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International audience; To eliminate the disadvantages of both the uncontrollability in the magnetic field of a permanent magnet excitation system and the high energy consumption of an electric excitation system in a traditional magnetically rotating arc plasma generator, a novel topology of a hybrid permanent magnet and electrically excited coil system is proposed. The proposed system will generate a large enough magnetic field to drive the arc rotation with a minimum consumption of materials and electric energy in the normal operation duty, and will guarantee a nearly zero magnetic field in the arc triggering stage. To optimize the hybrid excitation system, a comprehensive analysis and an optimization methodology; by combining finite element analysis, the moving the least squares approximation and an adaptive weighted particle swarm optimization, are proposed. Finally, a prototype hybrid excitation system is optimized with promising results in views of both saving a huge amount of electric power consumptions and ensuring a nearly zero magnetic field in the arc triggering.

This work investigates the antifungal effect of plasma polymer films produced by low-pressure RF-generated plasma system using acrylic acid, 2-hydroxyethyl methacrylate, and diethyl phosphite (DEP). Unmodified and plasma-modified polystyrene (PS) microplate wells were tested by 30 biofilm-positive Candida spp. isolated from blood samples and two control strains using a quantitative plaque assay method. Regardless of the precursors and plasma parameters, biofilm formation was inhibited for all plasma-modified microplate wells. The most significant anti-biofilm effect was observed on PS modified by DEP at 90 W plasma power with the inhibition of all Candida species' biofilm formation.

This research focuses on the development of a new technique of emission spectral analysis designed to accurately account for the background radiation. The technique enables the evaluation of background radiation while being unaffected by its spectral shape. This is possible through the use of standard data obtained in an analytical-line-recording process performed by light-intensity-to-electric-signal converters such as CCDs, PMTs, photodiodes, etc. This technique, when applied at a set RMS deviation of the analytical-line-radiation intensity, reduces the random error of a determined low impure-element concentration due to the optimal calibration-line slope. In areas of high concentrations, an accurate accounting of the background does little to affect the emission spectrometer’s measurement accuracy. This technique also allows the replication of calibration curves in spectrometers of the same type by a linear-intensity conversion with only two standard samples required. The technique was tested on SPAS-02 and SPAS-05 commercial spark spectrometers. The testing fully confirmed the aforementioned advantages of the developed technique. The authors also determined the applicability conditions of the conventional emission-spectrometer-recalibration method by a linear conversion of the analytical-line intensity.

The article describes a nonlinear theory of how the presence of third elements affects the results of analyzing the elemental composition of substances by means of atomic emission spectroscopy. The theory is based on the assumption that there is an arbitrary relationship between the intensity of the analytical line of the analyte and the concentration of impurities and alloying elements. The theory has been tested on a simulation problem using commercially available equipment (the SPAS-05 spark spectrometer). By comparing the proposed algorithm with the traditional one, which assumes that there is a linear relationship between the intensity of the analytical line of the analyte and the intensities of the spectral lines (or concentrations) in the substance, it was revealed that there is a severalfold decrease in the deviations of nominal impurity concentrations from the measured ones. The results of this study allow for reducing the number of analytical procedures used in analyzing materials that have different compositions and the same matrix element. For instance, it becomes possible to determine the composition of iron-based alloys (low-alloy and carbon steels; high-speed steels; high-alloy, and heat-resistant steels) using one calibration curve within the framework of a universal analytical method.

Field emitters and microplasmas often use series resistors to mitigate the rapid increase in current density that reduces device stability. This paper investigates the impact of external resistance on the transition of electron emission mechanism as a function of applied voltage $V_{app}$ , gap distance ${D}$ , and electron mobility $\mu $ . For low $\mu $ (high gas pressure), the circuit transitions from Fowler–Nordheim (FN) to space charge limited emission by Mott–Gurney (MG) and Child–Langmuir (CL) before reaching Ohm’s law (OL). At higher ${\mu }$ , a triple point arises where the asymptotic solutions for FN, MG, and CL intersect. This triple point is uniquely defined by ${D}$ , $\mu $ , or gap voltage $V_{g}$ while also defining a specific gap impedance $Z_{tp}$ . When $R \leq Z_{tp}$ , the electron emission transitions from FN to MG to CL to OL with increasing $V_{app}$ while MG and CL are bypassed at higher ${R}$ . For a given ${R}$ , increasing the applied voltage or emission current causes the gap to appear as a short.

The article presents a method of mathematical correction to be applied to the results of measuring the intensity of spectral lines using charge-coupled devices (CCDs) in the presence of the blooming effect. This technique is particularly applicable in atomic emission spectroscopy. It enables expansion of the dynamic range of spark emission spectrometers and significantly minimizes the result distortions of the measurements taken in the area of high element concentrations. The authors devised a mathematical model and proposed an algorithm to adjust the measured intensity of analytical lines at the photo detector upper limit, in addition to an algorithm for processing data from the spectra recording system. The proposed mathematical algorithm was integrated into the software for the SPAS-02 and SPAS-05 spark spectrometers produced in Russia, and tested in determining the chemical composition of steels. The findings show that the actual dispersion of the analytical line intensity distribution may exceed the measured dispersion by a factor of 1.5, and their intensities may differ by a factor of 2. This algorithm may be implemented in atomic emission spectrometer software and makes it possible to adjust the calibration curves for a range of high alloying element concentrations when the analytical line intensity is at the upper limit of the CCD dynamic range.

It has been shown that plasma generated in contact with liquid can be tailored to tune the composition of plasma functionalized liquids. For biomedical applications, it is necessary to understand the generation of the plasma treated liquids to modulate the composition and thus the biological response. In this work, two distinct discharge compositions were realized by modifying the location of the ground electrode in a pin-to-liquid plasma system. Through this simple modification to the configurations, the spatiotemporal characteristics of the discharge were significantly affected which, in turn, affected the composition of the generated plasma activated water (PAW). Colorimetric testing of the PAW generated from each system revealed that only one configuration was able to generate PAW with a high concentration of H2O2. Using time-, space-, and wavelength-resolved imaging of excited plasma species [OH, N2 (SPS), N2+ (FNS), and atomic O], the differences in PAW composition were linked to the differences observed in the discharge dynamics between the two configurations. UK Royal Society Royal Irish Academy Engineering and Physical Sciences Research Council

An adjoint method to calculate the gradient of island width in stellarators is presented and applied to a set of magnetic field configurations. The underlying method of calculation of the island width is that of Cary & Hanson (1991) (with a minor modification), and requires that the residue of the island centre be small. Therefore, the gradient of the residue is calculated in addition. Both the island width and the gradient calculations are verified using an analytical magnetic field configuration introduced in Reiman & Greenside (1986). The method is also applied to the calculation of the shape gradient of the width of a magnetic island in an NCSX vacuum configuration with respect to positions on a coil. A gradient-based optimization is applied to a magnetic field configuration studied in Hanson & Cary (1984) to minimize stochasticity by adding perturbations to a pair of helical coils. Although only vacuum magnetic fields and an analytical magnetic field model are considered in this work, the adjoint calculation of the island width gradient could also be applied to a magnetohydrodynamic (MHD) equilibrium if the derivative of the magnetic field with respect to the equilibrium parameters was known. Using the island width gradient calculation presented here, more general gradient-based optimization methods can be applied to design stellarators with small magnetic islands. Moreoever, the sensitivity of the island size may itself be optimized to ensure that coil tolerances with respect to island size are kept as high as possible., 41 pages, 8 figures

The current study investigates the load controlled fatigue properties of the microplasma arc welded thin titanium Grade 5 (6Al-4V) sheets. In order to explore the effect of weld geometry on the fatigue, two different welded joints were used in the experimental studies. Load controlled fatigue test results were evaluated to present an outlook on the behaviour of microplasma welded titanium alloy Grade 5 sheets under cyclic loading. Even though the previously published monotonic tests showed successful use of microplasma arc welding to join thin titanium Grade 5 sheets with mechanical properties comparable to the base metal, fatigue life of the welded joints was lower than the lives of samples without welds. In particular, the fatigue performance of overlap joints was very poor. This was presumed to be due to the changed material properties of the heat affected zone which was formed by the excess heat of the welding process as fractures often occurred at such locations. Based on experimental findings and fractographic observations, a clear adverse effect of welding process in material behaviour was discovered. Despite the concentrated heat of microplasma arc welding, post-weld heat treatment of the weld area is recommended to improve the mechanical behaviour of the welded joints. © MDPI AG. All rights reserved.

The SPARC tokamak is a critical next step towards commercial fusion energy. SPARC is designed as a high-field ($B_0 = 12.2$T), compact ($R_0 = 1.85$m,$a = 0.57$m), superconducting, D-T tokamak with the goal of producing fusion gain$Q>2$from a magnetically confined fusion plasma for the first time. Currently under design, SPARC will continue the high-field path of the Alcator series of tokamaks, utilizing new magnets based on rare earth barium copper oxide high-temperature superconductors to achieve high performance in a compact device. The goal of$Q>2$is achievable with conservative physics assumptions ($H_{98,y2} = 0.7$) and, with the nominal assumption of$H_{98,y2} = 1$, SPARC is projected to attain$Q \approx 11$and$P_{\textrm {fusion}} \approx 140$MW. SPARC will therefore constitute a unique platform for burning plasma physics research with high density ($\langle n_{e} \rangle \approx 3 \times 10^{20}\ \textrm {m}^{-3}$), high temperature ($\langle T_e \rangle \approx 7$keV) and high power density ($P_{\textrm {fusion}}/V_{\textrm {plasma}} \approx 7\ \textrm {MW}\,\textrm {m}^{-3}$) relevant to fusion power plants. SPARC's place in the path to commercial fusion energy, its parameters and the current status of SPARC design work are presented. This work also describes the basis for global performance projections and summarizes some of the physics analysis that is presented in greater detail in the companion articles of this collection.

International audience; A preliminary study of the design of an electrically small plasma-based resonator using a localized surface plasmon resonance (LSPR) above 1 GHz is presented. Such a resonator is intended to be used to develop an electrically small antenna with frequency agility. This resonator consists of a plasma discharge confined in a hemispherical glass shell 3 cm in diameter on a ground plane. From 1 to 1.5 GHz, the plasma electron density required to achieve the LSPR must be between 0.5 × 1011 and 1.4×1011 cm−3. Plasma losses are taken into account in this study and provide information on the required gas pressure. Typically for neon gas, the working pressure must be around 50 mTorr. A practical implementation using a miniature inductively coupled plasma (mICP) source is finally discussed.

The possibility of performing electron density and temperature measurements in a high power helicon plasma is a crucial issue in the framework of the AWAKE (Advanced WAKefield Experiment) project, which demonstrates acceleration of particles using $\text{GeV}~\text{m}^{-1}$ electric fields in plasmas. For AWAKE, a helicon is currently envisaged as a candidate plasma source due to its capability for low electron and ion temperature, high electron density and production of an elongated plasma column. A plasma diagnostic to accurately determine the electron density in AWAKE regimes would be a valuable supporting tool. A demonstration Thomson scattering (TS) diagnostic was installed and successfully tested on the resonant antenna ion device (RAID) at the Swiss Plasma Center of Ecole Polytechnique Fédérale de Lausanne. RAID produces a helicon plasma column with characteristics similar to those of the AWAKE helicon source, and is therefore an optimal testbed for application to the AWAKE device. The spectrometer employed in RAID is based on polychromators which collect the light scattered by plasma electrons in spectrally filtered wavelength regions. Results from TS on RAID demonstrate conditions of electron density and temperature respectively of $n_{e}=1.10\,(\pm 0.19)\times 10^{19}~\text{m}^{-3}$ and $T_{e}=2.3\,(\pm 0.6)~\text{eV}$ in a steady-state discharge in an Ar plasma with 5 kW of RF power. If the same polychromator system is used for AWAKE, where the electron density attained is $2\times 10^{20}~\text{m}^{-3}$ , the contribution to measurement error due to coherent scattering is ${\sim}2.5\,\%$ . Presented here are details of the TS diagnostic and the first tests in RAID, and the expectations for the system when employed on the AWAKE device.

Experimental data on the evolution of a helium atmospheric pressure plasma jet driven by two different voltage waveforms are presented. The characteristics of directed ionization waves (guided streamers) were compared for a sinusoidal voltage waveform with a frequency of 52 kHz and a voltage waveform that was formed via the superposition of 41.6 kHz bipolar square pulses and 300 kHz oscillations. With the sinusoidal voltage, two consecutive ionization waves were observed. With a special tailoring voltage, control of the guided streamer propagation in a stepwise mode was achieved. The observed second streamer and the second step of propagation could be regarded as a secondary ionization wave for both voltages. A change in the voltage waveform led to significant variations in the secondary ionization wave formation and streamer parameters. The voltage waveform enabled the number of ionization waves and their propagation to change, which provided the possibility of controlling the plasma parameters of the jet.

A gaseous plasma antenna array (PAA) is an aggregate of plasma discharges and possibly conventional metallic radiating elements, and it constitutes a promising alternative to metallic antennas for applications in which fast reconfiguration of radiation pattern, and gain is desired; such properties can be achieved by exploiting the electronic switch on/off condition of plasma discharges, and tuning of the plasma parameters. Here, the authors present a reconfigurable PAA that features a central metallic half-wavelength dipole working around 1.45 GHz, surrounded by a planar circular lattice of cylindrical plasma discharges. Customised plasma discharges have been realised, and filled with argon gas at 2 mbar so as to have a complete control on the plasma discharge properties (e.g. plasma frequency, collisional frequency). The magnitude of the reflection coefficient, and the gain pattern on the H -plane have been investigated numerically and experimentally; numerical and experimental results exhibit a good agreement and show that the central intrinsically omnidirectional antenna can provide simple beamforming capabilities upon turning on a subset of plasma discharges; as these plasma discharges are turned on, the authors have observed a maximum gain of ~5 dBi, a half-power beam width of 80°, and an angular steering resolution of ~15°.

In this study, the thermal characterisation of dielectric barrier discharge plasma actuation driven by radio frequency (RF) voltage waveform at low pressure is studied. The RF discharge images and voltage–current waveforms are quite different under 3 and 40 kPa. The thermographic method has been proposed for the spatial–temporal temperature field on the actuator surface . At 3 kPa, the high-temperature region is mainly concentrated on the surface of the high-voltage electrode. Along the spanwise direction, the surface temperature gradually increases until it reaches the maximum at the edge of the electrode and then decreases. Similarly, in the chordwise direction, there also exists the maximum value on the surface of the electrode. After discharge starts, the surface temperature rises rapidly, and subsequently, the increasing slope of temperature curves gradually decreases until thermal equilibrium has been reached at about 100 s. The effects of the pressure, duty cycle, and operating power on the thermal characterisation are also investigated experimentally. At low pressure, the discharge mode is diffuse glow discharge, and the high-temperature region covers the whole electrode. As the pressure increases the surface temperature ascends non-linearly, while the surface temperature is linearly dependent on the duty cycle and operating power.

The development of compact accelerator facilities providing high-brightness beams is one of the most challenging tasks in the field of next-generation compact and cost affordable particle accelerators, to be used in many fields for industrial, medical, and research applications. The ability to shape the beam longitudinal phase space, in particular, plays a key role in achieving high-peak brightness. Here we present a new approach that allows us to tune the longitudinal phase space of a high-brightness beam by means of plasma wakefields. The electron beam passing through the plasma drives large wakefields that are used to manipulate the time-energy correlation of particles along the beam itself. We experimentally demonstrate that such a solution is highly tunable by simply adjusting the density of the plasma and can be used to imprint or remove any correlation onto the beam. This is a fundamental requirement when dealing with largely time-energy correlated beams coming from future plasma accelerators.

The research concerned the possibility of using the microplasma welding technique for joining thin titanium alloy Grade 5 (6Al-4V) sheets. For this purpose, titanium reference samples without welds (Type 1) and two types of welded joints (butt joint - Type 2 and Type 3 overlap joint) were made with selected microplasma welding parameters for which strength parameters were determined and compared with the strength of the native material. The assessment of the connection quality was made on the basis of a monotonic tensile test. A metallographic analysis of the welded joints was made and the breakthroughs sample obtained during the tests was also carried out. In addition, strain distributions were determined in loaded sample types, which allowed investigating the impact of the heat affected zone size on the strength of welded joints subjected to monotonic tensile tests and Vickers hardness tests. Microplasma welded joints displayed relatively high brittleness. The failure locations are still influenced by heat affected zone despite the highly concentrated plasma beam of the microplasma arc welding. © 2018 Elsevier Ltd

The performance of atmospheric pressure dielectric barrier discharge (DBD) driven by dual-frequency sources of 200 kHz/13.56 MHz has been investigated numerically here in a one-dimensional fluid model. By varying the ratio of dual frequency excitation amplitudes, strong nonlinear coupling in the discharge is observed, with the electron density rising significantly due to the synergistic effect governing the ionization process. Moreover, it is shown that the phase shift between the dual frequencies also has an influence on the electron temperature and density. As to different high frequency components, the modulation of the electron temperature and density induced by the phase-shift also varies significantly. Those results then demonstrated the possibility of applying amplitude and/or phase modulations in a wide operation window to optimize the plasma parameters in dual-frequency DBDs with fixed frequencies.The performance of atmospheric pressure dielectric barrier discharge (DBD) driven by dual-frequency sources of 200 kHz/13.56 MHz has been investigated numerically here in a one-dimensional fluid model. By varying the ratio of dual frequency excitation amplitudes, strong nonlinear coupling in the discharge is observed, with the electron density rising significantly due to the synergistic effect governing the ionization process. Moreover, it is shown that the phase shift between the dual frequencies also has an influence on the electron temperature and density. As to different high frequency components, the modulation of the electron temperature and density induced by the phase-shift also varies significantly. Those results then demonstrated the possibility of applying amplitude and/or phase modulations in a wide operation window to optimize the plasma parameters in dual-frequency DBDs with fixed frequencies.

Dielectric Barrier Discharge (DBD) is a promising technique for producing plasma in atmospheric pressure and is gaining emphasis in several areas, especially in the biomedical and textile industries, among other. This is due to the fact that this plasma does not reach high temperatures, enabling its use on thermally sensitive materials. However, there is still the need for the development of research relating to the field of physical mechanisms of non-thermal plasma. In this work, we studied the behavior of plasma in DBD equipment, varying distance between electrodes. For this study, two distinct characterization techniques were used. The first, the Lissajous Figures method, is effective and precise in the electrical characterization of DBD equipment. The second technique used, Optical Emission Spectroscopy (OES) is an effective tool in the diagnosis of plasma. This tool enables the identification of excited species in plasma. With the data produced, it was possible to identify an appropriate distance for producing plasma with a higher intensity and homogeneity of active species.

A magnetic field configuration of an island divertor for a quasi-axisymmetric stellarator (CFQS) is proposed. The configuration incorporates large islands surrounding the core confinement region. The interface between the core region and the peripheral region of the island divertor is a clear magnetic separatrix similar to a tokamak divertor. The structure of divertor magnetic field lines is very regular without stochasticity and the connection length is sufficiently long for good divertor performance. Such a divertor configuration is produced in the magnetic field configuration for the CFQS device, which is now under construction in China.

This article presents the experimental work performed as part of the use of the non linear plasma-wave interactions in planar circuits to design microwave power limiters. A first non-resonant plasma-based microwave power limiter composed of a pre-ionized plasma discharge integrated into a 50 Ohms microstrip line has been experimentally characterized with steady-state and transient measurements. These results have been then confronted at each step to a resonant one using the same plasma discharge. This study highlights the effect of the resonance on the non linear plasma-wave interactions and its consequences on the behaviour and the performances of a plasma-based microwave power limiter.

International audience; The MISTRAL device is designed to produce a linear magnetized plasma column. It has been used a few years ago to study a nonlinear low frequency instability exhibiting an azimuthal number m = 2. By changing the experimental configuration of MISTRAL, this work shows experimental results on an m = 1 rotating instability with strongly different behavior. The spatio-temporal evolution of the ion velocity distribution function given by a laser-induced fluorescence diagnostic is measured to infer the radial and azimuthal velocities, ion fluxes, and electric fields. The naive image of a plasma exhibiting a global rotation is again invalidated in this m = 1 mode but in a different way. Contrary to the m = 2 mode, the rotation frequency of the instability is lower than the ion cyclotron frequency and ions exhibit a complex behavior with a radial outward flux inside the unstable arm and azimuthal ion fluxes always directed toward the unstable arm. The azimuthal ion velocity is close to zero inside the ionization region, whereas the radial ion velocity grows linearly with radius. The radial electric field is oriented inward inside the unstable arm and outward outside. An axial velocity perturbation is also present, indicating that contrary to the m = 2 mode, the m = 1 mode is not a flute mode. These results cannot be easily interpreted with existing theories.

A plasma pad that can be attached to human skin was developed for aesthetic and dermatological treatment. A polyimide film was used for the dielectric layer of the flexible pad, and high-voltage and ground electrodes were placed on the film surface. Medical gauze covered the ground electrodes and was placed facing the skin to act as a spacer; thus, the plasma floated between the gauze and ground electrodes. In vitro and in vivo biocompatibility tests of the pad showed no cytotoxicity to normal cells and no irritation of mouse skin. Antibacterial activity was shown against Staphylococcus aureus and clinical isolates of methicillin-resistant S. aureus. Furthermore, skin wound healing with increased hair growth resulting from increased exogenous nitric oxide and capillary tube formation induced by the plasma pad was also confirmed in vivo. The present study suggests that this flexible and wearable plasma pad can be used for biomedical applications such as treatment of wounds and bacterial infections.

Proceeding of: 33rd International Electric Propulsion Conference (IEPC 2013) A two-fluid 2-D model of the supersonic plasma flow in a propulsive magnetic nozzle (MN) is extended to include simple electron and ion thermodynamics to study the effects of electron cooling and ion thermal energy on the expansion. A faster electron cooling rate is seen to reduce plasma jet divergence, increase radial rarefaction, and enhance detachment from the closed magnetic lines. Ion thermal energy is converted to directed kinetic energy by the MN without the mediation of an ambipolar electric field, and alters the electric response of the plasma. This work has been supported by the European Space Agency project 'Helicon Plasma Thruster for Space Missions', grant number 4000107292/12/NL/CO. Additional support has been provided by Spain's R&D National Plan (Project AYA-2010-61699).

Static and dynamic control of the limiting threshold in a very low-loss plasma-based microstrip power limiter is investigated in order to prevent receivers from being threatened by high-power microwave (HPM). An analytic model of the microstrip circuit is proposed to derive the influence of its design on the limiting threshold of the microwave power limiter. Experimental results are in good agreement with those expected. Finally, an original approach to allow discrete limiting threshold tunability is presented and validated experimentally.

Made available in DSpace on 2018-11-28T12:27:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-05-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) In the atmospheric pressure discharge with arrangement of a syringe needle, a capillary, and an external disk, it was observed different operation modes according to the relative position of the electrodes. With external electrode over the shaft of the needle, a stable and steady plume is formed from the tip of the needle to the exterior of the capillary. The breakdown is governed by filamentary discharges that evolve randomly on time in the gap between the needle and the capillary. This mechanism changes to bullet-like discharge when the external disk is located off needle. The breakdown generates a large amount of charge that rises quickly and varies with the distance between the electrodes. The mean power is higher than that of the previous case and the plume generated, in interaction with external metallic surface, is more unstable to arc transition. Independently of the operation mode, high electric field at the bevel of the needle plays an important role on the evolution of the plume. The application of the plume to change the wettability properties of the polyethylene terephthalate indicated rapid augment of the hydrophilicy and treated area larger than the plume dimension. Sao Paulo State Univ, Fac Engn, SP 12516-410, Guaratingueta, Brazil Sao Paulo State Univ, Fac Engn, SP 12516-410, Guaratingueta, Brazil

The dielectric barrier discharge

Micro plasma devices (MPD) with power gains are of interest in applications involving operations in the presence of ionizing radiations, in propulsion, in control, amplification of high power electromagnetic waves, and in metamaterials for energy management. Here we review and discuss MPDs with an emphasis on new architectures that have evolved during the past 7 years. Devices with programmable impact ionization rates and programmable boundaries are developed to control the plasma ignition voltage and current to achieve power gain. Plasma devices with 1-10 μm gaps are shown to operate in the sub-Paschen regime in atmospheric pressures where ion-assisted field emission results in a breakdown voltage that linearly depends on the gap distance in contrast to the exponential dependence dictated by the Paschen curve. Small gap devices offer higher operation frequencies at low operation voltages with applications in metamaterial skins for energy management and in harsh environment inside nuclear reactors and in space. In addition to analog plasma devices, logic gates, digital circuits, and distributed amplifiers are also discussed.

The use of microplasma discharges as power-induced limiter elements in microstrip devices is proposed to protect receivers against high-power microwave threats. A microstrip bandpass filter integrating such a microplasma-based active microwave power limiter has been designed and measured. Power limitation is observed when the input power exceeds 19 dBm with a leakage power of 14 dBm. Due to the gaseous properties of the active medium, the proposed structure exhibits a very low additional insertion loss of 0.06 dB.

The past several years have witnessed the emergence of a subfield of photonics in which the unique optical and electronic properties of microplasmas and gases are coupled with solid phase materials and optical components to realize photodetectors, transistors, photonic crystals, laser sources, and lighting. Highlights of novel plasma or gas based photonic devices reported in 2010 are described.

The radio frequency (RF) inductively coupled plasma technique is a new and promising synthesis method of single-walled carbon nanotubes (SWCNTs) at large scales, for industrial and commercial applications. In this method, a mixture of carbon black and metal catalysts is directly vaporized by the RF plasma. Subsequently, inside the reactor chamber and under a controlled temperature gradient, carbon-metal clusters are formed and become the potential sites for nucleation and growth of SWCNTs. In this process, the local plasma properties and the thermo-fluid field in the system affect the yield rate of SWCNTs, and therefore it is important to find an appropriate operating condition, which maximizes the yield rate. Numerical modeling in conjunction with experimental studies can help investigate the contribution of the thermo-fluid field and process parameters to the formation of catalyst nanoparticles and carbon nanotubes in the induction thermal plasma system. The goal of this research is to carry numerical study of SWCNT growth in a RF induction thermal plasma system with a suitable chemistry model. This model is employed to investigate the influence of the thermo-fluid field and gas-phase reactions on carbon nanotube growth and to predict the SWCNT yield rate as a function of operating conditions. © 2011 by JSME.

Indexación: Scopus. The Plasma Focus (PF) is a kind of dense transient plasmas in with high-pulsed voltage. To produce devices for eld application it is necessary to obtain PF equipment able to operate for a long period of time. Thus, a reliability analysis is indispensable. In this work a reliability analysis program for plasma focus devices is presented. The program considers a criticality analysis using Failure Modes and Effects Criticality Analysis (FMECA) to identify the most important failure modes of the system. Said failure modes are studied operating the Plasma Focus for many cycles, obtaining from them the characteristic curves of V(t) and İ(t). Feature Extraction (FE) techniques are applied to obtain a list of parameters that correlate to the degrading process. Furthermore, Machine Learning tools are used to learn from the obtained data, linking the changes in these parameters during its life cycle to the decay of the system in hope for future implementation of a predictive maintenance system and a reference for data analysis and prediction in PFs. The study was applied to a portable plasma focus device operated at 2 joules of stored energy. © Published under licence by IOP Publishing Ltd. The work is supported by IAEA CRP contract 20370 and by grant ACT-1115, CONICYT, Chile. https://iopscience.iop.org/article/10.1088/1742-6596/1043/1/012049

In this work, several optical studies in an atmospheric pressure sliding plasma sheet have been performed. This discharge is generated using two electrodes flush mounted on an insulating flat plate (upper electrodes), and a third electrode flush placed on the opposite side of the plate facing the upper inter electrode gap (lower electrode). A dc negative voltage is applied to one of the two upper electrodes and to the lower electrode, while the other upper electrode is biased with an ac voltage. In this configuration a sliding discharge is produced on the flat plate within the upper electrode's gap. The sliding discharge optical emission of the spectral bands corresponding to the 0-0 transition of the second positive system of N2 (λ = 337.1 nm) and the first negative system of N2 + (λ = 391.4 nm) have been measured. Also the light spatial distribution in the plasma sheet has been studied using a CCD camera coupled to interferential filters corresponding to the wavelengths investigated. The reduced electric field in the plasma sheet has been derived from the measurement of the intensity ratio of the Nitrogen lines. This study has been realized varying the amplitude of the dc voltage and the amplitude and frequency of the ac voltage. The reduced electric field strength is found to be almost constant for all the experimental conditions, with a value of 500 ± 100 Td (1 Td = 1.10-17 V cm2). © 2006 IEEE. Fil: Lago, V.. Centre National de la Recherche Scientifique; Francia Fil: Grondona, Diana Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; Argentina Fil: Kelly, Hector Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; Argentina Fil: Sosa, Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Laboratorio de Fluidodinámica; Argentina Fil: Marquez, Adriana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; Argentina Fil: Artana, Guillermo Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Laboratorio de Fluidodinámica; Argentina

International audience; This experimental work deals with the exposition of Pinus Pinaster wood samples to a DBD afterglow. Electrical parameters like duty cycle and injected energy in the gas are being varied and the modifications induced by the afterglow on the wood are analysed by several macroscopic and microscopic ways like wettability, XPS analyses and also soaking tests of treated wood in a commercial fungicide solution. Soaking tests show that plasma treatment could enhance the absorption of fungicide into the wood. The wettability results point out that the plasma treatment can inflict on the wood different surface properties, making it hydrophilic or hydrophobic, when varying electrical parameters. XPS analyses reveal several chemical modifications like an increase of the O/C ratio and the presence of carboxyl groups on the surface after plasma treatments.

Microplasmas are currently used in displays, two-terminal breakdown switches, light sources, and medical instruments. They can also be used in miniaturized particle accelerators, micro-X-ray generators, UV and extreme UV sources, gas sensors, and in micropropulsion thrusters. They are also excellent candidates for applications in harsh environments that usually lead to the breakdown of silicon electronics. Here we develop their unique applications in X-band microwave analog and digital devices and circuits. To enable these applications, we identified a breakdown region, called sub-Paschen regime that enables generation of atmospheric plasmas at low voltages. The sub-Paschen regime, involves devices with a breakdown gap below 10 m in 1 atmosphere in air. This newly discovered operation regime enabled us to design plasma devices with relatively low operation voltages of 50-100 V. We developed microplasma devices similar to metal oxide semiconductor field effect transistors (MOSFETs) with drain, source, and gate regions that used plasma channels for switching or amplification. The gate field effect was successfully tested under both direct current (dc) and alternating current (ac) excitations. A drain current modulation frequency up to 7 GHz was obtained. Additionally, we implemented logic gates with microplasma devices to realize simple Boolean logic operations including OR, AND, NOT, and XOR. The gates were then combined to obtain a 1-bit half-adder circuit. The MOPFET developed in this work achieved 3x reduction in the breakdown (device turn-on) voltage by operating in the sub-Paschen regime. In addition to the scaling in breakdown voltage, the microplasma field effect transistors (MOPFETs) are at least 50x smaller compared to plasma transistors reported in the past. The smallest MOPFET used in this work had a source-drain gap of 1 μm and showed unprecedented functionalities derived from plasmas at a microscale.

The electrostatic response of the edge plasma to a magnetic island induced by resonant magnetic perturbations to the plasma edge of the circular limiter tokamak TEXTOR is analyzed. Measurements of plasma potential are interpreted by simulations with the Hamiltonian guiding center code Orbit. We find a strong correlation between the magnetic field topology and the poloidal modulation of the measured plasma potential. The ion and electron drifts yield a predominantly electron driven radial diffusion when approaching the island X-point while ion diffusivities are generally an order of magnitude smaller. This causes a strong radial electric field structure pointing outward from the island O-point. The good agreement found between measured and modeled plasma potential connected to the enhanced radial particle diffusivities supports that a magnetic island in the edge of a tokamak plasma can act as convective cell. We show in detail that the particular, non-ambipolar drifts of electrons and ions in a 3D magnetic topology account for these effects. An analytical model for the plasma potential is implemented in the code Orbit, and analyses of ion and electron radial diffusion show that both ion- and electron-dominated transport regimes can exist, which are known as ion and electron root solutions in stellarators. This finding and comparison with reversed field pinch studies and stellarator literature suggest that the role of magnetic islands as convective cells and hence as major radial particle transport drivers could be a generic mechanism in 3D plasma boundary layers.

Indexación: Scopus The plasma generated by plasma focus (PF) devices have substantially different physical characteristics from another plasma, energetic ions and electrons, compared with conventional plasma devices used for plasma nanofabrication, offering new and unique opportunities in the processing and synthesis of Nanomaterials. This article presents the use of a plasma focus of tens of joules, PF-50J, for the deposition of materials sprayed from the anode by the plasma dynamics in the axial direction. This work focuses on the determination of the most significant effects of the technological parameters of the system on the obtained depositions through the use of a statistical experimental design. The results allow us to give a qualitative understanding of the Ti film deposition process in our PF device depending on four different events provoked by the plasma dynamics: i) an electric erosion of the outer material of the anode; ii) substrate ablation generating an interlayer; iii) electron beam deposition of material from the center of the anode; iv) heat load provoking clustering or even melting of the deposition surface. https://aip.scitation.org/doi/pdf/10.1063/1.4997877

This work describes the experimental set up used for carrying out spectroscopic measurements in a plasma cathode electron beam (EB) gun. Advantages of plasma cathode guns over thermionic guns are described. The factors affecting electron beam power such as plasma pressure, excitation power and plasma chamber geometry are discussed. The maximum beam current extracted was 53 mA from a 0.5 mm diameter aperture in the plasma chamber. In this work, the electron source is an argon plasma excited at 84 MHz. The pressure in the plasma chamber was measured to be within 0.9 to 1.2 mbar and was controlled by varying gas flow rates. The vacuum chamber was at a pressure of 10^-5 mbar. TWI and Brunel University.

The use of a plasma microdischarge as a reconfigurable element for a frequency tunable microstrip antenna is theoretically and numerically investigated.

The present study examined the effect of Dielectric Barrier Discharge (DBD) plasma on bioaerosol particles. Different DBD plasma devices were designed and tested for their efficacy in inactivation of airborne bacteria. Bacterial aerosols were injected in / through the plasma stream and the treated bioaerosols were analyzed. The results indicated a complete inactivation of bioaerosol upon a very short exposure in the range of milliseconds to plasma discharge. A large system was designed to evaluate its efficacy to inactivate bacterial spores. After preliminary studies, to study the underlying mechanisms of inactivation, a single filament DBD plasma generating probe was developed and used for subsequent studies. In parallel, a near uniform aerosol generator (nebulizer) was optimized, and aerosol particle size characterized. The kinetics of bacterial inactivation produced by this system was investigated, and sub-lethal dose determined. We hypothesized that the prototype bacteria, Escherichia coli when present in aerosols and exposed to single filament DBD plasma system, activates intracellular reactive oxygen species (ROS). The predetermined sub-lethal dose of DBD plasma was used to study the cellular responses of Escherichia coli during its inactivation. Cell membrane is more vulnerable when bacteria are present in aerosols, and hence the changes in features, such as cellular respiration and growth, permeation, and depolarization were investigated following exposure to single filament DBD plasma system. During studies, the catalase mediated defense system was found to be involved predominantly in the management of intracellular ROS pool. Through the use of E. coli derivatives of specific gene mutation, we analyzed the involvement of heat stress-responsive genes. Although the plasma is considered non-thermal, localized heating and the generated interactive stress is likely involved in the inactivation of E. coli bioaerosol. These findings provide a new dimension in underlying mechanisms of E. coli inactivation during DBD plasma exposure.

Indispensable in CMOS manufacturing, plasma treatments may result in a latent damage in gate oxides. We propose a method to detect this latent damage as a function of the area of the multifingered metal pad connected to the gate, by using an experimental method based on constant current stress and oxide trapped charge measurements. We measured a power law behavior describing the dependence of the trapped charge on the injected charge.

Nanometer size field effect transistors can operate as efficient resonant or broadband terahertz detectors, mixers, phase shifters and frequency multipliers at frequencies far beyond their fundamental cut-of frequency. This work is an overview of some recent results concerning the THz detection by Si MOS transistors with back-gate, low temperatures operation, and circular polarization studies of nanometer scale field effect transistors for the detection of terahertz radiation. Also first results on graphene transistors are discussed.

The post-breakdown characteristics of field emission driven microplasma are studied theoretically and numerically. A cathode fall model assuming a linearly varying electric field is used to obtain equations governing the operation of steady state field emission driven microplasmas. The results obtained from the model by solving these equations are compared with particle-in-cell with Monte Carlo collisions simulation results for parameters including the plasma potential, cathode fall thickness, ion number density in the cathode fall, and current density vs voltage curves. The model shows good overall agreement with the simulations but results in slightly overpredicted values for the plasma potential and the cathode fall thickness attributed to the assumed electric field profile. The current density vs voltage curves obtained show an arc region characterized by negative slope as well as an abnormal glow discharge characterized by a positive slope in gaps as small as 10 ?m operating at atmospheric pressure. The model also retrieves the traditional macroscale current vs voltage theory in the absence of field emission. � 2013 AIP Publishing LLC.

The choice of material for a crucible is essential in hybrid microwave heating and graphite is one of the strong microwave absorbers which can sustain high temperatures. Experiments were carried out to investigate the microwave heating behavior of graphite combined with other materials to enhance efficiency. Mixtures comprising of graphite and magnetite or graphite and silicon carbide were found to have better microwave heating properties than pure components. The enhancement was likely due to microplasma generated by graphite in a microwave environment. Microwave heating of graphite-silicon carbide mixtures provided the best results in terms of high heating rates without arcing. The optimal combination of graphite-silicon carbide was identified and can be used as a starting material for making efficient crucibles and susceptors. � 2013 Elsevier Ltd.

A 1.5 m×1.8 m rectangular composite mirror composed of 138 segment hexagonal spherical mirrors was constructed for collecting Thomson scattered light from the Large Helical Device plasma. The hexagonal mirrors with side length of 87 mm were patched on the surface of a framework made of glass fiber reinforced plastic. The position and angular orientation of each mirror are adjusted with three pairs of push-and-pull screws attached to the back plane of the mirrors so that the image of a tiny light source (0.1 mm in diameter) formed by each segment mirror be minimized and coincide with each other on a charge coupled device plate. The optical quality and its long-term stability of the assembled mirror have been monitored and sufficient for the present purpose.

2D axisymmetric numerical calculations are conducted to model the thermo-fluid fields and chemical reactions leading to the formation of SWCNTs in an RF plasma system. A modified version of the SWCNT "reduced" chemical model is used to estimate the formation of SWCNT in an RF plasma system for the first time. The "reduced" model incorporates 14 species and 36 chemical reactions to predict the formation of metal and carbon clusters and SWCNTs. By combing the chemistry model into the RF plasma CFD code, the formation and development of carbon and metal catalyst clusters and their reactions which produce SWCNTs are shown. The chemistry model is shown to under-predict the yield rate of SWCNT. In order to better predict the yield rate, a sensitivity analysis is performed to modify the dominant reaction rates. The modified model predicts the yield of SWCNTs correctly within the range reported experimentally. However, more studies should be conducted to validate the accuracy of the model for different operating conditions., 12th High-Tech Plasma Processes Conference, HTPP 2012, 24 June 2012 through 29 June 2012, Bologna

The forcing behavior of a dielectric barrier discharge (DBD) actuator is investigated experimentally using a time-resolved particle image velocimetry (PIV) system in conjunction with a phase shifting technique. The spatio-temporal evolution of the induced flowfield is accurately captured within one high voltage (HV) cycle allowing the calculation of the instantaneous velocity and acceleration. Additional voltage and current measurements provide the power consumption for each case. Four different applied voltage waveform shapes are independently tested, namely, sine, square, positive sawtooth, and negative sawtooth at fixed applied voltage (10 kVpp) and carrier frequency (625 Hz). The instantaneous flowfields reveal the effect of the plasma forcing during the HV cycle. Sine waveform provides large positive forcing during the forward stroke, with minimal but still positive forcing during the backward stroke. Square waveform provides strong and concentrated positive and negative forcing at the beginning of the forward and backward stroke, respectively. Positive sawtooth provides positive but weak forcing during both strokes while the negative sawtooth case produces observable forcing only during the forward stroke. Results indicate the inherent importance of negative ions on the force production mechanisms of DBD’s. Furthermore, the revealed influence of the waveform shape on the force production can provide guidelines for the design of custom asymmetric waveforms for the improvement of the actuator’s performance.

International audience; Reactive RF plasmas are an excellent source for the production of nanoparticles. The field of application of nanoparticles is nowadays rapidly growing, as well as the request for investigations on the nanoparticle material itself. Thus, we deal with the emerging need for targeted sampling of nanoparticles from the plasma. We developed a sampling system based on the effect of thermophoresis on the transport of nanoparticles within the plasma bulk.

Väitekirja elektooniline versioon ei sisalda publikatsioone., Antud doktoritöös uuriti plasmaekraanide kaitsekihtide materjale ühe plasmaekraanide olulisima parameetri, süttimispinge, seisukohast. Plasmaekraanid koosnevad tuhandtetest gaaslahendusrakkudest ja ekraanide energiatarve ja maksumus on otseselt seotud rakkudes tekitatava gaaslahenduse süttimispingega - mida madalam süttimispinge, seda madalam energiatarve ja seda vähem maksavad ekraanis sisalduvad elektroonikakomponendid. Sünteesitud materjalide süttimispingete mõõtmiseks sadestati uuritavast materjalist kiled spetsiaalsetele alektroodalustele ja mõõdeti kahest vastakuti asetatud alusest koosneva testraku süttimispinge. Õhukeste kilede sadesamiseks kasutati impulss-lasersadestuse seadet. Töös käsitletud materjalideks olid BaGa2O4, BaY2O4 ning puhas ja dopeeritud MgO. Magneesium oksiidi - mis on ka hetkel plasmaekraanis tööstuslikult kasutatav kaitsekihi materjal - korral uuriti sadestustingimuste mõju kasvanud kilede struktuurile ning kilede struktuuri ja dopeerimise mõju gaaslahendusomadustele. Uuriti ka kahe potentsiaalse kaitsekihi asendusmaterjali, BaGa2O4 ja BaY2O4, kilede struktuuri ja gaaslahendusomadusi. Olulisimad faktorid madala süttimispinge saavutamiseks olid MgO kilede korral nende tihedus ja kristallilisus - mida suurem oli kilede tihedus ja kristallilisus, seda väiksem oli süttimispinge. Lisaks selgus analüüsiandmetest, et ka kilede suur pinnakaredus soodustab madala süttimispinge saavutamist. Doktoritöös sünteesiti ka vesinikuga dopeeritud MgO õhukesed kiled. Analüüs näitas, et vesinikulisand tekitas magnesium oksiidi kristallis defekte, mis on võimelised lõksustama elektrone. Need elektronlõksud mõjutasid kilede gaaslahendusomadusi nii, et dopeeritud kilede süttimispinge oli kuni 55 V (20%) madalam kui vesinikulisandita kilede süttimispinge. Kahe uuritud baariumi kolmikoksiidi, BaY2O4 ja BaGa2O4, korral saadi süttimispingete väärtusteks 210 V (BaY2O4) ja 257 V (BaGa2O4), mis on oluliselt kõrgemad võrreldes MgO kiledel mõõdetud väärtustega (, Plasma displays and liquid crystal displays are currently two main large screen display technologies oriented to home-consumers’ market. Besides other elements that influence the PDP characteristics most, the thin layer (protective layer) of MgO in plasma screen is one key element in PDPs and its properties have large influence on the display’s image quality, its lifetime, cost and power consumption. In this work, the morphological and defect structure of MgO thin films was modified by varying film synthesizing conditions. The influence of these modifications on films’ characteristics was studied from the standpoint of PDP applications. Some possible replacement materials for MgO were also investigated. The main attention was turned to the materials group of barium ternary oxides. The thin films, investigated in this work, were synthesized by the pulsed laser deposition (PLD) method. The firing voltage (FV) of the deposited samples, which is the direct indicator of the power consumption of the PDP device (low FV means low power consumption), was measured in our experiments. The density and the crystallinity of the MgO films were the main factors influencing the FV values – high density and crystallinity was accompanied by low FV values of the samples. It was also observed that the high surface roughness of the films favored the achieving of low FVs. MgO films with hydrogen impurities were synthesized. Analysis indicated that the hydrogen impurities in MgO crystal created defects capable of catching electrons. These electron traps influenced the electronic properties of the thin films so that they had up to 55 V (27%) lower FVs than the ones without the hydrogen impurities. Two barium ternary oxides, BaY2O4 and BaGa2O4, were considered as a plasma display protective coating material candidates. The FV values of BaY2O4 (210 V) and BaGa2O4 (257 V) were considerably higher as compared to the FVs of MgO films (