Showing papers in "IEEE Transactions on Plasma Science in 2000"

An overview of research using the one atmosphere uniform glow discharge plasma (OAUGDP) for sterilization of surfaces and materials

Abstract: The medical, food processing, and heating, ventilating, and air conditioning industries are searching for improved pasteurization, disinfection, and sterilization technologies. Candidate techniques must deal with and overcome such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, costs, and inefficiency in performance. We report the results of a plasma source, the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP), which operates at atmospheric pressure in air and produces antimicrobial active species at room temperature, OAUGDP exposures have reduced log numbers of Gram negative and Gram positive bacteria, bacterial endospores, yeast, and bacterial viruses on a variety of surfaces. The nature of the surface influenced the degree of lethality, with microorganisms on polypropylene being most sensitive, followed by glass, and cells embedded in agar. Experimental results showed at least a 5 log/sub 10/ CFU reduction in bacteria within a range of 50-90 s of exposure. After 10-25 s of exposure, macromolecular leakage and bacterial fragmentation were observed. Vulnerability of cell membranes to reactive oxygen species (ROC) is hypothesized. Results from several novel OAUGDP configurations are presented, including a remote exposure reactor (RER) which uses transported active species to sterilize material located more than 20 cm from the plasma generation site, and a second planar electrode configuration developed for air filter sterilization. Applications of these technologies to the healthcare industry, the food industry, and decontaminating surfaces compromised by biological warfare agents are discussed.

Generation of large-volume, atmospheric-pressure, nonequilibrium plasmas

Abstract: A review is presented of the issues associated with the generation of large-volume, high-pressure, nonequilibrium plasmas, as well as the approaches that have been developed for generating these plasmas using electrical discharges in gases. The various instabilities that have been overcome to obtained these plasmas as well as the techniques for quenching them are also reviewed. Last, recent efforts to obtain atmospheric pressure plasmas are discussed with particular emphasis on the capillary plasma electrode discharge, which we have used to obtain high (electron) density nonequilibrium plasmas.

Electroporation of cells and tissues

Abstract: Electrical pulses that cause the transmembrane voltage of fluid lipid bilayer membranes to reach at least U/sub m//spl ap/0.2 V, usually 0.5-1 V, are hypothesized to create primary membrane "pores" with a minimum radius of -1 nm. Transport of small ions such as Na/sup +/ and Cl/sup -/ through a dynamic pore population discharges the membrane even while an external pulse tends to increase U/sub m/, leading to dramatic electrical behavior. Molecular transport through primary pores and pores enlarged by secondary processes provides the basis for transporting molecules into and out of biological cells. Cell electroporation in vitro is used mainly for transfection by DNA introduction, but many other interventions are possible, including microbial killing. Ex vivo electroporation provides manipulation of cells that are reintroduced into the body to provide therapy. In vivo electroporation of tissues enhances molecular transport through tissues and into their constitutive cells. Tissue electroporation, by longer, large pulses, is involved in electrocution injury. Tissue electroporation by shorter, smaller pulses is under investigation for biomedical engineering applications of medical therapy aimed at cancer treatment, gene therapy, and transdermal drug delivery. The latter involves a complex barrier containing both high electrical resistance, multilamellar lipid bilayer membranes and a tough, electrically invisible protein matrix.

Probability theory of electron-molecule, ion-molecule, molecule-molecule, and Coulomb collisions for particle modeling of materials processing plasmas and cases

Abstract: The use of high plasma density and low gas density, a recent trend in plasma-assisted materials processing, requires a particle simulation method for plasmas and gas flows. The kinetic theory basis of the particle simulation method is first described. Based on this theoretical viewpoint, state-of-the-art probabilistic treatments of collisions are described for electron-molecule, ion-molecule, molecule-molecule, and Coulomb collisions.

Medical applications of electroporation

Abstract: In vivo electroporation, first reported in 1987, makes it possible to render cell membranes temporarily permeable to substances that otherwise would not be able to effectively enter the cell interior. Micro- or millisecond pulses of electrical field strengths exceeding the natural cellular transmembrane potential difference of approximately I V results in permeabilization ("poration") of cell membranes. This phenomenon opens up numerous applications in the medical field. Electroporative delivery of chemotherapeutic drugs into tumor cells has proven successful in clinical studies to treat malignant tumors and is nearing market Introduction in Europe. For gene therapy applications, delivery of DNA by electroporation into a variety of tissues has been shown to consistently result in a 100-1000-fold enhancement of gene expression. Other applications of electroporation discussed in this paper include intravascular delivery of drugs and genes with electroporation catheters, electroinsertion of molecules into membranes, intraocular delivery of drugs and genes, and transdermal drug delivery. The use of electroporation for drug and gene delivery in vivo is clearly gaining momentum, and new medical applications are emerging at an increasing rate.

A note on the possible electrostatic disruption of bacteria

Abstract: Recently published scanning electron and transmission electron photomicrographs of cells of the bacterium Escherichia coli exposed to plasma glow discharges at atmospheric pressure indicate physical disruption of their outer cell membranes. However, the mechanism of cell disruption was unclear. Here, we propose and model an electrophysical mechanism for this phenomenon, namely, the electrostatic disruption of the cell membrane, which takes place when it has acquired a sufficient electrostatic charge that the outward electrostatic stress exceeds its tensile strength. It also appears that surface roughness or irregularity would render it more sensitive to electrostatic disruption.

Biological decontamination by nonthermal plasmas

Abstract: Nonthermal gaseous discharges have been found to be effective agents for biological decontamination/sterilization. The ability to generate these discharges at atmospheric pressure makes the decontamination process practical and inexpensive. In addition, the fact that the plasmas generated by such discharges are cold makes their use suitable for applications where medium preservation is desired. To fully understand the biophysical and biochemical processes induced by the interaction of living cells with gaseous discharges, a multidisciplinary approach is required. In this paper, we present two studies on bacteria killing obtained by two different discharges: a glow discharge at atmospheric pressure and an enhanced corona discharge at atmospheric pressure.

A review of short pulse generator technology

Abstract: Today's ultrafast, pulse generators are capable of producing high-voltage pulses, (>1 kV), with fast, leading-edge rise times, (<1 ns). A review of generator implementation methods is presented that includes a detailed discussion of the various circuit designs and a list of commercially available high-voltage pulse generators. All of these generators are capable of rise times less than a few ns and voltages greater than several hundred volts. Finally, a brief description of the three primary switch types, reed, spark gap, and solid state is presented.

Thermal and nonthermal mechanisms of interaction of radio-frequency energy with biological systems

Abstract: This paper reviews thermal and nonthermal mechanisms of interaction between radiofrequency (RF) fields and biological systems, focusing on pulsed fields with high peak power but low duty cycle. Models with simplified geometry are used to illustrate the coupling between external electromagnetic fields and the body, and with cellular and subcellular structures. Mechanisms of interaction may be linear or nonlinear with field strength, and thermal or nonthermal. Each mechanism is characterized by a threshold field strength (below which no observable response is produced) and time constant of response. Several classes of nonthermal mechanisms of interaction are well established; however, the anticipated thresholds for producing observable effects are expected to be very high. The bioeffects literature contains many open questions, including many reports of effects that are not clearly interpretable in terms of the mechanisms discussed in this paper.

Geomagnetically induced currents during magnetic storms

Abstract: The electric field which is induced by geomagnetic storms drives currents in technological systems, such as electric power transmission grids, oil and gas pipelines, telecommunication cables, and railway equipment. These geomagnetically induced currents (GIC) cause problems to the systems. In power grids, transformers may be saturated due to GIC resulting in harmful effects and possibly even to a collapse of the whole system, as occurred in Quebec in March 1989. Transformers may also suffer from permanent damage. In buried pipelines, GIC can enhance corrosion and interfere with corrosion control surveys. Telecommunication systems as well as railway equipment may also malfunction due to GIC. The electric and magnetic fields observed at the Earth's surface primarily depend on magnetospheric-ionospheric currents and secondarily on currents induced in the Earth. The physical background and modeling of GIC are discussed in this paper. Special attention is paid to basic principles necessarily understood to get an insight into GIC phenomena. Recent developments in the use of the Complex Image Method (CIM) permit fast and accurate computations of the electric field suitable for time-critical applications like GIC forecasting.

Inactivation of food-borne enteropathogenic bacteria and spoilage fungi using pulsed-light

Abstract: The lethality of high-intensity pulsed-light emissions from low and high ultraviolet (UV) light sources on predetermined microbial populations has been investigated. Prior to treatment, the bacterial enteropathogens Bacillus cereus, Escherichia coli, and Salmonella enteritidis and the food-spoilage fungi Aspergillus niger and Fusarium culmorum were seeded separately onto the surface of either tryptone soya yeast extract or malt extract agar plates. Prescribed microbial population densities were applied to the test media and these samples were exposed to one of two light sources. These were low-pressure, xenon filled, flash lamps that produced either high or low UV intensities. They were operated in pulsed mode, being driven by a stacked Blurnlein table generator. Microbial samples were treated by exposure to different numbers of light pulses. The treated bacterial populations were reduced by /spl sim/8 log orders after 1000 light-pulses of the higher UV intensity light and the fungal counts had a corresponding reduction of 4.5 log orders. The fungus, Aspergillus niger, was shown to be significantly more resistant in spore form to the intense UV light compared with Fusarium culmorum. This resistance has been attributed to the high level of UV absorbance associated with the dark pigment present in A. niger. The pulsed light source of lower UV intensity was shown to be significantly less effective in reducing microbial populations.

Improvement of NO/sub X/ removal efficiency using short-width pulsed power

Abstract: Pulsed power has been used to remove nitric oxide (NO) in a mixture of nitrogen, oxygen, and water vapor simulating the flue gases from a power station stack. The effect of the pulsewidth at a fixed applied voltage on NO removal concentration was studied. The dependence of the energy efficiency of the removal of NO at a fixed applied voltage on the pulsewidth, on the removal ratio of NO and on the discharge current was investigated. This removal energy efficiency increases with decreasing pulsewidth and decreasing removal ratio of NO.

Overmoded GW-class surface-wave microwave oscillator

Abstract: Results of theoretical and experimental studies of a GW-class, large diameter microwave oscillator are presented The device consists of a large cross-section (overmoded), slow-wave structure with a unique profile of wall radius specifically designed to support surface waves and to provide a strong beam-wave coupling at moderate voltage (500 kV), an internal adjustable microwave reflector, a coaxial microwave extraction section, and a coaxial magnetically insulated field emission electron gun In preliminary experiments carried out at 83 GHz, the power level exceeding 05 GW and efficiency of 15% have been measured calorimetrically

Application of field emitter arrays to microwave power amplifiers

Abstract: This paper describes the operation of a field emitter array (FEA) as the electron source of a traveling-wave tube (TWT) amplifier. Issues of beam control and focus at high current density and low magnetic field are addressed as well as issues relating to the inherent high emittance of the FEA beam and cathode protection from ion bombardment. Large signal, nonlinear RF-modulated FEA-TWT interaction simulations show circuit efficiencies that approach 50%, even for minimal bunching of average-to-peak current ratios of 0.7-0.9. Direct radio frequency (RF) modulation at the cathode is predicted to significantly improve linearity in the high-efficiency regime as well as reduce harmonic power levels. An unmodulated C-Band FEA-TWT was built to test the focusing approach as well as the robustness of the emitters in an operating vacuum device. The device uses a 1-mm diameter Spindt emitter with a custom-designed electron gun and helix circuit. The FEA-TWT has operated to date with a maximum current of 91.3 mA and shows 99.5% transmission under both drive and no-drive conditions. Output power of the device is 55.0 W at 1.5 GHz with a saturated gain of 23.4 dB and efficiency of 17%, and performs as predicted by simulation. During all operation, the FEA emission appears extremely stable, with no temporal variations observed at any time.

Spacecraft charging, an update

Abstract: Twenty years after the landmark SCATHA program, spacecraft charging and its associated effects continue to be major issues for Earth-orbiting spacecraft. Since the time of SCATHA, spacecraft charging investigations were focused primarily on surface effects and spacecraft external surface design issues. Today, however, a significant proportion of spacecraft anomalies are believed to be caused by internal charging effects (charging and ESD events internal to the spacecraft Faraday cage envelope). This review will, following a brief summary of the state of the art in surface charging, concentrate on the problems introduced by penetrating electrons ("internal charging") and related processes (buried charge and deep dielectric charging). With the advent of tethered spacecraft and the deployment of the International Space Station, low altitude charging has taken on a new significance as well. These and issues tied to the dense, low altitude plasma environment and the auroral zone will also be briefly reviewed.

Electromanipulation of mammalian cells: fundamentals and application

Abstract: Electroinjection of membrane-impermeable xenomolecules into freely suspended mammalian cells (so-called electroporation) and cell-to-cell electrofusion are powerful tools for manipulation of the genom and the cytosol of cells. Both field pulse techniques are based on the temporary increase of the membrane permeability due to reversible electrical breakdown of the plasma membrane upon application of external high-intensity field pulses of very short duration. Membrane charging and permabilization caused by high-intensity field pulses are preceded and accompanied by transient electrodeformation forces, which lead to an elongation of the cells in low-conductivity media, thus affecting the membrane area of electropermabilization in response to a breakdown pulse. Transient stretching force assumes a maximum value in low-conductivities pulse media. This facilitates incorporation of membrane-impermeable xenomolecules and field-mediated hybridization as well. Therefore, high and reproducible fields of (genetically) manipulated cells can be expected provided that: 1) the duration of the high-intensity field pulses does not exceed shout 100 /spl mu/s and 2) that the (pulse or fusion) media are hypo-osmolar and exhibit a relatively low conductivities. Such media are also beneficial because field-inducted apoptosis does not occur under these conditions (in contrast to highly conductive media). Indeed, electroporation and electrofusion protocols that fulfill these requirements lead: 1) to high incorporation rates of plasmids (DNA) or artificial chromesomes into living cells without deterioration and 2) to the production of hybridoma cells (by fusion of tumor-infiltrating lymphocytes with heteromyeloma cells), which secrete functional human monoclonal antibodies. Human monoclonal antibodies that bind to and induce apoptosis in autologous tumor cells are promising gents for cancer treatment, as shown by first clinical trials.

The occurrence of operational anomalies in spacecraft and their relationship to space weather

Abstract: Modern spacecraft systems and subsystems appear to show an increasing susceptibility to effects of the space environment. This trend is probably due to "softer" designs of electronic components, reduction in subsystem sizes, and increases in performance demands and number of components within spacecraft. The major agents within the space environment that contribute to spacecraft anomalies can be reasonably well described. This paper reviews operational anomaly trends and assesses the identification and potential prediction of causative space weather agents.

A remote exposure reactor (RER) for plasma processing and sterilization by plasma active species at one atmosphere

Abstract: We have developed a remote exposure reactor (RER) in which the active species of air and other gases responsible for sterilization and processing effects are generated on flat panels in a surface layer of one atmosphere uniform glow discharge plasma (OAUGDP). These active species are convected by forced airflow at one atmosphere and near room temperature to a remote exposure chamber in which the workpiece is located. This allows workpieces of any size or shape to be sterilized or processed without direct contact with the plasma. Here, we report operation of the RER as a sterilizer with both single-pass and recirculating active species flow through the remote exposure chamber. We used the RER to reduce the numbers of two genera of microorganisms (Esherichia coli and Staphylococcus aureus) on test samples of polypropylene fabric. When the recirculating airflow configuration was employed, the population both of E. coli and S. aureas cells was reduced by at least five decades after only 25 s of exposure. Tests in the single pass airflow configuration produced similar results, with the E. coli and S. aureas populations decreased by at least four decades after 25 s of exposure.

Ultrahigh-intensity laser-produced plasmas as a compact heavy ion injection source : Laser and plasma accelerators

Abstract: The possibility of using high-intensity laser-produced plasmas as a source of energetic ions for heavy ion accelerators is addressed. Experiments have shown that neon ions greater than 6 MeV can be produced from gas jet plasmas, and well-collimated proton beams greater than 20 MeV have been produced from high-intensity laser solid interactions. The proton beams from the back of thin targets appear to be more collimated and reproducible than are high-energy ions generated in the ablated plasma at the front of the target and may be more suitable for ion injection applications. Lead ions have been produced at energies up to 430 MeV.

Modeling the triggering of streamers in air by ultrashort laser pulses

Abstract: The physical processes involved in the triggering of ionization waves (streamers) by ultrashort laser pulses, focused in air at 350 Torr and in a uniform electric field, are investigated by means of a one-dimensional (1-D) numerical model. The model describes the interaction of the laser pulse with air and takes into account many of the reactions in the laser-created plasma as well as the radial expansion of the plasma. Consequences of the model are that the threshold electric field for the appearance of streamers is an increasing function of the delay between the laser pulse and the electric field pulse and a decreasing function of the laser energy. Also, it appears that the electron temperature, the plasma density and radius, and the conduction of heat across the plasma boundaries play major roles in the capacity of the laser-created plasma to trigger streamers. The results of the model are compared with the available experimental data.

The role of outgassing in surface flashover under vacuum

Abstract: Results of high-speed electrical and optical diagnostics are used as a basis to discuss a new surface flashover model. Outgassing, caused by electron stimulated desorption, is found to play a crucial role in the temporal flashover development. Dielectric unipolar surface flashover under vacuum is experimentally characterized by a three-phase development, which covers a current range from 10/sup -4/ A to 100 A. Phase one comprises a fast (several nanoseconds) buildup of a saturated secondary electron avalanche reaching current levels of 10 to 100 mA. Phase two is associated with a slow current amplification reaching currents in the Ampere level within typically 100 ns. The final phase is characterized by a fast current rise up to the impedance-limited current on the order of 100 A. The development during phase two and three is described by a zero-dimensional model, where electron-induced outgassing leads to a Townsend-like gas discharge above the surface. This is supported by time-resolved spectroscopy that reveals the existence of excited atomic hydrogen and ionic carbon before the final phase. The feedback mechanism toward a self-sustained discharge is due to space charge leading to an enhanced field emission from the cathode. A priori unknown model parameters, such as outgassing rate and gas density buildup above the surface, are determined by fitting calculated results to experimental data. The significance of outgassing is also discussed with a view to microwave surface flashover.

Effect of glow discharge air plasma on grain crops seed

Abstract: Oat and barley seeds have been exposed to both continuous and pulsed glow discharge plasmas in air to investigate the effects on germination and sprout growth. Statistical analysis was used to evaluate the effect of plasma exposure on the percentage generation and length of sprout growth. A stimulating effect of plasma exposure was found together with a strong dependence on whether continuous or pulsed discharges were used.

Ultrahigh-intensity laser-produced plasmas as a compact heavy ion injection source

Abstract: The possibility of using high-intensity laser-produced plasmas as a source of energetic ions for heavy ion accelerators is addressed. Experiments have shown that neon ions greater than 6 MeV can be produced from gas jet plasmas, and well-collimated proton beams greater than 20 MeV have been produced from high intensity laser solid interactions. The proton beams from the back of thin targets appear to be more collimated and reproducible than are high-energy ions generated in the ablated plasma at the front of the target and may be more suitable for ion injection applications. Lead ions have been produced at energies up to 430 MeV.

Ion beam application in genetic modification

Abstract: People pay little attention to the interaction between low-energy ions and matter compared to that of high-energy ions. It is even more unusual to find studies of the interaction of low-energy ions and complicated organisms. The discovery of bioeffects induced by ion implantation has, however, opened a new branch in the field of ion beam applications in the life sciences. This paper reports recent advances in research on the role of low-energy ions in genetic modification.

An adaptive MHD method for global space weather simulations

Abstract: A 3D parallel adaptive mesh refinement (AMR) scheme is described for solving the partial-differential equations governing ideal magnetohydrodynamic (MHD) flows. This new algorithm adopts a cell-centered upwind finite-volume discretization procedure and uses limited solution reconstruction, approximate Riemann solvers, and explicit multi-stage time stepping to solve the MHD equations in divergence form, providing a combination of high solution accuracy and computational robustness across a large range in the plasma /spl beta/ (/spl beta/ is the ratio of thermal and magnetic pressures). The data structure naturally lends itself to domain decomposition, thereby enabling efficient and scalable implementations on massively parallel supercomputers. Numerical results for MHD simulations of magnetospheric plasma flows are described to demonstrate the validity and capabilities of the approach for space weather applications.

A comparison of pulsed and continuous ultraviolet light sources for the decontamination of surfaces

Abstract: The experimental results on the development of a decontamination process that uses ultraviolet light and chemical photosensitizer for disinfecting surfaces and solutions are reported. Reduction in the microbial viability as a function of applied UV fluence is presented for the inactivation of Bacillus subtilis spores. Results obtained with aqueous solutions and with surfaces indicate that pulsed UV light is more effective than continuous UV light. Nearly three orders of magnitude of enhanced inactivation have been achieved with the photosensitized UV process on surfaces.

Air filter sterilization using a one atmosphere uniform glow discharge plasma (the volfilter)

Abstract: Two characteristics of microorganisms-extremely small size (0.01 to a few micrometers) and the ability to reproduce-hinder the effective filtration of bacteria and viruses from indoor air. The microorganisms captured by a filter in spite of their small size can reproduce in situ and be released into the airstream, giving rise to the "sick building syndrome". The application of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) to a filter can address both these issues. At University of Tennessee at Knoxville, we have recently developed the "Volfilter", a planar version of the OAUGDP produced by attaching strip electrodes to both sides of a sheet of dielectric filter material and energizing the electrodes with a high-voltage, low-frequency RF source. After the filter material removes microorganisms from the airstream, the OAUGD plasma kills the captured microorganisms. The combination of an appropriate filter material and periodic application of the OAUGDP results in an effective capture and sterilization device even for the smallest microorganisms and requires minimum maintenance. This paper will describe results obtained during the operation of a laboratory-scale "Volfilter" challenged by two kinds of microorganisms, S. aureus and the bacterial virus Phi X 174. An objective of this work is to demonstrate that a "Volfilter" exposed to a OAUGDP will have the number of captured microorganisms on its surface reduced by a factor of one million.

Visualization and characterization of high-current diffuse vacuum arcs on axial magnetic field contacts

Abstract: We have investigated the behavior of drawn vacuum arcs for several designs of axial magnetic field (AMF) contacts using high-speed digital photography and arc voltage measurements, As the peak current was increased, a gradual transition occurred in the arc appearance from a multiple cathode-spot arc to the high-current diffuse mode, and then to a high-current diffuse columnar mode. Two relatively simple models based on the literature are used to explain the results. The first is an empirical criterion for using the arc voltage behavior to determine the maximum arc current for which an AMF geometry can produce a high-current diffuse mode from the initial bridge column arc. The second model predicts the highest arc current that can be forced into a fully diffuse mode for given values of the AMF and the contact arcing radius. The predictions of these models are compared to our experimental and analytical results.

Space-charge effects on multipactor on a dielectric

Abstract: Analyzes the effects of space charge shielding on the steady state of a multipactor discharge on a dielectric. Analytic methods are used to obtain an exact function for the potential in the discharge, assuming a Maxwellian distribution of emitted electrons. An equation for the amount of power deposited on the dielectric by the multipactoring electrons, for a given saturation level, is given. A simple method for obtaining the saturation level, for a given material, is obtained.

Pulsewidth limitation in the relativistic backward wave oscillator

Abstract: Spontaneous pulse shortening occurring in a relativistic backward wave oscillator (BWO) at gigawatt power levels is studied in experiment and theory. It is experimentally demonstrated that this phenomenon is accompanied by formation of an explosive-emission plasma at the surface of the corrugated slow-wave structure (SWS). Termination of microwave emission is explained by the increase of the BWO starting current from the absorption of the operating electromagnetic wave by electrons emitted from the plasma, whereas the intensity of the absorption radically increases offing to the presence of positive ions emitted from the plasma. Application of oil-free vacuum and electrochemical polishing of the SWS surface in an X-band BWO allowed generation of 3-GW, 26-ns microwave pulses with an energy of /spl sim/80 J, thereby demonstrating pulse lengthening by a factor of four.