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Measurements of electrical discharges caused by corona, glow discharges, and voltage breakdown under conditions encountered in aerospace vehicles operating within high altitudes
Originally, de Groot et al. examined electrical conductivity phenomena in terms of the thermodynamics of irreversible processes. They considered the system to be discontinuous and calculated only the differences between the opposing ends of the process. Thus these theories are phenomenological. In the present work, thermodynamics is developed as a continuous system based on hydrodynamics and the entropy production for a thin capillary. It is shown that electroconductivity can be interpreted without difficulty. For the electric double layer, the effects of electrolytes and surface conductivity and the gap width were calculated for the Gouy model.
Experiments were conducted to study the applicability of a double discharge stabilization scheme in conditions appropriate for high energy CO lasers in supersonic flows. A Ludwieg tube impulse flow facility and a ballasted capacitor bank provided essentially steady flow and discharge conditions (d.c.) for times longer than ten electrode length-flow transit times. Steady, arc-free, volume discharges were produced in a Mach 3 test cavity using an auxiliary discharge to stabilize the main discharge in N2 and He/CO mixture. A signigicant result is the lack of observed plasma E/N changes in response to auxiliary discharge current changes. Also, where glow discharges were obtained, the energy loading achieved was very much less than the threshold level required for laser operation.
Experiments have been conducted to study the applicability of a CW double-discharge stabilization scheme under conditions appropriate for high-energy lasers in supersonic flows. Steady arc-free volume discharges have been produced in a Mach 3 supersonic-flow test cavity using an auxiliary discharge to stabilize the main discharge at low-current densities in N2 and He/CO mixtures. A significant result is the lack of observed plasma E/N changes in response to auxiliary-discharge current changes. Also, where glow discharges were obtained, the energy loading achieved was less than the threshold required for laser operation.
Visible light emission is obtained from a plasma containing elemental barium including neutral barium atoms and barium ion species. Neutral barium provides a strong green light emission in the center of the visible spectrum with a highly efficient conversion of electrical energy into visible light. By the selective excitation of barium ionic species, emission of visible light at longer and shorter wavelengths can be obtained simultaneously with the green emission from neutral barium, effectively providing light that is visually perceived as white. A discharge vessel contains the elemental barium and a buffer gas fill therein, and a discharge inducer is utilized to induce a desired discharge temperature and barium vapor pressure therein to produce from the barium vapor a visible light emission. The discharge can be induced utilizing a glow discharge between electrodes in the discharge vessel as well as by inductively or capacitively coupling RF energy into the plasma within the discharge vessel.
Interpretations of microwave emission from Venus through experiments in which anomalous signals have been observed in X-band from glow discharges
The authors experimentally identified three distinct regimes with large differences in current collection in the presence of neutrals and weak magnetic fields. In magnetic field/anode voltage space the three regions are separated by very sharp transition boundaries. The authors performed a series of laboratory experiments to study the dependence of the region boundaries on several parameters, such as the ambient neutral density, plasma density, magnetic field strength, applied anode voltage, voltage pulsewidth, chamber material, chamber size and anode radius. The three observed regimes are: classical magnetic field limited collection; stable medium current toroidal discharge; and large scale, high current space glow discharge. There is as much as several orders of magnitude of difference in the amount of collected current upon any boundary crossing, particularly if one enters the space glow regime. They measured some of the properties of the plasma generated by the breakdown that is present in regimes II and III in the vicinity of the anode including the sheath modified electrostatic potential, I-V characteristics at high voltage as well as the local plasma density.
The emission from glow discharges in flowing air has been investigated in the 1- to 5-micron wavelength region with a vacuum spectrometer. Most of the spectral features observed in the pressure range of .5 to 10 torr are identified, including atomic lines of OI, NI, and HI and molecular bands of N2, NO, N2O, CO2, and CO. The spectra are presented as a function of pressure and a table compiled of the atomic lines. Of particular interest are the contrasts between the emission of the air discharge and that of the pure gases, nitrogen and oxygen. In addition, the results of studies of several discharge modes, employing steady voltages and pulsed, provide data on details of the energy flow within the plasma.
Hollow cathode operation and plasma discharge in mercury ion engine, potential distribution of glow discharge, and liquid metal MHD power conversion
Corona discharge is becoming more of a concern now that the space program is looking at higher power and voltage requirements for future missions. Improved detection methods for studying corona discharge will increase the knowledge base of how this phenomenon occurs, what effects it has on power systems, and how it is affected by outside influences. A better understanding of corona discharge will enable designers to improve on the space applications of insulation and dielectrics, and develop proper detection techniques. A test system was designed and constructed to measure the frequency spectrum of corona discharge current in low pressure. Various test samples in different arrangements were energized by ac voltage until corona discharge occurred. This same test was repeated at different pressures. The results indicate that the frequency spectrum of the discharge current changes with a change in pressure. At low pressures, the discharge frequency spectrum is concentrated in a narrow band with a peak at 17 kHz. As the pressure is increased, the spectral width increases to include components across a much broader band. Other tests were performed to correlate the frequency spectrum data to the shape of the discharge pulse and the physical appearance of the glow discharge.
A substrate is configured with first and second sets of electrodes, where the second set of electrodes is positioned asymmetrically between the first set of electrodes. When a RF voltage is applied to the electrodes sufficient to generate a discharge plasma (e.g., a one-atmosphere uniform glow discharge plasma) in the gas adjacent to the substrate, the asymmetry in the electrode configuration results in force being applied to the active species in the plasma and in turn to the neutral background gas. Depending on the relative orientation of the electrodes to the gas, the present invention can be used to accelerate or decelerate the gas. The present invention has many potential applications, including increasing or decreasing aerodynamic drag or turbulence, and controlling the flow of active and/or neutral species for such uses as flow separation, altering heat flow, plasma cleaning, sterilization, deposition, etching, or alteration in wettability, printability, and/or adhesion.
The electrostatic environment on Mars is controlled by its ever present atmospheric dust. Dust devils and dust storms tribocharge this dust. Theoretical studies predict that lightning and/or glow discharges should be present on Mars, but none have been directly observed. Experiments are planned to shed light on this issue.
Mass spectrometric analyses have been performed on the positive and negative species from discharges in Cs, He-Cs, and He-H2-Cs mixtures. Sampling was conducted through the electrodes of normal glow discharges and from close-spaced heated-cathode conditions, which approximate a cesium thermionic converter. No negative Cs ions were observed for Cs pressures less than .01 torr. Identified species included Cs(+), Cs2(+), Cs(-), and what appeared to be multiply charged ions. Low-mass negative and positive ions attributed to H2 were observed when an He-H2 mixture was also present in the discharge region.
The plasma generated in a pulsed slit discharge nozzle is used to form molecular ions in an astrophysically relevant environment. The plasma has been characterized as a glow discharge in the abnormal regime. Laboratory studies help understand the formation processes of polycyclic aromatic hydrocarbon (PAH) ions that are thought to be the source of the ubiquitous unidentified infrared bands.
High purity inorganic higher oxides of the alkali and alkaline earth metals are prepared by subjecting the hydroxide of the alkali and alkaline earth metal to a radio frequency discharge sustained in oxygen. The process is particulary adaptable to the production of high purity potassium superoxide by subjecting potassium hydroxide to glow discharge sustained in oxygen under the pressure of about 0.75 to 1.00 torr.
The production of light hydrocarbons by precipitating magnetospheric electrons in the Uranian stratosphere is simulated in laboratory experiments. The products of continuous-flow glow discharges of H2-He-CH4 mixtures containing 0.0012 or 0.022 mol pct CH4 at pressures 0.63-57 mbar are trapped at 77 K, measured manometrically, and identified by gas chromatography and mass spectroscopy; the results are presented in tables and characterized in detail. The globally averaged rate for the production of higher hydrocarbons by this mechanism on Uranus is estimated as 3 x 10 to the 6th C/sq cm sec and shown to be similar to that for photochemical production, while the local rate for the auroral zones is significantly higher than the corresponding photochemical rate. A decrease in yield with increasing molecular complexity is also noted.
Thunderstorms emit fluxes of gamma rays known as gamma-ray glows, sporadically observed by aircraft, balloons and from ground. Glows are observed as increased gamma-ray emissions by tens of percent up to two orders of magnitude above the background, sometimes abruptly terminated by lightning discharges. Glows are produced by the acceleration of energetic electrons in high electric field regions within thunderclouds, and contribute to charge dissipation. Glows are considered as quasi-stationary phenomena, with durations up to a few tens of seconds and spatial scales up to 10-20 kilometers. No measurement of the full extension in space and time of a gamma ray glow region and their occurring frequency has been reported so far. Here we show that tropical thunderclouds over ocean and coastal regions commonly emit gamma rays for hours over areas up to a few thousands of square kilometers. Emission is associated with deep convective cores; it is not uniform and continuous but shows characteristic timescales of 1-10 seconds and even sub-second for individual glows. The dynamics of gamma-glowing thunderclouds starkly contradicts the quasi-stationary picture of glows, but rather resembles that of a huge gamma-glowing «boiling pot» both in pattern and behavior.
The intensity ratio of two atomic or ionic spectral lines in a plasma is a function of electron temperature. By imaging two spectral lines, and computing the line ratio, pixel by pixel, an image of the electron temperature is produced. This is demonstrated using a dusty plasma consisting of submicron particles suspended in an argon RF glow discharge.