Research

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Research topics

1. Fundamental research of atmospheric pressure plasmas
    1.1. Introduction
    1.2. Diagnostic methods
    1.3. Numerical modeling
    1.4. DC glow discharge
    1.5. Transient spark
    1.6. Microwave plasma
    1.7. Discharges in porous materials and capillaries
    1.8. Discharges with water
2. Bio-medical plasma applications
3. Environmental plasma applications
4. Non-plasmatic environmental technologies

1.3. Numerical modeling

1.3.1. Monte Carlo simulations of electron dynamics

In Janda et al., Acta Physica Slovaca 55 (2005) 507-514, we present a free software for modeling the electron dynamics in the uniform electric field named Web-EEDF. It provides electron energy distribution function (EEDF), electron drift velocity, electron mobility, and collision frequency of electrons with neutrals as functions of reduced electric flied strength (E/N). EEDF (Fig. 1) enables us to calculate electron mean energy, electron mean free path, rate coefficients (Fig. 2) of electron-molecule collisional processes (e.g. excitation, attachment, ionization), and the branching of the electron energy towards these processes.

Calculated rate coefficients of electron-induced processes can facilitate better understanding of the importance of various reaction pathways leading to the decomposition of air pollutants in various gas mixtures. Despite its simplicity the Web-EEDF results are in good agreement with literature. It is also suitable for educational purposes by providing clearer insight in understanding physical and chemical mechanisms in plasma processes.

This electron dynamics modeling was further developed in Janda et al., Eur. J. Phys. D 45 (2007) 309-315. Motivated by the decomposition of CO₂ and the synthesis of amino acids in DC electrical discharges, we investigated the electron dynamics by Monte Carlo simulations in N₂/CO₂ gas mixtures. The results of the simulations include electron mean energy, drift velocity, collision frequency of electrons with neutrals, mean free path of electrons, rate coefficients of selected electron-impact processes, and ionization and attachment coefficients as functions of the reduced electric field strength and the composition of a gas mixture. The knowledge of these parameters is crucial for the understanding of plasma induced chemistry and behavior of electrical discharges in such mixtures.

The applied computational method was proved useful for the calculation of steady-state EEDFs and derived parameters characterizing electrons in homogeneous electric fields in various gaseous mixtures. Web-EEDF source code can be downloaded from http://enviro.fmph.uniba.sk/web-eedf. We are currently developing new version which will enable to simulate time evolution of EEDFs, or the relaxation of electrons in electron beams.

Fig. 1. Electron energy distribution functions (EEDF) in air as functions of reduced electric field strength (E/N).
 

Fig. 2. Rate coefficients of the most important electron impact reactions in N₂/CO₂ mixtures, E/N = 120 Td.
 

More details in:

http://enviro.fmph.uniba.sk/web-eedf

1.3.2. Plasma kinetics

The modeling of chemical kinetics aiming to calculate the density evolution of all species included in the kinetic model is an effective tool for complex systems description. In many cases, it is the most powerful way to solve problems where the complexity inhibits using analytical methods and direct experimental measurements. It is commonly used not only for modeling of cold plasma chemistry, but also for description of high temperature steady state arc plasma, nanosecond duration of streamer propagation, and other problems in plasma physics and chemistry.

We are currently developing chemical kinetic model fitted for the transient spark (TS) discharge. This model can be used to determine the evolution of density of various species. Moreover, this model is able to describe macroscopic parameters such as plasma conductivity and current density in the plasma channel. The validity of the model was tested by comparing calculated electron densities with experimental data (Fig. 3). This model is based on available open source package ZDPlaskin.

We studied the mechanism of the streamer-to-spark transition and breakdown in the TS using this model. We assume that the breakdown mechanism in TS is based on the gas density (N) decrease and can be summarized as follows: heating of the channel → increase of the pressure → hydrodynamic expansion → decrease of N in the core of the channel → increase of E/N → acceleration of ionization processes. However, this mechanism is influenced by species accumulated due to previous TS pulses at higher TS repetition frequencies. Sensitivity analysis focused on major electron loss and production processes indicates an important role of the amount of O₂ dissociated by the previous pulses. Lower density of O₂ means lower rate of electron attachment, while accumulated atomic oxygen atoms lead to acceleration of electron detachment processes.

Further research of this memory effect using improved version of our kinetic model simulating sequence of pulses is needed to verify this hypothesis. We further plan to use an improved version of our model to study generation of various reactive species by TS discharge.

Fig. 3. Comparison of measured and calculated electron densities during the spark phase of the transient spark discharge, repetition frequency around 1 kHz.
 

More details in:

Old website of our division.

In 2022 we organised 9th Central European symposium on Plasma Chemistry and COST Action CA19110 workshop.

In 2016 we organised 6th International Conference on Plasma Medicine, with almost 400 participants.

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Do not hesitate to contact us, if needed.

• hensel2 \at\ uniba.sk (head)
• janda1 \at\ uniba.sk (webmaster)
• +421-2-60295676
• Mlynská dolina F2
  Bratislava SK, 842 48