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Plasma, Volume 2, Issue 3 (September 2019) – 10 articles

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Open AccessArticle
Experimental Investigation on the Influence of Target Physical Properties on an Impinging Plasma Jet
Plasma 2019, 2(3), 369-379; https://doi.org/10.3390/plasma2030029 - 16 Sep 2019
Cited by 1 | Viewed by 1232
Abstract
The present work aims to investigate the interaction between a plasma jet and targets with different physical properties. Electrical, morphological and fluid-dynamic characterizations were performed on a plasma jet impinging on metal, dielectric and liquid substrates by means of Intensified Charge-Coupled Device (ICCD) [...] Read more.
The present work aims to investigate the interaction between a plasma jet and targets with different physical properties. Electrical, morphological and fluid-dynamic characterizations were performed on a plasma jet impinging on metal, dielectric and liquid substrates by means of Intensified Charge-Coupled Device (ICCD) and high-speed Schlieren imaging techniques. The results highlight how the light emission of the discharge, its time behavior and morphology, and the plasma-induced turbulence in the flow are affected by the nature of the target. Surprisingly, the liquid target induces the formation of turbulent fronts in the gas flow similar to the metal target, although the dissipated power in the former case is lower than in the latter. On the other hand, the propagation velocity of the turbulent front is independent of the target nature and it is affected only by the working gas flow rate. Full article
(This article belongs to the Special Issue Low Temperature Plasma Jets: Physics, Diagnostics and Applications)
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Open AccessReview
1995–2005: A Decade of Innovation in Low Temperature Plasma and Its Applications
Plasma 2019, 2(3), 360-368; https://doi.org/10.3390/plasma2030028 - 30 Aug 2019
Viewed by 1685
Abstract
Scientific breakthroughs tend to come in spurts when unique societal, economical, and political circumstances conspire (knowingly or unknowingly) and create an environment ripe for creativity. The field of low temperature plasma (LTP) recently experienced such an upheaval, which this paper attempts to relate [...] Read more.
Scientific breakthroughs tend to come in spurts when unique societal, economical, and political circumstances conspire (knowingly or unknowingly) and create an environment ripe for creativity. The field of low temperature plasma (LTP) recently experienced such an upheaval, which this paper attempts to relate in some details. There have been “roadmap” papers published before, which look towards the future of the field, but all roads start somewhere and even “new” roads are often paved over older roads that were discovered and traveled by early pioneers. With the sharp decrease in funding for fusion research in the USA in the early 1990s the plasma science community was faced with a dire situation that threatened to choke off plasma physics advances. However, in the background and far from the visibility accorded to fusion research, a few laboratories were quietly engaged in innovative research that in due time revolutionized the LTP field and breathed new life into plasma science. Groundbreaking applications of LTP were investigated that until today constitute most of the LTP research activities. These innovations spanned a wide spectrum that included the invention of novel devices, improvement of existing ones, and the deployment of these devices to areas ranging from industrial to biomedical applications. These efforts turned out to have impactful scientific and societal implications. In this paper plasma sources and applications developed during this uniquely innovative decade are briefly discussed. Full article
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Open AccessArticle
Investigation of Power Transmission of a Helium Plasma Jet to Different Dielectric Targets Considering Operating Modes
Plasma 2019, 2(3), 348-359; https://doi.org/10.3390/plasma2030027 - 22 Aug 2019
Cited by 2 | Viewed by 933
Abstract
The interaction of an atmospheric pressure plasma jet with different dielectric surfaces is investigated using a setup of two ring electrodes around a ceramic capillary. In this study, in addition to electrical measurement methods such as the determination of voltage and current, special [...] Read more.
The interaction of an atmospheric pressure plasma jet with different dielectric surfaces is investigated using a setup of two ring electrodes around a ceramic capillary. In this study, in addition to electrical measurement methods such as the determination of voltage and current, special emphasis was placed on the power measurements at the electrodes and the effluent. The power dissipation is correlated with Fourier-transform infrared (FTIR) absorption spectroscopy measurements of O3 and NO2 densities. The results show the correlation between the dielectric constant and the dissipated power at the target. The ratio between power dissipation at the grounded ring electrode and the grounded surface shows an increase with increasing dielectric constant of the target. A correlation of the results with bacteria, tissue and water as envisaged dielectric targets shows four times the power dissipation at the treatment spot between bacteria and tissue. Full article
(This article belongs to the Special Issue Low Temperature Plasma Jets: Physics, Diagnostics and Applications)
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Open AccessArticle
Reducing the Transition Hysteresis of Inductive Plasmas by a Microwave Ignition Aid
Plasma 2019, 2(3), 341-347; https://doi.org/10.3390/plasma2030026 - 16 Aug 2019
Viewed by 1086
Abstract
Inductive plasma discharge has been a part of continuous investigations since it was discovered. Especially the E- to H-mode transition and the hysteresis behavior have been topics of research in the last few decades. In this paper, we demonstrate a way to reduce [...] Read more.
Inductive plasma discharge has been a part of continuous investigations since it was discovered. Especially the E- to H-mode transition and the hysteresis behavior have been topics of research in the last few decades. In this paper, we demonstrate a way to reduce the hysteresis behavior by the usage of a microwave ignition system. With this system, a significant decrease of the needed coil current for the ignition of the inductive driven plasma is realized. For the microwave generation, a magnetron as in a conventional microwave oven is used, which offers a relatively inexpensive way for microwave ignition aid. At the measured pressure of 7.5 Pa, it was possible to reduce the needed coil current for the inductive mode transition by a factor of 3.75 compared to the mode transition current without the ignition aid. This was achieved by initiating the transition by a few seconds of microwave coupling. The performed simulations suggested that the factor can be further increased at higher pressures. That is especially interesting for plasmas that are hard to ignite or for RF-sources that cannot deliver high enough currents or frequencies for the ignition. Full article
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Open AccessEditorial
Special Issue on Low Temperature Plasma Jets
Plasma 2019, 2(3), 339-340; https://doi.org/10.3390/plasma2030025 - 31 Jul 2019
Cited by 1 | Viewed by 897
Abstract
Low temperature plasma jets are unique plasma sources capable of delivering plasma outside of the confinement of electrodes and away from gas enclosures/chambers [...] Full article
(This article belongs to the Special Issue Low Temperature Plasma Jets: Physics, Diagnostics and Applications)
Open AccessArticle
H-Mode Power Threshold Studies on MAST
Plasma 2019, 2(3), 328-338; https://doi.org/10.3390/plasma2030024 - 19 Jul 2019
Cited by 1 | Viewed by 1318
Abstract
Analysis of the L–H and H–L transition power thresholds (Pth) and pedestal parameters are presented for the mega ampere spherical tokamak (MAST). The dependencies of Pth on the average, core plasma electron density, X-point height, and plasma current are [...] Read more.
Analysis of the L–H and H–L transition power thresholds (Pth) and pedestal parameters are presented for the mega ampere spherical tokamak (MAST). The dependencies of Pth on the average, core plasma electron density, X-point height, and plasma current are described. Increasing X-point distance from the divertor floor over 10–12 cm is found to increase Pth by a factor of three, while X-point heights greater than this have no further influence. The X-point height dependence of Pth is also observed to be sensitive to the plasma current. An Ip decrease from 0.77 MA to 0.65 MA, is observed to lower Pth by a factor of three across the X-point height scan and increases the maximum X-point height at which Pth stops increasing by 3 cm. Finally, a comparison of the experimental results with the predictions by the finite beta drift wave model is made, which provides a reasonable condition for the transition into and out of the H-mode. Full article
(This article belongs to the Special Issue Magnetic Confinement Fusion)
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Open AccessReview
Applications of the COST Plasma Jet: More than a Reference Standard
Plasma 2019, 2(3), 316-327; https://doi.org/10.3390/plasma2030023 - 12 Jul 2019
Cited by 5 | Viewed by 1470
Abstract
The rapid advances in the field of cold plasma research led to the development of many plasma jets for various purposes. The COST plasma jet was created to set a comparison standard between different groups in Europe and the world. Its physical and [...] Read more.
The rapid advances in the field of cold plasma research led to the development of many plasma jets for various purposes. The COST plasma jet was created to set a comparison standard between different groups in Europe and the world. Its physical and chemical properties are well studied, and diagnostics procedures are developed and benchmarked using this jet. In recent years, it has been used for various research purposes. Here, we present a brief overview of the reported applications of the COST plasma jet. Additionally, we discuss the chemistry of the plasma-liquid systems with this plasma jet, and the properties that make it an indispensable system for plasma research. Full article
(This article belongs to the Special Issue Low Temperature Plasma Jets: Physics, Diagnostics and Applications)
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Open AccessArticle
Analysis of the Preheating Phase of Micro-Arc Discharge in Seawater, Operated Using a Needle-to-Plane Electrode with Variation in the Tip Shape
Plasma 2019, 2(3), 303-315; https://doi.org/10.3390/plasma2030022 - 08 Jul 2019
Cited by 1 | Viewed by 1033
Abstract
In this work, micro-arc discharge is investigated using a needle-to-plane electrode system placed with a micro-gap in highly conductive artificial seawater. A major problem with microarc discharge is the erosion of electrodes caused by the high current of the arc; however, it was [...] Read more.
In this work, micro-arc discharge is investigated using a needle-to-plane electrode system placed with a micro-gap in highly conductive artificial seawater. A major problem with microarc discharge is the erosion of electrodes caused by the high current of the arc; however, it was found that erosion of the needle electrode did not have any effect on the discharge process in the case of precise control of the discharge gap. A simple mathematical model was developed for a more detailed study of the preheating phase of the discharge. The modeling showed good agreement with the experimental results and confirmed that the needle electrode could be reused to generate reproducible micro-arc discharges even after the erosion caused by the arc. Moreover, it was found that, in certain conditions, the preheating phase could be simulated using a simple inductor-capacitor-resistor (LCR) oscillator model with a resistor instead of electrodes immersed in the liquid. It was confirmed that the shape of the needle electrode’s tip did not affect the measurement of optical emission spectra in the case of precise focusing, which could be used in the development of compact analytical tools for on-site analysis of deep-sea water using atomic emission spectroscopy. Full article
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Open AccessArticle
Hydrogen Peroxide Interference in Chemical Oxygen Demand Assessments of Plasma Treated Waters
Plasma 2019, 2(3), 294-302; https://doi.org/10.3390/plasma2030021 - 05 Jul 2019
Cited by 2 | Viewed by 1221
Abstract
Plasma-driven advanced oxidation represents a potential technology to safely re-use waters polluted with recalcitrant contaminants by mineralizing organics via reactions with hydroxyl radicals, thus relieving freshwater stress. The process results in some residual hydrogen peroxide, which can interfere with the standard method for [...] Read more.
Plasma-driven advanced oxidation represents a potential technology to safely re-use waters polluted with recalcitrant contaminants by mineralizing organics via reactions with hydroxyl radicals, thus relieving freshwater stress. The process results in some residual hydrogen peroxide, which can interfere with the standard method for assessing contaminant removal. In this work, methylene blue is used as a model contaminant to present a case in which this interference can impact the measured chemical oxygen demand of samples. Next, the magnitude of this interference is investigated by dosing de-ionized water with hydrogen peroxide via dielectric barrier discharge plasma jet and by solution. The chemical oxygen demand increases with increasing concentration of residual hydrogen peroxide. The interference factor should be considered when assessing the effectiveness of plasma to treat various wastewaters. Full article
(This article belongs to the Special Issue Low Temperature Plasma Jets: Physics, Diagnostics and Applications)
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Open AccessArticle
Emission Spectroscopic Characterization of a Helium Atmospheric Pressure Plasma Jet with Various Mixtures of Argon Gas in the Presence and the Absence of De-Ionized Water as a Target
Plasma 2019, 2(3), 283-293; https://doi.org/10.3390/plasma2030020 - 04 Jul 2019
Cited by 3 | Viewed by 1112
Abstract
A helium-based atmospheric pressure plasma jet (APPJ) with various flow rates of argon gas as a variable working gas was characterized by utilizing optical emission spectroscopy (OES) alongside the plasma jet. The spectroscopic characterization was performed through plasma exposure in direct and indirect [...] Read more.
A helium-based atmospheric pressure plasma jet (APPJ) with various flow rates of argon gas as a variable working gas was characterized by utilizing optical emission spectroscopy (OES) alongside the plasma jet. The spectroscopic characterization was performed through plasma exposure in direct and indirect interaction with and without de-ionized (DI) water. The electron density and electron temperature, which were estimated by Stark broadening of atomic hydrogen (486.1 nm) and the Boltzmann plot, were investigated as a function of the flow rate of argon gas. The spectra obtained by OES indicate that the hydroxyl concentrations reached a maximum value in the case of direct interaction with DI water as well as upstream of the plasma jet for all cases. The relative intensities of hydroxyl were optimized by changing the flow rate of argon gas. Full article
(This article belongs to the Special Issue Low Temperature Plasma Jets: Physics, Diagnostics and Applications)
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