Browsing by Subject "Electric discharges through gases"
Now showing 1 - 20 of 30
Results Per Page
Sort Options
Item A fast preionization source for diffuse discharges containing attachers(Texas Tech University, 1983-12) Cooper, James RandallDiffuse discharge opening switches and most excimer lasers must operate with gas mixtures containing attachers. In self sustained discharges, preionization is required for arc free initiation of these discharges. The preionizer must have a short rise and falltime and must have an extremely accurate timing system because of the attachers in the discharge gas. Also, this device must have sufficient power to produce large volumetrically uniform electron densities in gases at pressures in the one atmosphere range. This paper describes the design and construction of such a preionizer and gives an overview of various preionization techniques previously employed. The device presented here consists of eight coaxial cables for energy storage, which are switched through a master spark gap to eight cables terminated by individual multi-spark arrays. The preionizer and the main discharge are triggered by a single laser (with a beam splitter and with a variable optical delay on one of the beams). Experiments showing the influence of the delay, preionization pulse length, jitter, and durability of the spark sources on the main discharge are described.Item An electron beam controlled diffuse discharge switch(Texas Tech University, 1985-05) Harjes, Henry CharlesIn recent years there has been an increasing interest in the development of fast, repetitive, opening switches which would allow the use of inductive energy storage in repetitively operated pulsed power systems. An opening switch concept that shows promise for such operation is the electron beam controlled diffuse discarge switch (EBCS). An analysis of this switch that demonstrates the importance of the switch gas composition is presented and several desirable gas properties are identified. An experimental facility for the study of promising gases in a repetitively operated EBCS is also described. It includes an e-beam generating tetrode that is able to deliver an e-beam with a maximum energy of 250 keV, a risetime of 10 ns, a maximum pulse duration of lus, and a variable repetition frequency up to 25 MHz in a lys burst. Results of experiments in various switch gas mixtures are presented. Current gains of approximately 10 and opening times < 100 ns have been observed.Item An experimental and theoretical investigation of nonequilibrium behavior of electrons in gases(Texas Tech University, 1984-05) Young, Chris MorrowNot availableItem An investigation of electron beam initiated spark gap breakdown(Texas Tech University, 1979-12) Newton, Mark AllenA coaxial system was designed and constructed to investigate electron beam initiated discharges in high pressure gases. An electron beam was fired axially into a gap formed by an interruption in the center conductor of the coaxial system to initiate a discharge. Photographic techniques were used as diagnostics to examine the physical processes occurring in the discharge. Open shutter photographs revealed broad discharge channels with spatial dimensions approximately equal to the spatial dimensions of the electron beam. Streak photographs of the discharge provided evidence that an avalanche process was occurring in the discharge.Item Arc current, voltage, and resistance in a high energy, gas-filled spark gap(Texas Tech University, 1985-05) Maas, Brian LaneA spark gap was designed and constructed to measure the time dependent arc resistance. The arc current was measured and the arc resistance calculated using the current and the other circuit parameters. Typical operating parameters were: unipolar pulse, 35 kV breakdown voltage, 30 kA peak current, and 1.15 kJ total energy per shot. The dissipated arc energy was calculated from the arc current and resistance and found to be between 4.5% and 10.5% of the total energy. Arc resistance vs time curves were obtained for all possible combinations of three electrode materials (304 Stainless Steel, ACF-IOQ Graphite, and 3w3 Copper-Tungsten), three gases (Air, N2, and SF6), and three gas pressures ( 1 , 2, and 3 atmospheres). Statistical analysis was performed on the resultant data. Essential results are: within the statistical and measurement errors, the resistance is independent of the electrode material. For each gas, R is approximately proportional to pd (pressure and gap distance). The constants of proportionality are (31 ± 7) mΩ/(cm bar) for air, (47 + 15) mΩ/(cm bar) for N2, and (76 ± 17) mΩ/(cm bar) for SF6.Item Breakdown processes in laser triggered switching(Texas Tech University, 1983-05) Dougal, Roger AdelbertAn investigation of laser triggered switching using a 1.06 µ NdrYAG laser to trigger a uniform field gap filled with 800 Torr of N2 has been performed in the following triggering geometries: 1) Transverse not striking electrodes, 2) Coaxial not striking electrodes, 3) Coaxial striking target electrode, and 4) Coaxial striking recess in target electrode. Streak photography, time resolved spectroscopy, and current measurements reveal great differences in the breakdown processes for the various geometries. The major differences are attributable to laser field interaction with the incipient arc channel. All breakdown processes except types 2 and 3 look quite similar to an overvolted breakdown. Diagnostics of type 2 triggering have shown a laser assisted streamer propagating from the laser fireball to the opposite electrode. Streak photography shows the streamer precursor of the breakdown channel initially proceeds across the gap at a few times 10 cm/sec, but slows to about 2X10 cm/sec as it advances in the focal cone to regions of lower laser intensity. The laser interaction with the streamer produces a uniform, high conductivity channel which emits intense continuum light once ohmic heating raises the channel temperature. When delay is greater than the laser pulse length two distinct regions can be detected in the arc channel; one, laser assisted, showing the abrupt, uniform continuum luminosity, and the other not laser assisted, appearing much like a weakly overvolted breakdown process, exhibiting a glow discharge stage followed by thermalization proceeding from the ends of the glow region towards the middle at 10 cm/sec.Item Coating properties which increase the vacuum flashover strength of insulators(Texas Tech University, 1988-05) Leiker, Gary R.Item Design and construction of a diffuse discharge experiment(Texas Tech University, 1983-05) Hutcheson, George ZohnA definition and characterization of diffuse discharees is presented, and the conditions necessary for the production of diffuse discharges are discussed. The design and construction of an experimental device that produces diffuse discharges for the study of optically controlled diffuse discharge opening switches is described. It is shown that these control processes require diffuse discharges as a switch medium. Diagnostic voltage and current probes were built into the system and were found to have rise-times of less than 5 ns. The device constructed produces discharges in Helium at gas pressures up to 200 torr.Item Development of a 100 kilovolt two nanosecond risetime probe with DC response(Texas Tech University, 1986-08) Power, John FNot availableItem Development of intense light flashes and their application to discharge initiation(Texas Tech University, 1982-12) Alley, Michael PaulAn ultraviolet light flasher has been built which consists of a spark gap (Vs = 7 kV) mounted at the end of a coaxial transmission line so that current pulses of five nanosecond width are produced. Intensity studies of the flasher in the spectral range capable of producing photoelectric emission from the electrode in a pulsed discharge experiment were performed and statistical plots showing the variation in intensity at particular wavelengths are presented. The light from the flasher was focused on an electrode arrangement in a pressure-vacuum chamber. Current curves for single avalanches were recorded and the statistical distribution of the number of electrons produced by the flasher were found.Item Experimental investigations of subnanosecond gas breakdown(Texas Tech University, 2000-12) Short, Brent D.The recentiy developed concept of plasma limiters requires breakdown in gas with subnanosecond delays. If subnanosecond breakdown can be achieved in a transmission line or waveguide, most incoming power could be reflected, protecting any circuitry on the other side. This experiment consisted of a study of breakdown in gas using a needle tip to plane geometry with high voltage pulsers, ranging from 1 to 7.5 kV, with a typical risetime of 500 ps. The setup consists of a pulser feeding a 50 U transmission line to a needle-plane test gap inside a vacuum chamber, terminated in a 50Q load line. The needles used have a tip radius of less than 1|xm to produce a high electric field enhancement at the test gap. Measurements were taken from current and voltage sensors on the input transmission line, and the luminosity of discharge was measured with a photomultiplier tube. For voltages of 1.7 kV and below, a minimum breakdown delay of 12 ns was measured. At 15 kV, achieved with a 7.5 kV pulser with the voltage doubling at an open circuit at the test gap, subnanosecond breakdown delays were observed. The pressure was varied from 10^-6 Torr to 600 Torr to obtain breakdown delay characteristics according to pressure. The results of the fastest breakdown observed point toward a vacuum type discharge with field emitted electrons as the dominant breakdown mechanism, with a certain pressure of gas required to sustain the discharge across the test gap.Item Investigations of overvoltage breakdown(Texas Tech University, 1981-08) Levinson, Scott JosephAn experiment has been constructed to investigate the highly overvolted, electrical gas discharge for the following parameters: pressure (< 1 Torr - 1350 Torr), electrode spacing (1 and 2 cm), electric field (55-110 kV/cm) and electrode material (aluminum, brass, and graphite). In order to determine the effects of these parameters on the statistics associated with the observational time lag, an automated data acquisition system has been built to reduce large amounts of time lag data. An insulator has been placed over the anode in a number of experiments to examine the current waveforms resulting from electron space charge motion in the gap during the pre-breakdown stage. The results indicate that large^ fast rising (~ 1 ns) currents (~ 100 A) exist in the gap before a conducting plasma channel bridging the cathode and anode is formed. These initial currents appear to be the result of runaway electron space charge motion. The results of the statistical investigation indicate that: (1) the graphite electrode is a promising candidate in low jitter switching applications because of its large emissivity (~ le~/ns); (2) the statistics associated with the formative time lag are comparable to those of the statistical time lag (when graphite electrodes are used) at overvoltages as high as 400%. An apparent pressure dependency of the electron emission rate is a consequence of this result; (3) the formative time lag reaches an asymptotic value at the highest values of overvoltage investigated (- 2800%); and (4) the formative time lag is significantly larger than that predicted by the Streamer Theory (Raether's criteria), particularly at the highest values of overvoltage.Item Magnetic field control of low pressure diffuse discharges(Texas Tech University, 1986-05) Cooper, James RandallThe application of a magnetic field in a direction transverse to the electric field in a diffuse discharge cam have a strong effect on the transport parameters in the discharge medium and on the external characteristics of the discharge as a whole. The deviations in these transport parameters have been investigated in this work by means of Monte Carlo calculations and the electrical characteristics of the total discharge have been observed experimentally. The results of the theoretical investigation show that in attaching gas mixtures both the ionization and attachment rate coefficients in the positive column of the discharge are changed such that the combined effect results in an increase in resistivity. Monte Carlo calculations performed by other researchers indicate that a transverse magnetic field could have an even stronger effect on the electron energy distribution in the cathode fall region and consequently on the cathode fall voltage. Experimentally, it is seen that application of a crossed magnetic field to an abnormal glow discharge in attaching gases in a certain parameter range causes the discharge voltage to increase significantly. The effect seems to be most strongly influenced by processes in the cathode fall region.Item Item Negative differential conductivity in e-beam sustained diffuse discharges for switching applications(Texas Tech University, 1986-05) Strickland, Bryan EdwardIn e-beam sustained diffuse discharges in gas mixtures which contain small additives of electronegative gases, the discharge characteristic (current density versus reduced field strength) may exhibit negative differential conductivity (NDC) depending on the source function and the concentration of attacher gas. In discharges exhibiting negative differential conductivity, electron depleted domains of high electric field intensity are formed in the discharge. The results of electrical and optical measurements performed on an e-beam sustained diffuse discharge in a gas mixture of 2% C2F6 in 1 atm Ar are presented and compared with theoretical predictions. The steady state current density (J) versus reduced field strength (E/N) exhibits a strong negative differential conductivity in an E/N range of 2.5 Td < E/N < 5 Td. Time resolved photographs taken in this E/N range show distinct luminous layers perpendicular to the discharge axis.Item New infrared noble gas laser transitions between 3 microns and 18 microns(Texas Tech University, 1979-12) Brown, Eddie LeeNineteen new infrared laser transitions observed in Kr, Ar and Xe ranging from 3.631u to 17.233y are reported and identification of all but one of these transitions has been made. An identification of a previously observed but unidentified transition is given along with a method for assigning term assignment to observed transitions. The design and construction of a high power noble gas laser capable of operating at gas pressures as low as 5y and electric currents as high as 2KA is discussed.Item Optically controlled diffuse discharges for switching applications(Texas Tech University, 1986-08) Hutcheson, George ZohnDiffuse discharges containing electronegative gases, at present, are the only means capable of fast, repetitive, long-life operation as opening switches. Optical control of diffuse discharge switches has been proposed as both a means of sustaining and of enhancing the performance of such switches. Processes considered in this dissertation are photo ionization. photo detachment. and several approaches to optically enhanced attachment. Ultraviolet (UV) ionization has been used for several years now as a means of preionizing self-sustained diffuse discharges and, recently, has been used as a sustainment mechanism for diffuse discharge opening switches. Time-resolved measurements of the optical emission of a spark array, similar to those used for preionization or sustainment of diffuse discharges, are presented. Results of experiments in atmospheric pressure diffuse discharges containing admixtures of attachers, sustained and initiated by such a spark array, are also presented. Photo detachment is considered as a mechanism which could decrease switch losses and decrease switch closure time by counteracting dissociative attachment. Experimental results are presented demonstrating optically increased current densities, of as much as 900%, in externally sustained and externally initiated, atmospheric pressure, diffuse discharges containing 0^. This process proceeds through photodetachment of 0 by 590 nm light generated by a dye laser (0 +hu -• 0+e). Optically enhanced attachment through the generation of vibrationally excited attachers appears particularly attractive as a means to decrease turn-off or opening times for diffuse discharge switches. For some molecules attachment cross-sections can be increased by orders of magnitude by vibrational excitation. The influence of this effect on the resistivity of a discharge through IR pumping of NH.;^ and CpH^aF by a low power CO^ laser in continuous low pressure discharges is presented. UV enhanced attachment is also shown in gases containing molecules such as C^HpF^. CpHpClp, and CpH-Cl where UV photo dissociation produced vibrationally excited, strongly attaching, molecules (e.g.. C2H2F2+hu-C2H2+HF(v>1)).Item Optically enhanced attachment processes in diffuse discharges(Texas Tech University, 1987-05) Holmberg, Courtney DoyalDuring the last several years, interest In high voltage switches for pulsed power applications has increased significantly. One main concern in the field of pulsed power Is that of energy storage. While inductive energy storage systems have space and weight savings when compared with capacitive energy storage systems, they also require the use of a high power opening switch. Therefore, opening switch technology has started to be developed, and several concepts for opening switches are currently being studied. One particular concept is that of the diffuse discharge opening switch, which has several advantages over other types of opening switches. A significant advantage of the diffuse discharge opening switch is that it may be externally controlled by optical means or by an electron beam. In this paper, three experiments are presented which study the use of optically enhanced attachment as a discharge control mechanism in diffuse discharges. The first experiment demonstrates the effect of UV enhanced attachment in an externally sustained discharge. The second experiment shows the effect of IR illumination in a self sustained discharge. The last experiment demonstrates the effect of IR enhanced attachment in an externally sustained discharge. Future experiments in optically enhanced attachment are also discussed.Item Optimization of the discharge characteristics of an electron beam sustained discharge for opening switch applications(Texas Tech University, 1986-12) Korzekwa, Richard A.For an opening switch an attaching gas must be used to obtain a fast opening time in a diffuse discharge. In the process of optimizing gas mixtures in an electron beam sustained discharge, three different types of gas mixtures are presented. The first type of gas mixture utilizes one attaching gas, C2F6, Ternary gas mixtures, utilize two attaching gases, C2F6 and CF4, and are used in the optimization process for repetitive switching in an inductive energy storage system. The last type of gas mixture contains argon as a buffer gas with the Penning admixture C2H2, which increases the ionization efficiency of the gas mixture. Recommendations are made for a repetitive switch for inductive energy storage, a closing switch, and an opening switch.Item Optimization of the source function in an electron-beam sustained discharge containing attaching gases(Texas Tech University, 1986-08) Reinking, Gregory FranklinIn pulsed power work, large amounts of stored energy are frequently required. This energy may be stored more efficiently with respect to volume and weight with inductive storage rather than capacitive storage. In order to effectively transfer inductively stored energy to a load, a fast opening switch is necessary. Of the many opening switch methods under study, the externally sustained diffuse discharge switch has several advantages. In electron-beam sustained discharges, electrons are generated by the high energy beam electrons and depleted through recombination and attachment. The use of attachers is necessary to achieve fast opening times. This project considers the two processes, electron generation and depletion, which affect the conductivity of gas discharge switches. The optimization of electron generation is experimentally investigated through the introduction of a low ionization (Penning) additive to the switching gas mixture. The process of electron depletion is investigated theoretically with Monte Carlo Code calculations. These calculations concentrate on the thermalization process of the Initial fast electrons and the interaction of the thermalizing electrons with the attachers used in the gas discharge. The presented results provide information that is required to select suitable gas mixtures to optimize the efficiency of diffuse discharge switches.