Wide Range Of Gas Pressures Research Articles

Breakdown of Rod-Plane Gaps in SF6 Under Positive Switching Impulses

The effect of the front of impulse voltages on the breakdown of nonuniform gaps in SF6 has long been reported to be unsystematic. The present study provides an explanation to this phenomenon by examining the breakdown probability distributions of rod- plane gaps in SF6 over a wide range of gas pressure and under different impulse wave forms. The unsystematic effects of the impulse front are experimentally confirmed and are attributed to the coexistence of two main aspects of discharge-corona stabilization which increases the breakdown strength and whose effect disappears beyond a certain gas pressure, and the statistical formation delay which is responsible, under impulse voltages, for the creation of a voltage range of uncertainty where breakdown may or may not occur. By considering the "impulse breakdown threshold", rather than the 50% breakdown voltage, the effects of statistical formation are deleted and the systematic effect of corona stabilization is singled out. The work applies this analysis to SF6 gaps with different degrees of field nonuniformity.

Ionic recombination of Kr+ and Kr+2 with F− in dense buffer rare gases

Rates, α, for the recombination of Kr+ and Kr+2 with F− in various buffer rare gases (He, Ne, Ar, Kr, Xe) at 300 K are calculated for a wide range of gas pressures. For pressures 1–5 atm, the population of KrF* via recombination is greatest for Ne and Ar as third bodies, yielding α∼3×10−6 cm3 sec−1, while for pressures ≳10 atm, He is to be preferred as a buffer gas.

Dynamics of the development of breakdown near the surface of infrared optics elements in gaseous media

An experimental investigation was made of the influence of the pressure of the ambient gas on the shape of CO2 laser pulses transmitted by an NaCl sample after breakdown on its surface. A study was made of the dynamics of formation of a breakdown plasma initiated by surface breakdown in various gases: it was carried out in a wide range of gas pressures and incident radiation intensities. Measurements were made of the dependences of the velocity and maintenance threshold of optical detonation waves on the pressure of air when CO2 laser radiation was used. The absence (in some cases) of the visible traces of damage as a result of this breakdown and the opacity of the surfaces of infrared optics materials in gaseous media was attributed to the screening of the surface by an optical detonation wave.

Static field anode corona characteristics in sulphur hexafluoride

This paper reports the results of an experimental investigation of the static field anode corona characteristics in SF 6 over a wide range of gas pressures and field non-uniformities. In addition to the experimental study the theoretical streamer onset voltages of the various test gap geometry-pressure configurations were calculated and these are compared with the experimentally determined breakdown voltages and onset levels of the various stages of prebreakdown current activity. Also discussed is a method of estimating the minimum gas. pressure at which breakdown occurs in the absence of positive DC corona in a non-uniform field.

Sparking potentials of dry air, humid air and water vapour between concentric sphere-hemisphere electrodes

The sparking potentials of dry air, humid air and water vapour between a pair of concentric sphere-hemisphere electrodes are measured, for both voltage polarities of the inner electrode, over a wide range of gas pressures. In dry air, the measurements are conducted over nearly five orders of magnitude of gas pressure. In dry air and for gas pressure >100 torr, corona is observed to precede the breakdown of the gap when the inner sphere is made negative. On the other hand, the corona inception and the breakdown of the gap occurs at the same potential for the positive polarity of the inner electrode. The total secondary ionisation coefficient in dry air is evaluated from the measured sparking potential, and found to depend on the electrode polarity. The influence of the partial-water-vapour pressure on the sparking potential of air is measured. Practical mixtures of air and partial water vapour are employed. It is observed that the addition of water vapour increases the sparking potential for both the negative and the positive voltage polarities of the inner electrode. The relative increase in the sparking voltage depends on both the partial-water-vapour pressure and the total pressure of the mixture. The sparking potential of water vapour is found to be higher than that of dry air for the same gas pressure.

Time-Dependent Study of Vacuum-Ultraviolet Emission in Argon

A 250-keV pulsed electron accelerator was constructed for the excitation of noble gases, so that resonance radiation and continuous emission could be studied under conditions of good geometry with vacuum-ultraviolet spectroscopic techniques. For argon gas, time-dependent studies were carried out at the wave lengths of the $^{1}P_{1}$ resonance line, the $^{3}P_{1}$ resonance line, the 1100-\AA{} continuum, and the 1250-\AA{} continuum over a wide range of gas pressures. The $^{1}P_{1}$ resonance line decays exponentially with a lifetime which seems to be governed by the escape of resonance radiation to the walls of the apparatus and by three-body destruction of resonance states. The 1100-\AA{} continuum, on the other hand, decays exponentially with a lifetime more characteristic of two-body Franck-Condon collisions. The main continuum near 1250 \AA{} reaches a maximum well after the pulse of exciting electrons is terminated and then decays with a lifetime which is very long at low pressure but decreases to a constant value of 2.8 \ensuremath{\mu}sec at high pressures(about 1000 torr). From the data we suggest that the $^{1}P_{1}$ states, which are richly populated with charged particles, are converted to argon metastable molecules and these in turn are converted by collisions to a molecule which radiates the 1250-\AA{} continuum with the 2.8-\ensuremath{\mu}sec lifetime. Better fitting to the time-dependent emission at 1250 \AA{} is obtained by also including the known channel starting with $^{3}P_{2}$ metastable atoms which are converted to a radiating molecule by three-body collisions.

Radiation patterns of a slot antenna in the presence of a breakdown sheath

The experimental radiation patterns are measured for a 0.4\times0.9 -inch slot antenna in the presence of aperture breakdown over a wide range of gas pressures and breakdown power levels. It was found that pattern distortion caused by the breakdown plasma was not very significant. The overall signal attenuation, however, could be extremely severe, particularly below 0.5 torr.

Proton Excitation of the Argon Atom

Studies of the excitation of argon with 4-MeV protons have been carried out by making use of a vacuum ultraviolet scanning monochromator and a 6-MeV Van de Graaff accelerator. Protons were directed through the gas and then into a Faraday cup in an arrangement in which the relative intensity of emitted light could be studied over a wide range of gas pressure (1 to 1500 Torr). Four continua near 2100, 1900, 1300, and 1100 \AA{}, respectively, as well as escape radiation originating from the 1048 \AA{} resonance line, were studied as a function of pressure.Studies of the intensity of the four main continua (per unit of proton power dissipation) as a function of pressure led us to the conclusion that each continuum has a separate atomic precursor. We suggest that the 1300 \AA{} continuum and the 1100 \AA{} continuum are dissociative diatomic continua and originate from the $^{1}P_{1}(11.83\ensuremath{-}\mathrm{e}\mathrm{V})$ and the $^{3}P_{1} (11.62\ensuremath{-}\mathrm{e}\mathrm{V})$ resonance atomic states, respectively. We tentatively suggest that the continua near 2100 \AA{} and near 1900 \AA{} are recombination spectra involving the formation of argon excimers with binding energies of about 4 eV.The 1300 and 1100 \AA{} continua have been observed in gas discharges, but these were interpreted as a single continuum originating from the $^{3}P_{1}$ state. We believe that the present experimental method, which makes possible gas kinetic observations at spectroscopically defined photon energies, is indeed a powerful tool for the study of atomic and molecular structure and processes.

Total secondary ionization coefficients and breakdown potentials of monatomic gases between mild steel coaxial cylinders

A study of the breakdown potential at room and elevated temperatures has been made in very pure gas samples of helium, neon, argon, krypton and xenon, using mild steel concentric cylindrical electrodes. The gas pressure was varied over a range of almost four orders of magnitude, and the temperature of both the gas and the electrodes from 295-463 °K. At constant gas density, and for positive and negative wire (inner electrode), it is shown that the breakdown potential values are independent of gas temperature over the whole pressure and temperature ranges covered. This suggests that heating the electrodes and the gas has a negligible effect on the secondary electron yield in all the rare gases studied. The minimum sparking potential value for the negative wire was found to increase as the ionization potential of the gas decreased, while that of the positive wire was only slightly sensitive to the nature of the gas. It has been found that, when adequate precautions are taken to ensure a high standard of gas and electrode purity, the similarity theorem is obeyed in all the rare gases, for the positive as well as the negative wire breakdown, over a very wide range of gas pressure. The total electron yield due to secondary ionization processes was evaluated for each gas over a wide range of E/p0. Its value varied over a range of three orders of magnitude, depending on the type of the gas and the value of E/p0.

Total secondary ionization coefficients and breakdown potentials of hydrogen, methane, ethylene, carbon monoxide, nitrogen, oxygen and carbon dioxide between mild steel coaxial cylinders

Breakdown potentials of hydrogen, methane, ethylene, carbon monoxide, nitrogen and carbon dioxide were measured at room and at elevated temperatures, and oxygen at 296 °K, using mild steel cylindrical electrodes. The gas pressure was varied over a range of almost four orders of magnitude, and the temperature of both the gas and the metal electrodes from 294-468 °K. Two discharge tubes, having different electrode diameters but the same material composition, were employed. The breakdown potential values at constant gas density, and for positive and negative wire (inner electrode), were found to be independent of gas temperature over the whole of the pressure and temperature ranges covered. It has been found that, with the exception of nitrogen, the similarity theorem is obeyed in the gases studied. This theorem was found to hold for positive as well as negative wire breakdown over a very wide range of gas pressure. The total electron yield due to secondary ionization processes was evaluated over a wide range of E/po values. The value of the total secondary ionization coefficient varied over a range of seven orders of magnitude, depending on the nature of the gas and the ion energy. The total secondary ionization coefficient was found to be independent of target and gas temperature in the gases studied, over the range 294-468 °K.

Investigation of the operating characteristics of the 3.5 µ xenon laser

Amplification at 3.508 μ in pure xenon dc-excited discharges has been measured over a wide range of gas pressures and for several discharge diameters. For pressures greater than 10 mTorr, the unsaturated gain increases monotonically as the pressure decreases. Gain varies inversely as the radius for large bore (radius ≥ 3.5 mm) amplifers, but a complicated, pressure-dependent variation between gain and discharge diameter was observed in amplifiers of less than 3-mm diameter. Gain saturation occurs at low Signal levels and results in small output powers from conventional xenon lasers.