Plasma Sources Science and Technology - IOPscience

Plasma Sources Science and Technology - IOPscience
Plasma Sources Science and Technology
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The following article is
Open access
Physics and technology of magnetron sputtering discharges
J T Gudmundsson 2020
Plasma Sources Sci. Technol.
29
113001
View article
, Physics and technology of magnetron sputtering discharges
PDF
, Physics and technology of magnetron sputtering discharges
Magnetron sputtering deposition has become the most widely used technique for deposition of both metallic and compound thin films and is utilized in numerous industrial applications. There has been a continuous development of the magnetron sputtering technology to improve target utilization, increase ionization of the sputtered species, increase deposition rates, and to minimize electrical instabilities such as arcs, as well as to reduce operating cost. The development from the direct current (dc) diode sputter tool to the magnetron sputtering discharge is discussed as well as the various magnetron sputtering discharge configurations. The magnetron sputtering discharge is either operated as a dc or radio frequency discharge, or it is driven by some other periodic waveforms depending on the application. This includes reactive magnetron sputtering which exhibits hysteresis and is often operated with an asymmetric bipolar mid-frequency pulsed waveform. Due to target poisoning the reactive sputter process is inherently unstable and exhibits a strongly non-linear response to variations in operating parameters. Ionized physical vapor deposition was initially achieved by adding a secondary discharge between the cathode target and the substrate and later by applying high power pulses to the cathode target. An overview is given of the operating parameters, the discharge properties and the plasma parameters including particle densities, discharge current composition, electron and ion energy distributions, deposition rate, and ionized flux fraction. The discharge maintenance is discussed including the electron heating processes, the creation and role of secondary electrons and Ohmic heating, and the sputter processes. Furthermore, the role and appearance of instabilities in the discharge operation is discussed.
The following article is
Open access
Foundations of physical vapor deposition with plasma assistance
Jon Tomas Gudmundsson
et al
2022
Plasma Sources Sci. Technol.
31
083001
View article
, Foundations of physical vapor deposition with plasma assistance
PDF
, Foundations of physical vapor deposition with plasma assistance
Physical vapor deposition (PVD) refers to the removal of atoms from a solid or a liquid by physical means, followed by deposition of those atoms on a nearby surface to form a thin film or coating. Various approaches and techniques are applied to release the atoms including thermal evaporation, electron beam evaporation, ion-driven sputtering, laser ablation, and cathodic arc-based emission. Some of the approaches are based on a plasma discharge, while in other cases the atoms composing the vapor are ionized either due to the release of the film-forming species or they are ionized intentionally afterward. Here, a brief overview of the various PVD techniques is given, while the emphasis is on sputtering, which is dominated by magnetron sputtering, the most widely used technique for deposition of both metallic and compound thin films. The advantages and drawbacks of the various techniques are discussed and compared.
The following article is
Open access
Foundations of plasma enhanced chemical vapor deposition of functional coatings
R Snyders
et al
2023
Plasma Sources Sci. Technol.
32
074001
View article
, Foundations of plasma enhanced chemical vapor deposition of functional coatings
PDF
, Foundations of plasma enhanced chemical vapor deposition of functional coatings
Since decades, the PECVD (‘plasma enhanced chemical vapor deposition’) processes have emerged as one of the most convenient and versatile approaches to synthesize either organic or inorganic thin films on many types of substrates, including complex shapes. As a consequence, PECVD is today utilized in many fields of application ranging from microelectronic circuit fabrication to optics/photonics, biotechnology, energy, smart textiles, and many others. Nevertheless, owing to the complexity of the process including numerous gas phase and surface reactions, the fabrication of tailor-made materials for a given application is still a major challenge in the field making it obvious that mastery of the technique can only be achieved through the fundamental understanding of the chemical and physical phenomena involved in the film formation. In this context, the aim of this foundation paper is to share with the readers our perception and understanding of the basic principles behind the formation of PECVD layers considering the co-existence of different reaction pathways that can be tailored by controlling the energy dissipated in the gas phase and/or at the growing surface. We demonstrate that the key parameters controlling the functional properties of the PECVD films are similar whether they are inorganic- or organic-like (plasma polymers) in nature, thus supporting a unified description of the PECVD process. Several concrete examples of the gas phase processes and the film behavior illustrate our vision. To complete the document, we also discuss the present and future trends in the development of the PECVD processes and provide examples of important industrial applications using this powerful and versatile technology.
The following article is
Open access
Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments
Ronny Brandenburg 2017
Plasma Sources Sci. Technol.
26
053001
View article
, Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments
PDF
, Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments
Dielectric barrier discharges (DBDs) are plasmas generated in configurations with an insulating (dielectric) material between the electrodes which is responsible for a self-pulsing operation. DBDs are a typical example of nonthermal atmospheric or normal pressure gas discharges. Initially used for the generation of ozone, they have opened up many other fields of application. Therefore DBDs are a relevant tool in current plasma technology as well as an object for fundamental studies. Another motivation for further research is the fact that so-called partial discharges in insulated high voltage systems are special types of DBDs. The breakdown processes, the formation of structures, and the role of surface processes are currently under investigation. This review is intended to give an update to the already existing literature on DBDs considering the research and development within the last two decades. The main principles and different modes of discharge generation are summarized. A collection of known as well as special electrode configurations and reactor designs will be presented. This shall demonstrate the different and broad possibilities, but also the similarities and common aspects of devices for different fields of applications explored within the last years. The main part is devoted to the progress on the investigation of different aspects of breakdown and plasma formation with the focus on single filaments or microdischarges. This includes a summary of the current knowledge on the electrical characterization of filamentary DBDs. In particular, the recent new insights on the elementary volume and surface memory mechanisms in these discharges will be discussed. An outlook for the forthcoming challenges on research and development will be given.
The following article is
Open access
The physics of streamer discharge phenomena
Sander Nijdam
et al
2020
Plasma Sources Sci. Technol.
29
103001
View article
, The physics of streamer discharge phenomena
PDF
, The physics of streamer discharge phenomena
In this review we describe a transient type of gas discharge which is commonly called a streamer discharge, as well as a few related phenomena in pulsed discharges. Streamers are propagating ionization fronts with self-organized field enhancement at their tips that can appear in atmospheric air, or more generally in gases over distances larger than order 1 cm times
, where
is gas density and
is gas density under ambient conditions. Streamers are the precursors of other discharges like sparks and lightning, but they also occur in for example corona reactors or plasma jets which are used for a variety of plasma chemical purposes. When enough space is available, streamers can also form at much lower pressures, like in the case of sprite discharges high up in the atmosphere. We explain the structure and basic underlying physics of streamer discharges, and how they scale with gas density. We discuss the chemistry and applications of streamers, and describe their two main stages in detail: inception and propagation. We also look at some other topics, like interaction with flow and heat, related pulsed discharges, and electron runaway and high energy radiation. Finally, we discuss streamer simulations and diagnostics in quite some detail. This review is written with two purposes in mind: first, we describe recent results on the physics of streamer discharges, with a focus on the work performed in our groups. We also describe recent developments in diagnostics and simulations of streamers. Second, we provide background information on the above-mentioned aspects of streamers. This review can therefore be used as a tutorial by researchers starting to work in the field of streamer physics.
The following article is
Open access
Physics of laser-driven tin plasma sources of EUV radiation for nanolithography
Oscar O Versolato 2019
Plasma Sources Sci. Technol.
28
083001
View article
, Physics of laser-driven tin plasma sources of EUV radiation for nanolithography
PDF
, Physics of laser-driven tin plasma sources of EUV radiation for nanolithography
Laser-produced transient tin plasmas are the sources of extreme ultraviolet (EUV) light at 13.5 nm wavelength for next-generation nanolithography, enabling the continued miniaturization of the features on chips. Generating the required EUV light at sufficient power, reliability, and stability presents a formidable multi-faceted task, combining industrial innovations with attractive scientific questions. This topical review presents a contemporary overview of the status of the field, discussing the key processes that govern the dynamics in each step in the process of generating EUV light. Relevant physical processes span over a challenging six orders of magnitude in time scale, ranging from the (sub-)ps and ns time scales of laser-driven atomic plasma processes to the several
s required for the fluid dynamic tin target deformation that is set in motion by them.
The following article is
Open access
Foundations of plasma-assisted combustion: I. Fundamentals of combustion and plasma
S M Starikovskaia
et al
2026
Plasma Sources Sci. Technol.
35
023001
View article
, Foundations of plasma-assisted combustion: I. Fundamentals of combustion and plasma
PDF
, Foundations of plasma-assisted combustion: I. Fundamentals of combustion and plasma
The use of plasma as an innovative solution to enhance combustion has been the focus of intense research for the past two decades. Plasma-assisted ignition and combustion has emerged as a potential solution for numerous industrial applications. This Foundation paper consists of two parts. Part 1 introduces the context and is followed by a brief summary of the reviews done over the last two decades to show the continued relevance of the topic. We then focus on the fundamentals of combustion and introduce the main concepts of the field. In particular, we discuss combustion kinetics, flame propagation modes, and numerical modeling. Following this, a more in-depth description of plasma physics, specifically non-equilibrium plasma, is provided. As in the previous section, the main concepts are highlighted and defined. We discuss electron energy distribution functions, electron-impact cross-sections, and reaction rates, with a focus on dissociation and fast gas heating which are of particular relevance in the field of plasma-assisted combustion. Finally, elements of numerical modeling are provided. Part 2 of the article will describe the topic of plasma-assisted combustion from the description of fundamental mechanisms to novel combustion systems of importance for the energy transition.
The following article is
Open access
Review of nonequilibrium plasma kinetics in hypersonic flows
Timothy T Aiken
et al
2025
Plasma Sources Sci. Technol.
34
123001
View article
, Review of nonequilibrium plasma kinetics in hypersonic flows
PDF
, Review of nonequilibrium plasma kinetics in hypersonic flows
Ionization in hypersonic flows is a critical phenomenon impacting communications with the ground, wake flow radiation, and vehicle radiative heating. Accurate prediction of the formation and decay of these plasmas relies on a detailed treatment of a wide array of nonequilibrium energy exchanges and collisional-radiative kinetics. These processes may be resolved with varying levels of fidelity depending on the simulation quantity of interest and the computational resources available. In this paper, we review the current state of the art in plasma kinetics modeling for hypersonic flows, focusing particularly on species relevant to flight in Earth’s atmosphere for vehicles employing carbon-based ablative thermal protection systems (N
, O
, NO, N, O, CO
, NCO, C
, C
, CO, CN, C, N
, O
, NO
, N
, O
, CO
, CN
, C
, e
). The available modeling approaches for modeling ionized hypersonic flows are discussed, and the use cases for each are highlighted. Rate data are reviewed for nonequilibrium energy exchanges, dissociation, atom exchange, associative ionization, charge exchange, electron impact ionization, radiative recombination, and dielectronic recombination, as well as their reverse processes where relevant. Based on the scatter in published data, uncertainty bounds on the two-temperature rate coefficients involving the considered species are determined and provided. Finally, ground- and flight-test experimental data are reviewed and summarized. Critical areas for further model improvement are identified throughout, and high-priority validation needs are highlighted.
The following article is
Open access
Physics of plasma jets and interaction with surfaces: review on modelling and experiments
Pedro Viegas
et al
2022
Plasma Sources Sci. Technol.
31
053001
View article
, Physics of plasma jets and interaction with surfaces: review on modelling and experiments
PDF
, Physics of plasma jets and interaction with surfaces: review on modelling and experiments
Plasma jets are sources of repetitive and stable ionization waves, meant for applications where they interact with surfaces of different characteristics. As such, plasma jets provide an ideal testbed for the study of transient reproducible streamer discharge dynamics, particularly in inhomogeneous gaseous mixtures, and of plasma–surface interactions. This topical review addresses the physics of plasma jets and their interactions with surfaces through a pedagogical approach. The state-of-the-art of numerical models and diagnostic techniques to describe helium jets is presented, along with the benchmarking of different experimental measurements in literature and recent efforts for direct comparisons between simulations and measurements. This exposure is focussed on the most fundamental physical quantities determining discharge dynamics, such as the electric field, the mean electron energy and the electron number density, as well as the charging of targets. The physics of plasma jets is described for jet systems of increasing complexity, showing the effect of the different components (tube, electrodes, gas mixing in the plume, target) of the jet system on discharge dynamics. Focussing on coaxial helium kHz plasma jets powered by rectangular pulses of applied voltage, physical phenomena imposed by different targets on the discharge, such as discharge acceleration, surface spreading, the return stroke and the charge relaxation event, are explained and reviewed. Finally, open questions and perspectives for the physics of plasma jets and interactions with surfaces are outlined.
The following article is
Open access
Foundations of plasma-assisted combustion: II. Mechanisms and applications
C O Laux
et al
2026
Plasma Sources Sci. Technol.
35
023002
View article
, Foundations of plasma-assisted combustion: II. Mechanisms and applications
PDF
, Foundations of plasma-assisted combustion: II. Mechanisms and applications
In Part 1 of this topical review, we introduced the main concepts and the basic principles of combustion and plasmas. Part 2 will now examine the topic of plasma-assisted combustion (PAC) with an emphasis on applications to novel combustion systems, particularly those of importance for the energy transition. We start by providing an overview of laboratory experiments that have helped unveil the main fundamental mechanisms of PAC. We also describe some of the main advances achieved in numerical simulations of these rich and complex phenomena in three dimensional, turbulent flames. We then review applications of PAC to practical combustion systems representative of industrial configurations, emphasizing flame stabilization, lean blow-off limit extension, thermo-acoustic instability control, supersonic combustion and plasma detonation engines. Special attention is paid to the reduction of pollutants and the optimization of plasma power.
A study of Xe metastable neutrals in an electrodeless plasma thruster discharge
J Zhou
et al
2026
Plasma Sources Sci. Technol.
35
045013
View article
, A study of Xe metastable neutrals in an electrodeless plasma thruster discharge
PDF
, A study of Xe metastable neutrals in an electrodeless plasma thruster discharge
An axisymmetric hybrid particle/fluid code is used to study the effects of the Xe long-lifetime metastables
and
in an electrodeless plasma thruster discharge. Simulated plasma chemistry includes metastables population, depopulation, and internal exchange through direct electron impact processes together with spontaneous radiative decay from
states and resonant states
and
. Stepwise ionization from metastables and de-excitation at walls are also incorporated. Simulations are run for various absorbed powers and mass flows. Exchange rate from
to
is very high, making the role of
in ion production negligible. At low electron temperatures associated with low power–mass flow ratios, excitation becomes more frequent and the contribution of stepwise ionization to ion production is no more negligible. However, collisional de-excitation is also strong and often exceeds stepwise ionization, limiting a more relevant impact. In addition, roughly half of the apparent contribution of stepwise ionization arises from a shift of the ionization pathway from direct to stepwise channels. Consequently, the net increase in ion production, and the associated improvement in propellant utilization and thrust efficiency remain modest. Due to efficient depopulation mechanisms, the
density is very small compared with that of ground state neutrals, but it affects near infrared emissions used in optical emission spectroscopy. The simulated
/ground-state density ratio is compared with that obtained from the widely adopted local production balance assumption, which neglects convection. The analysis shows that this approximation is reasonable in a region close to the axis, but may fail at large radial positions, where convective effects become important, and thereby may introduce larger uncertainties in diagnostic interpretations.
capacitively coupled plasma—moment analysis of particle-in-cell modeling results
Shahid Rauf
et al
2026
Plasma Sources Sci. Technol.
35
045012
View article
, N2 capacitively coupled plasma—moment analysis of particle-in-cell modeling results
PDF
, N2 capacitively coupled plasma—moment analysis of particle-in-cell modeling results
A one-dimensional particle-in-cell/Monte Carlo collision simulation study of nitrogen (N₂) capacitively coupled plasma (CCP) is presented for a pressure range between 0.1 and 1.5 Torr (13.33–199.98 Pa). The primary objective is to use moment analysis of charged-particle data to systematically examine the validity of commonly employed assumptions in fluid plasma models for intermediate-pressure CCPs. The voltage and pressure range investigated include the CCP operating in the
and
modes as well as conditions with significant electron power absorption in the bulk plasma. At RF voltage
RF
= 200 V (amplitude) and ion-induced secondary electron emission coefficient
= 0.2, the bulk plasma region broadens with increasing pressure as a result of reduced electron and ion mean free paths. Electron power absorption increases in the bulk plasma at 0.5 Torr (66.66 Pa) and higher pressures, but it does not contribute significantly to plasma production. The plasma transitions from the α to γ-mode as
RF
is increased from 200 to 350 V at 0.1 Torr (13.33 Pa) with significant lowering of
and increase of electron density (
) in the bulk plasma. The collision frequencies for individual electron impact reactions as well as the total collision frequency do not exhibit a straight-forward one-on-one relationship to electron temperature (
) or total electron energy (
). This finding contrasts with the common assumption in fluid models for CCPs. Moment analysis of the momentum conservation equations reveals that the drift-diffusion approximation is valid for electrons in the bulk plasma and the pre-sheath region under both
- and
-mode conditions. While ion momentum transport is dominated by sheath acceleration and collisional damping, the inertia term in the ion momentum equation is important at all pressures considered. The
conservation equation indicates that power electrons gain from the electric field does not directly increase
, which is instead governed by collisional energy exchange. The electron heat flux exhibits complex behavior and, consistent with previous reports, the Fourier heat condition assumption in fluid plasma models is found to be invalid. A comparison of moment equations in the
and
modes at 0.1 Torr (13.33 Pa) shows that, while the overall structure of the moment equations remains consistent, electron energy and momentum exchange shift closer to the sheath edge in the
-mode. Overall, this study demonstrates that the primary limitations of fluid models for intermediate-pressure CCPs are the assumptions used to relate electron transport coefficients, electron heat conduction, and electron impact reaction rates to
or
. Accurate modeling of intermediate pressure CCPs therefore require incorporation of non-local and kinetic effects for electrons.
The following article is
Open access
Radial and axial electric field measurements in self-triggered multiperiodic AC plasma jets
Louis Saugé
et al
2026
Plasma Sources Sci. Technol.
35
045011
View article
, Radial and axial electric field measurements in self-triggered multiperiodic AC plasma jets
PDF
, Radial and axial electric field measurements in self-triggered multiperiodic AC plasma jets
AC-driven atmospheric pressure plasma jets can produce both positive and negative ionization fronts (IFs). Non perturbative electric field (
-field) probe measurements based on Pockels effect have been used to capture the dynamic of IFs. Under specific conditions of applied voltage and frequency, and in the presence of a grounded ring electrode, IFs self-trigger in less than 100 ns jitter, every
voltage periods, defining the so-called multi-periodic (MP) regime. The grounded electrode additionally extends multiperiodic plasma bullet length by up to a factor of two in the 2P mode, and the inter-electrode gap is shown to host multiple short intragap discharges preceding the emission of long bullets every two periods.
-field probe measurements have been used to determine the polarity of inter-electrode discharges and plasma bullets, revealing that positive and negative bullets deposit distinct surface charge densities inside the capillary. A newly identified 1.5P mode is characterized alongside the 2P mode: it produces short-range secondary bullets every period while generating long-range major bullets of opposite polarity every two periods. Mode stability mapping as a function of gas impurity levels demonstrates that increasing nitrogen and oxygen concentrations suppress higher-order MP modes while broadening the stability domain of the 1.5P regime.
Study on the mechanism of optimal magnetic field strength for helicon discharge of different gases in MPS-LD
Yao Peng
et al
2026
Plasma Sources Sci. Technol.
35
045010
View article
, Study on the mechanism of optimal magnetic field strength for helicon discharge of different gases in MPS-LD
PDF
, Study on the mechanism of optimal magnetic field strength for helicon discharge of different gases in MPS-LD
To achieve high density discharges of various gases in the multiple plasma simulation linear device (MPS-LD) and thereby provide the required plasma conditions for experimental simulation of plasma material interaction in tokamak environment, helicon wave discharge experiments using Ar, N
, He, and H
were carried out in the MPS-LD device, and the optimal magnetic field strength (
opt
) and its formation mechanism were systematically investigated. Langmuir probe and optical emission spectroscopy were employed to diagnose plasma parameters (electron density
, and the emission intensities of Ar I and other atomic, ionic, and molecular lines) under different experimental conditions (RF power, gas flow rate and magnetic field strength). The results show that for all discharge gases,
first increases and then decreases with the magnetic field strength, indicating the existence of
opt
corresponding to the maximum
. When the magnetic field strength exceeds
opt
, the radial
profile changes from a centrally peaked to an off-axis double-peaked structure, accompanied by a marked decrease in the central
. This is due to the outward shift of the mode conversion surface/layer (MCS/MCL), which moves the primary wave energy deposition region away from the plasma core. Moreover,
opt
increases with the atomic mass of the discharge gas. On this basis, the effects of RF power and gas flow rate on
opt
and
were further investigated. It was found that increasing power and flow rate enhances wave energy deposition in the plasma core, leading to increases in both
and
opt
in Ar and He discharges. This study clarifies the physical mechanism underlying the existence of
opt
for high density helicon discharges in MPS-LD and provides both theoretical and experimental support for further improving
in discharges of different gases.
On the applicability of a conducting fluid model to gas-discharge plasma
T V Gurkova
et al
2026
Plasma Sources Sci. Technol.
35
045009
View article
, On the applicability of a conducting fluid model to gas-discharge plasma
PDF
, On the applicability of a conducting fluid model to gas-discharge plasma
This work proposes a method for solving a self-consistent system of hydrodynamic equations describing non-equilibrium gas-discharge plasma with complex electric-field configurations. The method is based on a two-stage solution procedure. At the first stage, a simplified conducting-fluid model is used to determine the electric-field distribution based on prescribed input parameters such as plasma conductivity, discharge geometry, gas pressure, and discharge current. The resulting electric field sustains the prescribed discharge current. At the second stage, the resulting electric field is used as input for solving the full system of particle and energy balance equations for all plasma components. This second-stage solution yields a full set of self-consistent plasma parameters, for which the electric-field configuration sustains both the discharge current and the ionization balance. In addition to the electric-field configuration, the conducting-fluid model allows determination of potential jumps at metal-dielectric-plasma interfaces, space-charge layers, distortions of electric field, and other related effects. The applicability of the method is demonstrated using an axially uniform positive column as an example. The method is further illustrated by current flow in a glass tube with metal segments, as well as by metal probes with glass insulation located in a current-carrying plasma.
The following article is
Open access
Foundations of plasma-assisted combustion: II. Mechanisms and applications
C O Laux
et al
2026
Plasma Sources Sci. Technol.
35
023002
View article
, Foundations of plasma-assisted combustion: II. Mechanisms and applications
PDF
, Foundations of plasma-assisted combustion: II. Mechanisms and applications
In Part 1 of this topical review, we introduced the main concepts and the basic principles of combustion and plasmas. Part 2 will now examine the topic of plasma-assisted combustion (PAC) with an emphasis on applications to novel combustion systems, particularly those of importance for the energy transition. We start by providing an overview of laboratory experiments that have helped unveil the main fundamental mechanisms of PAC. We also describe some of the main advances achieved in numerical simulations of these rich and complex phenomena in three dimensional, turbulent flames. We then review applications of PAC to practical combustion systems representative of industrial configurations, emphasizing flame stabilization, lean blow-off limit extension, thermo-acoustic instability control, supersonic combustion and plasma detonation engines. Special attention is paid to the reduction of pollutants and the optimization of plasma power.
The following article is
Open access
Foundations of plasma-assisted combustion: I. Fundamentals of combustion and plasma
S M Starikovskaia
et al
2026
Plasma Sources Sci. Technol.
35
023001
View article
, Foundations of plasma-assisted combustion: I. Fundamentals of combustion and plasma
PDF
, Foundations of plasma-assisted combustion: I. Fundamentals of combustion and plasma
The use of plasma as an innovative solution to enhance combustion has been the focus of intense research for the past two decades. Plasma-assisted ignition and combustion has emerged as a potential solution for numerous industrial applications. This Foundation paper consists of two parts. Part 1 introduces the context and is followed by a brief summary of the reviews done over the last two decades to show the continued relevance of the topic. We then focus on the fundamentals of combustion and introduce the main concepts of the field. In particular, we discuss combustion kinetics, flame propagation modes, and numerical modeling. Following this, a more in-depth description of plasma physics, specifically non-equilibrium plasma, is provided. As in the previous section, the main concepts are highlighted and defined. We discuss electron energy distribution functions, electron-impact cross-sections, and reaction rates, with a focus on dissociation and fast gas heating which are of particular relevance in the field of plasma-assisted combustion. Finally, elements of numerical modeling are provided. Part 2 of the article will describe the topic of plasma-assisted combustion from the description of fundamental mechanisms to novel combustion systems of importance for the energy transition.
The following article is
Open access
Review of nonequilibrium plasma kinetics in hypersonic flows
Timothy T Aiken
et al
2025
Plasma Sources Sci. Technol.
34
123001
View article
, Review of nonequilibrium plasma kinetics in hypersonic flows
PDF
, Review of nonequilibrium plasma kinetics in hypersonic flows
Ionization in hypersonic flows is a critical phenomenon impacting communications with the ground, wake flow radiation, and vehicle radiative heating. Accurate prediction of the formation and decay of these plasmas relies on a detailed treatment of a wide array of nonequilibrium energy exchanges and collisional-radiative kinetics. These processes may be resolved with varying levels of fidelity depending on the simulation quantity of interest and the computational resources available. In this paper, we review the current state of the art in plasma kinetics modeling for hypersonic flows, focusing particularly on species relevant to flight in Earth’s atmosphere for vehicles employing carbon-based ablative thermal protection systems (N
, O
, NO, N, O, CO
, NCO, C
, C
, CO, CN, C, N
, O
, NO
, N
, O
, CO
, CN
, C
, e
). The available modeling approaches for modeling ionized hypersonic flows are discussed, and the use cases for each are highlighted. Rate data are reviewed for nonequilibrium energy exchanges, dissociation, atom exchange, associative ionization, charge exchange, electron impact ionization, radiative recombination, and dielectronic recombination, as well as their reverse processes where relevant. Based on the scatter in published data, uncertainty bounds on the two-temperature rate coefficients involving the considered species are determined and provided. Finally, ground- and flight-test experimental data are reviewed and summarized. Critical areas for further model improvement are identified throughout, and high-priority validation needs are highlighted.
Historical development of electron swarm physics based on the Boltzmann equation towards in-depth understanding of a low-temperature collisional plasma
Toshiaki Makabe and Hirotake Sugawara 2024
Plasma Sources Sci. Technol.
33
093001
View article
, Historical development of electron swarm physics based on the Boltzmann equation towards in-depth understanding of a low-temperature collisional plasma
PDF
, Historical development of electron swarm physics based on the Boltzmann equation towards in-depth understanding of a low-temperature collisional plasma
Theoretical study of the electron kinetics (i.e. the velocity distribution and the transport parameter) in gases is generally conducted using the electron Boltzmann equation. The year 2022 marked 150 years since the formulation of the Boltzmann equation. Even in the last several decades, the historical progress has been made synchronously with the development of innovative technologies in gaseous electronics and in combination with the appearance of computers with sufficient speed and memory. Electron kinetic theory based on the Boltzmann equation has mostly been developed as the swarm physics in the hydrodynamic regime in the dc and radio frequency electric fields. In particular, the temporal characteristics are understood in terms of the collisional relaxation times between electron and gas molecule. There are two main theoretical approaches based on the Boltzmann equation for finding the velocity distribution. One is the traditional description of the electron kinetics, starting from the Boltzmann statistics in velocity space under a uniform density or a small density gradient of electrons. The other most recent approach is based on the phase-space tracking of the velocity distribution where the electron transport parameter is given by the moment of the electron density distribution in position space. In the present paper, we will explore the historical development of the electron Boltzmann equation with respect to three key items: collision term, solution method, and intrinsic electron transport in a hydrodynamic regime involved as the key elements in the low-temperature collisional plasma. The important topics listed in a table are briefly noted and discussed.
A tutorial overview of the angular scattering models of electron–neutral, ion–neutral, neutral–neutral, and Coulomb collisions in Monte Carlo collision modeling on low-temperature plasma
Wei Yang 2024
Plasma Sources Sci. Technol.
33
023001
View article
, A tutorial overview of the angular scattering models of electron–neutral, ion–neutral, neutral–neutral, and Coulomb collisions in Monte Carlo collision modeling on low-temperature plasma
PDF
, A tutorial overview of the angular scattering models of electron–neutral, ion–neutral, neutral–neutral, and Coulomb collisions in Monte Carlo collision modeling on low-temperature plasma
Over the past decade, extensive modeling practices on low-temperature plasmas have revealed that input data such as microscopic scattering cross-sections are crucial to output macroscopic phenomena. In Monte Carlo collision (MCC) modeling of natural and laboratory plasma, the angular scattering model is a non-trivial topic. Conforming to the pedagogical purpose of this overview, the classical and quantum theories of binary scattering, such as the commonly used Born–Bethe approximation, are first introduced. Adequate angular scattering models, which MCC simulation can handle as input, are derived based on the above theories for electron–neutral, ion–neutral, neutral–neutral, and Coulomb collisions. This tutorial does not aim to provide accurate cross-sectional data by modern approaches in quantum theory, but rather to introduce analytical angular scattering models from classical, semi-empirical, and first-order perturbation theory. The reviewed models are expected to be readily incorporated into the MCC codes, in which the scattering angle is randomly sampled through analytical inversion instead of the numerical accept–reject method. These simplified approaches are very attractive, and demonstrate in many cases the ability to achieve a striking agreement with experiments. Energy partition models on electron–neutral ionization are also discussed with insight from the binary-encounter Bethe theory. This overview is written in a tutorial style in order to serve as a guide for novices in this field, and at the same time as a comprehensive reference for practitioners of MCC modeling on plasma.
High density atomic oxygen microwave plasma source characterized by quantitative Optical Emission Spectroscopy and Two Photon Laser Absorption Induced Fluorescence
Stefanović et al
View accepted manuscript
, High density atomic oxygen microwave plasma source characterized by quantitative Optical Emission Spectroscopy and Two Photon Laser Absorption Induced Fluorescence
PDF
, High density atomic oxygen microwave plasma source characterized by quantitative Optical Emission Spectroscopy and Two Photon Laser Absorption Induced Fluorescence
The Miniature Microwave Inductively Coupled Plasma (MMWICP) device is investigated as a potential source of atomic oxygen (O) for various applications, including ultra-thin barrier film deposition. To the best of our knowledge, this is the first study combining two-photon absorption laser-induced fluorescence (TALIF) with quantitative optical emission spectroscopy (OES) to determine the atomic oxygen density in microwave plasma. Due to its unique design, the MMWICP operates in a highly efficient H-mode, producing atomic oxygen densities of up to 7×1021 m−3 at a pressure of 150 Pa in pure oxygen. By adding 1% nitrogen to the gas mixture to enable OES measurements, the atomic oxygen density increases further, reaching up to 2×1022 m−3. In addition to dissociative attachment, which is the main production mechanism of atomic oxygen, heavy-particle collisions between oxygen molecules and nitrogen metastable molecules in the N₂(A) state most likely contribute to the observed enhancement of the O density. Along the effluent, O losses are negligible under the applied plasma conditions. The gas temperature decreases rapidly from 1400 K in the plasma center to values between 400 K and 500 K at a distance of 30 mm. A similar value of approximately 500 K in the plasma effluent is obtained from Doppler broadening of the two- photon excitation profile of atomic oxygen. A comparison of the two independent diagnostics for the atomic oxygen density shows that both methods exhibit similar qualitative behavior with respect to variations in gas pressure. However, the absolute atomic oxygen densities obtained by TALIF are two to three times higher than those derived from OES, although the respective error bars overlap. The uncertainties associated with both methods are discussed, together with possible approaches to improve the quantitative agreement between the two techniques.
Optimization-based reconstruction of parameterized electron energy distribution functions from optical emission spectra in low-pressure argon plasma
Huang et al
View accepted manuscript
, Optimization-based reconstruction of parameterized electron energy distribution functions from optical emission spectra in low-pressure argon plasma
PDF
, Optimization-based reconstruction of parameterized electron energy distribution functions from optical emission spectra in low-pressure argon plasma
The electron energy distribution function (EEDF) is a fundamental indicator of the nonequilibrium nature of low-temperature plasmas that govern electron-driven physical and chemical processes. In this study, an optimization-based inversion framework was developed to reconstruct parameterized EEDFs, described by a generalized functional form, in lowpressure argon plasmas; these EEDFs are reconstructed from optical emission spectra. A collisional-radiative model was coupled with a genetic algorithm to determine the parameters of the adopted generalized EEDF expression by fitting the intensities of the selected emission lines. Numerical tests demonstrated that the proposed method could accurately reproduce the prescribed EEDF shapes, and it exhibited a certain degree of robustness against spectral noise. The framework was further validated experimentally in two different argon-based inductively-coupled plasma systems; the retrieved EEDFs showed good agreement with those obtained from the Langmuir probe measurements, particularly in the low-energy region. The role of the metastable-assisted stepwise excitation from the 1s manifold in enhancing the spectral sensitivity to low-energy electrons was analyzed. These results indicate that the proposed approach provides a feasible and physically consistent solution for detailed diagnostics of non-equilibrium electron kinetics in low-pressure plasmas, and its applicability and limitations are clearly defined.
Analysis of electron power absorption and loss mechanisms in the discharge chamber of air-breathing radio-frequency ion thruster
Liu et al
View accepted manuscript
, Analysis of electron power absorption and loss mechanisms in the discharge chamber of air-breathing radio-frequency ion thruster
PDF
, Analysis of electron power absorption and loss mechanisms in the discharge chamber of air-breathing radio-frequency ion thruster
In recent years, very low Earth orbit (VLEO) has attracted growing interest for enabling higher-resolution Earth observation, shorter communication delays, and reduced launch costs. Air-breathing electric propulsion (ABEP), which employs upper atmospheric gas as propellant, has become a research hotspot. To investigate electron power absorption and loss mechanisms in an air-breathing radio-frequency (RF) ion thruster and improve ionization efficiency, a two-dimensional axisymmetric PIC-MCC simulation of the RIT-10 thruster was performed. Results show that increasing RF power enhances electron energy absorption and average energy. At low pressures, however, the reduced electron–neutral collision frequency relative to the coil frequency induces a large phase difference between the inductive field and electron current, leading to negative power absorption. Power loss analysis indicates that higher RF power increases losses through high-level excitation, ionization, and dissociation, while reducing low-level excitation. Comparisons between oxygen and nitrogen systems reveal that oxygen achieves superior ionization efficiency, with energy mainly lost via dissociation and ionization, whereas nitrogen predominantly loses energy through excitation. The ion beam consists mainly of N₂⁺ and O⁺. With increasing RF power, N₂⁺ production strengthens, raising its fraction from 32.82% to 37.25% while reducing O⁺ from 42.48% to 32.11%. Consequently, mass utilization and thrust efficiencies improve markedly, from 8.83% and 6.35% to 28.93% and 22.27%. These findings clarify key operational mechanisms of VLEO ABEP thrusters.
Study on spatiotemporal transient distribution characteristics and energy conversion mechanism of nanosecond pulse hollow cathode electron beam
Cao et al
View accepted manuscript
, Study on spatiotemporal transient distribution characteristics and energy conversion mechanism of nanosecond pulse hollow cathode electron beam
PDF
, Study on spatiotemporal transient distribution characteristics and energy conversion mechanism of nanosecond pulse hollow cathode electron beam
This study employs the PIC-MCC particle simulation method to investigate the spatiotemporal transient distribution characteristics and energy conversion mechanism of nanosecond pulse hollow cathode electron beams. Based on the evolution of physical processes during the three stages of electron beam generation, the study systematically analyzes the mechanism of spatiotemporal distribution characteristics by considering external influencing factors such as applied voltage and hollow cathode aperture, as well as internal factors such as electric field intensity within the cathode cavity. Additionally, the impact of both internal and external factors on the energy conversion efficiency of the electron beam is examined, revealing the underlying mechanisms for improving energy conversion efficiency. The simulation calculations of the physical model are carried out under an argon environment with a pressure of 0.3 Torr and a temperature of 300 K. The simulation models for spatiotemporal transient distribution and energy conversion efficiency are experimentally validated for rationality. The results show that, regarding the spatiotemporal transient distribution characteristics of the hollow cathode electron beam, the cathode aperture has a greater effect on total breakdown time than the applied voltage. During the current multiplication rise phase, the applied voltage plays a more significant role, determining the peak value and growth rate of beam current and energy. However, under any combination of applied voltage and aperture parameters, the spatial distribution of the electron beam consistently follows a Gaussian profile. The energy conversion efficiency of the hollow cathode electron beam exhibits a numerical relationship with the average electric field in the cathode cavity, which is an exponential relationship with negative proportional and exponential factors. Enhancing the energy conversion efficiency by increasing the electric field becomes limited once the field strength reaches a certain threshold.
How air impurities affect plasma in helium microdischarges at atmospheric pressure
Mandour et al
View accepted manuscript
, How air impurities affect plasma in helium microdischarges at atmospheric pressure
PDF
, How air impurities affect plasma in helium microdischarges at atmospheric pressure
The influence of trace air admixtures on the kinetics and macro-response of atmospheric-pressure helium microdischarges with a short 0.2 mm gap has been analyzed using a one-dimensional drift-diffusion fluid model that includes electron energy balance and incorporates air impurity traces within a helium plasma chemistry set. The baseline helium scheme resolves atomic states up to n = 4 levels and includes elastic scattering, excitation/de-excitation, direct and stepwise ionization, associative and Penning ionization, excimer formation/quenching, ion conversion, three-body and dissociative recombination, and radiation. Simulations show that ppm-level air can leave the current-voltage characteristic nearly unchanged while qualitatively rerouting the underlying kinetics: rapid charge transfer and Penning channels shift the cation composition from helium molecular and atomic ions to impurity ions, quench helium metastables/excimers, and modestly cool both electrons and gas via inelastic molecular pathways. These results explain why "pure-He" models sometimes match bulk electrical curves but not species-level physics. They also show impurity regimes where precise He-air chemistry is necessary for understanding diagnostics and for controlling and designing microplasma devices.
More Accepted manuscripts
The following article is
Open access
Radial and axial electric field measurements in self-triggered multiperiodic AC plasma jets
Louis Saugé
et al
2026
Plasma Sources Sci. Technol.
35
045011
View article
, Radial and axial electric field measurements in self-triggered multiperiodic AC plasma jets
PDF
, Radial and axial electric field measurements in self-triggered multiperiodic AC plasma jets
AC-driven atmospheric pressure plasma jets can produce both positive and negative ionization fronts (IFs). Non perturbative electric field (
-field) probe measurements based on Pockels effect have been used to capture the dynamic of IFs. Under specific conditions of applied voltage and frequency, and in the presence of a grounded ring electrode, IFs self-trigger in less than 100 ns jitter, every
voltage periods, defining the so-called multi-periodic (MP) regime. The grounded electrode additionally extends multiperiodic plasma bullet length by up to a factor of two in the 2P mode, and the inter-electrode gap is shown to host multiple short intragap discharges preceding the emission of long bullets every two periods.
-field probe measurements have been used to determine the polarity of inter-electrode discharges and plasma bullets, revealing that positive and negative bullets deposit distinct surface charge densities inside the capillary. A newly identified 1.5P mode is characterized alongside the 2P mode: it produces short-range secondary bullets every period while generating long-range major bullets of opposite polarity every two periods. Mode stability mapping as a function of gas impurity levels demonstrates that increasing nitrogen and oxygen concentrations suppress higher-order MP modes while broadening the stability domain of the 1.5P regime.
The following article is
Open access
Numerical 2D/3D modeling of surface ionization wave propagating in air over silicon
Antoine Herrmann
et al
2026
Plasma Sources Sci. Technol.
View article
, Numerical 2D/3D modeling of surface ionization wave propagating in air over silicon
PDF
, Numerical 2D/3D modeling of surface ionization wave propagating in air over silicon
In this study, we present a 2D/3D fluid model to simulate the propagation of a Surface Ionization Wave (SIW) in air at atmospheric pressure, initiated by a pin electrode placed in contact with a SiO₂ layer deposited on a p-doped silicon wafer, which is in turn in contact with glass placed over the ground. Thus, instead of studying a classical DBD (Dielectric Barrier Discharge), we focus here on a new type of discharge: the SeBD (Semiconductor Barrier Discharge). The model couples a drift-diffusion model in both air and silicon to resolve the temporal evolution of charged species: electrons, positive ions, and negative ions in air, as well as mobile electrons, holes, and immobile charges in silicon. Simulation results were validated against experimental data, including time-resolved imaging and current measurements, for doping levels of the p-doped silicon corresponding to resistivities of 3000, 40, and 10 Ω·cm. Using the 2D model, we demonstrate that higher doping levels lead to faster SIW ignition, driven by charge reorganization in silicon that enhances the electric field in air. From 3000 to 40 Ω·cm, increased doping also promotes confinement of the SIW toward the SiO₂-Si interface and increases photoelectron generation. However, increasing the doping further to 10 Ω·cm results in excessive confinement, which limits photoelectron production. Additionally, higher doping levels yield increases SIW current, attributed to greater charge density generated by the enhancement of the electric field component normal to the SiO2-Si interface. Extending the model to 3D reveals that doped silicon promotes uniform SIW propagation by enhancing photon-induced ionization, mitigating instabilities arising from the stochasticity of photoelectron production.
The following article is
Open access
Impact of N
addition on cation and anion chemistry in C
/ Ar plasmas
Isabel Tanarro
et al
2026
Plasma Sources Sci. Technol.
View article
, Impact of N2 addition on cation and anion chemistry in C2H2 / Ar plasmas
PDF
, Impact of N2 addition on cation and anion chemistry in C2H2 / Ar plasmas
The addition of (0.8-31%) N2 to C2H2/Ar RF glow discharges is investigated by mass spectrometry of neutrals and ions, and optical emission spectroscopy. During an  20 s initial transient after plasma ignition, C2nH2m molecules, C2 and CH appear and decay quickly, in parallel with a steep C2H2 dissociation and H2 rise, irrespective of the N2 initial content; N2 decreases, and HCN, HC3N and CN increase gradually, evolving afterwards to stable concentrations. Comparison with previous results suggests that these effects are related with dust formation over this transient, after which, dust disappears and ions begin to grow. Cations and anions up to masses > 200 u are detected in the steadystate. Protonated cations seem to dominate, together with those of pure hydrocarbons. Most cations decrease markedly with N2 growth, except those containing N. Conversely, nitrile anions appear even for the lowest N2 amount, and they increase by orders of magnitude with growing N2, while the hydrocarbon anions tend to disappear. Globally, a significant increase of plasma electronegativity with N2 content is observed. Likely assignments of the molecular compositions are proposed, based on the dependences of given ion masses on N2 content. Particular interest deserves the C2nH -and C2n-1N - families, the only anions identified till now in space. Their relative signals at the lowest N2 proportion agree with the column densities measured around a prototypical red giant star. The large sensitivity of the anion composition to small N2 amounts found in this work, and the coincidence in mass of N and CH2, might contribute to corroborate C2H -as the key ion for the main anion polymerization chain in C2H2 plasmas, instead of C2H2 -, proposed previously. Likely gas-phase reactions and the evidence of active surface chemistry are proposed for the rationalization of the results.
The following article is
Open access
Magnetically induced formation and disruption of striations in capacitively coupled radio-frequency CF
plasmas
Li Wang
et al
2026
Plasma Sources Sci. Technol.
View article
, Magnetically induced formation and disruption of striations in capacitively coupled radio-frequency CF4 plasmas
PDF
, Magnetically induced formation and disruption of striations in capacitively coupled radio-frequency CF4 plasmas
The influence of externally applied homogeneous transverse magnetic fields of up to 200 G on self-organized striations in capacitively coupled radio-frequency CF 4 plasmas is investigated using kinetic simulations. The striations are known to originate from a resonance between the applied radio-frequency and the eigenfrequency of the ion-ion plasma, the magnetic field is found to affect the striations indirectly through its impact on electron dynamics as ions do not get magnetized within the range of magnetic fields covered. Depending on the discharge conditions, increasing the magnetic field can either switch striations on or off and, in this way, strongly affect the spatial electron energy distribution function as well as the generation of process relevant charged and neutral species. We demonstrate that at some discharge conditions where striations form in the absence of a magnetic field, applying a moderate B-field can lead to the suppression of striations near the discharge center as a result of enhanced electron power absorption and a corresponding increase in electron density, enabling electrons to neutralize the space charge caused by the ion oscillations. We also illustrate the opposite effect that can occur at some other operating conditions, where the plasma operates close to the striation regime, but striations are absent due to insufficient ion densities, the magnetic field enhances the ion density and amplifies the local space charge formation, which can no longer be balanced by electrons. As a result, striations appear, inducing a transition from the drift ambipolar to a striation/magnetized drift ambipolar hybrid mode.
The following article is
Open access
Atomic layer etching of sputter-deposited AlN thin films in radiofrequency Cl
–Ar plasmas
Iurii Nesterenko
et al
2026
Plasma Sources Sci. Technol.
35
045008
View article
, Atomic layer etching of sputter-deposited AlN thin films in radiofrequency Cl2–Ar plasmas
PDF
, Atomic layer etching of sputter-deposited AlN thin films in radiofrequency Cl2–Ar plasmas
Atomic layer etching (ALE) of AlN is an important process for enabling high-precision patterning in advanced photonic and electronic devices. In this study, ALE of sputter-deposited AlN thin films was carried out using an ALE approach consisting of Cl
-based surface modification followed by an Ar ion bombardment step. The developed process exhibited highly self-limiting behavior with etch-per-cycle approaching the thickness of a single AlN monolayer, a process synergy of 82%, and a post-etch root mean square surface roughness as low as 0.6 nm. To define the ALE ion energy window, ion energy distribution functions were measured and calibrated by taking into account the voltage drop across the dielectric layer on the wafer surface. This calibration revealed a significant reduction in effective energy of ions reaching the wafer surface and a corresponding shift in the ALE ion energy window when expressed in terms of the peak-to-peak voltage. The ALE ion energy window for AlN was experimentally determined to be between 142 and 196 eV, which is in good agreement with molecular dynamics simulations predicting the lower threshold of the window to be 150 eV. These findings underscore the importance of considering dielectric stack thickness in ALE and conventional plasma processing.
The following article is
Open access
Hydrogen peroxide formation mechanisms in liquid anode and cathode discharges
Jae Hyun Nam
et al
2026
Plasma Sources Sci. Technol.
35
045004
View article
, Hydrogen peroxide formation mechanisms in liquid anode and cathode discharges
PDF
, Hydrogen peroxide formation mechanisms in liquid anode and cathode discharges
Hydrogen peroxide (H
) plays a key role in plasma-induced chemistry for various applications. The mechanisms governing the production of aqueous hydrogen peroxide, H₂O₂
aq
, in non-thermal plasma–liquid interactions, particularly the significant production rate dependence on liquid electrode polarity, have resulted in persistent controversy in the literature. We conduct spatiotemporal measurements of the gas phase H₂O₂ density at the interface of a pulsed helium plasma jet impinging on a liquid electrode, using photo-fragmentation laser-induced fluorescence. We show that gas phase H₂O₂ densities are unexpectedly similar for both discharge polarities. In contrast, complementary measurements of the liquid phase H₂O₂
aq
concentration show that the H₂O₂
aq
production is more than tenfold higher for a liquid cathode discharge compared to the liquid anode discharge. While this disparity cannot be reconciled by the solvation of gas phase H₂O₂, it can be explained by the enhanced H₂O₂
aq
yield in the liquid cathode configuration being predominantly driven by the production of aqueous hydroxyl radicals, OH
aq
, that are formed by incident positive ions. This hypothesis is further supported by experiments using various OH
aq
scavengers as well as modeling results. The reported findings highlight that ion-driven liquid-phase chemistry is the dominant mechanism responsible for the polarity dependence in H₂O₂ synthesis by plasmas in contact with an aqueous electrode.
The following article is
Open access
Electronic-specific modeling of a nonequilibrium recombining N
/Ar plasma and comparison with experiments
Ulysse Dubuet
et al
2026
Plasma Sources Sci. Technol.
35
045007
View article
, Electronic-specific modeling of a nonequilibrium recombining N2/Ar plasma and comparison with experiments
PDF
, Electronic-specific modeling of a nonequilibrium recombining N2/Ar plasma and comparison with experiments
An electronic-specific kinetic model for nitrogen–argon plasmas is developed by the reduction of a state-of-the-art vibronic-specific model. The model is used to study the nonequilibrium recombination of high-temperature nitrogen–argon plasmas, initially in local thermodynamic equilibrium at high temperature and atmospheric pressure, and forced to cool rapidly. Simulations using the electronic-specific model are performed along the axis of the tube. The results are compared with measurements of electron densities, ground state species (N), and several excited electronic states of N, N
(B, C), and N
(B), obtained in two sets of experiments. The simulations and measurements generally agree within a factor of 3, while the nonequilibrium degree is typically several orders of magnitude. A detailed analysis of the main processes governing the recombination of the plasma indicates that the transfer of electronic energy from N
(A) to N(
P) and the three-body recombination of N
by N-impact play key roles in the recombination kinetics. We show that accurate predictions of species densities depend primarily on accurate predictions of N
(A) and N(
P) densities, which must be the focus of future research efforts.
The following article is
Open access
CO
plasma in fluidized bed—DC glow discharge reactor
Carolina A Garcia-Soto
et al
2026
Plasma Sources Sci. Technol.
35
045006
View article
, CO2 plasma in fluidized bed—DC glow discharge reactor
PDF
, CO2 plasma in fluidized bed—DC glow discharge reactor
Plasma-catalysis holds great potential for efficient CO
recycling but the effectiveness of this approach depends on how plasma sources and catalytic materials are coupled. Fluidized bed (FB) reactors are interesting because they exhibit increased surface contact area between material particles and gas phase, and improved heat transfer. A low-pressure DC glow discharge (GD) in FB configuration, ignited with or without fluidized Al
particles, is investigated with optical emission spectroscopy. A decrease in oxygen atom density through the fluidization of the material and an increase in the intensity of CO systems, attributed to increased CO density and to a lesser extend to electric field changes, is observed in comparison to the plasma alone. This indicates that fluidized particles indeed cause a reduction in the O presence leading to an increase in CO density. The rotational temperature does not significantly change, despite the more efficient heat transfer to the wall expected in FB-GDs. This is attributed to the higher current density induced by the confinement of the plasma in the center of the tube by the charged particles. The plasma-assisted catalytic behavior is further investigated by infrared absorption spectroscopy downstream of the FB-GD, showing superior conversion performance compared to the GD alone. The development of this innovative route is crucial to understanding the enhancement of plasma-surface interaction for CO
recycling.
The following article is
Open access
Comparison of fluid and particle-in-cell 3D simulations of negative streamers in CO
with admixtures of C
Thomas J G Smits
et al
2026
Plasma Sources Sci. Technol.
35
045005
View article
, Comparison of fluid and particle-in-cell 3D simulations of negative streamers in CO2 with admixtures of C4F7N
PDF
, Comparison of fluid and particle-in-cell 3D simulations of negative streamers in CO2 with admixtures of C4F7N
CO
with an admixture of C
N could serve as an eco-friendly alternative to the extreme greenhouse gas SF
in high-voltage insulation. Streamer discharges in such gases are different from those in air due to the rapid conductivity decay in the streamer channels. Furthermore, since no effective photoionisation mechanism is known, we expect discharge growth to be more stochastic than in air. In this paper we investigate whether conventional fluid models provide an good approximation to a particle-in-cell model for negative streamers in CO
with admixtures of 1 or 10% C
N Higher fractions were not included, as C
N admixtures in high-voltage insulation rarely exceed 10% C
N. We focus on 3D simulations of negative streamers. First we review cross section databases for C
N and CO
. Then we compare a two-term Boltzmann solver with a Monte Carlo method to compute reaction and transport coefficients from the cross sections. Afterwards we compare 3D fluid simulations with the local field (LFA) or local energy approximation (LEA) against particle simulations. In general, we find that the results of particle and fluid models are quite similar. One difference we observe is that particle simulations are intrinsically stochastic, leading to more branching. Furthermore, the LEA model does not show better agreement with the particle simulations than the LFA model. We also discuss the effect and choice of different boundary conditions on the negative rod electrode.
The following article is
Open access
How fast does a vacuum surface discharge propagate?
Guangyu Sun 2026
Plasma Sources Sci. Technol.
35
045001
View article
, How fast does a vacuum surface discharge propagate?
PDF
, How fast does a vacuum surface discharge propagate?
Vacuum surface discharge on dielectric substrates is frequently observed in vacuum electronic devices and insulation systems, spanning gap distances from the sub-micrometer to millimeter scale and beyond. Such discharges propagate through a secondary electron emission avalanche (SEEA), in which field emission (FE) electrons multiply on the surface via successive secondary electron emission. Understanding the SEEA propagation speed (
) is essential for elucidating the underlying discharge physics and optimizing device performance. Despite extensive studies since the 1970s, no predictive theory has been available to calculate this key quantity or reveal its parametric dependencies. Here, we resolve this longstanding issue by introducing a charging-by-slice model, which yields a compact expression,
, linking the propagation speed to the cathode FE current and applied electric field. Theoretical predictions are validated by particle-in-cell simulations and experimental measurements, showing excellent agreement and revealing a
in the range of 10
–10
m s
−1
. The established theoretical framework advances both the fundamental understanding of device physics and the practical design of vacuum electronic and insulation systems.
More Open Access articles
Solving the Boltzmann equation to obtain electron transport coefficients and rate coefficients for fluid models
G J M Hagelaar and L C Pitchford 2005
Plasma Sources Sci. Technol.
14
722
View article
, Solving the Boltzmann equation to obtain electron transport coefficients and rate coefficients for fluid models
PDF
, Solving the Boltzmann equation to obtain electron transport coefficients and rate coefficients for fluid models
Fluid models of gas discharges require the input of transport coefficients and rate coefficients that depend on the electron energy distribution function. Such coefficients are usually calculated from collision cross-section data by solving the electron Boltzmann equation (BE). In this paper we present a new user-friendly BE solver developed especially for this purpose, freely available under the name BOLSIG+, which is more general and easier to use than most other BE solvers available. The solver provides steady-state solutions of the BE for electrons in a uniform electric field, using the classical two-term expansion, and is able to account for different growth models, quasi-stationary and oscillating fields, electron–neutral collisions and electron–electron collisions. We show that for the approximations we use, the BE takes the form of a convection-diffusion continuity-equation with a non-local source term in energy space. To solve this equation we use an exponential scheme commonly used for convection-diffusion problems. The calculated electron transport coefficients and rate coefficients are defined so as to ensure maximum consistency with the fluid equations. We discuss how these coefficients are best used in fluid models and illustrate the influence of some essential parameters and approximations.
Plasma–liquid interactions: a review and roadmap
P J Bruggeman
et al
2016
Plasma Sources Sci. Technol.
25
053002
View article
, Plasma–liquid interactions: a review and roadmap
PDF
, Plasma–liquid interactions: a review and roadmap
Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.
Aqueous-phase chemistry and bactericidal effects from an air discharge plasma in contact with water: evidence for the formation of peroxynitrite through a pseudo-second-order post-discharge reaction of H
and HNO
P Lukes
et al
2014
Plasma Sources Sci. Technol.
23
015019
View article
, Aqueous-phase chemistry and bactericidal effects from an air discharge plasma in contact with water: evidence for the formation of peroxynitrite through a pseudo-second-order post-discharge reaction of H2O2 and HNO2
PDF
, Aqueous-phase chemistry and bactericidal effects from an air discharge plasma in contact with water: evidence for the formation of peroxynitrite through a pseudo-second-order post-discharge reaction of H2O2 and HNO2
The formation of transient species (OH·, NO
·, NO radicals) and long-lived chemical products (O
, H
) produced by a gas discharge plasma at the gas–liquid interface and directly in the liquid was measured in dependence on the gas atmosphere (20% oxygen mixtures with nitrogen or with argon) and pH of plasma-treated water (controlled by buffers at pH 3.3, 6.9 or 10.1). The aqueous-phase chemistry and specific contributions of these species to the chemical and biocidal effects of air discharge plasma in water were evaluated using phenol as a chemical probe and bacteria
Escherichia coli.
The nitrated and nitrosylated products of phenol (4-nitrophenol, 2-nitrophenol, 4-nitrocatechol, 4-nitrosophenol) in addition to the hydroxylated products (catechol, hydroquinone, 1,4-benzoquinone, hydroxy-1,4-benzoquinone) evidenced formation of NO
·, NO· and OH· radicals and NO
ions directly by the air plasma at the gas–liquid interface and through post-discharge processes in plasma-activated water (PAW) mediated by peroxynitrite (ONOOH). Kinetic study of post-discharge evolution of H
and
in PAW has demonstrated excellent fit with the pseudo-second-order reaction between H
and
. The third-order rate constant
= 1.1 × 10
−2
−1
for the reaction
was determined in PAW at pH 3.3 with the rate of ONOOH formation in the range 10
−8
–10
−9
M s
−1
. Peroxynitrite chemistry was shown to significantly participate in the antibacterial properties of PAW. Ozone presence in PAW was proved indirectly by pH-dependent degradation of phenol and detection of
cis,cis
-muconic acid, but contribution of ozone to the inactivation of bacteria by the air plasma was negligible.
The following article is
Open access
Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments
Ronny Brandenburg 2017
Plasma Sources Sci. Technol.
26
053001
View article
, Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments
PDF
, Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments
Dielectric barrier discharges (DBDs) are plasmas generated in configurations with an insulating (dielectric) material between the electrodes which is responsible for a self-pulsing operation. DBDs are a typical example of nonthermal atmospheric or normal pressure gas discharges. Initially used for the generation of ozone, they have opened up many other fields of application. Therefore DBDs are a relevant tool in current plasma technology as well as an object for fundamental studies. Another motivation for further research is the fact that so-called partial discharges in insulated high voltage systems are special types of DBDs. The breakdown processes, the formation of structures, and the role of surface processes are currently under investigation. This review is intended to give an update to the already existing literature on DBDs considering the research and development within the last two decades. The main principles and different modes of discharge generation are summarized. A collection of known as well as special electrode configurations and reactor designs will be presented. This shall demonstrate the different and broad possibilities, but also the similarities and common aspects of devices for different fields of applications explored within the last years. The main part is devoted to the progress on the investigation of different aspects of breakdown and plasma formation with the focus on single filaments or microdischarges. This includes a summary of the current knowledge on the electrical characterization of filamentary DBDs. In particular, the recent new insights on the elementary volume and surface memory mechanisms in these discharges will be discussed. An outlook for the forthcoming challenges on research and development will be given.
The following article is
Open access
Physics and technology of magnetron sputtering discharges
J T Gudmundsson 2020
Plasma Sources Sci. Technol.
29
113001
View article
, Physics and technology of magnetron sputtering discharges
PDF
, Physics and technology of magnetron sputtering discharges
Magnetron sputtering deposition has become the most widely used technique for deposition of both metallic and compound thin films and is utilized in numerous industrial applications. There has been a continuous development of the magnetron sputtering technology to improve target utilization, increase ionization of the sputtered species, increase deposition rates, and to minimize electrical instabilities such as arcs, as well as to reduce operating cost. The development from the direct current (dc) diode sputter tool to the magnetron sputtering discharge is discussed as well as the various magnetron sputtering discharge configurations. The magnetron sputtering discharge is either operated as a dc or radio frequency discharge, or it is driven by some other periodic waveforms depending on the application. This includes reactive magnetron sputtering which exhibits hysteresis and is often operated with an asymmetric bipolar mid-frequency pulsed waveform. Due to target poisoning the reactive sputter process is inherently unstable and exhibits a strongly non-linear response to variations in operating parameters. Ionized physical vapor deposition was initially achieved by adding a secondary discharge between the cathode target and the substrate and later by applying high power pulses to the cathode target. An overview is given of the operating parameters, the discharge properties and the plasma parameters including particle densities, discharge current composition, electron and ion energy distributions, deposition rate, and ionized flux fraction. The discharge maintenance is discussed including the electron heating processes, the creation and role of secondary electrons and Ohmic heating, and the sputter processes. Furthermore, the role and appearance of instabilities in the discharge operation is discussed.
Gas temperature determination from rotational lines in non-equilibrium plasmas: a review
P J Bruggeman
et al
2014
Plasma Sources Sci. Technol.
23
023001
View article
, Gas temperature determination from rotational lines in non-equilibrium plasmas: a review
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, Gas temperature determination from rotational lines in non-equilibrium plasmas: a review
The gas temperature in non-equilibrium plasmas is often obtained from the plasma-induced emission by measuring the rotational temperature of a diatomic molecule in its excited state. This is motivated by both tradition and the availability of low budget spectrometers. However, non-thermal plasmas do not automatically guarantee that the rotational distribution in the monitored vibrational level of the diatomic molecule is in equilibrium with the translational (gas) temperature. Often non-Boltzmann rotational molecular spectra are found in non-equilibrium plasmas. The deduction of a gas temperature from these non-thermal distributions must be done with care as clearly the equilibrium between translational and rotational degrees of freedom cannot be achieved. In this contribution different methods and approaches to determine the gas temperature are evaluated and discussed. A detailed analysis of the gas temperature determination from rotational spectra is performed. The physical and chemical background of non-equilibrium rotational population distributions in molecular spectra is discussed and a large range of conditions for which non-equilibrium occurs are identified. Fitting procedures which are used to fit (non-equilibrium) rotational distributions are analyzed in detail. Lastly, recommendations concerning the conditions for which the gas temperatures can be obtained from diatomic spectra are formulated.
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The physics of streamer discharge phenomena
Sander Nijdam
et al
2020
Plasma Sources Sci. Technol.
29
103001
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, The physics of streamer discharge phenomena
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, The physics of streamer discharge phenomena
In this review we describe a transient type of gas discharge which is commonly called a streamer discharge, as well as a few related phenomena in pulsed discharges. Streamers are propagating ionization fronts with self-organized field enhancement at their tips that can appear in atmospheric air, or more generally in gases over distances larger than order 1 cm times
, where
is gas density and
is gas density under ambient conditions. Streamers are the precursors of other discharges like sparks and lightning, but they also occur in for example corona reactors or plasma jets which are used for a variety of plasma chemical purposes. When enough space is available, streamers can also form at much lower pressures, like in the case of sprite discharges high up in the atmosphere. We explain the structure and basic underlying physics of streamer discharges, and how they scale with gas density. We discuss the chemistry and applications of streamers, and describe their two main stages in detail: inception and propagation. We also look at some other topics, like interaction with flow and heat, related pulsed discharges, and electron runaway and high energy radiation. Finally, we discuss streamer simulations and diagnostics in quite some detail. This review is written with two purposes in mind: first, we describe recent results on the physics of streamer discharges, with a focus on the work performed in our groups. We also describe recent developments in diagnostics and simulations of streamers. Second, we provide background information on the above-mentioned aspects of streamers. This review can therefore be used as a tutorial by researchers starting to work in the field of streamer physics.
Plasma generation and plasma sources
H Conrads and M Schmidt 2000
Plasma Sources Sci. Technol.
441
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, Plasma generation and plasma sources
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, Plasma generation and plasma sources
This paper reviews the most commonly used methods for the
generation of plasmas with special emphasis on non-thermal, low-temperature
plasmas for technological applications. We also discuss various technical
realizations of plasma sources for selected applications. This paper is
further limited to the discussion of plasma generation methods that employ
electric fields. The various plasmas described include dc glow discharges,
either operated continuously (CW) or pulsed, capacitively and inductively
coupled rf discharges, helicon discharges, and microwave discharges.
Various examples of technical realizations of plasmas in closed structures
(cavities), in open structures (surfatron, planar plasma source), and in
magnetic fields (electron cyclotron resonance sources) are discussed in
detail. Finally, we mention dielectric barrier discharges as convenient
sources of non-thermal plasmas at high pressures (up to atmospheric
pressure) and beam-produced plasmas. It is the main objective of this paper
to give an overview of the wide range of diverse plasma generation methods
and plasma sources and highlight the broad spectrum of plasma properties
which, in turn, lead to a wide range of diverse technological and technical
applications.
Optical diagnostics of atmospheric pressure air plasmas
C O Laux
et al
2003
Plasma Sources Sci. Technol.
12
125
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, Optical diagnostics of atmospheric pressure air plasmas
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, Optical diagnostics of atmospheric pressure air plasmas
Atmospheric pressure air plasmas are often thought to be in local thermodynamic equilibrium owing to fast interspecies collisional exchange at high pressure. This assumption cannot be relied upon, particularly with respect to optical diagnostics. Velocity gradients in flowing plasmas and/or elevated electron temperatures created by electrical discharges can result in large departures from chemical and thermal equilibrium. This paper reviews diagnostic techniques based on optical emission spectroscopy and cavity ring-down spectroscopy that we have found useful for making temperature and concentration measurements in atmospheric pressure plasmas under conditions ranging from thermal and chemical equilibrium to thermochemical nonequilibrium.
Foundations of atmospheric pressure non-equilibrium plasmas
Peter J Bruggeman
et al
2017
Plasma Sources Sci. Technol.
26
123002
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, Foundations of atmospheric pressure non-equilibrium plasmas
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, Foundations of atmospheric pressure non-equilibrium plasmas
Non-equilibrium plasmas have been intensively studied over the past century in the context of material processing, environmental remediation, ozone generation, excimer lamps and plasma display panels. Research on atmospheric pressure non-equilibrium plasmas intensified over the last two decades leading to a large variety of plasma sources that have been developed for an extended application range including chemical conversion, medicine, chemical analysis and disinfection. The fundamental understanding of these discharges is emerging but there remain a lot of unexplained phenomena in these intrinsically complex plasmas. The properties of non-equilibrium plasmas at atmospheric pressure span over a huge range of electron densities as well as heavy particle and electron temperatures. This paper provides an overview of the key underlying processes that are important for the generation and stabilization of atmospheric pressure non-equilibrium plasmas. The unique physical and chemical properties of theses discharges are also summarized.
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1992-present
Plasma Sources Science and Technology
doi: 10.1088/issn.0963-0252
Online ISSN: 1361-6595
Print ISSN: 0963-0252