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Low temperature plasmas have been used in various plasma processing applications for several decades. But it is only in the last thirty years or so that sources generating such plasmas at atmospheric pressure in reliable and stable ways have become more prevalent. First, in the late 1980s, the dielectric barrier discharge was used to generate relatively large volume diffuse plasmas at atmospheric pressure. Then, in the early 2000s, plasma jets that can launch cold plasma plumes in ambient air were developed. Extensive experimental and modeling work was carried out on both methods and much of the physics governing such sources was elucidated. Starting in the mid-1990s, low temperature plasma discharges have been used as sources of chemically reactive species that can be transported to interact with biological media, cells, and tissues and induce impactful biological effects. However, many of the biochemical pathways whereby plasma affects cells remain not well understood. This situation is changing rather quickly because the field, known today as "plasma medicine," has experienced exponential growth in the last few years thanks to a global research community that engaged in fundamental and applied research involving the use of cold plasma for the inactivation of bacteria, dental applications, wound healing, and the destruction of cancer cells/tumors. In this perspective, the authors first review the physics as well as the diagnostics of the principal plasma sources used in plasma medicine. Then, brief descriptions of their biomedical applications are presented. To conclude, the authors' personal assessment of the present status and future outlook of the field is given. [ABSTRACT FROM AUTHOR]

Global model of atmospheric-pressure anodic arc in helium is developed. This type of discharge is currently used for efficient synthesis of various carbon nanostructures including carbon nanotubes. The model features include coupling between interelectrode plasma and electrodes, current continuity at electrodes, thermal regime of electrodes, and anode erosion. It is taken into account that arc radius increases linearly with the arc current according to experimental observation. Results indicate that substantial fraction of the current at the cathode is conducted by ions (0.7–0.9 of the total current). Calculated anode erosion rate and nonmonotonic voltage-current characteristic of the arc predicted by the model are in agreement with experimental data. It is concluded that nonmonotonic behavior of the arc voltage can be only reproduced by considering experimentally observed dependence of the arc radius on arc current. [ABSTRACT FROM AUTHOR]

Voltage-current (V-I) characteristics of the carbon nanotube producing anodic arc are measured for different gap sizes (up to 13 mm), anode compositions, and background He pressures (in the range of about 300–500 Torr). Arc is supported by the erosion of 6.35 mm hollow anode packed with composition of Ni, Y, and carbon powders. Experiments were carried out for the arc currents in the range of about 10–100 A. It is shown that V-I characteristics have a V-type shape with minimum point corresponded to arc current of about 25–30 A and arc voltage of 20–25 V at the gap of 2.5 mm. V-I characteristic shifts 15–25 V to higher arc voltages with increasing gap from 2.5 to 13 mm, while the position of voltage minimum shifts by about 15 A to higher arc currents. The increase in the metallic catalyst fraction in the anode composition (from C:Ni:Y=56:4:1 to 36:4:1) results in the slight decrease in the arc voltage (about a few volts) and slight shift of the minimum position to higher arc currents (5–10 A). Anode erosion rate increases from below 5 mg/s to about 44 mg/s with arc current increase from 40 A to about 100 A. [ABSTRACT FROM AUTHOR]

In this article we develop an analytical model of the Knudsen layer at the ablative wall taking into account the temperature gradient in the bulk gas. The analysis is based on the premise that the temperature gradient in the bulk gas can be taken into account in the velocity distribution function at the outer boundary of the Knudsen layer. The model uses a bimodal velocity distribution function in the Knudsen layer, which preserves the laws of conservation of mass, momentum, and energy and converges to the Chapman–Enskog velocity distribution function at the outer boundary of the layer. The model is applied to polyethylene ablation, for which two cases are considered: (a) the ablation process is due to pure heat conduction to the surface, with no external heating of the ablated surface, and (b) the ablation is due to both the thermal conduction and an external heating of the surface, e.g., vaporization of a metal exposed to laser radiation. The region of validity of the existing models and effect of the temperature gradient on the Knudsen layer properties are calculated. [ABSTRACT FROM AUTHOR]

Plasma transport in a hybrid dc vacuum arc plasma source for ion deposition and plasma immersion treatment is considered. It is found that external crossed electric and magnetic fields near the substrate can significantly reduce the relative amplitude of ion current fluctuations Īf at the substrate surface. In particular, Īf decreases with the applied magnetic field when the bias voltage exceeds 300 V, thus allowing one to reduce the deviations from the rated process parameters. This phenomenon can be attributed to an interaction between the metal-plasma jet from the arc source and the discharge plasma in the crossed fields. [ABSTRACT FROM AUTHOR]

Three-dimensional topography of microscopic ion fluxes in the reactive hydrocarbon-based plasma-aided nanofabrication of ordered arrays of vertically aligned single-crystalline carbon nanotip microemitter structures is simulated by using a Monte Carlo technique. The individual ion trajectories are computed by integrating the ion equations of motion in the electrostatic field created by a biased nanostructured substrate. It is shown that the ion flux focusing onto carbon nanotips is more efficient under the conditions of low potential drop Us across the near-substrate plasma sheath. Under low-Us conditions, the ion current density onto the surface of individual nanotips is higher for higher-aspect-ratio nanotips and can exceed the mean ion current density onto the entire nanopattern in up to approximately five times. This effect becomes less pronounced with increasing the substrate bias, with the mean relative enhancement of the ion current density ξi not exceeding ∼1.7. The value of ξi is higher in denser plasmas and behaves differently with the electron temperature Te depending on the substrate bias. When the substrate bias is low, ξi decreases with Te, with the opposite tendency under higher-Us conditions. The results are relevant to the plasma-enhanced chemical-vapor deposition of ordered large-area nanopatterns of vertically aligned carbon nanotips, nanofibers, and nanopyramidal microemitter structures for flat-panel display applications. [ABSTRACT FROM AUTHOR]

Several interrelated phenomena near the surface ablated into a discharge plasma, such as ablation and ionization in accelerated plasma are studied. Two characteristic ablation modes are identified, namely, ablation mode with a velocity at the Knudsen layer edge smaller than the local sound speed and a velocity at the Knudsen layer edge close to the sound speed. The existence of these two ablation modes is determined by the current density in the acceleration region. The nonequilibrium ionization region in the presence of strong electromagnetic plasma acceleration is studied. In the subsonic regime, the ionization region thickness is proportional to the ionization rate and inversely proportional to the magnetic field. Conditions for ionization equilibrium in the accelerating plasma are determined. The specific example of a micropulsed plasma thruster is considered. It is concluded that both the equilibrium and nonequilibrium ionization regimes occur in this device. [ABSTRACT FROM AUTHOR]

Ion current distribution in a system with crossed magnetic and electrical fields for plasma immersion ion implantation has been investigated. It is found that the ion current to a target has a nonmonotonic behavior with bias voltage when a magnetic field is applied. For instance, the current density has a maximum of about 150 A/m² at bias voltage of about 1 kV in the case of a magnetic field parallel to the target of about 0.035 T. These results are explained in terms of ionization by magnetized electrons in the E × B system. Our findings suggest that the system with crossed fields can be used for intense plasma immersed processing. [ABSTRACT FROM AUTHOR]

Segmented electrodes placed along a ceramic channel in a Hall thruster are shown to influence significantly the plasma potential distribution. Both the radial potential and the axial acceleration region are sensitive to the location of the segmented electrodes. The measured and theoretical potential profiles appear to be affected in detail by the electrode material (graphite) having lower secondary electron emission than the ceramic channel walls. The measured plasma potential profile is shown as well to correlate with the observed and desirable narrowing of the plasma plume emanating from the thruster. [ABSTRACT FROM AUTHOR]

Presents information on a study which determined the influence of positive bias on plasma and macroparticle flow in curved magnetized plasma ducts in filtered vacuum arc deposition systems. Macroparticle-plasma interaction; Results and discussion; Conclusions.

Provides information on a study which analyzed the free boundary plasma arc jet expansion based on a two-dimensional hydrodynamic model. Description of the model; Results and discussion; Conclusions.

Presents a theoretical study of the low-density plasma flow in an axial magnetic field to a disk-shaped anode in a vacuum arc. Importance of the expansion of low-density current carrying plasma jets in a magnetic field; Details on plasma in a vacuum arc.

Given the vast number of strategies used to control the behavior of laboratory and industrially relevant plasmas for material processing and other state-of-the-art applications, a potential user may find themselves overwhelmed with the diversity of physical configurations used to generate and control plasmas. Apparently, a need for clearly defined, physics-based classification of the presently available spectrum of plasma technologies is pressing, and the critically summary of the individual advantages, unique benefits, and challenges against key application criteria is a vital prerequisite for the further progress. To facilitate selection of the technological solutions that provide the best match to the needs of the end user, this work systematically explores plasma setups, focusing on the most significant family of the processes--control of plasma fluxes--which determine the distribution and delivery of mass and energy to the surfaces of materials being processed and synthesized. A novel classification based on the incorporation of substrates into plasma-generating circuitry is also proposed and illustrated by its application to a wide variety of plasma reactors, where the effect of substrate incorporation on the plasma fluxes is emphasized. With the key process and material parameters, such as growth and modification rates, phase transitions, crystallinity, density of lattice defects, and others being linked to plasma and energy fluxes, this review offers direction to physicists, engineers, and materials scientists engaged in the design and development of instrumentation for plasma processing and diagnostics, where the selection of the correct tools is critical for the advancement of emerging and high-performance applications. [ABSTRACT FROM AUTHOR]

This work reviews recent research efforts undertaken in the area non-equilibrium atmospheric plasma jets with special focus on experimental approaches. Physics of small non-equilibrium atmospheric plasma jets operating in kHz frequency range at powers around few Watts will be analyzed, including mechanism of breakdown, process of ionization front propagation, electrical coupling of the ionization front with the discharge electrodes, distributions of excited and ionized species, discharge current spreading, transient dynamics of various plasma parameters, etc. Experimental diagnostic approaches utilized in the field will be considered, including Rayleigh microwave scattering, Thomson laser scattering, electrostatic streamer scatterers, optical emission spectroscopy, fast photographing, etc. [ABSTRACT FROM AUTHOR]

The temporal evolution of a high pressure He arc producing nanotubes was considered and the Langmuir probe technique was applied for plasma parameter measurements. Two modes of arc were observed: cathodic arc where discharge is supported by erosion of cathode material and anodic arc which is supported by ablation of the anode packed with carbon and metallic catalysts in which carbon nanotubes are synthesized. Voltage-current (V-I) characteristics of single probes were measured and unusually low ratio of saturation current on positively biased probe to that on negatively biased of about 1-4 was observed. This effect was explained by increase of measured current at the negatively biased probe above the level of ion saturation current due to secondary electron emission from the probe surface. Since utilization of standard collisionless approach to determine plasma parameters from the measured V-I characteristic is not correct, the electron saturation current was used to estimate the plasma density. [ABSTRACT FROM AUTHOR]

Plasma enhanced techniques are widely used for synthesis of carbon nanostructures. The primary focus of this paper is to summarize recent experimental and theoretical advances in understanding of single-wall carbon nanotube (SWNT) synthesis mechanism in arcs, and to describe methods of controlling arc plasma parameters. Fundamental issues related to synthesis of SWNTs, which is a relationship between plasma parameters and SWNT characteristics are considered. It is shown that characteristics of synthesized SWNTs can be altered by varying plasma parameters. Effects of electrical and magnetic fields applied during SWNT synthesis in arc plasma are explored. Magnetic field has a profound effect on the diameter, chirality, and length of a SWNT synthesized in the arc plasma. An average length of SWNT increases by a factor of 2 in discharge with magnetic field and an amount of long nanotubes with the length above 5 μm also increases in comparison with that observed in the discharge without a magnetic field. In addition, synthesis of a few-layer graphene in a magnetic field presence is discovered. A coupled model of plasma-electrode phenomena in atmospheric-pressure anodic arc in helium is described. Calculations indicate that substantial fraction of the current at the cathode is conducted by ions (0.7–0.9 of the total current). It is shown that nonmonotonic behavior of the arc current-voltage characteristic can be reproduced taking into account the experimentally observed dependence of the arc radius on arc current. [ABSTRACT FROM AUTHOR]

Angular distribution of microscopic ion fluxes around nanotubes arranged into a dense ordered pattern on the surface of the substrate is studied by means of multiscale numerical simulation. The Monte Carlo technique was used to show that the ion current density is distributed nonuniformly around the carbon nanotubes arranged into a dense rectangular array. The nonuniformity factor of the ion current flux reaches 7 in dense (5×1018 m-3) plasmas for a nanotube radius of 25 nm, and tends to 1 at plasma densities below 1×1017 m-3. The results obtained suggest that the local density of carbon adatoms on the nanotube side surface, at areas facing the adjacent nanotubes of the pattern, can be high enough to lead to the additional wall formation and thus cause the single- to multiwall structural transition, and other as yet unexplained nanoscience phenomena. [ABSTRACT FROM AUTHOR]

Uniformity of postprocessing of large-area, dense nanostructure arrays is currently one of the greatest challenges in nanoscience and nanofabrication. One of the major issues is to achieve a high level of control in specie fluxes to specific surface areas of the nanostructures. As suggested by the numerical experiments in this work, this goal can be achieved by manipulating microscopic ion fluxes by varying the plasma sheath and nanorod array parameters. The dynamics of ion-assisted deposition of functional monolayer coatings onto two-dimensional carbon nanorod arrays in a hydrogen plasma is simulated by using a multiscale hybrid numerical simulation. The numerical results show evidence of a strong correlation between the aspect ratios and nanopattern positioning of the nanorods, plasma sheath width, and densities and distributions of microscopic ion fluxes. When the spacing between the nanorods and/or their aspect ratios are larger, and/or the plasma sheath is wider, the density of microscopic ion current flowing to each of the individual nanorods increases, thus reducing the time required to apply a functional monolayer coating down to 11 s for a 7-μm-wide sheath, and to 5 s for a 50-μm-wide sheath. The computed monolayer coating development time is consistent with previous experimental reports on plasma-assisted functionalization of related carbon nanostructures [B. N. Khare et al., Appl. Phys. Lett. 81, 5237 (2002)]. The results are generic in that they can be applied to a broader range of plasma-based processes and nanostructures, and contribute to the development of deterministic strategies of postprocessing and functionalization of various nanoarrays for nanoelectronic, biomedical, and other emerging applications. [ABSTRACT FROM AUTHOR]

Electron-wall interaction effects in Hall thrusters are studied through measurements of the plasma response to variations of the thruster channel width and the discharge voltage. The discharge voltage threshold is shown to separate two thruster regimes. Below this threshold, the electron energy gain is constant in the acceleration region and therefore, secondary electron emission (SEE) from the channel walls is insufficient to enhance electron energy losses at the channel walls. Above this voltage threshold, the maximum electron temperature saturates. This result seemingly agrees with predictions of the temperature saturation, which recent Hall thruster models explain as a transition to space-charge saturated regime of the near-wall sheath. However, in the experiment, the maximum saturation temperature exceeds by almost three times the critical value estimated under the assumption of a Maxwellian electron energy distribution function. The channel narrowing, which should also enhance electron-wall collisions, causes unexpectedly larger changes of the plasma potential distribution than does the increase of the electron temperature with the discharge voltage. An enhanced anomalous crossed-field mobility (near wall or Bohm-type) is suggested by a hydrodynamic model as an explanation to the reduced electric field measured inside a narrow channel. We found, however, no experimental evidence of a coupling between the maximum electron temperature and the location of the accelerating voltage drop, which might have been expected due to the SEE-induced near-wall conductivity. [ABSTRACT FROM AUTHOR]

In this paper a model of the quasineutral plasma and the transition between the plasma and the dielectric wall in a Hall thruster channel is developed. The plasma is considered using a two-dimensional hydrodynamic approximation while the sheath in front of the dielectric surface is considered to be one dimensional and collisionless. The dielectric wall effect is taken into account by introducing an effective coefficient of the secondary electron emission (SEE), s. In order to develop a self-consistent model, the boundary parameters at the sheath edge (ion velocity and electric field) are obtained from the two-dimensional plasma bulk model. In the considered condition, i.e., ion temperature much smaller than that of electrons and significant ion acceleration in the axial direction, the presheath scale length becomes comparable to the channel width so that the plasma channel becomes an effective presheath. It is found that the radial ion velocity component at the plasma–sheath interface varies along the thruster channel from about 0.5C[sub s] (C[sub s] is the Bohm velocity) near the anode up to the Bohm velocity near the exit plane dependent on the SEE coefficient. In addition, the secondary electron emission significantly affects the electron temperature distribution along the channel. For instance in the case of s=0.95, the electron temperature peaks at about 16 eV, while in the case of s=0.8 it peaks at about 30 eV. The predicted electron temperature is close to that measured experimentally. The model predictions of the dependence of the current–voltage characteristic of the E×B discharge on the SEE coefficient are found to be consistent with experiment. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines some effects that can occur due to the streaming plasma in an ion source configuration. Case of energetic ion beam formation; High voltage substrate in a drifting plasma stream; High voltage ion implantation using a gridless ion source.

Examines a hydrodynamic current carrying transition layer separating the plasma from electrically conducting or insulating walls. Placement of the plasma; Calculation on the sheath and presheath of the plasma situated in the magnetic field; Significance of Boltzmann distribution in measuring presheath thickness and plasma density distribution.

Investigates the effect of magnetic field on the plasma-wall transition layer using the two-fluid formulation. Quasi-neutral, near-sheath plasma with the presence of neutral particles; Influence of electrons to ion current ratio on the potential and velocity distribution in the near-sheath plasma.

The formation of vertically aligned, clearly separated, copper-capped carbon nanocones with a length of up to 500 nm and base diameter of about 150 nm via three-stage process involving magnetron sputtering, N2 plasma treatment, and CH4+N2 plasma growth is studied. The width of gaps between the nanocones can be controlled by the gas composition. The nanocone formation mechanism is explained in terms of strong passivation of carbon in narrow gaps, where the access of plasma ions is hindered and the formation of large CnH2n+2 molecules is possible. This plasma-enabled approach can be used to fabricate nanoelectronic, nanofluidic, and optoelectronic components and devices. [ABSTRACT FROM AUTHOR]

A new method for temporally resolved measurements of absolute values of plasma density applicable for wide spectrum of small-size atmospheric plasmas and utilizing Rayleigh microwave scattering on the tested plasma object is proposed. The absolute electron density measurements in an atmospheric plasma jet revealed presence of two consecutive breakdowns during the half-wave of the discharge-driven high voltage. The ionization mechanisms of both breakdowns are considered. [ABSTRACT FROM AUTHOR]

Temporally resolved evolution of parameters in atmospheric plasma jet is studied by means of microwave scattering, fast photographing, and measuring of jet currents. It is observed that streamer (“plasma bullet”) propagating along with gas flow is generated immediately after the breakdown. It is demonstrated that an afterglow plasma column remains on the way of streamer passing. Lifetime of the afterglow plasma column is 3–5 μs, which is longer than that of the streamer. [ABSTRACT FROM AUTHOR]

The interaction of the cold atmospheric plasma jet with fibroblast cells was studied. Plasma jet was initiated in the helium flow blowing through the syringe by application of high ac voltage to the discharge electrodes. The plasma jet had a length of 5 cm and a diameter of 1.5–2 mm in ambient air. Treatment of cells with plasma jet resulted in decreasing of cell migration rate, cell detachment, and appearance of “frozen” cells, while treatment with helium flow (no plasma) resulted in appearance of frozen cells only. A variety of cellular responses was explained by different intensities of treatment. [ABSTRACT FROM AUTHOR]

A discharge in crossed electric and magnetic fields (E×B) is considered. E×B discharge serves as a basis for Hall-effect plasma accelerators. In this letter the authors present conditions for formation of a kinetic anode layer by considering an interface between kinetic and hydrodynamic regions. It is found that the kinetic anode layer, which has a thickness of about the electron Larmor radius, is formed in the case of a high magnetic field. [ABSTRACT FROM AUTHOR]

It is shown that, owing to selective delivery of ionic and neutral building blocks directly from the ionized gas phase and via surface migration, plasma environments offer a better deal of deterministic synthesis of ordered nanoassemblies compared to thermal chemical vapor deposition. The results of hybrid Monte Carlo (gas phase) and adatom self-organization (surface) simulation suggest that higher aspect ratios and better size and pattern uniformity of carbon nanotip microemitters can be achieved via the plasma route. [ABSTRACT FROM AUTHOR]

The magnetic mirror effect is studied in the channel of a Hall thruster. It is shown that gradients in magnetic field affect the presheath structure and electric potential distribution. The length of the radial presheath region decreases in the presence of a magnetic field gradient. The two-dimensional potential shape can be affected by proper choice of the magnetic mirror ratio. In particular, it is possible to obtain a concave shape of the potential profile in the channel even in the case of a primarily radial magnetic field. This, in turn, can be used to efficiently control the ion dynamics in the acceleration region. [ABSTRACT FROM AUTHOR]

Transition between different plasma configurations is studied in a system with negative biased cylindrical target in crossed E&timesB fields. It was found that the diffuse plasma torus formed around the cylindrical target in relatively small magnetic field (0.02 T on target surface) changes the shape with magnetic field to form a thin disk with a width lower than 1 cm when target voltage is less than -400 V. The target current decreases sharply when the magnetic field reaches some critical value. When the target voltage exceeds 400 V, the target current increases with the magnetic field and the plasma has always toroidal shape. The plasma behavior can be understood taking in account the interaction of the drift currents and the magnetic field. [ABSTRACT FROM AUTHOR]

The sheath thickness in plasma immersion ion implantation has been investigated in the presence of a transverse magnetic field. It has been found that the steady-state sheath thickness increases with increasing magnetic field strength. This result is in line with a simplified model of the sheath in which the steady-state sheath thickness is determined by the plasma density and ion velocity at the sheath edge. These results suggest that a magnetic field may be used to control the high-voltage sheath in plasma immersion ion implantation. [ABSTRACT FROM AUTHOR]

Focuses on results of some experimental investigations of the axial ion charge state distribution (CSD) using a time-of-flight diagnostic. Dependence of the CSD on the axial distance from the plasma source region; Description of a model for the plasma jet expansion.

Arc discharge with catalyst-filled carbon anode in helium background was used for the synthesis of carbon nanoparticles. In this paper, we present the results of numerical simulation of carbon arc discharges with arc current varying from 10 A to 100 A in a background gas pressure of 68 kPa. Anode sublimation rate and current voltage characteristics are compared with experiments. Distribution of temperature and species density, which is important for the estimation of the growth of nanoparticles, is obtained. The probable location of nanoparticle growth region is identified based on the temperature range for the formation of catalyst clusters. [ABSTRACT FROM AUTHOR]

The new mode of Vacuum arc-Hot Refractory Anode Vacuum Arc-was studied experimentally using a Langmuir probe, two types of thermal probes, and film collection substrates. The plasma density, electron temperature, plasma energy flux, cathode erosion, mass deposition rate on a substrate, and macroparticle contamination in the deposited films were measured. The arc initially operated as a usual vacuum arc sustained by cathode spots, i.e., and the vapor and plasma source located at the cathode spot. At a later stage the anode heated up and metal vapor originating at the cathode was re-evaporated from the nonconsumable hot graphite anode. Initially, plasma density was about (3-4)·10[sup 20] m[sup -3] but it increased with time, reaching about 2·10[sup 21] m[sup -3] after 60 s in a 340 A arc. The electron temperature initially was about 1.6 eV and decreased with time to a steady-state value of about 1.1 eV after 20 s. The radial plasma energy flux generated by 175 and 340 A arcs was about 1 and 2 MW/m2, respectively, at 1.6 cm from the electrode axis. The deposition rate on substrates placed 110-120 mm from the electrode axis reached about 2 μm/min. The density of macroparticles found on substrates exposed during the first 60 s of arcing was ∼10[sup 3] macroparticles per mm2, however, this density was reduced to about 1 macroparticle per mm2 on substrates exposed to only the second 30 s period. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Measurements of the ion current collected by a substrate biased to high voltage have been carried out in plasma immersion ion implantation with a filtered vacuum arc plasma source. We have found that the ion saturation current increases with applied voltage and that this effect depends upon the angle of the normal to the substrate with respect to the plasma stream and on the distance of the substrate from the plasma duct exit. We also found that the ion current increases with increasing angle of the normal to the substrate with respect to the plasma stream. A model was developed for the sheath expansion in a nonuniform plasma with substantial ion drift velocity. We find that nonuniformity and high drift velocity lead to a decrease in sheath thickness. In a nonuniform plasma, the ion saturation current increases with applied voltage. The predictions of the model were found to be in good agreement with experiment. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A model of the electrical sheath between plasma and a positively biased wall has been developed for the case of the magnetic field perfectly parallel to the wall. The magnetized sheath and relatively large positive wall potential with respect to the plasma are considered, so that only electron current is present in the sheath. We show that the sheath thickness increases linearly with duct current density. There is good quantitative agreement between the calculated and experimental current–voltage duct characteristics. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A new plasma source design that merges the main characteristics of capacitive dielectric barrier discharge (DBD) and cold atmospheric plasma jet (CAPJ) is discussed. The DBD system contains a flexible, porous matrix consisting of silica aerogel, which is comprised between two biased electrodes. The helium flow supply subjected to a sinusoidal voltage of around 5 kV in amplitude and 15 kHz in frequency provides a set of plasma jets that propagates more than 1 cm beyond the active DBD region. The studied plasma multi-jet system consists of an array of three aligned jets that flow in the laminar regime, and it is intended for treating the surfaces of 3D objects and large areas. CAPJ performance is discussed as a hypothetical morphing source in flat and bent configurations. Electrical characterization and optical emission spectroscopy diagnostics have provided current-voltage waveforms and the composition of the CAPJ through the aerogel layer, respectively. This novel source is promising for biomedical applications that require full adaptation of plasma parameters to delicate samples, such as wound healing and treatment of surgical margins in plasma-based cancer surgery.

The electron temperature of small streamer plasmas with low ionization degree is difficult to measure using existing diagnostic technologies such as Langmuir probe and laser Thomson scattering. In this report, we introduce a method of average electron temperature estimation based on the electron continuity equation. The equation includes a temporal derivative of electron density as the summation of diffusion current, drift current, and electron gain/loss events. In the considered example, the electron density is measured using the Rayleigh scattering while the currents and the rate coefficients of those events are functions of the electric field, electron collision frequency, and electron temperature. Therefore, once the electric field and collision frequency are either measured or estimated, the only unknown in the equation is the average electron temperature which can be solved. It was estimated that electron temperature in the streamer peaks at about 3.9 eV for the given example.