Evgenia Benova

Modelling of an RF plasma shower

A capacitive radiofrequency (RF) discharge at atmospheric pressure is studied by means of a time-dependent, two-dimensional fluid model. The plasma is created in a stationary argon gas flow guided through two perforated electrodes, hence resembling a shower. The inner electrode, the electrode facing the flow entrance, is powered with a frequency of 13.56 MHz, and the outer electrode is grounded. The model solves the mass balance equations for the relevant active species and the electron energy balance equation in conjunction with the Poisson equation for the field sustaining the plasma. The mass balance equations of the active species are calculated using the drift–diffusion–convection approach, thus taking the bulk velocity into account. The velocity field is calculated with the Navier–Stokes module of the Plasimo toolkit. The plasma dynamics is studied in three connected regions; the space between the electrodes, the regions before the powered electrode and the extended region behind the grounded electrode. The effect of the shower holes and the recirculation gas flow on the plasma is examined.

An experimental study of the axial structure of a gas discharge sustained by a surface electromagnetic wave in the presence of a uniform external magnetic field

Examines experimentally the axial profiles of the plasma parameters (electron temperature Te and the electron number density n) of a helium low-pressure gas discharge column sustained by a travelling electromagnetic wave in the presence of a strong magnetic field for two values of magnetic induction corresponding to the magnitudes of omega c/ omega =2.5 and 5 respectively ( omega c is the electron cyclotron frequency and omega is the wave angular frequency). It is found that the electron temperature is diminished and the plasma density is increased (accompanied by a decrease of its axial gradient) in comparison with the magnitudes of the same parameters and characteristics of an isotropic plasma column. The measured axial plasma density gradients are compared with theoretically calculated ones and the agreement between theory and experiment is good.

Temperature diagnostics in a high-pressure hydrogen microwave plasma torch I: experimental characterization

We present preliminary results of an experimental study of a hydrogen plasma flame produced using a microwave axial injection torch (torche a injection axiale or TIA). This device usually runs in argon or helium at atmospheric pressure providing a stable discharge at high HF power levels and a two-temperature plasma. In the current work, hydrogen plasma is launched in a helium filled chamber to prevent hydrogen-air explosive reactions. Seven spectroscopic hydrogen lines have been detected in the visible spectrum (the Balmer series of hydrogen). Using a Boltzmannplot representation it is shown that the plasma is far from equilibrium, but the electron temperature still can be obtained from a modified plot via a p−x-correction, which shows that the lower energy levels of Balmer series of the hydrogen system is ruled by the excitation-saturation balance (ESB).

Characterization of a high-pressure hydrogen microwave plasma torch using the method of dBR

A hydrogen plasma flame produced by an axial injection torch powered at the microwave frequency of 2.45 GHz is studied using the method of disturbed Bilateral Relations (dBR). The application of this method which relates the influence of equilibrium disturbing, as produced by transport, to equilibrium restoring processes, reveals that the most dominant excitation balance is the Excitation Saturation Balance. Moreover, a global discharge model leads to an electron density of ne = 4.1020m?3 and an electron temperature of Te = 0.86 eV. The gas temperature was estimated to be Th = 0.3 eV. The values of ne and Te were found to be in good agreement with the value obtained with the modified Boltzmann-plot and the crossing method of Stark broadening. The dBR method points out that the first level in partial local Saha equilibrium will be the level with principal quantum number p = 10 which is in fair agreement with experimental results.

Surface-wave-sustained plasma torch for water treatment

In this study the effects of water treatment by surface-wave-sustained plasma torch at 2.45 GHz are studied. Changes in two directions are obtained: (i) changes of the plasma characteristics during the interaction with the water; (ii) water physical and chemical characteristics modification as a result of the plasma treatment. In addition, deactivation of Gram positive and Gram negative bacteria in suspension are registered. A number of charged and excited particles from the plasma interact with the water. As a result the water chemical and physical characteristics such as the water conductivity, pH, H2O2 concentration are modified. It is observed that the effect depends on the treatment time, wave power, and volume of the treated liquid. At specific discharge conditions determined by the wave power, gas flow, discharge tube radius, thickness and permittivity, the surface-wave-sustained discharge (SWD) operating at atmospheric pressure in argon is strongly non-equilibrium with electron temperature T e much higher than the temperature of the heavy particles (gas temperature T g). It has been observed that SWD argon plasma with T g close to the room temperature is able to produce H2O2 in the water with high efficiency at short exposure times (less than 60 sec). The H2O2 decomposition is strongly dependant on the temperature thus the low operating gas temperature is crucial for the H2O2 production efficiency. After scaling up the device, the observed effects can be applied for the waste water treatment in different facilities. The innovation will be useful especially for the treatment of waters and materials for medical application.

Investigation of the gas flow effect on an atmospheric pressure RF plasma torch

A cool atmospheric pressure non-thermal capactively-coupled RF discharge is studied. It is created between two parallel electrodes – a powered one supplied by 13.56 MHz, and a grounded one. The feed gas argon flows via holes between the electrodes where it is ionized. The plasma torch is studied by means of a time dependent two-dimensional fluid model. A simplified kinetic scheme with four active species is considered, namely argon excited atoms (Ar*), atomic (Ar+) ions, molecular (Ar2+) ions and electrons (e). The plasma dynamics in the space between the electrodes as well as in the extended region behind the grounded electrode is studied. The effect of the gas flow on the plasma is examined. Constriction of the plasma is induced by the field sustaining the discharge due to the sieve-like structure of the electrodes. As a result of the stationary gas flow the filaments extend beyond the electrodes ensuring a flow of active species in the afterglow.

Model of a stationary microwave argon discharge at atmospheric pressure

The many applications of microwave gas discharges at atmospheric pressure in various fields of science, technology and medicine require an adequate model of these discharges. Such a model is based on the electromagnetic waves propagation properties and on the elementary processes in the discharge bulk. In contrast to the microwave discharges at low-gas pressures, where many elementary processes might be ignored because of their negligible contribution to the electron and heavy particles balance equations, for such discharges at atmospheric pressure the consideration of a large number of collisional processes is mandatory. For the build of a successful discharge-column model one needs three important quantities, notably the power θ necessary for sustaining an electron—ion pair, electron—neutral collision frequency for momentum transfer ven, and gas temperature Tg. The first two key parameters are obtained by a collisional-radiative model of the argon at atmospheric pressure, while the microwave frequency...

Evaluation of the effect of cold atmospheric plasma on oxygenases’ activities for application in water treatment technologies

ABSTRACT Plasma-based technologies take an increasing place in the new conceptions of wastewater management as a promising tool for the treatment of persistent organic pollutants with low biodegradability. Plasma major advantage is the synergy of diverse active components with high oxidative action and additional benefits as disinfection of treated water. But the bactericidal effect of plasma can influence the treatment effectiveness when this technology is used in combination with biological methods for the removal of pollutants. The aim of this paper is to study the effect of non-thermal atmospheric plasma torch on key enzymes from phenol biodegradation pathways in Pseudomonas aureofaciens (chlororaphis) AP-9. The strain was isolated from contaminated soils and had a high potential for biodegradation of aromatic compounds. The used plasma source is surface-wave-sustained discharge operating at 2.45 GHz in argon produced by an electromagnetic wave launcher surfatron type. The enzyme activities of phenol 2-monooxygenase (P2MO), catechol 1,2-dioxygenase (C12DO), catechol 2,3-dioxygenase (C23DO), protocatechuate 3,4-dioxygenase (P34DO) and succinate dehydrogenase (SDH) were measured in control and after plasma treatment of 10, 30 and 60 s. At short-time treatment, the activities of intradiol dioxygenases increased with 26% and 59% for C12DO and P34DO, respectively. Other oxygenases and SDH were inhibited with 35% even at 10 s treatment. Longer treatment times had a clear negative effect but SDH kept the higher activity at 60 s treatment compared to the oxygenases. Our data suggest that plasma-based technologies are a useful approach for post-treatment of aryl-containing wastewater in order to increase the effectiveness of biological removal. GRAPHICAL ABSTRACT

Innovative sterilization technology - bacterial inactivation by cold argon plasma

Non-thermal (cold) plasma is subject of intensive scientific interest as an alternative sterilization technique for advanced control of microbial quality and safety in food biotechnology. The cold plasma is a flow of weakly ionized gas at atmospheric pressure that includes radicals, H O , O , ultraviolet radiation, charged particles, exited metastable atoms, electric fields. One of the major benefits of plasma-based technologies is the synergy between the strong effects of these highly active components that provides a high bactericidal efficiency at low costs, time-saving and non-toxicity. The aim of this study is to assess the bactericidal effect of cold argon plasma in liquids and surfaces, contaminated with Gram-negative and Gram-positive spore-forming bacteria. The used plasma source is surface-wave-sustained discharge (SWD) operating at 2.45 GHz in argon (plasma torch) produced by an electromagnetic wave launcher surfatron type. The bactericidal effect was studied by direct contact treatment of contaminated liquids and agar plates with Pseudomonas aureofaciens AP-9 and Brevibacillus laterosporus BT-271. The results show that the cold argon plasma is able to inactivate bacteria at short exposure time (under 1 min). The clear sterilization zones on treated surfaces with diameter depending on exposure time and initial bacterial density were obtained. In bacteria-contaminated liquids ‡ ‡ ‡ § | | ¶

Two-Dimensional Modeling of the Active Species Flow Generated by an Atmospheric Plasma Jet

A proper description of the flux of active species generated by cold atmospheric-pressure (AP) plasma jets is of crucial importance for plasma applications. To that end, a 2-D fluid model has been constructed to investigate the effect of the coupling between the plasma kinetics and plasma flow. It is shown that pure-argon cold AP RF plasma jets are not only controlled by diffusion losses but also by convective transport of argon molecular ions Ar2+.