Vasco Guerra

Technical University of Lisbon | UTL · Department of Physics (DF)

Vibrational distributions of electronically excited states of N2 obtained through dipole-allowed radiative transitions provide an important tool to study the kinetics of non-equilibrium plasmas under various discharge conditions and provide benchmark data for the validation of advanced kinetic schemes for numerical models. Our testing discharge is...

A Direct current (DC) nanosecond (ns)-pulsed plasma jet fed with N2 at near atmospheric pressure ( 20000 Pa) is studied using a transient zero-dimensional (0-D) model coupled with a two-term Boltzmann equation solver. Good agreement is observed between the simulated and measured plasma properties: including the electron density and the ratios of th...

A full set of vibrationally-resolved cross sections for electron impact excitation of NO(X2{\Pi}, v) molecules is calculated from ab initio molecular dynamics, in the framework of the local-complex-potential approach. Electron-vibration energy exchanges in non-equilibrium thermodynamic conditions are studied from a state-to-state model accounting f...

This work presents a detailed investigation aimed at understanding the key mechanisms governing nitric oxide (NO) production in N2–O2 discharges by systematically comparing experimental results to modeling data. The experimental phase capitalizes on radiofrequency (13.56 MHz) discharges, sustained at 5 mbar pressure conditions, featuring varying co...

Surface recombination in an oxygen DC glow discharge in a Pyrex (borosilicate glass) tube is studied via mesoscopic modelling and comparison with measurements of recombination probability. A total of 106 experimental conditions are assessed, with discharge current varying between 10 and 40 mA, pressure values ranging between 0.75 and 10 Torr, and f...

Vibrational distributions of electronically excited states of N2 obtained through dipole-allowed radiative transitions provide an important tool to study the kinetics of non-equilibrium plasmas under various discharge conditions and provide benchmark data for the validation of advanced kinetic schemes for numerical models. Our testing discharge is...

Non-equilibrium inductively coupled plasmas (ICPs) operating in hydrogen are of significant interest for applications including large-area materials processing. The spatial distribution of the atomic hydrogen is of significant importance. Increasing control of spatial gas heating, which drives the formation of neutral species density gradients and...

Vibrational distributions of electronically excited states of N 2 obtained through dipole-allowed radiative transitions provide an important tool to study the kinetics of non-equilibrium plasmas under various discharge conditions. In this work, we report, for the first time, streamer-induced visible/near-infrared-red emission spectra developing dur...

A fundamental study of \(\hbox {CO}_2\)/\(\hbox {CH}_4\) plasma is performed in a glow discharge at a few Torr. Experimental and numerical results are compared to identify the main reaction pathways. OES-based techniques and FTIR (Fourier Transform Infrared) spectroscopy are used to determine molecules densities and gas temperature. Several conditi...

In situ FTIR transmission experiments for CO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {CO}_2$$\end{document} and CO2\documentclass[12pt]{minimal} \usepacka...

A novel model is developed for atomic oxygen surface kinetics in silica-like walls, introducing a plasma-induced surface modification, which may impact intermediate pressure plasma reactors. The model is the first to reproduce experimental measurements in an oxygen glow discharge operating in the pressure range between 0.27 mbar (0.2 Torr) and 4 mb...

This paper reports our effort and findings in investigating streamer monofilament operated in barrier discharge setup in pure nitrogen at a pressure of 200 Torr. In order to grasp the sub-nanosecond nature of the streamer monofilament we used several diagnostics techniques: measurement of electrical characteristics, streamer imaging using 4-channel...

This work presents a numerical study of the electron kinetics under AC/DC electric fields and DC magnetic fields crossed at arbitrary angles. The physical phenomena are studied both in model gases (Reid-ramp and Lucas-Saelee) and in real gases (N 2 and Ar). The simulations are carried out with an upgraded version of the Monte Carlo open-source code...

This work presents a reaction mechanism for oxygen plasmas, i.e. a set of reactions and corresponding rate coefficients that are validated against benchmark experiments. The kinetic scheme is validated in a DC glow discharge for gas pressures of 0.2–10 Torr and currents of 10–40 mA, using the 0D LisbOn KInetics (LoKI) simulation tool and available...

This paper brings the comparison of performances of CO2 conversion by plasma and plasma-assisted catalysis based on the data collected from literature in this field, organised in an open access online database. This tool is open to all users to carry out their own analyses, but also to contributors who wish to add their data to the database in orde...

A fundamental study of CO2/CH4 plasma is performed in a glow discharge at a few Torr. Experimentaland numerical results are compared to identify the main reaction pathways. Optical Emission Spectroscopy -based techniques and FTIR (Fourrier Transform Infrared) spectroscopy are used to determine molecules densities and gas temperature.Several conditi...

In situ FTIR transmission experiments for CO2 and CO2-CH4 plasma were performed for a fundamentalstudy of surface plasma interaction with cerium oxide (CeO2) as catalytic surface. Utilizing a DC glow dischargeplasma reactor at low pressure, it was observed that CO2 gas adsorbs in the surface forming tridentatecarbonates and hydrogen carbonates. Whe...

This work explores the effect of N 2 addition on CO 2 dissociation and on the vibrational kinetics of CO 2 and CO under various non-equilibrium plasma conditions. A self-consistent kinetic model, previously validated for pure CO 2 and CO 2 -O 2 discharges, is further extended by adding the kinetics of N 2 . The vibrational kinetics considered inclu...

This work presents a reaction mechanism for oxygen plasmas, i.e. a set of reactions and corresponding rate coefficients that are validated against benchmark experiments. The kinetic scheme is validated in a DC glow discharge for gas pressures of 0.2-10 Torr and currents of 10-40 mA, using the 0D LisbOn KInetics (LoKI) simulation tool and available...

This work proposes a complete and consistent set of cross sections for electron collisions with water gas molecules to be published in the IST-Lisbon database on LXCat. The set is validated by the electron swarm analysis technique. The anisotropic angular distribution of electrons in rotational collisions is considered by means of the Born approxim...

Oxygen exchange kinetics in CO2–O2 and CO–O2 low-temperature RF plasmas are investigated by isotope tracing. Starting from C16O2–18O2 and C16O–18O2 gas mixtures, we observe a fast incorporation of 18O into CO and CO2 that cannot be explained solely by chemical reactions. By comparing our experimental results with those of a kinetic model, we demons...

This work focuses on the comparison between a zero-dimensional (0D) global model (LoKI) and a one-dimensional (1D) radial fluid model for the positive column of oxygen DC glow discharges in a tube of 1 cm inner radius at pressures between 0.5 Torr and 10 Torr. The data used in the two models are the same, so that the difference between the models i...

This work explores the effect of O 2 addition on CO 2 dissociation and on the vibrational kinetics of CO 2 and CO under various non-equilibrium plasma conditions. A self-consistent model, previously validated for pure CO 2 discharges, is further extended by adding the vibrational kinetics of CO, including electron impact excitation and de-excitatio...

Characterisation of the vibrational kinetics in nitrogen-based plasmas at atmospheric pressure is crucial for understanding the wider plasma chemistry, which is important for a variety of biomedical, agricultural and chemical processing applications. In this study, a 0-dimensional plasma chemical-kinetics model has been used to investigate vibratio...

This work explores the effect of N2 addition on CO2 dissociation and on the vibrational kinetics of CO2 and CO under various non-equilibrium plasma conditions. A self-consistent kinetic model, previously validated for pure CO2 and CO2-O2 discharges, is further extended by adding the kinetics of N2. The vibrational kinetics considered include levels...

This work focuses on the benchmarking between a zero-dimensional (0D) global model (LoKI) and a one-dimensional (1D) radial fluid model for the positive column of oxygen DC glow discharges in a tube of 1 cm inner radius at pressures between 0.5 Torr and 10 Torr. The data used in the two models are the same, so that the difference between the models...

This work explores the effect of O2 addition on CO2 dissociation and on the vibrational kinetics of CO2 and CO under various non-equilibrium plasma conditions. A self-consistent model, previously validated for pure CO2 discharges, is further extended by adding the vibrational kinetics of CO, including electron impact excitation and de-excitation (e...

This work proposes a complete and consistent set of cross sections for electron collisions with water molecules to be published in the IST-Lisbon database on LXCat. The set is validated from the comparison between experimental and computed electron swarm parameters. The former are collected from literature while the latter are calculated using a sp...

The LisbOn KInetics Monte Carlo (LoKI-MC) is an open-source simulation tool that solves the electron kinetics for low-temperature plasmas excited by uniform DC electric fields from different gas mixtures, using Monte Carlo techniques. Following the strategy and data organization of the LisbOn KInetics Boltzmann (LoKI-B) solver, the program easily a...

This work discusses the potential of combining non-thermal plasmas and conducting membranes for in situ resource utilization (ISRU) on Mars. By converting different molecules directly from the Martian atmosphere, plasmas can create the necessary feed-stock and base chemicals for processing fuels, breathing oxygen, building materials, and fertilizer...

Vibrational excitation represents an efficient channel to drive the dissociation of CO2 in a non-thermal plasma. Its viability is investigated in low-pressure pulsed discharges, with the intention of selectively exciting the asymmetric stretching mode, leading to stepwise excitation up to the dissociation limit of the molecule. Gas heating is cruci...

We present a detailed study of the density and kinetics of O2(b1Σg+) in steady-state and partially modulated DC positive column discharges in pure O2 for gas pressures of 0.3-10 Torr and 10-40 mA current. The time-resolved density of O2(b1Σg+) was determined by absolutely-calibrated optical emission spectroscopy (OES) of the A-band emission at 762...

A full set of vibrationally-resolved cross sections for electron impact excitation of NO(X 2Π, v) molecules is calculated from ab initio molecular dynamics, in the framework of the Local-Complex-Potential approach. Electron-vibration energy exchanges in non-equilibrium thermodynamic conditions are studied from a state-to-state model accounting for...

The time evolution of the CO2 dissociation fraction in pulsed discharges is studied through kinetic modeling. The simulations are compared against experimental data obtained in pulsed DC glow and radio-frequency discharges, operated with currents of about 40 mA and powers of 40 W, sustained under low gas pressures (< 600 Pa). The model is used to a...

A zero-dimensional (volume-averaged) and a pseudo-one-dimensional plug-flow (spatially resolved) model are developed to investigate atmospheric-pressure plasma jets operated with He, He/O 2 , He/N 2 and He/N 2 /O 2 mixtures. The models are coupled with the Boltzmann equation under the two-term approximation to self-consistently calculate the electr...

Numerous applications have required the study of CO2 plasmas since the 1960s, from CO2 lasers to spacecraft heat shields. However, in recent years, intense research activities on the subject have restarted because of environmental problems associated with CO2 emissions. The present review provides a synthesis of the current state of knowledge on th...

The role of anisotropic scattering in rotational collisions of electrons with CO molecules is investigated numerically with Monte Carlo (MC) simulations and with calculations using the Lisbon KInetics two-term Boltzmann solver (LoKI- B). The study adopts integral cross sections taken from the IST-Lisbon database of LXCat or extracted from Biagi’s c...

It has been recently advocated that Mars has excellent conditions for oxygen and fuel production directly from atmospheric CO2 using non-equilibrium plasmas. The Martian conditions would be favorable for vibrational excitation and/or enhanced dissociation by electron impact, two important pathways for CO2 plasma dissociation. Herein we confirm thes...

This work analyzes the temporal evolution of the electron kinetics in dry-air plasmas(80%N2:20%O2), excited by electric-field pulses with typical rise-times of 10−9and 10−6s,applied to a stationary neutral gaseous background at pressures of 105, 133 Pa and temperatureof 300 K. The study is based on the solution of the electron Boltzmann equation (E...

A zero-dimensional (volume-averaged) and a pseudo-one-dimensional (plug-flow) model are developed to investigate atmospheric-pressure plasma jet devices operated with He, He/O$_2$, He/N$_2$ and He/N$_2$/O$_2$ mixtures. The models are coupled with the Boltzmann equation under the two-term approximation to self-consistently calculate the electron ene...

The effect of oxygen atoms on the vibrational kinetics of CO2 and CO is studied in a DC glow discharge at reduced pressure by means of in situ FTIR spectroscopy. For this study we used two SiO2-based surface configurations: a smooth Pyrex discharge tube and a large specific surface material. The larger surface area enhances the O atom surface recom...

The use of plasmas for CO2 utilization has been under investigation in recent years following a wave of environmental awareness. In this work, previously published experimental results on vibrationally cold CO2 plasmas are modelled to define a reaction mechanism, i.e. a set of reactions and rate coefficients validated against benchmark experiments....

This work presents a kinetic Monte Carlo algorithm to solve the gas-phase chemistry in low-temperature plasmas, as a first effort to achieve a unified formulation of the electron and heavy-particle kinetics based on Monte Carlo techniques. The implemented algorithm is successfully validated in the thermodynamic limit from the comparison with the tr...

Plasma has been studied for several years to convert CO2 into value-added products. If CO2 could be converted in the presence of H2O as a cheap H-source for making syngas and oxygenates, it would mimic natural photosynthesis. However, CO2/H2O plasmas have not yet been extensively studied, not by experiments, and certainly not computationally. There...

The time evolution of the dissociation fraction in a pulsed radio-frequency CO2 discharge is studied by infra-red absorption. A large parametric study performed in a closed reactor brings valuable information about both dissociation and recombination processes. The CO2 conversion shows a time evolution initially controlled by electron impact dissoc...

The number of numerical models and their complexity are increasing rapidly. This goes together with a bigger impact in various fields, but also with a growing opacity. In the case of a deterministic model with hundreds of inputs, it can become difficult, while crucial, to identify which mechanisms are the most influential on the results. Screening...

The time-dependent evolution of the energy transfer into gas heating in the afterglow of pulsed CO2 and CO2–N2 glow discharges produced in cylindrical tubes at low pressures (1–5 Torr) is theoretically investigated, by developing a self-consistent model that couples the time-dependent gas thermal balance equation with the vibrational kinetics. The...

Several CO2 electron impact dissociation cross sections are available in the literature, different in magnitude and threshold, hindering the understanding of CO2 dissociation mechanisms under gas discharges. This work reports the experimental validation of the electron impact CO2 dissociation cross section using two complementary methods: through t...

This work explores the effect of nitrogen addition on CO2 dissociation under various non-equilibrium plasma conditions. Experiments are performed in non-thermal plasmas sustained by DC pulsed discharges, for pressure and current ranges of 1 to 5 Torr and 20 to 50 mA, respectively. A self-consistent model, previously validated for pure CO2 discharge...

This work proposes a complete and consistent set of cross sections for electron impact collisions with carbon monoxide (CO), to be published in the IST-Lisbon database with LXCat. The set is validated by comparing swarm parameters calculated using the two-term Boltzmann solver LoKI-B with available experimental data. A severe inconsistency between...

In this work we undertake an experimental investigation of plasmas in DC glow discharge, in CO 2 /Ar/N 2 mixture, for pressures in range 1-6 Torr and currents from 10 to 50 mA, with gas at room and Mars-like temperatures. The vibrational temperatures, the conversion factor and the reduced electric field are measured. The study shows that Martian co...

Oxygen atom densities were measured in situ in a CO2 glow discharge, at pressures between 0.2 and 5 Torr (26.7–666.6 Pa). Two measurement techniques were compared, namely optical emission actinometry (using Ar as the actinometer) and high-resolution two-photon absorption laser induced fluorescence normalised to Xe, and were found to give consistent...

This paper reviews the basics of kinetic modelling in low-temperature N2–O2 plasmas, including the strong coupling between electron, vibrational, chemical and surface kinetics. The main approaches to investigate each of these kinetics are outlined and the most widely used ones are discussed in some detail. The interdependency of the different kinet...