Modelling of chemical reactions in plasma

The paper is devoted to theoretical investigation of interaction of pulsed high current electron beam with gas substance. As a result of the interaction the formation of chemical active plasma can be observed. One of the key parameter for theoretical analyze of the process is the electron distribution function. Within the framework of the Boltzmann approach we obtained the dynamical equation for electron distribution function depending on the electron energy, coordinate and time

Probing photo-ionization: simulations of positive streamers in varying N2:O2 mixtures

Photo-ionization is the accepted mechanism for the propagation of positive streamers in air though the parameters are not very well known; the efficiency of this mechanism largely depends on the presence of both nitrogen and oxygen. But experiments show that streamer propagation is amazingly robust against changes of the gas composition; even for pure nitrogen with impurity levels below 1 ppm streamers propagate essentially with the same velocity as in air, but their minimal diameter is smaller, and they branch more frequently. Additionally, they move more in a zigzag fashion and sometimes exhibit a feathery structure. In our simulations, we test the relative importance of photo-ionization and of the background ionization from pulsed repetitive discharges, in air as well as in nitrogen with 1 ppm O2 . We also test reasonable parameter changes of the photo-ionization model. We find that photo- ionization dominates streamer propagation in air for repetition frequencies of at least 1 kHz, while in nitrogen with 1 ppm O2 the effect of the repetition frequency has to be included above 1 Hz. Finally, we explain the feather-like structures around streamer channels that are observed in experiments in nitrogen with high purity, but not in air.Comment: 12 figure

Spatial coupling of particle and fluid models for streamers: where nonlocality matters

Particle models for streamer ionization fronts contain correct electron energy distributions, runaway effects and single electron statistics. Conventional fluid models are computationally much more efficient for large particle numbers, but create too low ionization densities in high fields. To combine their respective advantages, we here show how to couple both models in space. We confirm that the discrepancies between particle and fluid fronts arise from the steep electron density gradients in the leading edge of the fronts. We find the optimal position for the interface between models that minimizes computational effort and reproduces the results of a pure particle model.Comment: 4 pages, 5 figure

The effect of photoemission on nanosecond helium microdischarges at atmospheric pressure

Atmospheric-pressure microdischarges excited by nanosecond high-voltage pulses are investigated in helium-nitrogen mixtures by first-principles particle-based simulations, which include VUV resonance radiation transport via the tracing of photon trajectories. The VUV photons, of which the frequency redistribution in the emission processes is included in some detail, are found to modify the computed discharge characteristics remarkably, due to their ability to induce electron emission from the cathode surface. Electrons created this way enhance the plasma density, and a significant increase of the transient current pulse amplitude is observed. The simulations allow the computation of the density of helium atoms in the 21P resonant state, as well as the density of photons in the plasma and the line shape of the resonant VUV radiation reaching the electrodes. These indicate the presence of significant radiation trapping in the plasma and photon escape times longer than the duration of the excitation pulses are found

The 2017 Plasma Roadmap: Low temperature plasma science and technology

Journal of Physics D: Applied Physics published the first Plasma Roadmap in 2012 consisting of the individual perspectives of 16 leading experts in the various sub-fields of low temperature plasma science and technology. The 2017 Plasma Roadmap is the first update of a planned series of periodic updates of the Plasma Roadmap. The continuously growing interdisciplinary nature of the low temperature plasma field and its equally broad range of applications are making it increasingly difficult to identify major challenges that encompass all of the many sub-fields and applications. This intellectual diversity is ultimately a strength of the field. The current state of the art for the 19 sub-fields addressed in this roadmap demonstrates the enviable track record of the low temperature plasma field in the development of plasmas as an enabling technology for a vast range of technologies that underpin our modern society. At the same time, the many important scientific and technological challenges shared in this roadmap show that the path forward is not only scientifically rich but has the potential to make wide and far reaching contributions to many societal challenges.I Adamovich et al 2017 J. Phys. D: Appl. Phys. 50 32300

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

Evolution of atomic oxygen density in the early afterglow of a nanosecond CO 2 discharge

International audienceIn low temperature nonequilibrium plasmas, the dominating channel of CO 2 conversion is usually the dissociation of mixture molecules by electron impact under high electric field and high deposited energy, which can be provided by nanosecond discharges. It is important to apply time-resolved measurements of major species like atomic oxygen in the CO 2 discharges to better understand the dynamic processes. The nanosecond discharge was initiated in the capillary tube with 2.0 mm of internal diameter and 52.89 mm of inter-electrode distance. High-voltage pulses (9 kV of amplitude, 30 ns of FWHM and 10 Hz of repetitive frequency) were delivered via the coaxial cable. CO 2 under 19.5 mbar flowed at the rate of 10 sccm so that each discharge was initiated in the new gas portion. Two-photon absorption laser-induced fluorescence (TALIF) was used to measure the absolute density of atomic oxygen in the afterglow. The ground-state O atoms were excited by a 225.7 nm focused laser pulse, and 845 nm fluorescence signal was detected by a photomultiplier (PMT). An optical pulse slicer was used to narrow the bandwidth of the laser pulse to determine the effective decay rates of the excited O atoms. Calibration was taken by Xe-TALIF under the pressure of 2 mbar. The measured electrical parameters of the CO 2 discharge show that the reduced electric field reaches 700 Td and the specific deposited energy is almost 1 eV/particle immediately after the first nanosecond pulse. The TALIF measurements indicate a temporal profile of O(3p 3P 0,1,2) effective decay rates between 0.3 to 0.9 ns-1 and ground-state O-atom absolute density between 10 16 to 10 17 cm -3, which gives the dissociation rate up to 20 % in a single pulse.Acknowledgements The work was partially done in the framework of activity of E4C Interdisciplinary Center of IPP.References [1] G.V. Pokrovskiy, PhD Thesis, l’Institut Polytechnique de Paris (2021) [2] G.V. Pokrovskiy, N.A. Popov and S.M. Starikovskaia, Plasma Sources Sci. Techn., 31(3), 035010 (2022)