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Item type: Item , The effect of pre- and post-mixing N2 on discharge characteristics and production of reactive species in a pulsed-DC Ar plasma jet(Bristol : IOP Publ., 2026) Kumar KC, Sushil; Ghimire, Bhagirath; Taniguchi, Fumiya; Hong, Sung-Ha; Oh, Jun-Seok; Szili, Endre J.This study investigated the effects of pre- and post-mixing nitrogen (N2) on the discharge characteristics as well as the production of reactive oxygen and nitrogen species (RONS) in an atmospheric-pressure argon (Ar) pulsed-direct current plasma jet. Plasma is generated by mixing 0%–1% N2 with Ar gas within the gas line (termed as pre-mixing) and in the inter-electrode separation region (termed as post-mixing). Hydrogen peroxide (H 2 O 2 ) and nitrite (NO 2 − ) were measured as markers of reactive oxygen species and reactive nitrogen species, respectively. Both mixing methods produced similar total RONS levels: increasing the N2 fraction reduced H2O2 , while NO2 − peaked at 0.6% N 2 then declined. Despite both methods producing similar RONS concentrations, pre- and post-mixing had differing effects on the intrinsic discharge properties. Pre-mixing produced greater changes in discharge current ( I D ) and power ( P av ), resulting in a decrease by 85.5% and 46.7% from 0% to 1% N2 mixing, respectively. Whereas I D and P av were only moderately affected by post-mixing decreasing by 28.8% and 14.9% from 0% to 1% N 2 mixing, respectively. Electron temperature ( T e ) rose sharply from 1.01 up to 1.55 eV with 1% N2 pre-mixing but only to 1.39 eV with equivalent post-mixing. The gas temperature at the ground electrode increased to 61.2 °C for pre-mixing versus 58.4 °C for post-mixing with 1% N2 . However, post-mixing had a greater effect on diminishing UV photon emission, which significantly decreased H2O2 generation via UV photolysis. These findings demonstrate that although pre- and post-discharge mixing with N2 results in similar levels of plasma jet produced RONS, the method of mixing alters plasma characteristics in different ways that might affect the plasma jet’s performance and safety in certain biomedical applications.Item type: Item , Boosting the NOx production in microwave air plasma : a synergy of chemistry and vibrational kinetics(Bristol : IOP Publ., 2026) Shen, Q.; Pikalev, A.; Gans, J.; Kuijpers, L.; Hughes, A.; Guerra, V.; van de Sanden, M. C. M.This study employs a quasi-1.5D multi-temperature model to investigate the mechanisms governing NO x production and energy costs in microwave plasma reactors operating at 80 mbar, focusing on the interplay of vibrational, chemical, and electron kinetics, thermodynamics, and transport processes across the discharge and afterglow. In the plasma discharge zone, non-thermal processes enhance NO x production as electrons transfer energy effectively to the vibrational mode of N 2 . However, the non-thermal enhancement is found to diminish rapidly within the central-afterglow region. The simulation results show good agreement with experimental data for both the temperature profile and energy cost. Turbulent effects facilitate radial NO diffusion into cooler regions while simultaneously enhancing cooling of the axial region. These findings highlight the potential to improve NO x synthesis efficiency by optimizing turbulence and maintaining non-thermal conditions, offering new opportunities for the advancement of plasma-based chemical processes.Item type: Item , Transient global modeling of the hydrogen dissociator in hydrogen masers : breakdown dynamics, steady-state efficiency, and wall effects(Bristol : IOP Publ., 2026) Liang, Yue; Xie, Yong-hui; Shuai, Tao; Chen, Peng-fei; Pei, Yu-xian; Pan, Xiao-yan; Zhao, Yang; Xu, Hao-tian; Xia, Tian; Hu, Wang-wangThe hydrogen dissociator is a critical component in a hydrogen maser for generating hydrogen atoms. The reliability of its ignition process governs the operational reliability of the maser, and its steady-state dissociation efficiency directly affects overall clock performance. However, plasma models for such sources have mostly focused on steady-state behavior, overlooking the complex transient evolution from breakdown to steady operation. Here we develop a zero-dimensional global model that follows the inductively coupled plasma in a hydrogen maser dissociator from initial breakdown, through millisecond-scale relaxation, to the final steady state. The simulations show that the breakdown-field threshold depends strongly and non-monotonically on radio-frequency (RF) frequency. At low RF frequencies the breakdown field is highly sensitive to frequency changes, whereas at higher frequencies it varies much more gently, which helps explain the engineering preference for comparatively high operating frequencies and clarifies the trade-off between ignition efficiency and operational reliability. They further show that simply increasing input power is not an effective route to higher steady-state dissociation efficiency, because elevated temperature sharply enhances hydrogen atom recombination on the bulb wall and accelerate irreversible material aging. The model thus provides a new theoretical framework for dissociator design, shifting optimization from power escalation to refined strategies: reliable ignition via RF frequency selection and sustained efficiency via materials solutions that suppress wall recombination, offering practical guidance for operating-parameter optimization and long-term reliability improvement.Item type: Item , Determining the electric field in a 10 ns pulsed plasma in fuel-air mixtures using EFISH(Bristol : IOP Publ., 2026) Rahman, Md. Ziaur; Kliewer, Christopher J.; Patterson, Brian D.; Jiang, ChunqiTransient plasma ignition (TPI) utilizes non-equilibrium plasmas, produced by nanosecond high-voltage pulses, to improve lean-fuel combustion performance and reduce emission. It is known that the relatively high reduced electric field ( E / N ) in TPI plays an important role in generating energetic electrons and facilitating energy-efficient radical productions, resulting in reliable ignition for lean combustion. Determining the reduced electric field in the discharge is hence important for the understanding of the TPI process and ultimately allowing for the control of the plasma chemistry. This study reports spatiotemporally resolved measurements of the electric field ( E ) in a 10 ns pulsed plasma that is produced by a pin-to-pin electrode configuration in extremely lean CH 4 /air mixtures, with the equivalent ratio (ϕ ) ranging from 0.4 to 0.8, at 1 bar using the electric field induced second harmonic generation technique. At a relatively low voltage such as 8 kV, a streamer discharge is typically initiated between the electrodes. The peak electric field was found to be 45 kV cm −1 , corresponding to an E / N of 184 Td, for an 8 kV pulse in a lean (ϕ = 0.4) CH 4 /air mixture at 1 bar. Increasing the pulse voltage to be ⩾ 13 kV under a single pulse operation would cause the discharge to transition to a spark, which was found necessary to achieve reliable ignition for combustion. The peak E was measured to be 66 kV cm −1 or an E / N of 405 Td, for a 13 kV pulse. Interestingly, the E reaches its maximum during the rising phase of the voltage pulse and drops quickly as the current increasing. The radially symmetric electric field was found highest near the high voltage pin, followed by that near the ground pin, and lowest near the midplane. The effect of the pulse repetition frequency on E / N was studied by employing two-pulse sequences with various pulse-to-pulse delays ranging from 10 to 1000 µ s. Measurements of the electric field during the 2nd voltage pulse revealed that the transient spark occurred at a lower voltage with a lower peak E ( i.e. 40–48 kV cm −1 ), but corresponding to a greatly enhanced E / N due to the elevation in the gas temperature of the discharge. In addition, the impact of ϕ on E was found insignificant, implying that the measurements obtained at the extreme lean conditions can be applied to stoichiometric or richer fuel-air mixtures.Item type: Item , On the drift-diffusion analysis of the Pulsed Townsend experiment : a fitting algorithm and benchmark study(Bristol : IOP Publ., 2026) Vemulapalli, Hanut; Akbas, Mücahid; Muccignat, Dale; Boyle, Greg; White, Ron D.; Franck, Christian M.Electron transport properties in gases and gas mixtures can be determined from measurements with a Pulsed-Townsend experiment. Analytical solutions of a drift-diffusion equation are fitted to the measured experimental waveforms to determine electron transport coefficients. However, it is not always unambiguously clear what the published measurement data ultimately represents, under which assumptions published transport data have been derived, and how large the uncertainty is. To address this, we first present an open source code for the analysis of the Pulsed-Townsend experiment waveforms. We then use this code to fit synthetic waveforms generated by Monte-Carlo simulations to estimate the accuracy of transport data obtained by curve fitting. Two benchmark simulation cases are considered: a representative case that closely replicates a typical Pulsed-Townsend experiment and an idealised case that replicates the assumptions that underpin the state of the art analytic solution. For each case simulations are performed for three different gases (Ar, CO 2 and SF 6 ) and over a wide range of electric field strengths (10-1000 Td), densities (10 22 - 10 24 m -3 ) and electrode spacings (10-30 mm). For the representative model, while the error in the extracted transport coefficients can be as good as 0.1%, it deteriorates with decreasing pressure, decreasing electrode gap distance and increasing electric field strength. While significantly reduced errors were found for the idealised model, errors exceeding 10% were still present in some regimes. We show that these errors are strongly correlated with the third-order transport coefficient, which calls into question the accuracy of analyses that do not account for it, especially for experiments operated at low pressures and small electrode spacings.Item type: Item , Review of nonequilibrium plasma kinetics in hypersonic flows(Bristol : IOP Publ., 2025) Aiken, Timothy T.; Carter, Nicholas A.; Boyd, Iain D.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 2 , O 2 , NO, N, O, CO 2 , NCO, C 3 , C 2 , CO, CN, C, N 2 + , O 2 + , 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.Item type: Item , Quantitative imaging of H₂O₂ and HO₂ in a cold plasma jet by photofragmentation laser-induced fluorescence(Bristol : IOP Publ., 2026) Pfaff, Sebastian; Huang, Erxiong; Frank, Jonathan H.Accurate determination of the concentrations of reactive oxygen and nitrogen species (RONS) in low-temperature plasmas is critical to understand the interactions between the plasma and treatment targets. While laser-induced fluorescence (LIF) is commonly used to measure plasma species, hydrogen peroxide (H₂O₂) and the hydroperoxyl radical (HO₂), two important RONS, are not directly accessible by LIF due to their predissociative electronically excited states. Instead, photofragmentation laser-induced fluorescence (PF-LIF) can be used, where H₂O₂ or HO₂ is photodissociated by a pump laser to produce OH molecules, which are then detected by LIF using a probe laser. However, differentiating the PF-LIF signals of HO₂ and H₂O₂ remains challenging as both species produce OH photofragments. This work demonstrates a method for quantitative PF-LIF imaging measurements of HO₂ and H₂O₂ concentrations using the COST reference microplasma jet. By leveraging the different photodissociation dynamics of HO₂ and H₂O₂, we separate their individual contributions to the PF-LIF signal. The presented method involves combining calibrated signals from rotationally excited OH molecules resulting from H₂O₂ photofragmentation with signals from OH molecules in the rotational ground state. Applicable to any steady-state reactive flow, this method can be used not only in plasma applications, but also in the fields of combustion diagnostics and catalysis.Item type: Item , Study of CO2 recombination kinetics(Bristol : IOP Publ., 2025) Grimaldi, Corentin H. C.; McGuire, Sean; Laux, Christophe O.This paper presents an analysis of thermochemical data obtained in a high temperature recombining CO 2 mixture at atmospheric pressure. For the analysis, three kinetic models taken from the literature are used. All models appear to capture the measured CO density evolution. However, they all underpredict the measured CO 2 density evolution by a multiplicative factor of roughly five. Modifications to the baseline models are considered. A Monte-Carlo analysis is used to simultaneously vary several rates, and as part of an effort to modify the baseline models in as minimal a way as possible. Furthermore, the Monte-Carlo analysis allows us to identify different modifications to the baseline models that result in good agreement with experiment. This offers a level flexibility in the choice of modifications made, in order to account for prior knowledge of certain reaction rates that may be well known. In several cases, the suggested modifications require an increase of the rate of CO 2 recombination by a factor of approximately 10. We argue that such an increase could be explained by recombination through excited states of CO 2 .Item type: Item , Ion emission properties of tin plasmas generated by 2 μm-wavelength laser pulses(Bristol : IOP Publ., 2025) de Lange, S. J. J.; Gonzalez, J.; Engels, D. J.; Kohlmeier, F. M.; Sheil, J.Using radiation-hydrodynamic simulations, we investigate the properties of ion emission from a plasma generated by irradiating tin droplets with λlaser = 2 μm-wavelength laser light. Two cases are considered: first a ‘short pulse’ (27 ns-long) case with laser intensity Ilaser ∼ 10 11 W cm−2 that can be readily benchmarked with present experimental systems. Then, a ‘long pulse’ case is studied, in which the droplet is irradiated until it is fully vaporized, which takes ∼ 150 ns. The kinetic energy-resolved ion spectra in both cases feature a high-energy peak on the order of keVs. At lower kinetic energies the spectra are substantially different: the short pulse spectrum exhibits much higher ion numbers due to plasma cooling at the end of the pulse, which is not present in the long pulse case. The following quantities of interest are analyzed: angle-dependence of the peak kinetic energy, total kinetic energy, and total ion number, as well as intensity-dependence of the kinetic energy peak. To provide a measure of non-fluid behavior of the expanding plasma, we calculate the local Knudsen number; though the obtained values are significant, the kinetic energy data are found to be reliable, and can be extrapolated to larger distances.Item type: Item , Foundations of plasma-assisted combustion : II. Mechanisms and applications(Bristol : IOP Publ., 2026) Laux, C. O.; Perrin-Terrin, J.-B.; Lafaurie, V.; Starikovskaia, S. M.In Part 1 of this Foundation paper, 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.Item type: Item , Electronegativity effects on plasma dynamics in He/O2 RF microplasma jets at atmospheric pressure(Bristol : IOP Publ., 2025) Vogelhuber, L.; Korolov, I.; Vass, M.; Nösges, K.; Bolles, T.; Köhn, K.; Klich, M.; Brinkmann, R. P.; Mussenbrock, T.This work investigates the transitions between ohmic mode and Penning-Gamma mode in a capacitively coupled radio frequency micro atmospheric pressure plasma jets operated in He/O 2 mixtures by comparing phase-resolved optical emission spectroscopy measurements of helium excitation with numerical simulations. The simulations employ a hybrid model that treats electrons kinetically via particle-in-cell/Monte Carlo collision simulation, while ions and neutrals are modeled based on fluid dynamics. These results reveal that an increasing electronegativity causes inhomogeneities in the bulk electric field, consequently modulating the electron impact excitation dynamics. A good agreement was found between experiments and simulations.Item type: Item , EUV-induced low pressure hydrogen and H2/Sn plasmas(Bristol : IOP Publ., 2025) Piskin, Tugba; Volynets, Vladimir; Lee, Hyunjae; Nam, Sang Ki; Kushner, Mark J.The continuing decrease in feature size in microelectronics fabrication has been enabled by a progressive decrease in the wavelengths for photolithography. The recent deployment of extreme ultra-violet (EUV) lithography systems with photon wavelengths centered at 13.5 nm has enabled feature sizes below 10 nm. One method to produce EUV photon fluxes is to ablate and ionize tin droplets with pulsed lasers. A possible consequence of the ablation is that the resulting tin vapor may coat optical components. By filling the chamber with low-pressure H 2 gas that does not significantly absorb the EUV photons, a low-density plasma is produced by the EUV photon flux that dissociates and ionizes the hydrogen. Tin films on optics can then be etched by H atoms and ions producing stannane (SnH 4 ), which can then be pumped away. In this paper, results from a computational investigation of the plasma formation that occurs by EUV photon fluxes (13.5 nm, 92 eV) passing through low pressure H 2 and tin vapor are discussed. Electron energy distributions produced by the photo-generated primary electrons and the resulting plasma densities are discussed as a function of the background gas pressure, metal vapor and pulse power format.Item type: Item , Multi-diagnostic characterization of inductively coupled discharges with tailored waveform substrate bias for precise control of plasma etching(Bristol : IOP Publ., 2025) Giesekus, Jonas; Pletzer, Anton; Beckfeld, Florian; Noesges, Katharina; Bock, Claudia; Schulze, JulianPrecise control of ion energy distribution functions (IEDFs) is crucial for selectivity as well as control over sputter rate and substrate damage in nanoscale plasma processes. In this work, a low frequency (100 kHz) tailored pulse-wave-shaped bias voltage waveform is applied to the substrate electrode of an inductively coupled plasma (ICP) and its effects on the IEDF, electron density, electron dynamics and the etch rates of silicon dioxide as well as amorphous silicon are investigated in a commercial 200 mm reactive ion etching reactor. While the tailored waveform substrate bias hardly affects the electron density above the substrate and the spatio-temporally resolved electron power absorption dynamics, it is found to affect the ion flux to the substrate at high ICP source powers. Monoenergetic IEDFs with a full width at half maximum below 10 eV are realized with mean ion energies ranging from 20 eV to 100 eV in both argon and SF6 . Using a modified voltage allows generating two independently controllable peaks in the IEDF. The monoenergetic IEDFs are used to determine the Ar ion sputter threshold energies of amorphous silicon and silicon dioxide to be 23 eV and 37 eV, respectively. This enables selective etching of these two materials by Ar ion sputtering based on tailoring the IEDF to ensure that all incident ions are within this narrow ion energy selectivity window.Item type: Item , Azimuthal magnetic field gradient effects on the performance and stability of a 5 kW Hall effect thruster(Bristol : IOP Publ., 2025) Chhavi, Chhavi; Walker, Mitchell L. R.Hall effect thruster (HET) component manufacturing defects can result in non-uniformities in the plasma plume, significantly affecting thruster performance. The present work quantifies the effect of an azimuthal magnetic field gradient on the thrust, stability, and efficiency of a 5 kW HET. The study introduces an azimuthal magnetic field gradient inside the discharge channel of the P5, a 5 kW HET, through modifications of the outer magnetic coil circuit to simulate the impact of a manufacturing defect in the magnetic circuit. Far-field plasma probes are utilized to measure plasma properties to compare them to the measured performance. A three-dimensional sweep probe apparatus quantifies the effect of the azimuthal magnetic field gradient on the direction of the thrust vector. The azimuthal magnetic field gradient results in decreased stability during operation. The peak-to-peak discharge current oscillations increase by 31.1%, efficiency decreases by 25.7% and thrust decreases by 3.5% (2.7 mN) due to a 16.6% decrease in the local magnetic field resulting in an extreme gradient condition (0.36 G/°). The sweep probe apparatus observes a 24% decrease in the ion beam current and a 5.8° spatial deviation in the thrust vector for the HET with a 0.36 G/° magnetic field gradient. The study presents a physics-based framework that elucidates the observed patterns in thruster performance caused by variations in plasma characteristics. Through the physics-based performance model proposed in the study, the impact of the azimuthal magnetic field gradient on the electron parameters, such as the electron temperature is established. The impact of the azimuthal magnetic field gradient on HET performance and stability is established in the physics-based model by understanding the impact of such a gradient on the motion of the charged particles by utilizing plasma plume parameters.Item type: Item , Characterization of O3 species in a planar atmospheric pressure dielectric barrier discharge reactor using Ar/O2 mixtures by a microsecond unipolar pulsed power source(Bristol : IOP Publ., 2025) Lin, Kun-Mo; Lai, Wei-Hong; Liu, Jie-WeiThis work investigates the O 3 generated in a planar atmospheric pressure dielectric barrier discharge (APDBD) reactor using Ar/0.5% O 2 as the working mixture with a microsecond pulsed power to analyze detailed species and reaction variations in the discharge zone. The numerical model integrates both the 1D plasma fluid model (PFM) and 3D gas flow model (GFM) to predict the O 3 generation in conjunction with the analysis of dominant species and mechanisms. The discharge uniformity is confirmed by the ICCD photograph taken, which justifies the implementation of the 1D PFM. The experimental measurements validate the simulated current, power consumption, reactor surface temperature, and O 3 concentrations at different regions. The uniform APDBDs using Ar/O 2 mixtures provide a simplified platform for exploring reaction mechanisms in Ar discharges under atmospheric pressure in contrast to their typical filamentary features. The analysis shows that atomic oxygen is the dominant species of O 3 generation, while excited oxygen molecules (i.e. O 2 (a) and O 2 (b)) are the dominant species of O 3 consumption. The variations of dominant generation and consumption reaction distributions reveal detailed interactions among species presented, leading to the differences between those predicted by the 1D PFM with all reactions and the integration of 1D PFM and 3D GFM. The developed numerical model provides an appropriate process considering both discharge dynamics and species transport behavior to predict variations of reactive species generated in the discharge zone.Item type: Item , Azimuthal and axial structures in 3D particle-in-cell simulation of Penning discharge(Bristol : IOP Publ., 2025) Papahn Zadeh, M.; Likhanskii, A.; Smolyakov, A.; Tyushev, M.; Chopra, N.; Romadanov, I.; Raitses, Y.We report the results of a 3D particle-in-cell simulation of cylindrical Penning discharge with the axial magnetic field in the so-called reflex configuration, where the cathode and anti-cathode are biased to the same negative potential. The discharge is supported by thermal electron emission from the cathode. Electron and ion collisions, including ionization, are fully accounted for. The emphasis is on a specific regime in which the plasma potential at the center of the discharge is positive with respect to the chamber walls, serving as an anode. Spatial and temporal scales of the observed azimuthal and axial fluctuations and structures are characterized. It is suggested that azimuthal structures are caused by the dissipative gradient-drift instability. We find that the axial fluctuations related to the plasma-beam instabilities are weakly correlated with the azimuthal perturbations of the density, so that the azimuthal modes rotate as a whole and do not show any axial shear. The behavior of the electric potential is more involved, demonstrating intermittent standing wave and propagating structures in the axial direction that modulate the electron transport, producing the standing wave pattern (along the z -direction) in the radial electron flux.Item type: Item , Determination of the accuracy of actinometry and line ratio techniques in an O2 glow discharge : II. Electric field measurements with Ar and Xe admixtures(Bristol : IOP Publ., 2026) Kuijpers, L.; Baratte, E.; Guaitella, O.; Booth, J.-P.; Guerra, V.; van de Sanden, M. C. M.; Silva, T.A line-ratio method for determining the reduced electric field is benchmarked against independent measurements from electrostatic probes and cavity ring-down spectroscopy. The method is applied to oxygen DC glow discharges with trace admixtures of argon and xenon. A corona model incorporating fluorescence quenching by heavy species is used to simulate the emission, with electron-impact excitation rates calculated using the LisbOn KInetics Boltzmann solver. The excitation cross sections and quenching coefficients are those proposed and validated for actinometry in part one of this combined study (Baratte et al 2025 Plasma Sources Sci. Technol. ). The reduced electric field is determined over a pressure range of 0.55 to 5 Torr (at 40 mA) and a current range of 15 to 50 mA (at 5 Torr). Consistent agreement with measured emission line intensities is achieved when applying a correction factor of 0.55 to 5 Torr (at 40 mA) and a current range of 15 to 50 mA (at 5 Torr). Consistent agreement with measured emission line intensities is achieved when applying a correction factor of κc,Ar = 3 ± 0.5to the excitation cross sections for the argon lines at 750 nm and 811 nm. With this correction, the reduced electric field values obtained from the line-ratio method are in good agreement with direct measurements. A comparison of different line ratios is presented, showing that the best performance is achieved using the ratio of the Ar 750 nm and Xe 828 nm lines. This ratio is particularly sensitive to changes in the electron energy distribution function, due to the large difference in excitation thresholds, while remaining independent of the knowledge of species densities.Item type: Item , Determination of the accuracy of actinometry and line ratio techniques in an O2 glow discharge : I. Comparison of absolute oxygen atom densities with CRDS measurements(Bristol : IOP Publ., 2026) Baratte, E.; Kuijpers, L.; Silva, T.; Guerra, V.; van de Sanden, M. C. M.; Booth, J.-P.; Guaitella, O.The accuracy of oxygen atom density measurements in plasmas by optical emission actinometry was tested by comparison to simultaneous direct absorption measurements on the 1D2← 3P2 transition by cavity ringdown spectroscopy (CRDS). The accuracy of the latter technique depends only on the accuracy to which the transition probability is known. Measurements were performed on a glow discharge in O2 operating between 0.5 and 5 Torr, and using both Ar and Xe as the actinometer gas. The rate constants for electron impact excitation, and thus the actinometry calibration factors, were calculated from the (measured) reduced electric field using a Boltzmann equation solver (Loki-B). Several sets of cross-section were tested for the EEDF calculation and for the electron impact excitation to the specific levels of O, Ar and Xe used for actinometry. The best results were obtained with the IST Lisbon cross-section set for O2 and O, and the BSR500 excitation cross-sections for Ar and Xe. Good agreement with the CRDS trends and absolute values was observed when using Xe as the actinometer gas, whereas with Ar the trends were well reproduced but it was necessary to increase the electron impact cross-section of the transition Ar((1S0 → 2p1) of the BSR500 database by a factor of 3±0.3 to reproduce the absolute values.Item type: Item , Spatial profile of argon (1s5) metastables in an electron beam generated plasma(Bristol : IOP Publ., 2025) Kondeti, V. S. Santosh K.; Chopra, Nirbhav S.; Yatom, Shurik; Raitses, YevgenyElectron beams with an applied magnetic field generate a secondary cold plasma with a selective chemical composition, featuring low-energy ions and metastable species in the discharge periphery, ideal for low-damage plasma treatment of material substrates. In this work, we studied the plasma generated by an e-beam using a 4 kV voltage in a pure argon gas environment under a magnetic field of 150 G and in the pressure range of 25–90 mTorr. We measured the absolute spatial density profile of argon (1 s 5 ) metastables in an electron beam generated plasma by laser-induced fluorescence and found it to be of the order of 10 16 m −3 . The electron temperature and the electron density measured by a Langmuir probe were of the order of 10 16 m −3 and less than an eV respectively. Electron-impact quenching was identified as a significant loss mechanism for the Ar(1s 5 ) state, leading to the saturation of the metastable density at higher pressures. Outside the primary ionization region, the spatial distribution of argon metastables followed a linear diffusion profile, indicating negligible additional production in those regions.Item type: Item , Heated supersonic plasma flow reactor for spectroscopic studies of plasma chemistry and plasma assisted combustion(Bristol : IOP Publ., 2025) Ting, L.-T.; Mays, C.; Dundore, T.; Young, M.; Raskar, S.; Adamovich, I. V.A high-pressure heated plasma flow reactor excited by a ns pulse discharge, followed by a rapid supersonic expansion via a contoured nozzle, is used for time-resolved measurements of the products of plasma chemical reactions. The expansion is used to freeze the plasma-induced chemical reactions and reduce the absorption linewidth, as well as the range of rotational states populated, to facilitate the detection of the reaction products by mid-IR laser absorption spectroscopy. The feasibility of this approach is demonstrated by the measurements of CO product in plasma-excited CO 2 –Ar, CH 4 –O 2 –Ar, C 2 H 4 –O 2 –Ar, and C 4 H 10 –O 2 –Ar mixtures, to quantify the effect of CO 2 dissociation and fuel oxidation in the plasma. In the experiment, a flow of the reactants passes through a thermal storage section, heated in a tube furnace to the plenum temperature of up to T 0 = 600–700 K, at a pressure of P 0 = 300 Torr. The heated flow is excited in a diffuse ns pulse discharge operated in burst mode. Downstream of the discharge excitation section, the flow expands through a Mach 4 nozzle into a supersonic test section, with optical access provided via the ports in the side walls. Absorption by CO in the test section is measured by a tunable quantum cascade mid-IR laser at the sampling rate of 100 kHz. The time-resolved flow temperature and the CO number density are inferred from the absorption line shape. The results are compared with the kinetic modeling predictions, quantifying the effect of the mixture composition, discharge burst duration, pulse repetition rate, and plenum temperature on the kinetics of plasma chemical reactions.