N onequilibrium anoscale ew horizons

Plasmas Reactive: Modelling and Engineering (N-PRiME)

KIT meetings

Our Keep-in-Touch (KIT) meetings are a regular forum where our PhD students, Post-docs and researchers showcase their research work.

In special occasions we also invite Very Important Persons to deliver a seminar in KIT VIP-meetings.

The meetings take place at least once per month, during the academic year, and recently they are being held online via the zoom platform.

December, 07

From Huygens to ESTHER
Lionel Marrafa, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal

Focusing on previous ESA missions and studies, the talk shall illustrate their link with basic research in the field of aerodynamics and plasmas and more specifically of nonequilibrium radiating flows. Huygens mainly, but also IRDT (Inflatable Reentry and Descent Technology Demonstrator), IRENE (Italian Reentry Nacelle Experiment, to test a deployable braking device) and PHOEBUS (a demonstrator for future sample return capsules) shall be presented.

November, 16

Gas heating mechanisms in plasmas: an overview
Carlos Pintassilgo, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
Faculdade de Engenharia, Universidade do Porto, Porto, Portugal

This talk reports a comprehensive picture of the main gas heating mechanisms in plasma discharges in different gases and mixtures, such as pure N2, N2-NO, N2 O2 (including air-like mixtures), and CO2. Modelling predictions, based on the numerical solutions of the time-dependent gas thermal balance equation, are systematically compared to experimental results.

November, 02

Vibrational kinetics of CO2 in non-thermal plasma: a diagnostic study - VIP-meeting
Richard Engeln, Department of Applied Physics (PMP), Eindhoven University of Technology, Eindhoven, The Netherlands

Vibrational excitation is seen as the panacea for efficient CO2 dissociation in plasma. During the presentation I will discuss the development of diagnostic techniques to increase our current level of understanding of the vibrational kinetics within CO2 discharges, with the intention to ultimately contribute to a controlled and efficient dissociation process in plasma.

October, 19

The quest for deterministic direct plasma synthesis of nanostructures - VIP-meeting
Uros Cvelbar, Jozef Stefan Institute, Ljubljana, Slovenia

Building 1D or 2D nanostructures like nanowires or nanowalls is important for numerous applications requiring large-scale nanomaterials production. Here, plasmas present a great opportunity since nanowires or nanowalls in plasmas are produced not only faster but in bulk quantities with high quality. These quantities are orders larger in quantity and time than any other comparing processing method available today. However, to master these processes in plasmas, understanding basic mechanisms underlying the growth of any nanostructure in plasma is extremely important. Here, we have selected the direct plasma synthesis to study these mechanisms, where nanostructures are grown directly on exposed materials to only gaseous discharges.

July, 12

2021 update of the SPARK Line-by-Line "Libre" nonequilibrium radiation code
Mário Lino da Silva, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal

This talk presents the recent release of the 3.0 version of the SPARK Line-by-Line (LbL) code. SPARK LbL (formerly called SPARTAN) is a Line-by-Line radiation code specifically tailored for the simulation of radiation from hot, nonequilibrium gases and plasmas. The code has been developed continuously for the last 15 years and applied to solve radiative transfer problems in aerospace applications (namely atmospheric entry spacecraft).

June, 14

Simulation of effects of magnetic field using a Monte Carlo framework
Kryštof Mrózek, Department of Physical Electronics, Faculty of Science, Masaryk University, Czech republic

Electron energy distribution function (EEDF) is important characteristic of almost every discharge. Its knowledge can help greatly plasma diagnostics and also if it often necessary to know EEDF in order to be able to accurately model plasma discharge. At the moment there are several freely available tools (Bolsig+, LoKI-B) which calculates EEDF by solving Boltzmann kinetic equation using so-called two-term approximation. These frameworks are quite fast but two-term approximation might not be sufficient for certain types of plasma or for calculating swarm parameters like diffusion coefficient of electrons or reaction rate coefficients. One possible alternative to two-term approximation is to use more robust, albeit slower, Monte-Carlo based solvers.

May, 17

A few notes on the solution of the electron Boltzmann equation for swarms and the fitting of cross sections
Nuno Pinhão, Instituto de Plasmas e Fusão Nuclear, Campus Tecnológico e Nuclear/ Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal

In this talk we discuss a few problems on the interpretation of electron swarm data and the fitting of electron collision cross sections.

April, 19

Graphene-Based Hybrid Nanostructures Production Using Plasma-Based Methods
Ana Dias, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

One of the main challenges in the materials nanoscience research area lies in the sensitivity and complexity of the synthesis processes. Plasmas are an alternative and sustainable strategy to synthesize disruptive nanostructures since they allow the effective control over the nucleation and assembling mechanisms at atomic scale level. In the present work a microwave plasma-based method [1][2] at atmospheric pressure conditions is used to produce multiple free-standing carbon nanostructures, i.e., N-graphene and N-graphene-metal-based composites (NGMCs), possessing unique features that make them valuable in a wide range of applications.

March, 22

Towards a detailed reaction mechanism set for CO2-H2O low temperature plasmas
Tiago Silva, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

The vision of using plasmas to transform CO2 into valuable products has become well recognized by the scientific plasma community. This is motivated by the potential of plasmas to activate CO2 at reduced energy cost and excite CO2 vibrations that efficiently contribute to overcome the dissociation barrier. Therefore, investigation of the steps involved in plasma decomposition of CO2 is a key issue to move from the laboratory level towards industrial sector. This contribution is devoted to the modeling of CO2-H2O discharges, operating at pressures ranging from 1 to 5 torr.

February, 15

Non-equilibrium kinetics in CO2-N2 plasmas
Chloé Fromentin, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

The aim of this work is precisely to investigate the kinetics of CO2-N2 plasmas. A zerodimensional kinetic model for glow-type discharges in CO2, CO2-O2 and CO2-N2 is being developed. The model couples the electron kinetics, described by the electron Boltzmann equation, to a system of rate balance equations describing the creation and loss of vibrational and electronic excited states, different radicals and ions.

January, 18

ESTHER qualification campaign and first experimental results
Ricardo Ferreira, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

This presentation will focus on the ESTHER qualification activities that have been carried over the last 6 months, namely mechanical design, the laser ignition system and the first experimental shots in the isochoric combustion chamber. The shots are analysed and compared to the test scale combustion chamber “Bombe”. A Fourier Transform analysis of the pressure signal is carried out to infer on the acoustic pressure waves and sound speed inside the chamber. Furthermore, a qualitative analysis of the influence different combustion parameters is presented as well as a discussion on the upcoming test campaign.

December, 14

Aerodynamic study of atmospheric-pressure plasma jets
Duarte Gonçalves, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

Atmospheric-Pressure Plasma Jets (APPJs) have been used for scientific and industrial applications due to their ability to generate reactive species at high pressure while providing means to carry them into a target. An imposed flow assumes a jet structure, repetitive discharges generate the plasma, and the plasma itself affects the flow. APPJs present also an opportunity for new modelling strategies to explain the underlying mechanisms of the aeroelectro-dynamic interactions controlling these jets. We engage on this challenge by exploring the aerodynamics of APPJs using both modelling and experimental approaches.

November, 23

Kinetic Monte Carlo models to study the heavy-species and electron kinetics
Tiago Dias, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

In this presentation, we discuss our recent efforts towards a unified KMC formulation of complex plasma-chemistry models. We start by presenting and validating an innovative KMC approach to solve the chemical kinetics. Then, we show our first steps to study the electron kinetics through well-stablished MC techniques. Finally, we discuss on how we will selfconsistently couple these formulations in the near future.

July, 03

A compact FMCW reflectometer/interferometer design for the monitoring of atmospheric entry flows
Ricardo Ferreira, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

On the next experimental fusion reactors, the number of suitable diagnostics to measure relevant plasma quantities is very limited. Millimetre wave diagnostics are one of the obvious choice due to the limited in-vessel access requirements and front-end robustness. Frequency-Modulated Continuous-Wave (FMCW) reflectometry is a wellestablished technique to measure electron density profiles and to provide feedback for plasma position and shape control in such applications. This work presents the reflectometer architecture, discussing the main key design features and the prototype expected performance and valid test regions. Also, it compares its expected performance to previous similar experiments.

June, 26

Plasma reforming for oxygen production on Mars
Polina Ogloblina, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

In this seminar the results of experimental investigation of plasmas created in a simple and reproducible DC glow discharge, are going to be presented. The plasma under study is a mixture of CO2 with 2% of Ar and 2% of N2, for pressures in range 1–6 Torr and currents from 10 to 50 mA, both with gas at room (300 K) and Mars-like (220 K) temperatures. The CO2 and CO vibrational temperatures, the conversion factor and the reduced electric field are measured in these conditions. Experimental results and modelling predictions are compared for pure CO2 plasma at Earth and Mars-like temperatures.

May, 22

Optimization methods for cross section fitting of swarm data
Nuno Pinhão, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

The use of numerical optimization methods is tempting but conventional algorithms fail in this type of problem. On this talk we discuss the application of evolutionary computing methods to automatic fitting of cross sections. After briefly introducing the formalism adopted in this work for a) the analysis of swarm experiments and b) the evolutionary methods, we apply these concepts to cross section fitting. We start with a simple model gas and a genetic algorithm allowing to introduce the basic concepts of this field. Then we study the evolution of a population of cross sections and see how good fitting parameters are obtained as well as a statistical estimation of the uncertainty of the cross sections. The statistical analysis of the optimized solutions also show the presence of correlations between different cross sections. Finally we apply these algorithms to real gases.

May, 8

Influence of N2 on the asymmetric vibrating mode of CO2
Loann Terraz, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal

The effect of nitrogen addition in CO2 cold plasmas is explored in this presentation, and more specifically, the influence of N2 on the asymmetric population CO2(000v3), in order to reach an energy-efficient dissociation involving non-equilibrium processes. Experimental results show a greater conversion rate of CO2 into CO when N2 gas at room temperature is added to the plasma. Experiments are performed in non-thermal plasmas sustained by DC pulsed discharges, for pressure and current ranges of [1; 5] Torr and [20; 50] mA, respectively. A self-consistent model, previously validated for pure CO2 discharges, is further extended to take into account e-V, V-T and V-V reactions involving N2. The presentation focuses on the validation of the model, as well as the choice of the databases, by comparing the time-resolved densities of CO2(0v2l20) and CO2(000v3) between experimental results and modelling ones.

March, 20

Modelling the vibrational kinetics of CO2 through the Fokker-Planck approach - VIP-meeting
Pedro Viegas, Dutch Institute for Fundamental Energy Research, Computational Plasma Physics and Chemistry group, 5600 HH Eindhoven, The Netherlands

Low-temperature plasmas allow to convert greenhouse CO2 into new carbon-neutral fuels or useful chemicals with high energy efficiency. In order to understand and optimize these systems, reactor models that also take into account vibrational nonequilibrium have to be developed. However, the calculation of the vibrational distribution function (VDF) through the usual state-to-state (STS) approach compromises the computational efficiency of multidimensional models. In this presentation, a new approach is presented, more computationally efficient than the STS method, to calculate the VDF of the asymmetric stretching mode of CO2, based on the drift-diffusion Fokker-Planck (FP) equation. It is shown that the FP approach to vibrational kinetics can be self-consistently used in plasma models and the validation of this method is discussed, by comparing VDFs calculated through FP and STS simulations.

January, 17

Kinetic and fluid modeling of non-equilibrium electron and ion transport in gaseous and liquid matter - VIP-meeting
Ron White, College of Science & Engineering, James Cook University, Townsville, 4810, QLD, Australia

Accurate modelling of electron and ion transport in plasmas, plasma-liquid and plasmatissue interactions is dependent on (amongst other things) (i) the existence of accurate and complete sets of cross-sections, (ii) an accurate treatment of electron/ion transport in these phases, (iii) accurate description of other processes present e.g. localization (trapping), bubbles, etc. and (iv) understanding of the electron transport across the gas-liquid interface. The accuracy and completeness of electron-biomolecule cross-section sets can be assessed by comparison of calculated transport coefficients with those measured using a pulsed-Townsend swarm experiment of de Urquijo and co-workers. In this presentation we will present results from our recent studies of electrons in water, as the natural surrogate for human tissue.