This work presents a study of the influence of dielectric permittivity on the interaction between a positive pulsed He plasma jet and a 0.5 mm-thick dielectric target, using a validated two-dimensional numerical model. Six different targets are studied: five targets at floating potential with relative permittivities ϵr= 1, 4, 20, 56 and 80; and one grounded target of permittivity ϵr=56. The temporal evolution of the charging of the target and of the electric field inside the target are described, during the pulse of applied voltage and after its fall. It is found that the order of magnitude of the electric field inside the dielectric targets is the same for all floating targets with ϵr≥4. For all these targets, during the pulse of applied voltage, the electric field perpendicular to the target and averaged through the target thickness, at the point of discharge impact, is between 1 and 5 kV cm−1. For the two remaining targets (ϵr=1 and grounded target with ϵr=56), the field is significantly higher than for all the other floating targets.

VL - 40 IS - 3 U1 -FP

U2 -CPPC

U5 - 210172762b5b6e45f876d52e29b63afb ER - TY - JOUR T1 - Insight into contraction dynamics of microwave plasmas for CO2 conversion from plasma chemistry modelling JF - Plasma Sources Science and Technology Y1 - 2020 A1 - Viegas, P. A1 - Vialetto, L. A1 - Wolf, A. J. A1 - Peeters, F. J. J. A1 - Groen, P. W. C. A1 - Righart, T. W. H. A1 - Bongers, W. A. A1 - van de Sanden, M. C. M. A1 - Diomede, P. AB -This work addresses plasma chemistry in the core of a vortex-stabilized microwave discharge for CO2 conversion numerically, focusing on the pressure-dependent contraction dynamics of this plasma. A zero-dimensional model is presented for experimental conditions in a pressure range between 60 and 300 mbar and a temperature range between 3000 and 6500 K. Monte Carlo Flux simulations, which describe electron kinetics, are self-consistently coupled to the plasma chemistry model. The simulation results show that an increase in pressure is accompanied by a transition in neutral composition in the plasma core: from a significant amount of CO2 and O2 at low pressures to a O/CO/C mixture at high pressures, the composition being determined mostly by thermal equilibrium and by transport processes. The change of temperature and composition with pressure lead to higher ionisation coefficient and more atomic ion composition in the plasma core. These changes result in an increase in ionisation degree in the plasma core from 10-5 to 10-4. These factors are shown to be fundamental to drive contraction in the CO2 microwave discharge.

VL - 29 IS - 10 U1 -MaSF

U2 -PSFD

U5 - a9fe60d3219bf2dc2a2efd8c5ae44d0f ER - TY - JOUR T1 - Benchmarking of Monte Carlo Flux simulations of electrons in CO2 JF - Plasma Sources Science and Technology Y1 - 2020 A1 - Vialetto, L. A1 - Viegas, P. A1 - Longo, S. A1 - Diomede, P. AB - Electron velocity distribution functions (EVDFs) in CO2 obtained by means of the Monte Carlo Flux (MCF) method are compared with results from two-term and multi-term Boltzmann solvers. The MCF method provides detailed calculations of the EVDF through a highly efficient variance reduction technique. Benchmark calculations of Legendre polynomial coefficients of the EVDF expansion are reported for a wide range of reduced electric fields (E/N), showing excellent agreement with multi-term solutions. Rate coefficients of inelastic processes calculated from two-term Boltzmann solvers differ significantly, up to 70%, from MCF and multi-term solutions, due to the anisotropy of the EVDF. An extension of the method to consider the thermal distribution of the background gas is also presented. This extension, together with an accurate description of the population of rotationally and vibrationally excited states, provides excellent agreement with measured transport coefficients at low E/N. A good agreement is obtained at moderate E/N between experimental values of dissociation rate coefficients and MCF calculations after careful consideration and analysis of several cross sections data sets. VL - 29 IS - 11 U1 - FP U2 - CPPC U5 - d757814300e3d4a3d4e6ba2a804f3832 ER - TY - JOUR T1 - Validation of the Fokker-Planck Approach to Vibrational Kinetics in CO2 Plasma JF - Journal of Physical Chemistry C, The Y1 - 2019 A1 - Viegas, P. A1 - M. C. M. van de Sanden A1 - Longo, S. A1 - Diomede, P. AB -The Fokker-Planck (FP) approach to describe vibrational kinetics numerically is validated in this work. This approach is shown to be around 1000 times faster than the usual state-to-state (STS) method to calculate a vibrational distribution function (VDF) in stationary conditions. Weakly ionized, nonequilibrium CO2 plasma is the test case for this demonstration, in view of its importance for the production of carbon-neutral fuels. VDFs obtained through the resolution of an FP equation and through the usual STS approach are compared in the same conditions, considering the same kinetic data. The demonstration is shown for chemical networks of increasing generality in vibrational kinetics of polyatomic molecules, including V-V exchanges, V-T relaxation, intermode V-V' reactions, and excitation through e-V collisions. The FP method is shown to be accurate to describe the vibrational kinetics of the CO2 asymmetric stretching mode, while being much faster than the STS approach. In this way, the quantitative validity of the FP approach in vibrational kinetics is assessed, making it a fully viable alternative to STS solvers, that can be used with other processes, molecules, and physical conditions.

VL - 123 IS - 37 U1 -MaSF

U2 -CPPC

U5 - f45be36311abe6172c63785e2bc729ba ER - TY - RPRT T1 - Self-consistent diffusion approach to CO2 vibrational kinetics Y1 - 2019 A1 - Viegas, P. A1 - M. C. M. van de Sanden A1 - Longo, S. A1 - Diomede, P. JF - ISPC 2019, 24th International Symposium on Plasma Chemistry CY - Naples, Italy UR - https://www.ispc-conference.org/ispcproc/ispc24/226.pdf N1 - 2019/06/14 U1 -FP

U2 -CPPC

U5 - e407240114b3f1f39e3a4d604af28e28 ER - TY - RPRT T1 - A diffusion approach to vibrational kinetics of molecules in plasma Y1 - 2019 A1 - Longo, S. A1 - Viegas, P. A1 - M. C. M. van de Sanden A1 - Diomede, P. JF - 46th EPS Conference on Plasma Physics 2019 (EPS-46) CY - Milan, Italy UR - https://www.epsplasma2019.eu/ N1 - 2019/07/12 U1 -FP

U2 -CPPC

U5 - 5fd54dd45a221443de0af14da6872313 ER - TY - RPRT T1 - Self-consistent Fokker-Planck approach to CO2 vibrational kinetics Y1 - 2019 A1 - Viegas, P. A1 - M. C. M. van de Sanden A1 - Longo, S. A1 - Diomede, P. JF - 34th International Conference on Phenomena in Ionized Gases (ICPIG) 2019 CY - Sapporo, Japan UR - http://icpig2019.qe.eng.hokudai.ac.jp/ N1 - 2019/07/19 U1 -FP

U2 -CPPC

U5 - 27149d371cc140083cfe82a4e7cd1186 ER -