Showing papers in "IEEE Transactions on Plasma Science in 2008"

Cold Atmospheric Plasma: Charged Species and Their Interactions With Cells and Tissues

Abstract: Cold atmospheric plasma (CAP) treatment of living tissues becomes a popular topic in modern plasma physics and in medical sciences. The plasma is capable of bacterial inactivation and noninflammatory tissue modification, which makes it an attractive tool for wound healing and the treatment of skin diseases and dental caries. There are still many open issues with regard to the mechanisms of action of the plasma on bacteria and mammalian cells and tissues, both from the biological and the physical perspective. For example, the chemistry of CAP and the exact roles of various plasma constituents in tissue treatment are not yet fully resolved. In this paper, we shall concentrate on the charged species (electrons and ions) in the plasma. The selected physical properties of typical atmospheric plasma sources will be discussed; experiments will be confronted with theoretical considerations, and several biomedical aspects of CAP treatment will be surveyed.

The Effect of Intense Subnanosecond Electrical Pulses on Biological Cells

Abstract: Nanosecond electrical pulses have been successfully used to treat melanoma tumors by using needle arrays as pulse delivery systems. Reducing the pulse duration of intense electric field pulses from nanoseconds into the subnanosecond range will allow us to use wideband antennas to deliver the electromagnetic fields into tissue with a spatial resolution in the centimeter range. To explore the biological effect of intense subnanosecond pulses, we have developed a generator that provides voltage pulses of 160 kV amplitude, 200 ps rise time, and 800 ps pulse width. The pulses are delivered to a cylindrical Teflon chamber with polished flat electrodes at either end. The distance between the electrodes is variable and allows us to generate electric fields of up to 1 MV/cm in cell suspensions. The pulses have been applied to B16 (murine melanoma) cells, and the plasma membrane integrity was studied by means of trypan blue exclusion. For pulse amplitudes of 550 kV/cm, approximately 50% of the cells took up trypan blue right after pulsing, whereas only 20% were taking it up after 1 h. This indicates that the plasma membrane in a majority of the cells affected by the pulses recovers with a time constant of about 1 h. The cells that show trypan blue uptake after this time suffer cell death through apoptosis. Evaluation of the experimental results and molecular dynamics modeling results indicate that with a pulse duration of 800 ps, membrane charging and nanopore formation are the dominant bioelectric effects on B16 cells. This information has been used in a continuum model to estimate the increase in membrane permeability and, consequently, the increase in pore size caused by repetitive pulsing.

Nanosecond-Pulsed Uniform Dielectric-Barrier Discharge

Abstract: The authors report a new nanosecond-pulsed dielectric-barrier discharge (DBD) for sterilization and other medical applications. In the literature, several discharges have been reported, with pulse durations on the order of hundreds of nanoseconds. In this paper, a novel pulsed DBD has been developed, with only few tens of nanosecond pulsewidths working uniformly over large range of electrode gap distance in air under atmospheric pressure.

Active Gate Control for Current Balancing of Parallel-Connected IGBT Modules in Solid-State Modulators

Abstract: In modern pulsed power systems, often, fast solid-state switches like MOSFETs and insulated gate bipolar transistor (IGBT) modules are used to generate short high power pulses. In order to increase the pulsed power, solid-state switches have to be connected in series or in parallel. Depending on the interconnection of the switches, parameter variations in the switches and in the system can lead to an unbalanced voltage or current. Therefore, the switches are generally derated, which results in an increased number of required devices, cost, and volume. With an active gate control, derating and preselection of the switching devices can be avoided. In this paper, an active gate control of paralleled IGBT modules, which has been developed for converters with inductive load, is explained in detail and adapted to a solid-state modulator. This paper focuses on achieving a low-inductance IGBT current measurement, the control unit implementation with a field-programmable gate array and a digital signal processor, as well as the balancing of the pulse currents.

Underwater Electrical Wire Explosion and Its Applications

Abstract: Results of an investigation of underwater electrical wire explosions using high-power microsecond and nanosecond generators are reported. Different diagnostics, including electrical, optical, and spectroscopic, together with hydrodynamic and magnetohydrodynamic simulations, were used to characterize parameters of the discharge channel and generated strong shock waves. It was shown that the increase in the rate of the energy input into exploding wire allows one to increase wire temperature and amplitude of shock waves. Estimated energy deposition into Cu and Al wire material of up to 200 eV/atom was achieved. The spectroscopic analysis of the emitted radiation has unveiled no evidence for the formation of a shunting plasma channel. Analysis of the generated shock waves shows that ~15% of the deposited energy is transferred into the mechanical energy of the water flow. Also, it was shown that converging shock waves formed by underwater explosion of cylindrical wire arrays can be used to achieve extremely high pressure at the axis of implosion. A pressure up to 0.25 Mbar at 0.1 mm distance from the axis of the implosion at a stored energy of ~4 kj was demonstrated. A model explaining the nature of similarity parameters, which have been phenomenologically introduced in earlier research, was suggested.

Space Applications of High-Power Microwaves

Abstract: Schemes have been suggested for transferring energy from Earth-to-space, space-to-Earth, and space-to-space using high-power microwave (HPM) beams. All use power beaming. Microwave beams have been studied for propelling spacecraft for launch to orbit, orbit raising, launch from orbit into interplanetary and interstellar space, and deployment of large space structures. The microwave thermal rocket, called the ldquomicrowave thermal thruster,rdquo is a reusable single-stage vehicle that uses an HPM beam to provide power to a heat-exchanger propulsion system, with double the specific impulse of conventional rockets. Orbital missions include orbit raising and space solar power. Microwave-propelled sails are a new class of spacecraft that promises to revolutionize future space probes. Experiments and simulations have verified that sails riding beams can be stable on the beam for conical sail shapes. Beam-driven sail flights have now demonstrated the basic features of the beam-driven propulsion. Beams can also carry angular momentum and communicate it to a sail to help control it in flight. An early mission for microwave space propulsion is dramatically shortening the time needed for sails to escape Earth's orbit. A number of missions for beam-driven sails have been quantified for high-velocity mapping of the outer solar system, Kuiper Belt, the Heliopause, and the penultimate interstellar precursor mission. For large HPM systems at fixed effective isotropic radiated power, minimum capital cost is achieved when the cost is equally divided between antenna gain and radiated power. This is a driver when considering design of power-beaming systems such as interstellar Beacons, which the Search for Extraterrestrial Intelligence is searching for. Much of the technical means for these applications are already in hand. Microwave and millimeter-wave array antennas are already in use for astronomy; sources at high frequencies are being developed for fusion and the military. Development of high-power arrays is needed. A synergistic way to develop a space power-beaming infrastructure is incremental buildup, addressing lower power applications first, and then upgrading.

SPIS Open-Source Code: Methods, Capabilities, Achievements, and Prospects

Abstract: In this paper, recent improvements in the modeling capabilities of the Spacecraft Plasma Interaction Software (SPIS) code are presented. New developments still in progress are also reported. They should in particular allow modeling of fast dynamical phenomena, including processes as challenging as the second part of ESDs, i.e., the vacuum arc and its related flashover plasma expansion. The first, electronic, part of ESDs is already modeled. The range of SPIS application domains and studies is reviewed. An interesting study case, the assessment of charging at multiple-scale levels, is presented here in more detail. Charging in geostationary-Earth-orbit conditions is simulated from the spacecraft scale down to a solar-cell-gap (hence, decameters to millimeter) scale. This self-consistent computation shows that macroscopic inverted-voltage-gradient (IVG) cases may differ at microscopic scales close to a solar-cell gap, due to the local blocking of secondary emission by the small-scale electric-field configuration. We consider this effect as the likely origin of the different ESD triggering thresholds, depending whether IVG is obtained by electrons or plasma.

Numerical Model of an Argon Atmospheric Pressure RF Discharge

Abstract: Radio-frequency discharges are known to operate in two different regimes. The alpha regime of low current density and the gamma regime with higher current density. Our recent simulation results suggest that the formation of filaments observed in an atmospheric pressure argon discharge under RF excitation could be triggered by the regime transition alphararrgamma. A unidimensional fluid model taking into account the external circuit shows that above 120 mA/cm2 , the differential conductivity of the discharge becomes negative with a rapid increase in density which can lead to the formation of filaments. As the transition to the gamma regime is due to secondary electrons, this threshold value depends on the secondary emission coefficient. In the gamma regime, the instantaneous cathode is sustained by secondary electron emission, which drastically changes the behavior of the discharge. In this paper, we present a numerical analysis of the transition between the two regimes and discuss how this could result in the filamentary mode observed in argon RF discharges.

Chemical Mechanisms of Bacterial Inactivation Using Dielectric Barrier Discharge Plasma in Atmospheric Air

Abstract: Nonthermal plasma generated by parallel-plate dielectric-barrier discharge with 60-kHz high-voltage power was used to sterilize the bacteria in atmospheric air. Two kinds of typical bacteria, gram-negative E. coli (ATCC8099) and grampositive S. aureus (ATCC6538), were used as test strains. Bacteria cells held by cover-glass were placed on the bottom electrode. By adjusting the applied voltage, gap spacing, and treatment time, the effects of plasma and electric field on bacteria inactivation were investigated. The transmission electron microscope was used to observe the damage of cells treated by plasma. The concentrations of K+, protein, and nucleic acid leaked from cells were measured for detecting the cytoplasm status after plasma treatment. Experimental results showed that almost 100% of S. aureus and E. coli strains were killed in less than 10- and 7-s plasma treatment, respectively. It is concluded that the reactive oxygen species (ROS) in plasma play a dominant role in the inactivation process but not the electric field. It is supposed that the ROS can oxidize the cell membrane and then damage the protein and nucleic acid inside the cells and, thus, kill the bacteria.

The Plasma Pencil: A Source of Hypersonic Cold Plasma Bullets for Biomedical Applications

Abstract: Cold plasma jets and their interaction with materials and media have recently been very active research topics. The low gas temperature enables applications in various fields, including medicine. In bioapplications, for example, it involves radiation and reactive species created by the plasma jet to modify or kill prokaryotic cells (bacteria) or eukaryotic cells (mammalian cells). In this paper, we present photographs of a pulsed cold plasma plume/jet that turned out to be a series of high-velocity plasma ldquobulletsrdquo or ldquopackets.rdquo These bullets travel at hypersonic speeds, and these transport with them chemically reactive species and deliver them to the surface of samples under treatment.

Review of Cold Cathode Research at the Air Force Research Laboratory

Abstract: Over the last decade, the Air Force Research Laboratory, Directed Energy Directorate (AFRL/DE) has engaged in a high current density field emission cathode research program. This program explored the aspects of cathode materials as well as the details of cathode geometries and emission physics. This paper summarizes the results of this ongoing research effort to date. We review the history and motivation for the program, which provide insight into the physics issues of concern for various vacuum electronic sources. One important aspect of the program consists of the investigation of new cathode materials. For many high power microwave (HPM) sources, neutral out-gassing, which ties critically with cathode materials, plays a key role in the effective operation of the source. These material properties influence plasma formation, which in turn dictates the operation of an HPM device. For a cathode material, AFRL chose to focus on cesium-iodide-coated carbon fiber cathodes, which we discuss in detail here. A second important aspect of the program consists of understanding emission physics and the optimum geometries for a cathode. This aspect couples closely with electron beam quality, which in turns effects the electron beam interaction with microwaves in the HPM structure. This paper concludes with a discussion of the implementation of the cathode material on both a Magnetically Insulated transmission Line Oscillator and a relativistic magnetron.

${\tt ALaDyn}$ : A High-Accuracy PIC Code for the Maxwell–Vlasov Equations

Abstract: In this paper, we present acceleration by laser and dynamics of charged particles (ALaDyn), a particle-in-cell code, to investigate the interaction of a laser pulse with a preformed plasma and/or an externally injected beam. The code, fully parallelized, works in 1D, 2D, and 3D Cartesian geometry, and it is based on compact high-order finite-difference schemes ensuring higher spectral accuracy. We discuss the features, the performances, and the validation tests of the code. We finally present a preliminary application on a physically relevant case based on the PLASMON-X experiment of the CNR-INFN.

A Theoretical Analysis of Vacuum Arc Thruster and Vacuum Arc Ion Thruster Performance

Abstract: Thrusters that exploit vacuum arc discharges to produce high-velocity plasma jets directly or as sources of plasma that is subsequently accelerated electrostatically have been proposed or are currently under development. Vacuum arc discharges exhibit certain regularities in their behavior that allow the performance of these thrusters to be described by simple semiempirical models. Empirical data on the current density distribution, charge state and velocity of ions created in vacuum arc discharges, and the total cathode mass loss rate are used to develop expressions for the expected thrust and specific impulse as a function of thruster geometry. Thruster electrical efficiency and thrust-to-power ratio are calculated based on measurements of the burning voltage for given thruster operating parameters. Estimates of achievable thruster performance for a wide range of cathode materials are presented. This analysis suggests that thrusters using vacuum arc sources can be operated efficiently with a range of propellant options that gives great flexibility in specific impulse. In addition, the efficiency of plasma production in these devices appears to be largely independent of scale because the metal vapor is ionized within tens of micrometers of the cathode electron emission sites, so this approach is well suited for micropropulsion.

Development of Multi-Utility Spacecraft Charging Analysis Tool (MUSCAT)

Abstract: A new numerical software package to analyze spacecraft charging, named ldquomulti-utility spacecraft charging analysis toolrdquo (MUSCAT), has been developed. MUSCAT consists of an integrated graphical user interface tool called ldquoVineyardrdquo and the solver. Vineyard enables satellite engineers to compute spacecraft charging with little knowledge of the numerical calculations. Functions include 3-D satellite modeling, parameter input such as material and orbit environment, data transfer, and visualization of numerical results. Fundamental physical processes of charged-particle-surface interaction are included in the solver. These functions enable MUSCAT to analyze spacecraft charging at geostationary orbit, low Earth orbit, and polar Earth orbit (PEO). The numerical solver code is parallelized for high-speed computation, and the algorithm is optimized to achieve analysis of large-scale PEO satellite in the design phase. Variable time steps are also used to calculate the rapid change of the spacecraft body potential and the gradual change of the differential voltage in a single simulation with a practical number of iterations. In this paper, the functionality, algorithms, and simulation examples of MUSCAT are presented.

Neutral Depletion in a Collisionless Plasma

Abstract: Neutral depletion can significantly affect the steady state of low-temperature plasmas. Recent theoretical analyses predicted unexpected effects of neutral depletion in both collisional and collisionless regimes. In this paper, we address the effects of neutral depletion on the steady state of a collisionless plasma generated in a collisionless neutral gas. The neutrals and the plasma are coupled only through volume ionization and wall recombination. For a closed system with zero mass flow, the density profiles of both plasma and neutrals are found, and values for the rate of depletion at asymptotic limits are derived. It is shown that the pressure of the collisionless neutral gas is maximal where the density is minimal. This is in contrast to the case in which the neutral gas is thermalized. For an open system of a nonzero mass flow, analytical expressions are derived for the profiles of the plasma and the neutral flows. Considering such a configuration for a plasma thruster, we calculate the expected thrust, propellant utilization, specific impulse, and efficiency. The energy cost for ionization and backwall energy losses are shown to significantly reduce the efficiency.

Numerical Modeling of Electron Beams Accelerated by the Radio Frequency Boundary Sheath

Abstract: The stochastic heating of electrons by the radio frequency boundary sheath in capacitively coupled plasmas is not completely understood or at least agreed upon by researchers. To aid in understanding this phenomena, a conceptually simple simulation of electron heating is presented. A fluid model is used to calculate the electric fields in the discharge, and a Monte Carlo simulation is used to calculate electron distribution functions. The plots of the density of energetic electrons are presented in this paper. They show electron beams that have been accelerated by the sheath.

Decomposition of Dye in Water Solution by Pulsed Power Discharge in a Water Droplet Spray

Abstract: A method for decomposing dye by spraying water solution of dye into nonequilibrium plasma in gas phase was investigated using a pulsed-corona discharge reactor. The corona reactor consists of a discharge wire and a cylindrical electrode. The water solution of indigo carmine with a concentration of 20 mg/L was sprayed into the reactor from a showerhead. The sprayed water solution was circulated into the reactor. The dependence of the discharging power injected into the reactor on the decomposition rates of chromogenic and unsaturated bonds in indigo carmine was investigated. Indigo blue was decolored by 1-min circulation with the discharging power of 8.6 W. The nuclear magnetic resonance spectrometry showed that indigo carmine was decomposed completely by 60-min treatment. The chromogenic and unsaturated bonds were almost decomposed at 9 and 360 J/mg, respectively. As the discharging power increased, the decomposition rates of both bonds in indigo carmine increased. The decomposition rates of the chromogenic bond showed equal values in equal discharging power regardless of the difference of discharge repetition rate and charging voltage of the capacitor. In contrast, the higher repetitive pulses were more effective for the decomposition of the unsaturated bond rather than the magnitude of charging voltage in equal discharging power.

Numerical Modeling and Optimization of Electric Field Distribution in Subcutaneous Tumor Treated With Electrochemotherapy Using Needle Electrodes

Abstract: Electrochemotherapy (ECT) is an effective antitumor treatment employing locally applied high-voltage electric pulses in combination with chemotherapeutic drugs. For successful ECT, the entire tumor volume needs to be subjected to a sufficiently high local electric field, whereas, in order to prevent damage, the electric field within the healthy tissue has to be as low as possible. To determine the optimum electrical parameters and electrode configuration for the ECT of a subcutaneous tumor, we combined a 3-D finite element numerical tumor model with a genetic optimization algorithm. We calculated and compared the local electric field distributions obtained with different geometrical and electrical parameters and different needle electrode geometries that have been used in research and clinics in past years. Based on this, we established which model parameters had to be taken into account for the optimization of the local electric field distribution and included them in the optimization algorithm. Our results showed that parallel array electrodes are the most suitable for the spherical tumor geometry, because the whole tumor volume is subjected to sufficiently high electric field while requiring the least electric current and causing the least tissue damage. Our algorithm could be a useful tool in the treatment planning of clinical ECT as well as in other electric field mediated therapies, such as gene electrotransfer, transdermal drug delivery, and irreversible tissues ablation.

DBD Plasma Jet in Atmospheric Pressure Argon

Abstract: Nonthermal plasma jet was generated by dielectric barrier discharge (DBD) with a 34-kHz sinusoidal power supply in argon. The power consumption ranged from several to tens of watts. The flow rate of argon, which was detected by an anemometer, greatly affected the discharge images. The gas flow temperature of the DBD plasma was measured with a thermocouple, and it was shown that, when the flow rate of argon was relatively high, its temperature was similar to room temperature and the plasma jet indicated the glow discharge characteristics. The low-temperature plasma jet is suitable for medical sterilization and surface modification of materials with irregular shapes.

The Biomedical Applications of Plasma: A Brief History of the Development of a New Field of Research

Abstract: This paper is an essay narrating the recent history of the introduction of the biomedical applications of nonthermal plasmas to the plasma science research community.

Ion Mobility Spectrometry: Ion Source Development and Applications in Physical and Biological Sciences

Abstract: The utility of ion mobility spectrometry (IMS) has been steadily growing, and it cuts across diverse areas in physical and biological sciences. The development of ion sources, particularly in the context of IMS, is described. IMS ion sources operate efficiently in ambient environment and yield ions for a wide range of complex molecules including biological materials. While significant progress has been made in this area through the development of a variety of ion sources, further research to address several key issues, namely, ionization processes, reaction chemistry, and overall system miniaturization for field deployment of IMS, is the primary focus of current activities. Aside from reviewing the present state of the art of ion sources for IMS, this paper has discussed the wide range of applications and current trends of research in the field.

Gas Cluster Ion Beam Equipment and Applications for Surface Processing

Abstract: A gas cluster is an aggregate of a few to several thousands of gaseous atoms or molecules, and it can be accelerated to the desired energy after ionization. Since the kinetic energy of an atom in a cluster is equal to the total energy divided by the cluster size, a quite-low-energy ion beam can be realized. Although it is difficult to obtain low-energy monomer ion beams due to the space charge effect, equivalently low-energy ion beams can be realized by using cluster ion beams at relatively high acceleration voltages. The low-energy feature and the dense energy deposition at a local area are important characteristics of the irradiation by gas cluster ions. The diameter of a gas cluster with a cluster size of several thousands is only a few nanometers, so that thousands of atoms or molecules penetrate the target in an area that is only a few nanometers in diameter, which causes multiple collisions between target and cluster atoms. Therefore, all of the impinging energy of a gas cluster ion is deposited at the surface region, and this dense energy deposition is the origin of enhanced sputtering yields, crater formation, shock-wave generation, and other nonlinear effects. It is almost 20 years since the gas cluster ion beam (GCIB) equipment was first built in our laboratory. Since then, various kinds of GCIB equipment were constructed, and, currently, a GCIB system for 300-mm-diameter Si wafers is available. GCIB machines are being used for industrial applications, where a surface process is required. Surface smoothing, shallow doping, low-damage etching, trimming, and thin-film formations are promising applications of GCIBs. In this paper, the formation of the GCIB and the configuration of the GCIB equipment are summarized. Then, fundamental irradiation effects of the GCIB are discussed from the viewpoint of low-energy irradiation, sputtering, and dense energy deposition. Last, various applications of the GCIB are explained.

Permanent Magnet Helicon Source for Ion Propulsion

Abstract: Helicon sources have been proposed by at least two groups for generating ions for space propulsion: the Helicon Double Layer Thruster (HDLT) concept at the Australian National University and the Variable Specific Impulse Magnetohydrodynamic Rocket (VASIMR) concept at the Johnson Space Center in Houston. These sources normally require a large electromagnet and power supply to produce the magnetic field. At this stage of research, emphasis has been on the plasma density and ion current that can be produced, but not much on the weight, size, impulse, and gas efficiency of the thruster. This paper concerns the source itself and shows that great savings in size and weight can be obtained by using specially designed permanent magnets (PMs). This PM helicon design, originally developed for plasma processing of large substrates, is extended here for ion thrusters of both the HDLT and VASIMR types. Measured downstream densities are on the order of 1012 cm-3 , which should yield much higher ion currents than reported so far. The design principles have been checked experimentally, showing that the predictions of the theory and computations are reliable. The details of two new designs are given here to serve as examples to stimulate further research on the use of such sources as thrusters.

Inactivation of Aquatic Microorganisms by Low-Frequency AC Discharges

Abstract: Hybrid gas-liquid electrical discharge has been investigated in recent years as an innovative technology for contaminated water treatment. A high-voltage pulsed-power supply is commonly needed for the generation of electrical discharges. This paper aims, in lieu of cost effectiveness, to evaluate the degradation efficiency of electrical discharges with an alternating-current (ac) power since it is generally cheaper than a pulsed one. An ac power supply with a fixed voltage of 13 kV and a fixed frequency of 60 Hz is therefore adopted in this paper for the inactivation of aquatic microorganism. The energies required for one log order of reduction of E. coli, S. aureus, and Yeast were 23, 34, and 31 J/ml, respectively. The energy efficiencies achieved with an ac power in this paper are comparable with other studies that achieved with a pulsed-power.

Modeling Electrostatic Levitation of Dust Particles on Lunar Surface

Abstract: This paper presents a simulation model on electrostatic levitation of lunar dust particles in the lunar terminator region. Full-particle particle-in-cell simulations are carried out using real ion to electron mass ratio to obtain plasma sheath, surface charging, and the transition point of surface electric field. Test particle simulations are carried out to simulate the levitation of dust particles from lunar surface. Results show that the dust levitation condition in the terminator region is sensitively influenced by the ambient plasma condition and surface charging, and the levitation altitude varies significantly even for small changes of the sun elevation angle.

Stabilization of a Swirled Propane–Air Flame Using a Nanosecond Repetitively Pulsed Plasma

Abstract: Stabilization of lean premixed flames is a very promising way to reduce pollutant emissions in industrial burners such as gas turbines or aircraft engines. By applying an ultrashort repetitively pulsed discharge (6.8 kV, 15-ns duration, 30 kHz), stable flames can be obtained under the equivalence ratio limit without plasma. In this paper, this technique is used to stabilize a confined propane-air flame created by a swirled injector. The discharge is generated using a ring high-voltage electrode placed 5 mm downstream of the exit of the injector.

A New Concept for the Collection of an Electron Beam Configured by an Externally Applied Axial Magnetic Field

Abstract: A new concept for the collection of an electron beam, which is configured by an externally applied axial magnetic field, is presented. The two major advantages of this new idea are the significant increase of the collector efficiency and the reduction of the power absorption on the collector wall. To demonstrate the concept, an indicative collector design has been prepared for the hollow electron beam of the European 170-GHz 2-MW coaxial gyrotron for the international thermonuclear experimental reactor. The simulation shows that the efficiency of this advanced collector is more than 90%.

Pulsed Electrical Discharge in Water Generated Using Porous-Ceramic-Coated Electrodes

Abstract: A special metallic electrode covered by a thin layer of porous ceramic prepared by the technology of thermal plasma spraying has been developed and used for the generation of large-volume nonthermal plasma in water. Images of multichannel pulsed electrical discharge generated in water at the composite electrode as a function of solution conductivity are presented.

Novel Closing Switches Based on Propagation of Fast Ionization Fronts in Semiconductors

Abstract: Power kilovolt electric pulses with subnanosecond rise time can be formed by means of semiconductor switches based on the propagation of ionization fronts in Si structures. We describe a new generation of such devices-which are deep-level dynistors (DLDs). The triggering of the ionization front in the DLDs occurs due to the field-enhanced ionization of deep-level electron traps. The DLDs are able to form high-current pulses with subnanosecond rise time and low residual voltage just after switching. We describe two power generators based on the DLDs as examples. In addition, we discuss the possibility of picosecond switching based on tunneling-assisted impact-ionization fronts.

Time Resolved Measurements of Streamer Inception in Air

Abstract: Images show how an ionization cloud forms at the needle electrode, how the cloud evolves into a shell, and how one or more streamers emerge from this shell and propagate.