Plasma

19 pages, 470 KiB

Open AccessArticle

Extracting Physical Information from the Voigt Profile Using the Lambert W Function

by Jean-Christophe Pain

Plasma 2024, 7(2), 427-445; https://doi.org/10.3390/plasma7020023 - 27 May 2024

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Spectral line shapes are a key ingredient of hot-plasma opacity calculations. Since resorting to elaborate line-shape models remains prohibitive for intensive opacity calculations involving ions in different excitation states, with L, M, etc., shells are populated, and Voigt profiles often represent [...] Read more.

Spectral line shapes are a key ingredient of hot-plasma opacity calculations. Since resorting to elaborate line-shape models remains prohibitive for intensive opacity calculations involving ions in different excitation states, with L, M, etc., shells are populated, and Voigt profiles often represent a reliable alternative. The corresponding profiles result from the convolution of a Gaussian function (for Doppler and sometimes ionic Stark broadening) and a Lorentzian function, for radiative decay (sometimes referred to as “natural” width) and electron-impact broadening. However, their far-wing behavior is incorrect, which can lead to an overestimation of the opacity. The main goal of the present work was to determine the energy (or frequency) at which the Lorentz wings of a Voigt profile intersect with the underlying Gaussian part of the profile. It turns out that such an energy cut-off, which provides us information about the dominant line-broadening process in a given energy range, can be expressed in terms of the Lambert W function, which finds many applications in physics. We also review a number of representations of the Voigt profile, with an emphasis on the pseudo-Voigt decomposition, which lends itself particularly well to cut-off determination. Full article

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41 pages, 3035 KiB

Open AccessReview

Plasma Control: A Review of Developments and Applications of Plasma Medicine Control Mechanisms

by Jonathan E. Thomas and Katharina Stapelmann

Plasma 2024, 7(2), 386-426; https://doi.org/10.3390/plasma7020022 - 27 May 2024

Viewed by 716

Abstract

Cold atmospheric plasmas (CAPs) within recent years have shown great promise in the field of plasma medicine, encompassing a variety of treatments from wound healing to the treatment of cancerous tumors. For each subsequent treatment, a different application of CAPs has been postulated [...] Read more.

Cold atmospheric plasmas (CAPs) within recent years have shown great promise in the field of plasma medicine, encompassing a variety of treatments from wound healing to the treatment of cancerous tumors. For each subsequent treatment, a different application of CAPs has been postulated and attempted to best treat the target for the most effective results. These treatments have varied through the implementation of control parameters such as applied settings, electrode geometries, gas flow, and the duration of the treatment. However, with such an extensive number of variables to consider, scientists and engineers have sought a means to accurately control CAPs for the best-desired effects in medical applications. This paper seeks to investigate and characterize the historical precedent for the use of plasma control mechanisms within the field of plasma medicine. Current control strategies, plasma parameters, and control schemes will be extrapolated through recent developments and successes to gain better insight into the future of the field and the challenges that are still present in the overall implementation of such devices. Proposed approaches, such as data-driven machine learning, and the use of closed-loop feedback controls, will be showcased as the next steps toward application. Full article

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20 pages, 6436 KiB

Open AccessReview

Advanced Diagnostics of Electrons Escaping from Laser-Produced Plasma

by Josef Krása, Michal Krupka, Shubham Agarwal, Vincenzo Nassisi and Sushil Singh

Plasma 2024, 7(2), 366-385; https://doi.org/10.3390/plasma7020021 - 13 May 2024

Viewed by 384

Abstract

This article provides an up-to-date overview of the problems associated with the detection of hot electrons escaping from laser-produced plasma and corresponding return current flowing from the ground to the target, which neutralises the positive charge occurring on the target due to the [...] Read more.

This article provides an up-to-date overview of the problems associated with the detection of hot electrons escaping from laser-produced plasma and corresponding return current flowing from the ground to the target, which neutralises the positive charge occurring on the target due to the escaped electrons. In addition, the target holder system acts as an antenna emitting an electromagnetic pulse (EMP), which is powered by the return target. If the amount of positive charge generated on the target is equal to the amount of charge carried away from the plasma by the escaping electrons, the measurement of the return current makes it possible to determine this charge, and thus also the number of escaped electrons. Methods of return current detection in the mA–10 kA range is presented, and the corresponding charge is compared to the charge determined using calibrated magnetic electron energy analysers. The influence of grounded and insulated targets on the number of escaped electrons and EMP intensity is discussed. In addition to EMP detection, mapping of the electrical potential near the target is mentioned. Full article

(This article belongs to the Special Issue Latest Review Papers in Plasma Science 2023)

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11 pages, 4437 KiB

Open AccessArticle

Shock–Discharge Interaction Model Extended into the Third Dimension

by Anna Markhotok

Plasma 2024, 7(2), 355-365; https://doi.org/10.3390/plasma7020020 - 11 May 2024

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Abstract

This work is an addition to the previously developed two-dimensional model of the shock–plasma interaction, extending it into the third dimension. The model can trace the evolution of the state of the hypersonic flow and the shock front refracted at a thermal discontinuity. [...] Read more.

This work is an addition to the previously developed two-dimensional model of the shock–plasma interaction, extending it into the third dimension. The model can trace the evolution of the state of the hypersonic flow and the shock front refracted at a thermal discontinuity. The advantages of using the spherical coordinate system for this type of problem include increased transparency in interpreting the solution and a shortened calculation procedure, because all the changes to the front are reduced to one distortion component. Although the vorticity generation triggered at the interface is a consequence of the refraction and tied to the steep changes in the front, it is shown here that this is not because of an instant parameter jump at the interface due to refraction itself. Full article

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26 pages, 2456 KiB

Open AccessReview

The Phenomenon of a Cathode Spot in an Electrical Arc: The Current Understanding of the Mechanism of Cathode Heating and Plasma Generation

by Isak I. Beilis

Plasma 2024, 7(2), 329-354; https://doi.org/10.3390/plasma7020019 - 26 Apr 2024

Viewed by 454

Abstract

A vacuum arc is an electrical discharge, in which the current is supported by localized cathode heating and plasma generation in minute regions at the cathode surface called cathode spots. Cathode spots produce a metallic plasma jet used in many applications (microelectronics, space [...] Read more.

A vacuum arc is an electrical discharge, in which the current is supported by localized cathode heating and plasma generation in minute regions at the cathode surface called cathode spots. Cathode spots produce a metallic plasma jet used in many applications (microelectronics, space thrusters, film deposition, etc.). Nevertheless, the cathode spot is a problematic and unique subject. For a long time, the mechanisms of spot initiation, time development, instability, high mobility, and behavior in magnetic fields have been described by approaches that caused some controversy. These spot characteristics were discussed in numerous publications over many years. The obscurity and confusion of different studies created the impression that the cathode spot is a mysterious phenomenon. In the present work, a number of typical representative publications are reviewed with the intention of clarifying problems and contradictions. Two main theories of cathodic arcs are presented along with an analysis of the experimental data. One of the approaches illustrates the cathode heating by Joule energy dissipation (volume heat source, a sharp rise in current density, etc.), nearly constant cathode potential drop, and other certain initial conditions. On the other hand, a study using a mathematically closed approach shows that the spot initiation and development are determined not by electron emission current rise but by a rise in arc power density, affecting heat sources including the energy of ion flux to the cathode (surface heat source). Full article

(This article belongs to the Special Issue Latest Review Papers in Plasma Science 2023)

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13 pages, 5830 KiB

Open AccessArticle

Determination of Highly Transient Electric Field in Water Using the Kerr Effect with Picosecond Resolution

by Petr Hoffer, Václav Prukner, Garima Arora, Radek Mušálek and Milan Šimek

Plasma 2024, 7(2), 316-328; https://doi.org/10.3390/plasma7020018 - 22 Apr 2024

Viewed by 690

Abstract

This study utilizes the Kerr effect in the analysis of a pulsed electric field (intensity ~10⁸ V/m, limited by the liquid dielectric strength) in deionized water at the sub-nanosecond time scale. The results provide information about voltage waveforms at the field-producing anode [...] Read more.

This study utilizes the Kerr effect in the analysis of a pulsed electric field (intensity ~10⁸ V/m, limited by the liquid dielectric strength) in deionized water at the sub-nanosecond time scale. The results provide information about voltage waveforms at the field-producing anode (160 kV peak, du/dt > 70 kV/ns). The analysis is based on detecting the phase shifts between measured and reference pulsed laser beams (pulse width, 35 ps; wavelength, 532 nm) using a Mach–Zehnder interferometer. The signal-to-noise ratio of the detected phase shift is maximized by an appropriate geometry of the field-producing anode, which creates a correctly oriented strong electric field along the interaction path and simultaneously does not electrically load the feeding transmission line. The described method has a spatial resolution of ~1 μm, and its time resolution is determined by the laser pulse duration. Full article

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16 pages, 36305 KiB

Open AccessArticle

Short-Term Oxidation of HfB₂-SiC Based UHTC in Supersonic Flow of Carbon Dioxide Plasma

by Aleksey V. Chaplygin, Elizaveta P. Simonenko, Mikhail A. Kotov, Vladimir I. Sakharov, Ilya V. Lukomskii, Semen S. Galkin, Anatoly F. Kolesnikov, Anton S. Lysenkov, Ilya A. Nagornov, Artem S. Mokrushin, Nikolay P. Simonenko, Nikolay T. Kuznetsov, Mikhail Y. Yakimov, Andrey N. Shemyakin and Nikolay G. Solovyov

Plasma 2024, 7(2), 300-315; https://doi.org/10.3390/plasma7020017 - 19 Apr 2024

Viewed by 901

Abstract

The short-term (5 min) exposure to the supersonic flow of carbon dioxide plasma on ultrahigh-temperature ceramics of HfB₂-30vol.%SiC composition has been studied. It was shown that, when established on the surface at a temperature of 1615–1655 °C, the beginning of the [...] Read more.

The short-term (5 min) exposure to the supersonic flow of carbon dioxide plasma on ultrahigh-temperature ceramics of HfB₂-30vol.%SiC composition has been studied. It was shown that, when established on the surface at a temperature of 1615–1655 °C, the beginning of the formation of an oxidized layer takes place. Raman spectroscopy and scanning electron microscopy studies showed that the formation of a porous SiC-depleted region is not possible under the HfO₂-SiO₂ surface oxide layer. Numerical modeling based on the Navier–Stokes equations and experimental probe measurements of the test conditions were performed. The desirability of continuing systematic studies on the behavior of ultrahigh-temperature ZrB₂/HfB₂-SiC ceramics, including those doped with various components under the influence of high-enthalpy gas flows, was noted. Full article

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16 pages, 2298 KiB

Open AccessReview

Recent Developments in the Use of Plasma in Medical Applications

by Fiona O’Neill, Liam O’Neill and Paula Bourke

Plasma 2024, 7(2), 284-299; https://doi.org/10.3390/plasma7020016 - 10 Apr 2024

Viewed by 901

Abstract

A detailed review of the scientific literature was undertaken to examine the most recent developments in plasma processing in the field of medicine. The first part of the review includes a detailed breakdown of the different types of coatings that can be applied [...] Read more.

A detailed review of the scientific literature was undertaken to examine the most recent developments in plasma processing in the field of medicine. The first part of the review includes a detailed breakdown of the different types of coatings that can be applied onto medical devices using plasma, with a specific focus on antimicrobial surfaces. The developments in plasma-deposited biocompatibles, drug delivery and adhesive coatings in 2023 are described, and specific applications in additive manufacturing are highlighted. The use of plasma and plasma-activated liquids as standalone therapeutics continues to evolve, and pertinent advances in this field are described. In addition, the combination of plasma medicine with conventional pharmaceutical interventions is reviewed, and key emerging trends are highlighted, including the use of plasma to enhance drug delivery directly into tissue. The potential synergies between plasma medicine and chemotherapeutics for oncology and infection treatment are a growing area, and recent advancements are noted. Finally, the use of plasma to control excess antibiotics and to intentionally degrade such materials in waste streams is described. Full article

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Plasma, Volume 7, Issue 2 (June 2024) – 8 articles

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