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Volume 7
Issue 2
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Plasma, Volume 7, Issue 2 (June 2024) – 4 articles

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26 pages, 725 KiB  
Review
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 (registering DOI) - 26 Apr 2024
Viewed by 83
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)
13 pages, 5830 KiB  
Article
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 327
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  
Article
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 527
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  
Review
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 473
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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