to short‐pulse operation and efficient electrical‐to‐optical energy conversion. Characteristic times for establishment of a conductive discharge gap in the heavy rare gases are consistent with breakdown by the single‐stroke leader mechanism. The electrical strength of the gap following discharge remains low for a time which is much greater than the current duration. The delay in recovery is believed to be controlled by continued substrate ablation occurring after the discharge rather than to ...
TL;DR: In this paper, the authors showed that high power input causes fast sheath formation (100 keV) photons with which the insulator surface is irradiated during discharge initiation or using insulators with coppered surface.
Abstract: Discharge initiation and sheath formation are serious problems of high current (several MA) dynamical pinches because of the enormous power input. The fast 300 kV plasma focus SPEED 2 allowed studying the discharge behaviour in a wide range of power input (10-100 GW) previously not accessible. The main results are: (i) high power input causes fast sheath formation ( 100 keV) photons with which the insulator surface is irradiated during discharge initiation and sheath formation or using insulators with coppered surface.
TL;DR: In this article, the characteristics of high-temperature and high-energy-density plasma beams in a "gas tunnel" were experimentally clarified, and it was found that almost fully ionized plasma was obtained in the gas tunnel even at a small current of 200 A.
Abstract: The characteristics of high‐temperature and high‐energy‐density plasma beams in a ‘‘gas tunnel’’ were experimentally clarified. A strong vortex flow at a high flow rate forms a radial pressure distribution with a sharp gradient. This produces a ‘‘gas tunnel’’ in the center, where the pressure is very low. In this study, this type of gas tunnel was applied to the production of plasma, and high‐temperature and high‐energy‐density plasma beams were easily obtained. The plasma arc produced in this gas tunnel has a higher temperature and electron density than a conventional plasma arc because of a strong thermal pinch effect. Measurement of the properties of this plasma arc was primarily carried out by means of spectroscopy, and it was found that almost fully ionized plasma was obtained in the gas tunnel even at a small current of 200 A. In addition, a temperature of more than 3×104 K was achieved by increasing the arc current. A plasma jet generated in the gas tunnel has a very high electrical potential gradient of more than 40 V/cm and high thermal efficiency, and it is relatively easy to obtain an extremely high power of more than 200 kW.
TL;DR: In this article, an x-ray preionized avalanche discharge-pumped XeCl laser capable of producing output pulses of greater than 250 ns FWHM duration and energies of ∼ 1 J was reported.
Abstract: This paper describes an x‐ray preionized avalanche discharge‐pumped XeCl laser capable of producing output pulses of greater than 250‐ns FWHM duration and energies of ∼1 J. This represents the longest pulse duration yet reported from such a high‐power laser. Nevertheless, the laser output pulse is shown to terminate while the laser is still apparently under strong electrical excitation. The severity of this premature laser termination has been found to be dependent on both the partial pressure of the halogen donor molecule, HCl, in the laser gas mixture, and on the magnitude of the electrical excitation rate. Investigations of the discharge homogeneity, using time‐integrated and time‐resolved photographic observation of the discharge, scattering of a short duration dye laser probe beam, and time‐integrated and time‐resolved fluorescence spectra of species within the laser gas mixture have led to the conclusion that it is the formation of small, discrete current channels in the body of the discharge which ...
TL;DR: In this article, the intensity distribution along the discharge axis in a parallel-plate RF-glow discharge was measured in the pressure range of 80 mtorr to 1 torr in nitrogen, argon, and mixtures including attaching gases.
Abstract: The intensity distribution along the discharge axis in a parallel-plate RF-glow discharge was measured in the pressure range of 80 mtorr to 1 torr in nitrogen, argon, and mixtures including attaching gases. Time-averaged spectroscopic measurements showed that the large intensity variations are caused by variations in electron density, at least in the space between electrodes and intensity maxima. In this space, the electron temperature was found to be constant; it decreases towards the center of the discharge. With decreasing pressure, in gases with lower collision frequency and at lower RF frequencies, the intensity peaks move away from the electrodes. Adding an attaching gas made the intensity distribution more uniform. A dc bias voltage on one electrode does not alter the distribution until very high voltages are applied. Time-resolved measurements indicate intensity peaks initially moving away from the electrode negative at a particular half-cycle of the RF frequency with intensities corresponding to the averaged distributions. The peaks are attenuated beyond the maximum, and their velocity increases towards the center and can become negative in time. A simple model including time- and spatially varying oscillations shows the same behavior.
TL;DR: In this paper, the radial density distribution for each of the species and the radial temperature distributions for the electron and the neutral gases were calculated for low-pressure Hg-Ar positive column with a model which accounts for radial transport mechanisms.
Abstract: The low‐pressure Hg–Ar positive column is studied with a model which accounts for radial transport mechanisms. The model calculates, not assumes, the radial density distribution for each of the species and the radial temperature distributions for the electron and the neutral gases. Solutions to the discharge equations are found for specified values of the wall (Hg reservoir) temperature, electric current, Ar pressure, and tube diameter. These solutions compare favorably with available parametric data for 3.6‐ and 1.4‐cm‐diam. discharge tubes. The model is used to investigate effects such as radial cataphoresis, the effect of radiation trapping on radial distributions, and deviations from a radially uniform electron temperature. The work supports some of the simplifying assumptions often made in modeling the discharge at the standard fluorescent lamp operating condition, such as a radially invariant electron temperature, the use of a constant escape factor to describe radiation trapping, and negligible radial cataphoresis. Under conditions of high Ar pressure, the assumption of a radially invariant electron temperature is found to be less valid.
Patent•
24 Nov 1986
TL;DR: In this article, a dielectric core is constructed and arranged to focus the electric discharge into a passage formed about the periphery of the core, thereby enabling the use of energy levels substantially higher than would be possible without the focusing means.
Abstract: The energizer (10) includes an electric discharge apparatus (14) for creating an electric discharge and a focusing mechanism (40) for focusing the electric discharge on a fluid to be energized. In a preferred embodiment of the invention, the focusing mechanism takes the form of a dielectric core (40) which is constructed and arranged to focus the electric discharge into a passage formed about the periphery of the core (58) thereby enabling the use of energy levels substantially higher than would be possible without the focusing means (40). A method of energizing a fluid is taught which includes introducing the fluid into a confined region, providing an electric discharge for energizing the fluid and focusing the discharge into the confined region.
TL;DR: In this article, an electric-discharge F2 laser emitting at 157.6 nm was constructed and a study of its spectral, energy, and temporal characteristics was made of spectral and energy properties.
Abstract: An electric-discharge F2 laser emitting at 157.6 nm was constructed. A study was made of its spectral, energy, and temporal characteristics. High values of the output power W and efficiency of an F2 laser were obtained by increasing the pressure in the He–F2 active medium to 10 atm, which made it possible to achieve W = 3 MW, efficiency of 0.17%, and specific output energy in excess of 1J/liter. Each of the two components of the output spectrum was ~ 0.02 nm wide.
TL;DR: In this paper, a simple model using an asymmetrical double probe theory was presented to describe a planar glow discharge, which reasonably agrees with available experimental results for a capacitively coupled excitation electrode and frequencies of about 100 kHz.
Abstract: A simple model, using an asymmetrical double probe theory, is presented to describe a rf planar glow discharge. It reasonably agrees with available experimental results for a capacitively coupled excitation electrode and frequencies of about 100 kHz.
TL;DR: In this article, the authors characterize the nature of discharge and noise pulses when using capacitive couplers mounted on each phase leads and an RF current transformer mounted on the neutral lead for signal detection.
Abstract: Changes with time in the partial discharge (PD) activity originating in a generator stator's insulation system provide information about the electrical integrity of the stator winding. It is desirable to measure PD during normal service to minimize costs. To do this successfully, the influence of electrical interference must be reduced. Tests are reported which characterize the nature of discharge and noise pulses when using capacitive couplers mounted on each of the phase leads and an RF current transformer mounted on the neutral lead for signal detection. Significant differences between PD and electrical noise have been observed.
TL;DR: In this paper, the developing length of corona streamers in air is measured at a pulse duration of 3 ns, an applied voltage of 7-20 kV, and a gas pressure of 150-760 Torr.
Abstract: The nanosecond time‐scale developing mechanisms of positive and negative corona streamers on the insulation surface are investigated using a square pulse generator and the Lichtenberg figure technique. The developing length of the corona streamers in air is measured at a pulse duration of 3 ns, an applied voltage of 7–20 kV, and a gas pressure of 150–760 Torr. The results are compared with those obtained in the time range of 5–920 ns. The ratio of the developing length obtained at a certain pressure and that obtained at atmospheric pressure becomes a constant value irrespective of the magnitude of the applied voltage, and it increases as the gas pressure is reduced. The time lag of corona streamer inception increases with decreasing pressure. The time lag for the negative corona streamer obtained at a voltage of 20 kV is 0.1 ns at atmospheric pressure and 0.35 ns at a pressure of 150 Torr, while that for the positive corona streamer obtained at the same voltage, is 0.55 ns at the atmospheric pressure and ...
TL;DR: In this article, lower hybrid waves were used to suppress internal disruptions occurring in an inductively driven discharge by lower hybrid wave that drove the plasma current in the same direction as the inductively-driven current.
Abstract: Internal disruptions occurring in an inductively driven discharge are suppressed by lower hybrid waves that drive the plasma current in the same direction as the inductively driven current. Upon suppression, in the central region a finite-amplitude, non-growing m = 1 oscillation is observed and strong electron heating is measured.
Patent•
22 Dec 1986
TL;DR: In this paper, the authors proposed to prevent an increase of electrode consumption and any roughness of surface quality on a machining surface from occurring by turning a discharge current pulse to OFF at once as long as the specified period when detecting an electric short and a momentary cut between an electrode an a workpieces, and making a discharge value so as to be gradually increased simultaneously with the elapse of an on-period of the discharge current pulses.
Abstract: PURPOSE: To prevent an increase of electrode consumption and any roughness of surface quality on a machining surface from occurring, by turning a discharge current pulse to OFF at once as long as the specified period when detecting an electric short and a momentary cut between an electrode an a workpieces, and making a discharge current value so as to be gradually increased simultaneously with the elapse of an on-period of the discharge current pulse. CONSTITUTION: The discharge current detecting signal detected by a current detecting resistor RS is compared with the reference value, preset so as to cause a discharge current to be gradually increased, forming a control signal which control a transistor T. In consequence, as for a discharge current pulse, the current value is gradually increased as desired. And, if time from that point of starting the discharge current pulse and size of the current value at that time are selected, electrode consumption is always kept in the constant value and in no case increased even if the discharge current pulse is turned off at any point of time in the midway. Therefore, when a momentary cut and a short are detected and thereby the discharge current pulse is turned to OFF at once, such a fear that the electrode consumption is increased and the quality of a machining surface is roughed is brought to nothing even if it is any point of time in the discharge current pulse. COPYRIGHT: (C)1988,JPO&Japio
Patent•
19 Jul 1986
TL;DR: In this article, a wire electrode is travelingly put around two carrying parts 34, and passes through a through hole of a wire guide 32 provided between said carrying parts, while an elevating means 33 which operates the wire guide vertically, is provided on the lower part of the wireguide 32.
Abstract: PURPOSE:To enable machining and making correction of an engraving electrode with said engraving electrode kept installed on an electric discharge machine by providing a wire electrode and a wire guide between the support head and the table of said electric discharge machine. CONSTITUTION:A servo-head 21 is installed on the top center of an electric discharge machine 20, operates in the horizontal direction by means of servo- motors provided on its both ends, while operates in the vertical direction by means of a hydraulic cylinder provided on the upper part. A wire electrode 30 is travelingly put around two carrying parts 34, and passes through a through hole of a wire guide 32 provided between said carrying parts. An elevating means 33 which operates the wire guide vertically, is provided on the lower part of the wire guide 32.
TL;DR: In this article, the discharge and output characteristics of a capacitor-transfer discharge excimer laser with automatic preionization (API) have been studied to improve the laser efficiency, showing that efficient energy transfer from the storage capacitor to the discharge capacitor is essential for improvement in the overall efficiency.
Abstract: Energy transfer aspects in a capacitor‐transfer‐type discharge excimer laser with automatic preionization (API) have been studied to improve the laser efficiency. Detailed measurements on the discharge and output characteristics of the XeCl laser show that efficient energy transfer from the storage capacitor to the discharge capacitor is essential for improvement in the overall efficiency. The circuit analysis based on the measurements suggests that the API discharge excimer laser could be operated with an electrical efficiency of about 4%. The overall efficiencies of 2.9, 2.8, and 1.3% have been obtained with the XeCl, KrF, and ArF lasers, respectively.
TL;DR: In this paper, the high Rydberg spectra of atomic helium np 1P states were measured up to n=46 in the negative glow region of a discharge, with mJ=±1 polarization, by optogalvanic spectroscopy.
Abstract: The high Rydberg spectra of atomic helium np 1P states were measured up to n=46 in the negative glow region of a discharge, with mJ=±1 polarization, by optogalvanic spectroscopy. The net electric field values in the negative glow region, in the transition region between the negative glow and the positive column, and also on the radial axis of the positive column were determined from series‐termination measurements. The spatial variations of the ion density in the negative glow region were also obtained from the net‐field measurements.
TL;DR: In this paper, the probability of electrical breakdown in neon is investigated under a pressure of 13.3 mbar, using the breakdown time-delay measurement method, and it is found, by applying a laser spectroscopy technique, that the 1S5 metastable states of neon atoms dominantly contribute to the breakdown probability in the moment when more than 1 s has passed after the previous discharge.
Abstract: The probability of electrical breakdown in neon is investigated under a pressure of 13.3 mbar, using the breakdown time-delay measurement method. It is found, by applying a laser spectroscopy technique, that the 1S5 metastable states of neon atoms dominantly contribute to the breakdown probability in the moment when more than 1 s has passed after the previous discharge. With this method the presence of 1S5 states of Ne atoms is detected in the gas, under the pressure mentioned, up to about 500 s after the cessation of the breakdown.
TL;DR: In this paper, a planar magnetron device using permanent magnets in a DC discharge for thin film preparation is studied. But the minimum value of discharge threshold voltages lie in a wide region of pressure*gap length in comparison to that in the normal discharge without the magnets, resulting in a more stable discharge.
Abstract: Plasma production is studied with a planar magnetron device using permanent magnets in a DC discharge for thin film preparation. The minimum value of discharge threshold voltages is found to lie in a wide region of pressure*gap length in comparison to that in the normal discharge without the magnets, resulting in a more stable discharge. Strongly inhomogeneous ion density in the radial direction is observed in a region close to the magnetics under the cathode to form a visible ring. Primary electrons and high electron temperatures are observed around the cathode, while the ion temperature is spatially homogeneous. The drift velocity caused by the effect of the electric and magnetic fields is directly measured to keep the value roughly constant in the longitudinal direction. A typical thin film of SnO2 prepared by the plasma CVD technique in this device is presented.
TL;DR: In this paper, the influence of metal fluorides on discharge behavior has been examined for several electrode materials: brass, copper, stainless steel, aluminum, and nickel, in sulphur hexafluoride (SF6) discharge at a pressure of 200 torr and in SF6 glow discharges at a few torr.
Abstract: In a sulphur hexafluoride (SF6) discharge, regions of metal fluoride develop with time on the electrode surfaces as a result of chemical reaction between the electrode material and fluorine produced in the discharge. The influence of these fluorides on discharge behavior has been examined for several electrode materials: brass, copper, stainless steel, aluminum, and nickel, in SF6 positive corona discharges at a pressure of 200 torr and in SF6 glow discharges at a few torr. For observation and photography of the low-intensity corona discharges, an image intensifier system was used. For most of the electrode materials, the surface buildup of metal fluoride causes the structure of the discharges to be modified with time, and bright spots or filaments develop at the electrodes in times of the order of minutes. For nickel electrodes, the electrode-fluorine reaction is very slow, and little change in discharge behavior is observed, even after several hours. Nickel clearly represents the best choice of electrode material for any discharge device using a fluoride medium, particularly when uniformity and stability are required over long periods of time.