Plasma

25 pages, 11985 KiB

Open AccessArticle

Plasma Dynamics and Electron Transport in a Hall-Thruster-Representative Configuration with Various Propellants: II—Effects of the Magnetic Field Topology

by Maryam Reza, Farbod Faraji and Aaron Knoll

Plasma 2024, 7(3), 680-704; https://doi.org/10.3390/plasma7030035 - 16 Aug 2024

Abstract

We investigate the effects of the magnetostatic (

B

) field topology on the plasma behavior in a 2D collisionless simulation setup that represents an axial–azimuthal cross-section of a Hall thruster. The influence of the

B

-field topology is assessed in terms of [...] Read more.

We investigate the effects of the magnetostatic (

B

) field topology on the plasma behavior in a 2D collisionless simulation setup that represents an axial–azimuthal cross-section of a Hall thruster. The influence of the

B

-field topology is assessed in terms of two principal design properties of the field in a typical Hall thruster, i.e., the field’s peak intensity along the axial direction, and the field’s axial distribution. The effects of the field’s intensity are investigated for three propellants—xenon, krypton, and argon. Whereas, the effects of the axial profile of the magnetic field are studied only for the xenon propellant as an example. We primarily aim to understand how the changes in the

B

-field topology affect the spectra of the resolved instabilities as well as the electrons’ transport characteristics and the contributions of various momentum terms to transport. The numerical observations on the instabilities’ characteristics are compared against the relevant existing theories to determine the extent to which the simulated and the theoretically predicted characteristics are consistent across the studied parameter space. It was, most notably, found that modes related to ion acoustic instability are dominantly present across the simulation cases. The ion transit time instability additionally develops at the highest

B

-field intensities as a long-wavelength structure. The main influence of the axial profile of the

B

field on the plasma discharge was observed to be in terms of the electrons’ transport characteristics. Where possible, the insights from the simulations are discussed with respect to the relevant experimental observations available in the literature. Full article

(This article belongs to the Special Issue Feature Papers in Plasma Sciences 2023)

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29 pages, 11770 KiB

Open AccessArticle

Plasma Dynamics and Electron Transport in a Hall-Thruster-Representative Configuration with Various Propellants: I—Variations with Discharge Voltage and Current Density

by Maryam Reza, Farbod Faraji and Aaron Knoll

Plasma 2024, 7(3), 651-679; https://doi.org/10.3390/plasma7030034 - 6 Aug 2024

Cited by 1

Abstract

The results from a wide-ranging parametric investigation into the behavior of the collisionless partially magnetized plasma discharge of three propellants—xenon, krypton, and argon—are reported in this two-part article. These studies are performed using high-fidelity reduced-order particle-in-cell (PIC) simulations in a 2D configuration that [...] Read more.

The results from a wide-ranging parametric investigation into the behavior of the collisionless partially magnetized plasma discharge of three propellants—xenon, krypton, and argon—are reported in this two-part article. These studies are performed using high-fidelity reduced-order particle-in-cell (PIC) simulations in a 2D configuration that represents an axial–azimuthal cross-section of a Hall thruster. In this part I paper, we discuss the effects of discharge voltage and current density (mass flow rate). Our parametric studies assess the spectra of the resolved instabilities under various plasma conditions. We evaluate the ability of the relevant theories from the literature to explain the variations in the instabilities’ characteristics across the studied plasma parameter space and for various propellants. Moreover, we investigate the changes in the electrons’ cross-magnetic-field transport, as well as the significance of the contribution of different momentum terms to this phenomenon across the analyzed cases. In terms of salient observations, the ion acoustic instability (IAI)-related modes are found to be dominant across the simulation cases, with the ion transit time instability also seen to develop at low current density values. Across the explored parameter space, the instabilities have the main contributions to the electrons’ transport within the plume region. The peak of the electric momentum force term, representing the effect of the instabilities, overall shifts toward the plume as either the current density or the discharge voltage increases. The numerical findings are compared against relevant experimental observations reported in the literature. Full article

(This article belongs to the Special Issue Feature Papers in Plasma Sciences 2023)

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20 pages, 5459 KiB

Open AccessArticle

Comparative Studies on the Radiative Heat Transfer in Arc Plasma and Its Impact in a Model of a Free-Burning Arc

by Margarita Baeva, Yann Cressault and Petr Kloc

Plasma 2024, 7(3), 631-650; https://doi.org/10.3390/plasma7030033 - 5 Aug 2024

Abstract

The radiative heat transfer in arc plasma models is considered from the point of view of its description in terms of a net emission coefficient, the method of spherical harmonics in its lowest order, and the discrete ordinate method. Net emission coefficients are [...] Read more.

The radiative heat transfer in arc plasma models is considered from the point of view of its description in terms of a net emission coefficient, the method of spherical harmonics in its lowest order, and the discrete ordinate method. Net emission coefficients are computed, applying approximate analytical and numerical approaches and a multi-band representation of the spectral absorption coefficient with three kinds of its averaging and two datasets. Self-consistent access to the radiative heat transfer is applied to a two-dimensional axisymmetric model of a free-burning arc in argon at atmospheric pressure. The results obtained from the models employing the net emission coefficient, the method of spherical harmonics, and the discrete ordinate method are compared. Full article

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Graphical abstract

15 pages, 8648 KiB

Open AccessArticle

Influence of Voltage Rising Time on the Characteristics of a Pulsed Discharge in Air in Contact with Water: Experimental and 2D Fluid Simulation Study

by Antoine Herrmann, Joëlle Margot and Ahmad Hamdan

Plasma 2024, 7(3), 616-630; https://doi.org/10.3390/plasma7030032 - 5 Aug 2024

Abstract

In the context of plasma–liquid interactions, the phase of discharge ignition is of great importance as it may influence the properties of the produced plasma. Herein, we investigated the influence of voltage rising time (

τ_{r i s e}

) on discharge [...] Read more.

In the context of plasma–liquid interactions, the phase of discharge ignition is of great importance as it may influence the properties of the produced plasma. Herein, we investigated the influence of voltage rising time (

τ_{r i s e}

) on discharge ignition in air as well as on discharge propagation on the surface of water. Experimentally,

τ_{r i s e}

was adjusted to 0.1, 0.4, 0.6, and 0.8 kV/ns using a nanosecond high-voltage pulser, and discharges were characterized using voltage/current probes and an ICCD camera. Faster ignition, higher breakdown voltage, and greater discharge current (peak value) were observed at higher

τ_{r i s e}

. ICCD images revealed that higher

τ_{r i s e}

also promoted the formation of more filaments, with increased radial propagation over the water surface. To further understand these discharges, a previously developed 2D fluid model was used to simulate discharge ignition and propagation under various

τ_{r i s e}

conditions. The simulation provided the spatiotemporal evolution of the E-field, electron density, and surface charge density. The trend of the simulated position of the ionization front is similar to that observed experimentally. Furthermore, rapid vertical propagation (<1 ns) of the discharge towards the liquid surface was observed. As

τ_{r i s e}

increased, the velocity of discharge propagation towards the liquid increased. Higher

τ_{r i s e}

values also led to more charges in the ionization front propagating at the water surface. The discharge ceased to propagate when the charge number in the ionization front reached 0.5 ×

10^{8}

charges, irrespective of the

τ_{r i s e}

value. Full article

(This article belongs to the Special Issue Processes in Atmospheric Pressure Plasmas)

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31 pages, 14363 KiB

Open AccessArticle

Hybrid Dielectric Barrier Discharge Reactor: Characterization for Ozone Production

by Dariusz Korzec, Florian Freund, Christian Bäuml, Patrik Penzkofer and Stefan Nettesheim

Plasma 2024, 7(3), 585-615; https://doi.org/10.3390/plasma7030031 - 27 Jul 2024

Abstract

The generation of ozone by dielectric barrier discharge (DBD) is widely used for water and wastewater treatment, the control of catalytic reactions, and surface treatment. Recently, a need for compact, effective, and economical ozone and reactive oxygen–nitrogen species (RONS) generators for medical, biological, [...] Read more.

The generation of ozone by dielectric barrier discharge (DBD) is widely used for water and wastewater treatment, the control of catalytic reactions, and surface treatment. Recently, a need for compact, effective, and economical ozone and reactive oxygen–nitrogen species (RONS) generators for medical, biological, and agricultural applications has been observed. In this study, a novel hybrid DBD (HDBD) reactor fulfilling such requirements is presented. Its structured high-voltage (HV) electrode allows for the ignition of both the surface and volume microdischarges contributing to plasma generation. A Peltier module cooling of the dielectric barrier, made of alumina, allows for the efficient control of plasma chemistry. The typical electrical power consumption of this device is below 30 W. The operation frequency of the DBD driver oscillating in the auto-resonance mode is from 20 to 40 kHz. The specific energy input (SEI) of the reactor was controlled by the DBD driver input voltage in the range from 10.5 to 18.0 V, the Peltier current from 0 to 4.5 A, the duty cycle of the pulse-width modulated (PWM) power varied from 0 to 100%, and the gas flow from 0.5 to 10 SLM. The operation with oxygen, synthetic air, and compressed dry air (CDA) was characterized. The ultraviolet light (UV) absorption technique was implemented for the measurement of the ozone concentration. The higher harmonics of the discharge current observed in the frequency range of 5 to 50 MHz were used for monitoring the discharge net power. Full article

(This article belongs to the Special Issue Processes in Atmospheric Pressure Plasmas)

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19 pages, 4598 KiB

Open AccessArticle

Toroidal CO₂ Plasma Sources with Low- and High-Frequency Power Coupling Configurations for Improved Energy Transfer Efficiencies

by E. J. Devid, W. A. Bongers, P. W. C. Groen, M. van Ginkel, S. J. Doyle, F. M. A. Smits, C. F. A. M. van Deursen, K. Serras, S. Labeur, M. A. Gleeson and M. C. M. van de Sanden

Plasma 2024, 7(3), 566-584; https://doi.org/10.3390/plasma7030030 - 24 Jul 2024

Abstract

Electrodeless Low-Frequency (LF)/Radio-Frequency (RF) plasma sources often suffer from low power coupling efficiencies due to the lack of overlapping field with the dynamic plasma load. However, the power supplies for these plasma sources typically have very high power efficiencies (>90%) and are more [...] Read more.

Electrodeless Low-Frequency (LF)/Radio-Frequency (RF) plasma sources often suffer from low power coupling efficiencies due to the lack of overlapping field with the dynamic plasma load. However, the power supplies for these plasma sources typically have very high power efficiencies (>90%) and are more cost-effective compared to microwave sources. If the coupling efficiency to the plasma can be increased, these plasma sources offer a competitive technology for the sustainable electrification of the chemical industry. This work experimentally investigates five power coupling methods, applied to toroidal CO₂ plasmas in a quartz vessel. The research was based on similar ferrite coupling as used in energy-efficient plasma lamps. The higher resistance of the CO₂ plasma decreased the power coupling from 90% (for mercury-vapor plasma) to 66% at 1 mbar. High coupling efficiencies in LF/RF powered discharges can be achieved in two manners: either the inductance of the transformer cores can be increased, or the electromagnetic wave frequency can be increased. Furthermore, additional ferrite cores in parallel with the primary coils can be used to increase the impedance transformation. An experiment with six ferrite cores with a single primary winding in parallel, at a frequency of about 10 MHz and a power of 1 kW, showed that this frequency has a detrimental effect on the magnetic permeability and the losses in the ferrite result in a decrease of coupling to 33% at 1.5 mbar. At a frequency of 66 kHz with a nanocrystalline soft magnetic material core, a coupling of 89% was achieved in 1.5 mbar plasma for a power of 3.1 kW. This configuration exhibits decreasing coupling efficiencies at higher pressures since the plasma impedance increases, which again limits the coupling of the transformer due to a lack of inductance. The investigation of alternative coreless coil plasma configurations resulted in coupling efficiencies up to 89% decreasing to 50% at 102 mbar for a toroidal plasma enclosed by toroidally spiraling coils. Full article

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35 pages, 13372 KiB

Open AccessReview

A Review of Experimental Investigations into the Time Evolution of Low-Pressure Capacitively Coupled Plasmas in Their Early Stages of Development

by Pietro Mandracci

Plasma 2024, 7(3), 531-565; https://doi.org/10.3390/plasma7030029 - 22 Jul 2024

Abstract

Capacitively coupled plasma (CCP) discharges working at low pressure are widely used for the synthesis of thin films and the modification of the surface properties of materials. Due to their importance, considerable research was carried out over the years to understand their working [...] Read more.

Capacitively coupled plasma (CCP) discharges working at low pressure are widely used for the synthesis of thin films and the modification of the surface properties of materials. Due to their importance, considerable research was carried out over the years to understand their working mechanisms, and the physical properties of the CCP discharges were measured by many research groups, while simulations of their characteristics were often performed using both fluid and kinematic models. However, most of the simulation and characterization work found in the literature is focused on the discharge steady-state characteristics, since most of the applications rely on its properties, while less information is available on the early stages. In fact, the initial stages of CCP plasma discharges are of great importance to improve the understanding of their ignition process as well as to figure out the working mechanism of pulsed discharges, the use of which has increased in importance in recent years. In this work, a review of the results published in recent years concerning the physical mechanisms involved in the very first stages of low-pressure CCP discharges is presented, focusing on the first few microseconds of discharge time. Full article

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14 pages, 1127 KiB

Open AccessArticle

Analysis of ICRF Heating Schemes in ITER Non-Active Plasmas Using PION+ETS Integrated Modeling

by Tomas Bensadon, Mervi J. Mantsinen, Thomas Jonsson, Dani Gallart, Xavier Sáez and Jordi Manyer

Plasma 2024, 7(3), 517-530; https://doi.org/10.3390/plasma7030028 - 19 Jul 2024

Abstract

The PION code has been integrated into the European Transport Solver (ETS) transport workflow, and we present the first application to model Ion Cyclotron Resonance Frequency (ICRF) heating scenarios in the next-step fusion reactor ITER. We present results of predictive, self-consistent and time-dependent [...] Read more.

The PION code has been integrated into the European Transport Solver (ETS) transport workflow, and we present the first application to model Ion Cyclotron Resonance Frequency (ICRF) heating scenarios in the next-step fusion reactor ITER. We present results of predictive, self-consistent and time-dependent simulations where the resonant ion concentration is varied to study its effects on the performance, with a special emphasis on the resulting bulk ion heating and thermal ion temperature. We focus on two ICRF heating schemes, i.e., fundamental H minority heating in a ⁴He plasma at 2.65 T/7.5 MA and a three-ion ICRF scheme consisting of fundamental ³He heating in a H-⁴He plasma at 3.3 T/ 8.8 MA. The H minority heating scenario is found to result in strong absorption by resonant H ions as compared to competing absorption mechanisms and dominant background electron heating for H concentrations up to 10%. The highest H absorption of ∼80% of the applied ICRF power and highest ion temperature of ∼15 keV are obtained with an H concentration of 10%. For the three-ion scheme in 85%:15% H:⁴He plasma, PION+ETS predicts ³He absorption in the range of 21–65% for ³He concentrations in the range of 0.01–0.20%, with the highest ³He absorption at a ³He concentration of 0.20%. Full article

(This article belongs to the Special Issue New Insights into Plasma Theory, Modeling and Predictive Simulations)

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7 pages, 3579 KiB

Open AccessBrief Report

Positive- and Negative-Polarity Nanosecond-Pulsed Cryogenic Plasma in Liquid Argon

by Danil Dobrynin and Alexander Fridman

Plasma 2024, 7(3), 510-516; https://doi.org/10.3390/plasma7030027 - 29 Jun 2024

Abstract

This work reports on observations of positive and negative nanosecond-pulsed discharge in liquid argon. The structures of both positive and negative discharges, their sizes, and the propagation velocities exhibit remarkable similarity. Similar to the streamers in liquid nitrogen and gases, negative streamers require [...] Read more.

This work reports on observations of positive and negative nanosecond-pulsed discharge in liquid argon. The structures of both positive and negative discharges, their sizes, and the propagation velocities exhibit remarkable similarity. Similar to the streamers in liquid nitrogen and gases, negative streamers require higher applied voltages (electric fields) and propagate to shorter distances. For both polarities, the spectra are almost identical and appear to be a superposition of strongly broadened atomic lines, with preliminary analysis of broadening indicating densities of about 40% that of liquid. Full article

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12 pages, 9212 KiB

Open AccessArticle

Modeling Study of OH Radical-Dominated H-Abstraction Reaction for Understanding Nucleotides Oxidation Induced by Cold Atmospheric Plasmas

by Yu-Xuan Jiang, Yang Chen and Yuan-Tao Zhang

Plasma 2024, 7(2), 498-509; https://doi.org/10.3390/plasma7020026 - 19 Jun 2024

Abstract

In recent years, plasma medicine, as an innovative and rapidly growing field, has garnered increasing attention. Nonetheless, the fundamental mechanisms of the interaction processes of cold atmospheric plasma (CAP) and biomolecules remain under investigation. In this paper, a reactive molecular dynamic (MD) simulation [...] Read more.

In recent years, plasma medicine, as an innovative and rapidly growing field, has garnered increasing attention. Nonetheless, the fundamental mechanisms of the interaction processes of cold atmospheric plasma (CAP) and biomolecules remain under investigation. In this paper, a reactive molecular dynamic (MD) simulation with ReaxFF potential was performed to explore the interactions of reactive oxygen species (ROS) produced in CAP, exemplified by OH radicals, and four distinct oligonucleotides. The breakage of single-stranded oligonucleotides induced by OH is observed in the simulation, which could seriously influence the biological activity of cellular DNA. The base release induced by OH radicals means the loss of base sequence information, and the H-abstraction at nucleobases affects the gene strand complementarity, gene transcription, and replication. In addition, the dose effects of OH radicals on bond formation and breaking of oligonucleotides are also discussed by adjusting the number of ROS in the simulation box. This study can enhance the comprehension of interactions between CAP and DNA, thereby indicating possible improvements in plasma device optimization and operation for medical applications. Full article

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33 pages, 1733 KiB

Open AccessReview

The Promising Potential of Cold Atmospheric Plasma Therapies

by Beata Stańczyk and Marek Wiśniewski

Plasma 2024, 7(2), 465-497; https://doi.org/10.3390/plasma7020025 - 12 Jun 2024

Abstract

The outstanding properties and chemistry of cold atmospheric plasma (CAP) are not sufficiently understood due to their relatively complex systems and transient properties. In this paper, we tried to present a detailed review of the applications of CAP in modern medicine, highlighting the [...] Read more.

The outstanding properties and chemistry of cold atmospheric plasma (CAP) are not sufficiently understood due to their relatively complex systems and transient properties. In this paper, we tried to present a detailed review of the applications of CAP in modern medicine, highlighting the biochemistry of this phenomenon. Due to its unique characteristics, CAP has emerged as a promising tool in various medical applications. CAP, as a partially—or fully ionized—gas-retaining state of quasi-neutrality, contains many particles, such as electrons, charged atoms, and molecules displaying collective behaviour caused by Coulomb interactions. CAP can be generated at atmospheric pressure, making it suitable for medical settings. Cold plasma’s anti-microbial properties create an alternative method to antibiotics when treating infections. It also enhances cell proliferation, migration, and differentiation, leading to accelerated tissue regeneration. CAP can also be a powerful tool in anti-tumour therapies, stem cell proliferation, dental applications, and disease treatment, e.g., neurology. It is our belief that this article contributes to the deeper understanding of cold plasma therapy and its potential in medicine. The objective of this study is to demonstrate the potential of this relatively novel approach as a promising treatment modality. By covering a range of various biomedical fields, we hope to provide a comprehensive overview of CAP applications for multiple medical conditions. In order to gain further insight into the subject, we attempted to gather crucial research and evidence from various studies, hopefully creating a compelling argument in favour of CAP therapy. Our aim is to highlight the innovative aspects of CAP therapy where traditional methods may have limitations. Through this article, we intend to provide a convenient reference source for readers engaged in the examination of CAP’s potential in medicine. Full article

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19 pages, 1331 KiB

Open AccessArticle

Importance of the Rotational Transform for L–H Transitions in the TJ-II Stellarator

by Boudewijn Philip van Milligen, Teresa Estrada, Benjamin Carreras, Luis García and the TJ-II Team

Plasma 2024, 7(2), 446-464; https://doi.org/10.3390/plasma7020024 - 12 Jun 2024

Abstract

We study the effect of the rotational transform profile on the L–H confinement transitions in the neutral beam-heated plasmas in the TJ-II stellarator. The rotational transform profile in the vacuum is determined by the external coil currents but is modified by the plasma [...] Read more.

We study the effect of the rotational transform profile on the L–H confinement transitions in the neutral beam-heated plasmas in the TJ-II stellarator. The rotational transform profile in the vacuum is determined by the external coil currents but is modified by the plasma current,

I_{p}

. We find that L–H confinement transitions systematically occur when the configuration and plasma current are such that a low-order rational is placed in the plasma edge region, with a distribution centered around

ρ = 0.8 \pm 0.05

. It is suggested that magnetohydrodynamic turbulence plays an important role in triggering the L–H transitions at TJ-II. Full article

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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

Abstract

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

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

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

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

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

Cited by 1

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

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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Plasma

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