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Breakdown time lags in short vacuum gaps
Classified abstracts 5437-5445 12 5437. Breakdown time lags in sbort vacmun gapps (GB)
Measurements of breakdown time lags have been made in gaps of up to 1 mm in ultra-high vacuum. A clear discontinuity has been found in the distribution of these times demonstrating that breakdown takes place either within 30 ns of applying the voltage or after a long time delay of up to several ms. Comparison of measured and calculated data suggests that, as the applied voltage is increased, there may be a change in breakdown mechanism from one involving heating and evaporation of the emitting site at the cathode to one involving evaporation of the target site at the anode. .I D Chalmers and B D Phukan, Vacuum, 32 (3), 1982, 1455150. 12 5438. Discharge energy loading characteristics of a UV-preionized TEA CO, laser. (USA) The effects of ultraviolet (uv) preionization energy and initial electron number density on discharge loading are experimentally clarified in a uv preionized TEA CO, laser. Dependence of laser output energy on the spatial uniformity of the preionization has also been examined. In order to produce the laser output energy efficiently, the input energy for the uv preionizer is required to be in excess of 2% of the input energy for the main discharge. With the sufficient initial electron number density, the laser energy was little dependent on the spatial nonuniformity of preionization in the discharge volume at low-energy loadings (5 100 J/l). At higher energy loadings, the laser output energy was found to depend not only on the initial electron number density but also on the spatial uniformity of the preionization. (Japan) Sbubichi Suz&i et al, Reu Sci Instrum, 53 (2), 1982, 184-186. 12 5439. Considerable change in dc breakdown characteristics of positive-
conce~~trations of NO, CO,
point-plaoe~ps due to varyittg and intensity of irradiation. (GB)
and H,O in air
The sparking potential of dc positive-point-plane gaps in air for the centimetre gap range shows an abrupt change at a critical gap length d,. The value of d, is affected markedly by the intensity of irradiation and by concentrations of COz, Hz0 and NO, produced by the discharges in air. The change in d, leads to a pronounced change in breakdown characteristics. This e&t becomes more striking as the degree of nonuniformity of the gap is reduced and can be demonstrated clearly by using a flow system to avoid the accumulation effect of the decomposition products produced by successive discharges. (Japan) Y G&o, J Phys D: Appl Phys, 15 (7), 1982, 1217-1225. 12 5440. Studies of tbe anode region of a high-intensity argon arc. (USA) This paper is concerned with experimental and analytical/numerical studies of the anode region of an atmospheric pressure argon arc in a current range from 100 to 300 A. The arc arrangement allows unobstructed viewing of the entire anode region, including the anode itself, and it is also suitable for simulating short as well as long arcs. Depending on the flow situation in the anode region, two different types of stable arc roots are observed. The diffuse anode arc root, characterized by a strong flow impinging on the anode surface, is well known from free-burning, short arcs. The second type reveals a more or less severe constriction in front of the anode, caused by the entrainment of gas into the arc, resulting in an anode jet. Measurements of the induced flow at the cathode of such an arc show a linear increase of the induced mass flow rate with increasing current. This correlation can be confirmed by a simple analysis. A fastscanning, computer-controlled system has been used for spectrometric measurements ofthe temperature distribution for both modes of anode arc roots, assuming local thermodynamic equilibrium (LTE) in the arc. The maximum temperatures in the arc core compare favourably with calculated temperature distributions of the constricted mode. The calculated isotherms, however, show a substantial shift which is probably
due to the chosen boundary conditions at the end of the constrictor tube. N Sanders et al, J Appl Phys, 53 (6), 1982,41364145. 12 5441. A probe technique for determining tbe electrical potentials in an ionized corona field for the measurement of resistivity of electrostatically precipitated deposits. (USA)
In order to determine the resistivity of an electrostatically precipitated particulate layer of high resistivity material, a new technique is described using a conducting potential probe. The space-charge potentials are first determined by the probe in a small parallel plate precipitator with wire-toplate spacing of 75 mm at several distances from the collector plate, and a short extrapolation gives the potential at the dust surface Using this 344
potential and the associated measurements of collected layer thickness and current density, the operational resistivity p/ of such a layer is determined while subject to the corona currents and high electric fields of normal electrostatic precipitator operation. The theory is given for the conducting potential probe in a unidirectional ionized field of a single wire to parallel plate unit. An example of the field dependence of the operational resistivity of a fly ask is given. (Australia) P R C Chard, J Appl Phys, 53 (3), 1982, 1437-1444. 12 5442. Fiid emission of metal ions and microparticles. (GB) By applying an intense electric field to the end of a thin tungsten needle, covered with a film of molten gold, a beam of fast positive singly and multiply charged atomic and molecular Au ions and of Au microparticles is emitted from the needle tip in uecuo. When such a composite beam passes through a transverse electric field, the deflected particles form a cigar-shaped deposit on a target showing that the particles are charged and that the spot shape was distorted by a non-uniformity of the deflecting field. The absence of an undeflected deposit suggests a negligible number of uncharged beam particles. In contrast, by deflection in a transverse magnetic field B the beam is split into a number of circular spots which are found to he on a straight line. Their displacements correspond to Au:+ (charged microparticles) and Au+, Ai?+ etc, each spot representing a beam component of trajectory radius (Mu/@). o being the drift velocity and 4 the general charge of the particle mass M. From the thickness of the individual deposits the intensity of the beam components has been estimated. The fairly sharp boundaries of the circular spots indicate that the velocity distribution of each component is relatively narrow. Thus both ions and charged microparticles seem to originate from the same apex sites and to be ‘released’ by conservative field forces. SPll~mpsoaandAvonEngel,JPhysD: ApplPhys, 15(5), 1982,925-931. 12 5443. Electron energy diitributiols in the mercury discbarge positive column. (GB) The electron energy distribution functions in mercury discharge positive columns are measured by the Druyvestyn second difIerentia1 method and compared to those calculated numerically from the Boltzmann equation under the same discharge conditions. The discharge parameters are measured directly and fed into the Bohzmann equation computation code. The shapes of the distributions are found to agree approximately but the mean energies have large disagreement. A method of obtaining the measured distribution from the calculation by modifying the data fed into the computation code and correlating the result with the simple electron temperature measurement is suggested. H T Saelee, .I Phys D: Appl Phys, 15 (5), 1982, 873-883. 12 5444. Energy trarspurt in dc and ac vortex stabilized arcs. (GB) By measuring the power balance for high current ac and dc vortex stabilized arcs it has been shown that the radiative efficiencies of ac and dc arcs are comparable to each other at similar power input levels. The electrode power balance has also been determined as a function of the significant arc parameters (current I, gas pressure, flow direction and rate). For 150 A
Measurements of breakdown time lags have been made in gaps of up to 1 mm in ultra-high vacuum. A clear discontinuity has been found in the distribution of these times demonstrating that breakdown takes place either within 30 ns of applying the voltage or after a long time delay of up to several ms. Comparison of measured and calculated data suggests that, as the applied voltage is increased, there may be a change in breakdown mechanism from one involving heating and evaporation of the emitting site at the cathode to one involving evaporation of the target site at the anode. .I D Chalmers and B D Phukan, Vacuum, 32 (3), 1982, 1455150. 12 5438. Discharge energy loading characteristics of a UV-preionized TEA CO, laser. (USA) The effects of ultraviolet (uv) preionization energy and initial electron number density on discharge loading are experimentally clarified in a uv preionized TEA CO, laser. Dependence of laser output energy on the spatial uniformity of the preionization has also been examined. In order to produce the laser output energy efficiently, the input energy for the uv preionizer is required to be in excess of 2% of the input energy for the main discharge. With the sufficient initial electron number density, the laser energy was little dependent on the spatial nonuniformity of preionization in the discharge volume at low-energy loadings (5 100 J/l). At higher energy loadings, the laser output energy was found to depend not only on the initial electron number density but also on the spatial uniformity of the preionization. (Japan) Sbubichi Suz&i et al, Reu Sci Instrum, 53 (2), 1982, 184-186. 12 5439. Considerable change in dc breakdown characteristics of positive-
conce~~trations of NO, CO,
point-plaoe~ps due to varyittg and intensity of irradiation. (GB)
and H,O in air
The sparking potential of dc positive-point-plane gaps in air for the centimetre gap range shows an abrupt change at a critical gap length d,. The value of d, is affected markedly by the intensity of irradiation and by concentrations of COz, Hz0 and NO, produced by the discharges in air. The change in d, leads to a pronounced change in breakdown characteristics. This e&t becomes more striking as the degree of nonuniformity of the gap is reduced and can be demonstrated clearly by using a flow system to avoid the accumulation effect of the decomposition products produced by successive discharges. (Japan) Y G&o, J Phys D: Appl Phys, 15 (7), 1982, 1217-1225. 12 5440. Studies of tbe anode region of a high-intensity argon arc. (USA) This paper is concerned with experimental and analytical/numerical studies of the anode region of an atmospheric pressure argon arc in a current range from 100 to 300 A. The arc arrangement allows unobstructed viewing of the entire anode region, including the anode itself, and it is also suitable for simulating short as well as long arcs. Depending on the flow situation in the anode region, two different types of stable arc roots are observed. The diffuse anode arc root, characterized by a strong flow impinging on the anode surface, is well known from free-burning, short arcs. The second type reveals a more or less severe constriction in front of the anode, caused by the entrainment of gas into the arc, resulting in an anode jet. Measurements of the induced flow at the cathode of such an arc show a linear increase of the induced mass flow rate with increasing current. This correlation can be confirmed by a simple analysis. A fastscanning, computer-controlled system has been used for spectrometric measurements ofthe temperature distribution for both modes of anode arc roots, assuming local thermodynamic equilibrium (LTE) in the arc. The maximum temperatures in the arc core compare favourably with calculated temperature distributions of the constricted mode. The calculated isotherms, however, show a substantial shift which is probably
due to the chosen boundary conditions at the end of the constrictor tube. N Sanders et al, J Appl Phys, 53 (6), 1982,41364145. 12 5441. A probe technique for determining tbe electrical potentials in an ionized corona field for the measurement of resistivity of electrostatically precipitated deposits. (USA)
In order to determine the resistivity of an electrostatically precipitated particulate layer of high resistivity material, a new technique is described using a conducting potential probe. The space-charge potentials are first determined by the probe in a small parallel plate precipitator with wire-toplate spacing of 75 mm at several distances from the collector plate, and a short extrapolation gives the potential at the dust surface Using this 344
potential and the associated measurements of collected layer thickness and current density, the operational resistivity p/ of such a layer is determined while subject to the corona currents and high electric fields of normal electrostatic precipitator operation. The theory is given for the conducting potential probe in a unidirectional ionized field of a single wire to parallel plate unit. An example of the field dependence of the operational resistivity of a fly ask is given. (Australia) P R C Chard, J Appl Phys, 53 (3), 1982, 1437-1444. 12 5442. Fiid emission of metal ions and microparticles. (GB) By applying an intense electric field to the end of a thin tungsten needle, covered with a film of molten gold, a beam of fast positive singly and multiply charged atomic and molecular Au ions and of Au microparticles is emitted from the needle tip in uecuo. When such a composite beam passes through a transverse electric field, the deflected particles form a cigar-shaped deposit on a target showing that the particles are charged and that the spot shape was distorted by a non-uniformity of the deflecting field. The absence of an undeflected deposit suggests a negligible number of uncharged beam particles. In contrast, by deflection in a transverse magnetic field B the beam is split into a number of circular spots which are found to he on a straight line. Their displacements correspond to Au:+ (charged microparticles) and Au+, Ai?+ etc, each spot representing a beam component of trajectory radius (Mu/@). o being the drift velocity and 4 the general charge of the particle mass M. From the thickness of the individual deposits the intensity of the beam components has been estimated. The fairly sharp boundaries of the circular spots indicate that the velocity distribution of each component is relatively narrow. Thus both ions and charged microparticles seem to originate from the same apex sites and to be ‘released’ by conservative field forces. SPll~mpsoaandAvonEngel,JPhysD: ApplPhys, 15(5), 1982,925-931. 12 5443. Electron energy diitributiols in the mercury discbarge positive column. (GB) The electron energy distribution functions in mercury discharge positive columns are measured by the Druyvestyn second difIerentia1 method and compared to those calculated numerically from the Boltzmann equation under the same discharge conditions. The discharge parameters are measured directly and fed into the Bohzmann equation computation code. The shapes of the distributions are found to agree approximately but the mean energies have large disagreement. A method of obtaining the measured distribution from the calculation by modifying the data fed into the computation code and correlating the result with the simple electron temperature measurement is suggested. H T Saelee, .I Phys D: Appl Phys, 15 (5), 1982, 873-883. 12 5444. Energy trarspurt in dc and ac vortex stabilized arcs. (GB) By measuring the power balance for high current ac and dc vortex stabilized arcs it has been shown that the radiative efficiencies of ac and dc arcs are comparable to each other at similar power input levels. The electrode power balance has also been determined as a function of the significant arc parameters (current I, gas pressure, flow direction and rate). For 150 A