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Plasma, Volume 6, Issue 1 (March 2023) – 14 articles

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17 pages, 2243 KiB  
Article
The Post-Shock Nonequilibrium Relaxation in a Hypersonic Plasma Flow Involving Reflection off a Thermal Discontinuity
Plasma 2023, 6(1), 181-197; https://doi.org/10.3390/plasma6010014 - 06 Mar 2023
Cited by 1 | Viewed by 1044
Abstract
The evolution in the post-shock nonequilibrium relaxation in a hypersonic plasma flow was investigated during a shock’s reflection off a thermal discontinuity. It was found that within a transitional period, the relaxation zone parameters past both the reflected and transmitted waves evolve differently [...] Read more.
The evolution in the post-shock nonequilibrium relaxation in a hypersonic plasma flow was investigated during a shock’s reflection off a thermal discontinuity. It was found that within a transitional period, the relaxation zone parameters past both the reflected and transmitted waves evolve differently compared to that in the incident wave. In a numerical example for the non-dissociating N2 gas heated to 5000 K/10,000 K across the interface and M = 3.5, the relaxation time determined for the transmitted wave is up to 50% shorter and the relaxation depth for both waves is significantly reduced, thus resulting in a weakened wave structure. The results of the extension into larger values of heating strength and the shock Mach numbers are discussed. The findings can be useful in the areas of research involving strong shocks interacting with optical discharges or other heated media on the scale where the shock structure becomes important. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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19 pages, 2899 KiB  
Article
Plane Parallel Barrier Discharges for Carbon Dioxide Splitting: Influence of Discharge Arrangement on Carbon Monoxide Formation
Plasma 2023, 6(1), 162-180; https://doi.org/10.3390/plasma6010013 - 06 Mar 2023
Cited by 6 | Viewed by 1726
Abstract
A planar volume dielectric barrier discharge (DBD) in pure carbon dioxide (CO2) for the formation of carbon monoxide (CO) is examined by combined electrical and CO density measurements. The influence of the type of electrode, the barrier material, the barrier thickness, [...] Read more.
A planar volume dielectric barrier discharge (DBD) in pure carbon dioxide (CO2) for the formation of carbon monoxide (CO) is examined by combined electrical and CO density measurements. The influence of the type of electrode, the barrier material, the barrier thickness, and the discharge gap on the plasma power and the CO formation is analyzed systematically. The electrical characterization by means of charge-voltage plots is based on the simplest equivalent circuit model of DBDs, extended by the so-called partial surface discharge effect and the presence of parallel parasitic capacitances. The stackable discharge arrangement in this study enables one to elucidate the influence of parasitic capacitances, which can be overlooked in the application of such plasma sources. The determination of the discharge voltage from charge-voltage plots and the validity of the so-called Manley power equation are revised by taking into account non-uniform coverage as well as parasitic capacitances. The energy yield (EY) of CO is analyzed and compared with the literature. No correlations of EY with the mean reduced electric field strength or the geometric parameters of the DBD arrangement are observed. Full article
(This article belongs to the Special Issue Dielectric Barrier Discharges 2023)
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23 pages, 7129 KiB  
Article
Application of Plasma Bridge for Grounding of Conductive Substrates Treated by Transferred Pulsed Atmospheric Arc
Plasma 2023, 6(1), 139-161; https://doi.org/10.3390/plasma6010012 - 05 Mar 2023
Cited by 1 | Viewed by 1428
Abstract
An atmospheric pressure plasma jet (APPJ) sustained by a pulsed atmospheric arc (PAA) transferred on an electrically conducting surface was operated with a mean power of 700 W, a pulse frequency of 60 kHz, and a gas mixture of N2 and H [...] Read more.
An atmospheric pressure plasma jet (APPJ) sustained by a pulsed atmospheric arc (PAA) transferred on an electrically conducting surface was operated with a mean power of 700 W, a pulse frequency of 60 kHz, and a gas mixture of N2 and H2 with up to 10% H2, flowing at 30 to 70 SLM. It was shown that the plasma bridge ignited between the grounded injector and electrically conducting and floating substrates can be used for electrical grounding. This allowed for arc transfer on such substrates. The plasma bridge was stable for Argon flow through the injector from 3 to 10 SLM. Its length was between 5 and 15 mm. The plasma bridge current was 350 mA. The copper contact pads on an alumina electronic board were treated using the plasma bridge sustained by Ar injection for grounding. First, an oxide film of about 65 nm was grown by a compressed dry air (CDA) plasma jet. Then, this film was reduced at a speed of 4 cm2/s by forming gas 95/5 (95% of N2 and 5% of H2) plasma jet. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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12 pages, 2207 KiB  
Article
Electrocoalescence of Water Droplets
Plasma 2023, 6(1), 127-138; https://doi.org/10.3390/plasma6010011 - 01 Mar 2023
Viewed by 1404
Abstract
An experimental setup has been created to study the electrocoalescence of submillimeter- and millimeter-sized water droplets on a hydrophobic dielectric surface. The dependences of the interdroplet distance on the droplet radius are studied. It is shown that drops on a hydrophobic surface exhibit [...] Read more.
An experimental setup has been created to study the electrocoalescence of submillimeter- and millimeter-sized water droplets on a hydrophobic dielectric surface. The dependences of the interdroplet distance on the droplet radius are studied. It is shown that drops on a hydrophobic surface exhibit patterns of spatial arrangement that are characteristic of drops of a droplet cluster and fog. The electric field strengths at which mass coalescence of droplets begin are measured. A new model of electrocoalescence based on the state diagram of a drop-ion plasma is proposed. The possible role of electrocoalescence in the problem of rapid rain formation in atmospheric clouds is discussed. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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12 pages, 3859 KiB  
Article
CO2 Decomposition in Microwave Discharge Created in Liquid Hydrocarbon
Plasma 2023, 6(1), 115-126; https://doi.org/10.3390/plasma6010010 - 27 Feb 2023
Cited by 3 | Viewed by 1504
Abstract
The task of CO2 decomposition is one of the components of the problem associated with global warming. One of the promising directions of its solution is the use of low-temperature plasma. For these purposes, different types of discharges are used. Microwave discharge [...] Read more.
The task of CO2 decomposition is one of the components of the problem associated with global warming. One of the promising directions of its solution is the use of low-temperature plasma. For these purposes, different types of discharges are used. Microwave discharge in liquid hydrocarbons has not been studied before for this problem. This paper presents the results of a study of microwave discharge products in liquid Nefras C2 80/120 (petroleum solvent, a mixture of light hydrocarbons with a boiling point from 33 to 205 °C) when CO2 is introduced into the discharge zone, as well as the results of a study of the discharge by optical emission spectroscopy and shadow photography methods. The main gas products are H2, C2H2, C2H4, CH4, CO2, and CO. No oxygen was found in the products. The mechanisms of CO2 decomposition in the discharge are considered. The formation of H2 occurs simultaneously with the decomposition of CO2 in the discharge, with a volumetric rate of up to 475 mL/min and energy consumption of up to 81.4 NL/kWh. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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12 pages, 3294 KiB  
Article
Understanding the Role of Plasma Bullet Currents in Heating Skin to Mitigate Risks of Thermal Damage Caused by Low-Temperature Atmospheric-Pressure Plasma Jets
Plasma 2023, 6(1), 103-114; https://doi.org/10.3390/plasma6010009 - 27 Feb 2023
Cited by 3 | Viewed by 1697
Abstract
Low-temperature atmospheric-pressure plasma jets are generally considered a safe medical technology with no significant long-term side effects in clinical studies reported to date. However, there are studies emerging that show plasma jets can cause significant side effects in the form of skin burns [...] Read more.
Low-temperature atmospheric-pressure plasma jets are generally considered a safe medical technology with no significant long-term side effects in clinical studies reported to date. However, there are studies emerging that show plasma jets can cause significant side effects in the form of skin burns under certain conditions. Therefore, with a view of developing safer plasma treatment approaches, in this study we have set out to provide new insights into the cause of these skin burns and how to tailor plasma treatments to mitigate these effects. We discovered that joule heating by the plasma bullet currents is responsible for creating skin burns during helium plasma jet treatment of live mice. These burns can be mitigated by treating the mice at a further distance so that the visible plasma plume does not contact the skin. Under these treatment conditions we also show that the plasma jet treatment still retains its medically beneficial property of producing reactive oxygen species in vivo. Therefore, treatment distance is an important parameter for consideration when assessing the safety of medical plasma treatments. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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14 pages, 504 KiB  
Article
Investigation of Machine Learning Techniques for Disruption Prediction Using JET Data
Plasma 2023, 6(1), 89-102; https://doi.org/10.3390/plasma6010008 - 24 Feb 2023
Viewed by 1387
Abstract
Disruption prediction and mitigation is of key importance in the development of sustainable tokamak reactors. Machine learning has become a key tool in this endeavour. In this paper, multiple machine learning models are tested and compared. A focus has been placed on the [...] Read more.
Disruption prediction and mitigation is of key importance in the development of sustainable tokamak reactors. Machine learning has become a key tool in this endeavour. In this paper, multiple machine learning models are tested and compared. A focus has been placed on the analysis of a transition to dimensionless input quantities. The methods used in this paper are the support vector machine, two-tiered support vector machine, random forest, gradient-boosted trees and long-short term memory. The performance between different models is remarkably similar, with the support vector machine attaining a slightly better accuracy score. The similarity could indicate issues with the dataset, but further study is required to confirm this. Both the two-tiered model and long-short term memory performed below expectations. The former could be attributed to an implementation which did not allow error propagation between tiers. The latter could be attributed to high noise and low frequency of the input signals. Dimensionless models experienced an expected decrease in performance, caused by a loss of information in the conversion. However, random forest and gradient boosted trees experienced a significantly lower decrease, making them more suitable for dimensionless predictors. From the disruption detection times, it was concluded that several disruptions could be predicted at more than 600 ms in advance. A feature importance study using the random forest indicated the negative impact of high noise and missing data in the database, suggesting improvements in data preparation for future work and the potential reevaluation of some of the selected portable features due to poor performance. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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17 pages, 7958 KiB  
Review
Flexible Cold Atmospheric Plasma Jet Sources
Plasma 2023, 6(1), 72-88; https://doi.org/10.3390/plasma6010007 - 16 Feb 2023
Cited by 4 | Viewed by 4050
Abstract
The properties of non-thermal atmospheric pressure plasma jets (APPJs) make them suitable for industrial and biomedical applications. They show many advantages when it comes to local and precise surface treatments, and there is interest in upgrading their performance for irradiation on large areas [...] Read more.
The properties of non-thermal atmospheric pressure plasma jets (APPJs) make them suitable for industrial and biomedical applications. They show many advantages when it comes to local and precise surface treatments, and there is interest in upgrading their performance for irradiation on large areas and uneven surfaces. The generation of charged species (electrons and ions) and reactive species (radicals), together with emitted UV photons, enables a rich plasma chemistry that should be uniform on arbitrary sample profiles. Lateral gradients in plasma parameters from multi-jets should, therefore, be minimized and addressed by means of plasma monitoring techniques, such as electrical diagnostics and optical emission spectroscopy analysis (OES). This article briefly reviews the main strategies adopted to build morphing APPJ arrays and ultra-flexible and long tubes to project cold plasma jets. Basic aspects, such as inter-jet interactions and nozzle shape, have also been discussed, as well as potential applications in the fields of polymer processing and plasma medicine. Full article
(This article belongs to the Special Issue Latest Review Papers in Plasma Science 2023)
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14 pages, 3890 KiB  
Article
Analysis and Mitigation of Pulse-Pile-Up Artifacts in Plasma Pulse-Height X-ray Spectra
Plasma 2023, 6(1), 58-71; https://doi.org/10.3390/plasma6010006 - 02 Feb 2023
Cited by 1 | Viewed by 1649
Abstract
Pulse pile-up in pulse-height energy analyzers increases when the incident rate of pulses increases relative to the inverse of the dead time per pulse of the detection system. Changes in the observed energy distributions with incident rate and detector-electronics-formed pulse shape then occur. [...] Read more.
Pulse pile-up in pulse-height energy analyzers increases when the incident rate of pulses increases relative to the inverse of the dead time per pulse of the detection system. Changes in the observed energy distributions with incident rate and detector-electronics-formed pulse shape then occur. We focus on weak high energy tails in X-ray spectra, important for measurements on partially ionized, warm (50–500 eV average electron energy), pure hydrogen plasma. A first-principles two-photon pulse-pile-up model is derived specific to trapezoidal-shaped pulses; quantitative agreement is found between the measurements and the model’s predictions. The model is then used to diagnose pulse-pile-up tail artifacts and mitigate them in relatively low count-rate spectra. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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13 pages, 2975 KiB  
Article
Physical Properties of Plasma-Activated Water
Plasma 2023, 6(1), 45-57; https://doi.org/10.3390/plasma6010005 - 30 Jan 2023
Cited by 4 | Viewed by 2527
Abstract
Recent observations of plasma-activated water (PAW)’s surfactant behavior suggest that the activation of water with non-equilibrium plasma can decrease the surface tension of the water. This suggested change to the surface tension also indicates that the addition of plasma can lead to changes [...] Read more.
Recent observations of plasma-activated water (PAW)’s surfactant behavior suggest that the activation of water with non-equilibrium plasma can decrease the surface tension of the water. This suggested change to the surface tension also indicates that the addition of plasma can lead to changes in the physical properties of the water, knowledge of which can expand existing PAW applications and open new ones. While the chemical behavior of PAW has been extensively analyzed, to the best of our knowledge the physical properties of PAW have not been investigated. This study focuses on the need for experimental determination of PAW’s physical properties—namely, surface tension, viscosity, and contact angle. The experimental results of this study show that the addition of plasma lowers the surface tension of water at room temperature, increases the viscosity of water at high temperatures, and lowers the contact angle of droplets on glass surfaces at room temperatures. Potential factors influencing these changes include plasma alteration of the mesoscopic structure of water at low temperatures and plasma additives acting as foreign particles in water at higher temperatures. Ultimately, this investigation demonstrates that the physical properties of water change due to plasma activation, which could lead to potential industrial applications of PAW as a surfactant or as a washing-out and cleaning agent. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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9 pages, 1099 KiB  
Article
Pulsed Plasma Accelerator
Plasma 2023, 6(1), 36-44; https://doi.org/10.3390/plasma6010004 - 28 Jan 2023
Cited by 1 | Viewed by 1384
Abstract
In this paper, we consider the acceleration of plasma fluxes in crossed electromagnetic fields. The possible technical approach to a prospective plasma accelerator is discussed. A simple hydrodynamic model describing the dynamics of the plasma ring in these fields is proposed. Based on [...] Read more.
In this paper, we consider the acceleration of plasma fluxes in crossed electromagnetic fields. The possible technical approach to a prospective plasma accelerator is discussed. A simple hydrodynamic model describing the dynamics of the plasma ring in these fields is proposed. Based on this model, the estimations of basic characteristics for the accelerated flux are calculated for typical experimental conditions. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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7 pages, 1366 KiB  
Article
Laser–Plasma Wake Velocity Control by Multi-Mode Beatwave Excitation in a Channel
Plasma 2023, 6(1), 29-35; https://doi.org/10.3390/plasma6010003 - 20 Jan 2023
Viewed by 1346
Abstract
The phase velocity of a laser-driven wakefield can be efficiently controlled in a plasma channel. A beatwave of two long laser pulses is used. The frequency difference between these two laser pulses equals the local plasma frequency, so that the slow resonant excitation [...] Read more.
The phase velocity of a laser-driven wakefield can be efficiently controlled in a plasma channel. A beatwave of two long laser pulses is used. The frequency difference between these two laser pulses equals the local plasma frequency, so that the slow resonant excitation of the plasma wave is possible. Because the driver energy is spread over many plasma periods, the interference pattern can run with an arbitrary velocity along the channel and generate the wakefield with the same phase velocity. This velocity is defined by the channel radius and the structure of laser transverse modes excited in the channel. The wake velocity can be matched exactly to the witness velocity. This can be the vacuum speed of light for ultra-relativistic witnesses, or subluminal velocities for low-energy, weakly relativistic witnesses such as muons. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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2 pages, 152 KiB  
Editorial
Acknowledgment to the Reviewers of Plasma in 2022
Plasma 2023, 6(1), 27-28; https://doi.org/10.3390/plasma6010002 - 17 Jan 2023
Viewed by 875
Abstract
High-quality academic publishing is built on rigorous peer review [...] Full article
26 pages, 690 KiB  
Article
Hydrogen-, Helium-, and Lithium-like Bound States in Classical and Quantum Plasmas
Plasma 2023, 6(1), 1-26; https://doi.org/10.3390/plasma6010001 - 28 Dec 2022
Cited by 2 | Viewed by 1593
Abstract
We study the effective interactions and the mass action constants for pair and triple associations in classical and quantum plasmas. Avoiding double counting, we derive new expressions for the mass action constants. The calculations resulted in values that were substantially smaller than the [...] Read more.
We study the effective interactions and the mass action constants for pair and triple associations in classical and quantum plasmas. Avoiding double counting, we derive new expressions for the mass action constants. The calculations resulted in values that were substantially smaller than the standard ones in relevant temperature ranges by up to 50 percent. On this basis, we determine the pressure of H, He and Li plasmas and the osmotic coefficient of electrolytes with higher charges such as, e.g., seawater. Classical and quantum Coulomb systems show strong similarities. The contributions in low orders with respect to the interaction e2 are suppressed by thermal and screening effects. The contributions of weakly bound states, near the continuum edge, to the mass action constants are reduced, replacing the exponential functions with cropped exponentials. The new mass action constants are consistent with well-known extended limiting cases of screening effects. We analyze classical examples including the salts CaCl2 and LaCl3, and a model of seawater including multiple associations. In the case of quantum systems, we follow the work of Planck–Brillouin–Larkin for H plasmas and study He and Li plasmas. The equation of state (EoS) for wide-density regions is obtained through the concatenation of the EoS for the low-density region of partial ionization with the EoS of degenerate plasmas, where all bound states are dissolved and Fermi, Hartree–Fock and Wigner contributions dominate. Full article
(This article belongs to the Special Issue Feature Papers in Plasma Sciences)
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