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Presents information on a study which evaluated the penetration and equilibrium of the velocity distribution function of an initially monoenergetic electron beam. Calculation of the production of bulk electrons and excited atomic states in the plasma; Velocity distribution of nonthermal electrons during penetration of a Maxwellian plasma; Numerical solution of the Fokker-Plancl equation.

Examines the lock-on effect in pulsed-power semiconductor switches. Outcome of the lock-on effect; Characteristics of the effect; Requirement of a certain minimum bias field for triggering lock-on.

The population of the n=2 level of atomic hydrogen and the collisional relaxation rates of the n=3 and n=4 levels during the conductive phase in the positive column of a high-current ( J∼100–400 A/cm2) pulse in a hydrogen thyratron were measured. These results demonstrate laser-induced fluorescence to be a useful in situ diagnostic for high-current switch plasmas. [ABSTRACT FROM AUTHOR]

This letter analyzes the transport of an electron beam that is produced during the conductive phase operation in the cathode fall of a pseudospark or back lighted thyratron for applications that require a high brightness electron source. The beam is estimated to traverse the device without thermalization if the plasma density is ≤2.5×1015 cm-3. High brightness electron sources are necessary for various new plasma based devices, and these results encourage consideration of this electron beam as a new candidate for applications including microwave generation sources, electron sources for accelerators, and plasma based accelerators which require improved cathodes. [ABSTRACT FROM AUTHOR]

Deals with a study of the photoluminescence spectra of gallium arsenide (GaAs)/AlGaAs multiple-quantum well structures with varying thicknesses as a function of excitation intensity and polarization. Luminescence spectra of four different multi-quantum wells with different layer thickness; Experimental details; Results and discussion.

Excited by 5 ns, 8 kV voltage pulses, a 260 μm-diameter, 8mm long helium plasma jet was generated with a single-electrode configuration in ambient air. Application of fast high voltage pulses (⩾1012 V s-1) resulted in rapid acceleration of the microplasma plumes; within 5 ns the plume velocity reached 8×105 m/s, almost three times higher than that of the plasma jet generated with the pulsed voltage of the same amplitude but with a lower increase rate (1011 V s-1). Importantly, the ultrashort electric pulses were able to efficiently deposit energy in the plasma during the initiation process, which may be responsible for the rapid acceleration of the ionization wavefronts during the streamer onset, as well as efficient production of reactive plasma species including O(5P) and N+2 (B2Σ+u) via electron-induced processes. Emission spectral comparison between the plasma jets excited with 5 ns voltage pulses and with 140 ns voltage pulses showed enhanced O(5P) and N+2 (B2Σ+u emission by the shorter pulses than the longer ones, while the vibrational and rotational temperature for both plasma jets are at 3000K and 300 K, respectively. [ABSTRACT FROM AUTHOR]

Transient plasma generated by high-voltage nanosecond pulses in a pulsed corona configuration has proven to be an efficient medium for e.g., air purification applications. In this article, we present a study on boosting the energy efficiency of such a system by using a special type of plasma reactor: the multiple-wire plasma reactor. The basic principle of such a reactor is that it has a lower transmission-line impedance than a normal wire-cylinder reactor while at the same time still producing the required high electric fields necessary for plasma generation. The lower impedance of the reactor results in a smaller impedance mismatch between the high-voltage pulse source and the reactor, thereby minimizing pulse reflections on the source-reactor interface, increasing the energy efficiency of the system. We calculate the impedance of the multiple-wire reactor and assess both the electrical energy efficiency as well as the chemical efficiency of the plasma by measuring electrical energies and ozone concentrations generated by the plasma when energized by a fast solid-state nanosecond pulse source (with 7-ns rise time pulses of up to 20kV) for a range of multiple-wire plasma reactor parameters. We show that with the multiple-wire reactor we can almost double the energy efficiency of the reactor (from 45% to 85%), reduce the voltage stress in the system by 29%–31% and increase the system efficiency by 95%–98% when using a multiple-wire electrode geometry (as compared to a single-wire system). [ABSTRACT FROM AUTHOR]

This work presents a simple method for calculating the conductivity, electron temperature, and electric field in a high-current hydrogen thyratron positive column as functions of the current density and electron density. The method is based on an analysis that takes into account the partially ionized nature of the plasma, and includes the effects of electron-electron and electron-ion collisions. Data are presented for a typical thyratron discharge (hydrogen pressure 0.4 Torr, current density 50–250 A/cm2, electron density 2–8×1014 cm-3). The electron temperature is found to be close to 1 eV, while the electric field ranges between 5 and 15 V/cm. [ABSTRACT FROM AUTHOR]

Extremely high cold cathode emission and a plasma current density that is much higher than commercial glow discharge hot cathode switches have been obtained in a flash-triggered hollow cathode thyratron-type switch that operates in a glow mode. The cold cathode emission is higher by several orders of magnitude than emission from thermionic cathodes in high-power hydrogen thyratrons, without arc formation. Peak current >17 kA, dI/dt>3×1011 A/s, and power gain >1400 are observed. The switch has been successfully operated as a thyratron substitute in a commercial XeCl excimer laser. The work demonstrates a new approach to thyratron-type switches, and a wide range of technologically useful physical processes that are poorly understood. [ABSTRACT FROM AUTHOR]

Experimental measurements in the positive column of wall-confined high-current hydrogen thyratron discharges show a pronounced increase in atomic hydrogen excited state populations after the end of the current pulse. The decay rate of the electron and excited state population is observed to decrease as the energy flux increases. A time-dependent collisional-radiative model is used to calculate electron and excited state densities. This model is in reasonable agreement with experimental measurements and explains the afterpulse behavior. The analysis shows that the coupling between electron and atom temperatures is an important mechanism in high-power thyratron recovery. A new method using laser-induced fluorescence to obtain time-resolved Stark broadening data for electron density measurements is presented. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the triggered breakdown in low-pressure hollow cathode discharges. Influence of the discharge conditions, geometry and trigger conditions on the time to breakdown in helium; Relation between the time to breakdown and the geometrical distribution of injected charge; Importance of the various parameters which can influence the time to breakdwon in pseudospark discharges.

Examines the switching characteristics of silicon and GaAs-based devices operating in the low- and high-field regimes. Characteristics of an ideal power switch; Applications of high-power switches; Steady-state analysis of silicon- and GaAs-based majority carrier devices; Advantage of photoconductive switches over optothyristors.

Presents information on a study which analyzed the anomalously large cathode emission observed in the superdense glow of pseudospark and back-lighted thyratrons. Description of the discharge geometry used in the experiments; Results for both electron temperature and density; Discussion on cathode emission and current balance.

In this work two-photon absorption laser-induced fluorescence was used to measure oxygen atom (O) concentrations in streamer discharge afterglow in a variety of fuel/air mixtures in order to account for the O reaction pathways in transient plasma ignition. It is demonstrated that O atoms are generated in high concentration (~5 x 1017 cm-3) directly below the high-voltage anode in a point-to-plane geometry. The corresponding lifetimes in air were on the order of hundreds of microseconds. Fuel chemistry provides consumption pathways via chain branching reactions even without sustained combustion, and the corresponding O-atom lifetimes were much shorter than in air and dependent on the fuel concentration. At the richest conditions, corresponding to a fuel--air equivalence ratio of 2.4, O lifetimes were on the order a few microseconds or less. These experimental results are compared to modelling estimates in order to better understand the role of atomic oxygen in the chemical processes leading to ignition. [ABSTRACT FROM AUTHOR]

Achieving effective ignition of reacting mixtures using nanosecond pulsed discharge non-equilibrium transient plasma (TP), requires that the effects of several experimental parameters be quantified and understood. Among them are the electrode geometry, the discharge location especially in non-premixed systems, and the relative ignition performance by spark and TP under the same experimental conditions. In the present investigation, such issues were addressed experimentally using a cylindrical constant volume combustion chamber and a counterflow flame configuration coupled with optical shadowgraph that enables observation of how and where the ignition process starts. Results were obtained under atmospheric pressure and showed that the electrode geometry has a notable influence on ignition, with the needle-to-semicircle exhibiting the best ignition performance. Furthermore, it was determined that under non-premixed conditions discharging TP in the reactants mixing layer was most effective in achieving ignition. It was also determined that in the cases considered, the TP induced ignition initiates from the needle head where the electric field and electron densities are the highest. In the case of a spark, however, ignition was found to initiate always from the hot region between the two electrodes. Comparison of spark and TP discharges in only air (i.e. without fuel) and ignition phenomena induced by them also suggest that in the case of TP ignition is at least partly non-thermal and instead driven by the production of active species. Finally, it was determined that single pulsed TP discharges are sufficient to ignite both premixed and non-premixed flames of a variety of fuels ranging from hydrogen to heavy fuels including F-76 diesel and IFO380 bunker fuel even at room temperature. [ABSTRACT FROM AUTHOR]

The radiation produced when a relativistically moving plasma/gas boundary (i.e., an ionization front) passes between alternatively biased capacitor electrodes is studied. Results of an experiment based on a design which incorporates the capacitor electrodes into an X band waveguide are presented. The waveguided design effectively couples nearly three orders of magnitude more power into the output than the previously unguided designs. Linear theory is extended to include the depletion of the laser energy as it propagates through the ionizable gas (i.e., laser depletion), and the effect of finite output pulse duration. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This letter presents evidence for large-area (≊1 cm2) cathode superemission (∼10 000 A/cm2) into a high-current glow discharge in a pseudospark or back lighted thyratron switch. Cathodes studied with a scannning electron microscope following operation at 6–8 kA, ≊1 μs pulse length, and 105 pulses in a low-pressure H2 discharge show evidence of melting of a thin surface layer within a radius of ∼4 mm, indicating that the discharge is a superdense glow with a cross-sectional area of the order of 1 cm2, rather than an arc. Further supporting evidence is provided by streak camera data. An ion beam present during the avalanche phase of the discharge is responsible for heating the cathode surface resulting in a significant field-enhanced thermionic emission. [ABSTRACT FROM AUTHOR]

The use of nonequilibrium plasma generated by nanosecond discharges to ignite fuel/air mixtures, known as transient plasma ignition (TPI), has been shown to effectively reduce ignition delay and improve engine performance relative to spark ignition for combustion engines. While this method is potentially useful for many engine applications, at present the underlying physics are poorly understood. This work uses coherent anti-Stokes Raman spectroscopy (CARS) to measure the rotational and vibrational excitation of nitrogen molecules in the discharge afterglow in a variety of fuel/air mixtures outside the limits of combustion in order to elucidate the thermal behaviour of TPI. The time evolution of relative populations of vibrationally excited states of nitrogen in the electronic ground state are reported for each gas mixture; it is shown that generation of these vibrationally excited states is inefficient during the discharge in air but that generation occurs at a high rate roughly 5 µs following the discharge; with the addition of fuels vibrationally excited states are observed during the discharge but an increase in population is still seen at 5 µs. Possible mechanisms for this behaviour are discussed. In addition, rotational temperature increases of at least 500 K are reported for all gas mixtures. The effect of this temperature increase on ignition, reaction rates, and thermal energy pathways are discussed. [ABSTRACT FROM AUTHOR]

To add to the understanding of the properties of functionalized carbon nanotubes in biological applications, we report a monotonic pH sensitivity of the intracellular fluorescence emission of single-walled carbon nanotube-fluorescein carbazide (SWCNT-FC) conjugates in human ovarian cancer cells. Light-stimulated intracellular hydrolysis of the amide linkage and localized intracellular pH changes are proposed as mechanisms. SWCNT-FC conjugates may serve as intracellular pH sensors. [ABSTRACT FROM AUTHOR]