Dr. Petr Lukeš
Department of Pulse Plasma Systems
Institute of Plasma Physics AS CR, v.v.i.
Za Slovankou 3, 182 00 Prague 8, CZECH REPUBLIC

Place:  Pulse Plasma Systems Bldg., Office: E 104
Tel.:     (+420) 266 053233,     Fax:     (+420) 286 592 644
Email:  

http://www.ipp.cas.cz/?detail=lukesp



Selected Publications with Abstracts


Potential of Pulsed Corona Discharges Generated in Water for the Degradation of Persistent Pharmaceutical Residues

Water Res. 84: 127-135 (2015)
Banaschik R., Lukes P., Jablonowski H., Hammer M.U., Weltmann K.-D., Kolb J.F.

Abstract: Anthropogenic pollutants and in particular pharmaceutical residues are a potential risk for potable water where they are found in increasing concentrations. Different environmental effects could already be linked to the presence of pharmaceuticals in surface waters even for low concentrations. Many pharmaceuticals withstand conventional water treatment technologies. Consequently, there is a need for new water purification techniques. Advanced oxidation processes (AOP), and especially plasmas with their ability to create reactive species directly in water, may offer a promising solution. We developed a plasma reactor with a coaxial geometry to generate large volume corona discharges directly in water and investigated the degradation of seven recalcitrant pharmaceuticals (carbamazepine, diatrizoate, diazepam, diclofenac, ibuprofen, 17α-ethinylestradiol, trimethoprim). For most substances we observed decomposition rates from 45% to 99% for treatment times of 15-66min. Especially ethinylestradiol and diclofenac were readily decomposed. As an inherent advantage of the method, we found no acidification and only an insignificant increase in nitrate/nitrite concentrations below legal limits for the treatment. Studies on the basic plasma chemical processes for the model system of phenol showed that the degradation is primarily caused by hydroxyl radicals.

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Tandem Shock Waves in Medicine and Biology: A Review of Potential Applications and Successes

Shock Waves (2015) Article in Press
Lukes P., Fernández F., Gutiérrez-Aceves J., Fernández E., Alvarez U.M., Sunka P., Loske A.M.

Abstract: Shock waves have been established as a safe and effective treatment for a wide range of diseases. Research groups worldwide are working on improving shock wave technology and developing new applications of shock waves to medicine and biology. The passage of a shock wave through soft tissue, fluids, and suspensions containing cells may result in acoustic cavitation i.e., the expansion and violent collapse of microbubbles, which generates secondary shock waves and the emission of microjets of fluid. Cavitation has been recognized as a significant phenomenon that produces both desirable and undesirable biomedical effects. Several studies have shown that cavitation can be controlled by emitting two shock waves that can be delayed by tenths or hundreds of microseconds. These dual-pulse pressure pulses, which are known as tandem shock waves, have been shown to enhance in vitro and in vivo urinary stone fragmentation, cause significant cytotoxic effects in tumor cells, delay tumor growth, enhance the bactericidal effect of shock waves and significantly increase the efficiency of genetic transformations in bacteria and fungi. This article provides an overview of the basic physical principles, methodologies, achievements and potential uses of tandem shock waves to improve biomedical applications.

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Pressure Field Around Underwater Negative Streamers

IEEE Trans. Plasma Sci. 43 (5): 1787-1792 (2015)
Hoffer P., Kolacek K., Lukes P., Stelmashuk V.

Abstract: In this paper, experimental observations of propagation of negative streamers in distilled water (conductivity of 1.7 µS/cm) in a needle-plane electrode geometry (gap of 6 mm) are described. The spatially resolved pressure field surrounding the tip of streamer channel in the given moment was determined by Mach–Zehnder interferometer with second harmonic of Nd:YAG laser as a source. The high-voltage needle electrode was brought on the potential of 23 kV and that remained practically unchanged during streamers propagation, while a significant noise with amplitude of several amperes was visible on the waveform of discharge current. Analysis of captured interferograms shows that propagation of negative streamers is not uniform: an active (propagating) streamer produces continuous moving pressure field (similar to that of moving object) with maximum amplitude greater than 40 MPa on the streamer tips and an inactive streamer nearly stops propagating being surrounded by a nearly spherical pressure wave moving away from the streamer’s tip. The inactive state can last even longer than 200 ns.

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Membrane Damage and Active But Nonculturable State in Liquid Cultures of Escherichia coli Treated with an Atmospheric Pressure Plasma Jet

Bioelectrochemistry 103: 7-14 (2015)
Dolezalova E., Lukes P.

Abstract: Electrical discharge plasmas can efficiently inactivate various microorganisms. Inactivation mechanisms caused by plasma, however, are not fully understood because of the complexity of both the plasma and biological systems. We investigated plasma-induced inactivation of Escherichia coli in water and mechanisms by which plasma affects bacterial cell membrane integrity. Atmospheric pressure argon plasma jet generated at ambient air in direct contact with bacterial suspension was used as a plasma source. We determined significantly lower counts of E. coli after treatment by plasma when they were assayed using a conventional cultivation technique than using a fluorescence-based LIVE/DEAD staining method, which indicated that bacteria may have entered the viable-but-nonculturable state (VBNC). We did not achieve resuscitation of these non-culturable cells, however, we detected their metabolic activity through the analysis of cellular mRNA, which suggests that cells may have been rather in the active-but-nonculturable state (ABNC). We hypothesize that peroxidation of cell membrane lipids by the reactive species produced by plasma was an important pathway of bacterial inactivation. Amount of malondialdehyde and membrane permeability of E. coli to propidium iodide increased with increasing bacterial inactivation by plasma. Membrane damage was also demonstrated by detection of free DNA in plasma-treated water.

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In vivo Effects of Focused Shock Waves on Tumor Tissue Visualized by Fluorescence Staining Techniques

Bioelectrochemistry 103: 103-110 (2015)
Lukes P., Zeman J., Horak V., Hoffer P., Pouckova P., Holubova M., Hosseini S.H.R., Akiyama H., Sunka P., Benes J.

Abstract: Shock waves can cause significant cytotoxic effects in tumor cells and tissues both in vitro and in vivo. However, understanding the mechanisms of shock wave interaction with tissues is limited. We have studied in vivo effects of focused shock waves induced in the syngeneic sarcoma tumor model using the TUNEL assay, immunohistochemical detection of caspase-3 and hematoxylin–eosin staining. Shock waves were produced by a multichannel pulsed-electrohydraulic discharge generator with a cylindrical ceramic-coated electrode. In tumors treated with shock waves, a large area of damaged tissue was detected which was clearly differentiated from intact tissue. Localization and a cone-shaped region of tissue damage visualized by TUNEL reaction apparently correlated with the conical shape and direction of shock wave propagation determined by high-speed shadowgraphy. A strong TUNEL reaction of nuclei and nucleus fragments in tissue exposed to shock waves suggested apoptosis in this destroyed tumor area. However, specificity of the TUNEL technique to apoptotic cells is ambiguous and other apoptotic markers (caspase-3) that we used in our study did not confirmed this observation. Thus, the generated fragments of nuclei gave rise to a false TUNEL reaction not associated with apoptosis. Mechanical stress from high overpressure shock wave was likely the dominant pathway of tumor damage.

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Properties of Water Surface Discharge at Different Pulse Repetition Rates

J. Appl. Phys. 116 (12): 123304 (2014)
Ruma, Hosseini S.H.R., Yoshihara K., Akiyama M., Sakugawa T., Lukes P., Akiyama H.

Abstract: The properties of water surface discharge plasma for variety of pulse repetition rates are investigated. A magnetic pulse compression (MPC) pulsed power modulator able to deliver pulse repetition rates up to 1000 Hz, with 0.5 J per pulse energy output at 25 kV, was used as the pulsed power source. Positive pulse with a point-to-plane electrode configuration was used for the experiments. The concentration and production yield of hydrogen peroxide (H2O2) were quantitatively measured and orange II organic dye was treated, to evaluate the chemical properties of the discharge reactor. Experimental results show that the physical and chemical properties of water surface discharge are not influenced by pulse repetition rate, very different from those observed for under water discharge. The production yield of H2O2 and degradation rate per pulse of the dye did not significantly vary at different pulse repetition rates under a constant discharge mode on water surface. In addition, the solution temperature, pH, and conductivity for both water surface and underwater discharge reactors were measured to compare their plasma properties for different pulse repetition rates. The results confirm that surface discharge can be employed at high pulse repetition rates as a reliable and advantageous method for industrial and environmental decontamination applications.

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Aqueous-Phase Chemistry and Bactericidal Effects from an Air Discharge Plasma in Contact with Water: Evidence for the Formation of Peroxynitrite through a Pseudo-Second-Order Post-Discharge Reaction of H2O2 and HNO2

Plasma Sources Sci. Technol. 23 (1): 015019 (2014)
Lukes P., Dolezalova E., Sisrova I., Clupek M.

Abstract: The formation of transient species (OH·, NO2·, NO radicals) and long-lived chemical products (O3, H2O2, NO3-, NO2-) produced by a gas discharge plasma at the gas–liquid interface and directly in the liquid was measured in dependence on the gas atmosphere (20% oxygen mixtures with nitrogen or with argon) and pH of plasma-treated water (controlled by buffers at pH 3.3, 6.9 or 10.1). The aqueous-phase chemistry and specific contributions of these species to the chemical and biocidal effects of air discharge plasma in water were evaluated using phenol as a chemical probe and bacteria Escherichia coli. The nitrated and nitrosylated products of phenol (4-nitrophenol, 2-nitrophenol, 4-nitrocatechol, 4-nitrosophenol) in addition to the hydroxylated products (catechol, hydroquinone, 1,4-benzoquinone, hydroxy-1,4-benzoquinone) evidenced formation of NO2·, NO· and OH· radicals and NO+ ions directly by the air plasma at the gas-liquid interface and through post-discharge processes in plasma-activated water (PAW) mediated by peroxynitrite (ONOOH). Kinetic study of post-discharge evolution of H2O2 and NO2- in PAW has demonstrated excellent fit with the pseudo-second-order reaction between H2O2 and NO2-. The third-order rate constant k = 1.1 × 103 M-2 s-1 for the reaction NO2- + H2O2 + H+ → ONOOH + H2O was determined in PAW at pH 3.3 with the rate of ONOOH formation in the range 10-8 - 10-9 M s-1. Peroxynitrite chemistry was shown to significantly participate in the antibacterial properties of PAW. Ozone presence in PAW was proved indirectly by pH-dependent degradation of phenol and detection of cis,cis-muconic acid, but contribution of ozone to the inactivation of bacteria by the air plasma was negligible.

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Focused Tandem Shock Waves in Water and their Potential Application in Cancer Treatment

Shock Waves 24 (1): 51-57 (2014)
Lukes P., Sunka P., Hoffer P., Stelmashuk V., Pouckova P., Zadinova M., Zeman J., Dibdiak L., Kolarova H., Tomankova K., Binder S., Benes J.

Abstract: The generator of two focused successive (tandem) shock waves (FTSW) in water produced by underwater multichannel electrical discharges at two composite electrodes, with a time delay between the first and second shock waves of 10 µs, was developed. It produces, at the focus, a strong shock wave with a peak positive pressure of up to 80 MPa, followed by a tensile wave with a peak negative pressure of up to -80 MPa, thus generating at the focus a large amount of cavitation. Biological effects of FTSW were demonstrated in vitro on hemolysis of erythrocytes and cell viability of human acute lymphoblastic leukemia cells as well as on tumor growth delay ex vivo and in vivo experiments performed with B16 melanoma, T-lymphoma, and R5-28 sarcoma cell lines. It was demonstrated in vivo that FTSW can enhance antitumor effects of chemotherapeutic drugs, such as cisplatin, most likely due to increased permeability of the membrane of cancer cells induced by FTSW. Synergetic cytotoxicity of FTSW with sonosensitive porphyrin-based drug Photosan on tumor growth was observed, possibly due to the cavitation-induced sonodynamic effect of FTSW.

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Formation of ROS and RNS in Water Electro-Sprayed through Transient Spark Discharge in Air and their Bactericidal Effects

Plasma Proc. Polym. 10 (7): 649-659 (2013)
Machala Z., Tarabova B., Hensel K., Spetlikova E., Sikurova L., Lukes P.

Abstract: Chemical and bactericidal effects induced by plasma in water upon electro-spraying through DC-driven positive transient spark discharge in air were investigated. Inactivation of E. coli was determined in dependence on pH (controlled by buffers) and correlated with chemical changes induced in water. Productions of hydrogen peroxide, nitrites, nitrates, peroxynitrites, and pH changes were determined, and the extent of oxidative stress induced in bacteria was evaluated. The degree of inactivation and oxidative damage of bacteria increased with the increasing acidity of the solution. Acidified nitrites interacting with hydrogen peroxide were determined as the most important bactericidal ROS/RNS agents in plasma-treated water. A possible role of peroxynitrites, ozone, and metal nanoparticles is discussed.

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Effects of Pulse Frequency of Input Power on the Physical and Chemical Properties of Pulsed Streamer Discharge Plasmas in Water

J. Phys. D: Appl. Phys. 46 (12): 125202 (2013)
Ruma, Lukes P., Aoki N., Spetlikova E., Hosseini S.H.R., Sakugawa T., Akiyama H.

Abstract: A repetitive pulsed-power modulator, which employs a magnetic pulse compression circuit with a high-speed thyristor switch, was used to study the effects of the pulse repetition rate of input power on the physical and chemical properties of pulsed discharges in water. Positive high-voltage pulses of 20 kV with repetition rates of up to 1 kHz were used to generate a discharge in water using the point-to-plane electrode geometry. By varying the pulse repetition rate, two distinct modes of the discharge plasma were formed in water. The first mode was characterized by the formation of a corona-like discharge propagating through water in the form of streamer channels. The second mode was formed typically above 500 Hz, when the formation of streamer channels in water was suppressed and all plasmas occurred inside a spheroidal aggregate of very fine gas bubbles surrounding the tip of the high-voltage electrode. The production of hydrogen peroxide, degradation of organic dye Acid Orange 7 (AO7) and inactivation of bacteria Escherichia coli by the discharge in water were studied under different discharge plasma modes in dependence on the pulse repetition rate of input power. The efficiency of both chemical and biocidal processes induced by the plasma in water decreased significantly with pulse repetition rates above 500 Hz.

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High Power DC Diaphragm Discharge Excited in a Vapor Bubble for the Treatment of Water

Plasma Chem. Plasma Proc. 33 (1): 83-95 (2013)
Lukes P., Clupek M., Babicky V., Spetlikova E., Sisrova I., Marsalkova E., Marsalek B.

Abstract: Novel apparatus for the generation of underwater plasma based on DC diaphragm discharge excited in a vapor bubble has been developed for decontamination and disinfection of conductive water. The apparatus allows deposition of relatively high applied power into the discharge (order of kW) and the treatment of a relatively large volume of liquid (order of L/min). The apparatus is operated at the quasi-pulse regime with self-terminating discharge pulses (with a repetition rate of 15–20 Hz) generated upon the formation of the vapor bubble inside the diaphragm (capillary) and its subsequent breakdown. The effects of input power, solution conductivity and the method of liquid flow through the reactor on the plasmachemical yield of H2O2 production and degradation of phenol have been determined. The biocidal effects of the apparatus were evaluated on inactivation of bacteria E. coli and E. faecalis suspended in aqueous NaCl solutions and on growth inhibition of the cyanobacterium Planktothrix sp. in natural lake water. The apparatus proved to be capable of efficiently reducing biological contamination in water, especially when operated in the plug-flow regime (up to a 5-log reduction in bacteria after 3 passes through the reactor). In the case of cyanobacteria, the growth inhibition further proceeded after exposure to the discharge and one pass of the biomass through the reactor was sufficient to reduce the algae in the water.

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Emission Spectra of a Pulse Needle-to-Plane Corona-like Discharge in Conductive Aqueous Solutions

Plasma Sources Sci. Technol. 21 (5): 055031 (2012)
Simek M., Clupek M., Babicky V., Lukes P., Sunka P.

Abstract: We explored basic optical and electrical characteristics of a positive corona-like discharge produced in conductive aqueous solutions by periodic high-voltage pulses. Emission spectra of the discharge were acquired in a needle-to-plate electrode geometry and analysed in the UV–vis–NIR spectral range with nanosecond time resolution for the solution conductivity of 100 and 500 µS/cm. The most important emission features are due to electronic excitation of HI, OI, OII and OH species. We found evidence of significant time-dependent line-shape broadening of selected HI and OI transitions. The observed broadening is attributed to the dynamic Stark and pressure broadening mechanisms and significantly increases with the aqueous solution conductivity. Electron densities were estimated by fitting a single Voigt peak function to the observed Hα profiles, and can reach as much as ne ≈ 4 × 1018 cm-3 (tD = 300 ns at 100 µS/cm solution conductivity) and ne ≈ 5 × 1018 cm-3 (tD = 1 µs at 500 µS/cm). Temporal evolution of the partially resolved rotational structure of the OH emission reaches a maximum during the discharge decay, with the onset significantly delayed with respect to the streamer ignition.

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Plasma Chemistry and Catalysis in Gases and Liquids

Wiley-VCH, Weinheim, Germany, ISBN: 978-3-527-33006-5 (2012)
Parvulescu V. I., Magureanu M. and Lukes P. (Eds.)

Book description: The book provides an overview of the basic principles of plasma-chemical and plasma-catalytic processes generated by electrical discharges in gas, liquid and gas/liquid environments, which is addressed by major experts in the fields of plasma physics, plasma chemistry and plasma catalysis. The book is divided into four major sections containing altogether 9 chapters that cover the state of the art of this topic in both fundamental and applied aspects.

BOOK'S TABLE OF CONTENT

Chapter 6: Elementary Chemical and Physical Phenomena in Electrical Discharge Plasma in Gas-Liquid Environments and in Liquids, p. 183-239

Chapter 7: Aqueous-Phase Chemistry of Electrical Discharge Plasma in Water and in Gas-Liquid Environments, p. 241-307

Chapter 8: Biological Effects of Electrical Discharge Plasma in Water and in Gas-Liquid Environments, p. 309-352

The Chapters 6-8 present a state-of-art fundamental and applied knowledge on plasma chemical processes associated with non-equilibrium plasma generated by electrical discharges in liquids and gas/liquid environments. In these chapters for the first time a comprehensive overview of the elementary chemical and physical phenomena in low-temperature plasma in liquid and gas/liquid environments is provided including fundamental mechanisms of plasma generation by electrical discharges in water and gas-liquid environments, chemistry and reaction kinetics of primary and secondary species generated by plasma in water and gas/liquid interfaces, mechanisms of interaction of plasma with chemical and biological content in water, plasma-catalytic processes in water and gas-liquid environments, and environmental and biomedical applications of plasma in water and gas-liquid environments.

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Generation of Focused Shock Waves in Water for Biomedical Applications

Plasma for Bio-Decontamination, Medicine and Food Security, Series NATO Science for Peace and Security Series – A: Chemistry and Biology, Chapter 31, (Eds. Z. Machala, K. Hensel, Y. Akishev), Springer, ISBN 978-94-007-2851-6, p. 403-416 (2012)
Lukes P., Sunka P., Hoffer P., Stelmashuk V., Benes J., Pouckova P., Zadinova M., Zeman J.

Abstract: The physical characteristics of focused two-successive (tandem) shock waves (FTSW) in water and their biological effects are presented. FTSW were ­generated by underwater multichannel electrical discharges in a highly conductive saline solution using two porous ceramic-coated cylindrical electrodes of different diameter and surface area. The primary cylindrical pressure wave generated at each composite electrode was focused by a metallic parabolic reflector to a common focal point to form two strong shock waves with a variable time delay between the waves. The pressure field and interaction between the first and the second shock waves at the focus were investigated using schlieren photography and polyvinylidene fluoride (PVDF) shock gauge sensors. The largest interaction was obtained for a time delay of 8–15 µs between the waves, producing an amplitude of the negative pressure phase of the second shock wave down to -80 MPa and a large number of cavitations at the focus. The biological effects of FTSW were demonstrated in vitro on damage to B16 melanoma cells, in vivo on targeted lesions in the thigh muscles of rabbits and on the growth delay of sarcoma tumors in Lewis rats treated in vivo by FTSW, compared to untreated controls.

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Biological Effects of Tandem Shock Waves Demonstrated on Magnetic Resonance

Bratislava Med. J. 113 (6): 335-338 (2012)
Benes J., Zeman J., Pouckova P., Zadinova M., Sunka P., Lukes P.

Abstract: The biological effects of the tandem shock waves generated by the new source on rats hepatic tissue and rabbit femoral muscle in vivo were studied in this work using magnetic resonance imaging. MR images showed tissue damage in focus. There was damage of the liver tissue, muscle and also stomach wall. We found that the tandem shock waves are able to damage the acoustically homogeneous soft tissue in the focus, i.e. in the depth. In tissues in front of the focus, there is, however, no damage.

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Discharge Filamentary Patterns Produced by Pulsed Corona Discharge at the Interface Between a Water Surface and Air

IEEE Trans. Plasma Sci. 39 (11): 2644-2645 (2011)
Lukes P., Clupek M., Babicky V.

Abstract: Pulsed corona discharge in atmospheric air was generated above a water surface using a reticulated vitreous carbon planar electrode. The effects of the discharge gap spacing and solution conductivity on the characteristics of the discharge were studied. Images of the discharge filamentary patterns propagating over the water surface are presented.

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The Catalytic Role of Tungsten Electrode Material in the Plasmachemical Activity of a Pulsed Corona Discharge in Water

Plasma Sources Sci. Technol. 20 (3): 034011 (2011)
Lukes P., Clupek M., Babicky V., Sisrova I., Janda V.

Abstract: The effects of tungsten material used as a high-voltage needle electrode on the production of hydrogen peroxide and the degradation of dimethylsulfoxide (DMSO) caused by a pulsed corona discharge in water were investigated. A reactor of needle–plate electrode geometry was used. The erosion of the tungsten electrodes by the discharge was evaluated. The yields of H2O2 production and the decomposition of DMSO by the discharge, which were obtained using the tungsten electrodes, were compared with those determined for titanium electrodes. The electrode erosion increased significantly with an increase in the solution conductivity. A large fraction (50–70%) of the eroded tungsten electrode material was released into the solution in dissolved form as tungstate WO42- ions. A correlation between the amount of eroded tungsten material released into the solution and the chemical effects induced by the discharge was determined. Lower yields of H2O2 and a higher degradation of DMSO by the discharge were obtained using the tungsten electrodes than were determined using titanium electrodes. Tungstate ions were shown to play a dominant role in the decomposition of H2O2, which was produced by the discharge using a tungsten electrode. The higher degradation of DMSO that was determined for tungsten was attributed to the tungstate-catalyzed oxidation of DMSO by H2O2, in addition to the oxidation of DMSO by OH radicals. Such a mechanism was supported by the detection of degradation by-products of DMSO (methanesulfonate, sulfate and dimethyl sulfone). The catalytic role of tungstate ions in the plasmachemical activity of the discharge generated using a tungsten electrode was also demonstrated on a pH-dependent decomposition of H2O2 and DMSO.

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Effects of Tandem Shock Waves Combined with Photosan and Cytostatics on the Growth of Tumours

Folia Biol.57 (6): 255-260 (2011)
Benes J., Pouckova P., Zeman J., Zadinova M., Sunka P., Lukes P., Kolarova H.

Abstract: Shock waves, pressure waves manifested as a sharp increase in positive pressure followed by a decrease and the negative part of the wave, are not only used to treat concrements in medicine. Recently, research has been focused on the possibility of their use for damaging the tumour tissue. In contrast to concrements, which are different from the surrounding tissue by their acoustic impedance, the tumour tissue has the same acoustic impedance as the surrounding soft tissue. Therefore, we have developed a new source of shock waves, which is based on the principle of multichannel discharge. This new source generates two successive shock waves (tandem shock waves). The first shock creates acoustic non-homogeneity and cavitations in the tissue, and the second shock is damped in it. In this work we demonstrated the effect of tandem shock waves on the muscle tissue in depth. The damage is shown on the images from the magnetic resonance imaging and histological sections. In the further part of the experiment, we investigated the in vivo effects of tandem shock waves in combination with Photosan and cisplatin on the tumour tissue. The application of tandem shock waves resulted in the inhibition of tumour growth, compared with controls, in both parts of the experiment. The largest inhibition effect was observed in the groups of tandem shock waves combined with Photosan and in the second part with cisplatin.

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The Role of Surface Chemistry at Ceramic/Electrolyte Intefaces in the Generation of Pulsed Corona Discharges in Water Using Porous Ceramic-Coated Rod Electrodes

Plasma Proc. Polym. 6 (11): 719-728 (2009)
Lukes P., Clupek M., Babicky V., Sunka P.

Abstract: Effects associated with the electrical breakdown of water using porous ceramic-coated rod electrodes were investigated for two types of ceramics, oxide (corundum) and silicates (almandine). Properties of the ceramic layer and its interaction with the electrolyte were found as important factors in the generation of electrical discharges in water. Initiation of the discharge depended not only on the permittivity and porosity of the ceramic, but also the surface charge formed on the ceramic, which was determined by the polarity of the applied voltage, and the pH and chemical composition of aqueous solution. An electrical double layer associated with the buildup of surface charge at ceramic/electrolyte interface affected the electric field distribution on the ceramic electrode. Using monopolar high voltage pulses, this layer became polarized, which, under certain experimental conditions, eventually quenched the electrical discharge in water. Applying bipolar pulses eliminated these effects.

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Pulsed Electrical Discharge in Water Generated Using Porous Ceramic Coated Electrodes

IEEE Trans. Plasma Sci. 36 (4): 1146-1147 (2008)
Lukes P., Clupek M., Babicky V., Sunka P.

Abstract: A special metallic electrode covered by a thin layer of porous ceramic prepared by the technology of thermal plasma spraying has been developed and used for generation of large volume non-thermal plasma in water. Images of multichannel pulsed electrical discharge generated in water at the composite electrode as a function of solution conductivity are presented.

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Ultraviolet Radiation from the Pulsed Corona Discharge in Water

Plasma Sources Sci. Technol. 17 (2): 024012 (2008)
Lukes P., Clupek M., Babicky V., Sunka P.

Abstract: Quantitative analysis of ultraviolet radiation from the pulsed corona discharge in water with needle-plate electrode geometry (~ 1-3 J/pulse) was performed using the potassium ferrioxalate actinometry. Photon flux J190-280 and radiant energy Q190-280 of the UV light emitted from the discharge at spectral region 190-280 nm was determined in dependence on the applied voltage (17-29 kV, positive polarity) and the solution conductivity (100-500 µS/cm). The intensity of the UV radiation strongly increased with increasing water conductivity and applied voltage. Depending on the applied voltage the determined photon flux varied by more than two orders in magnitude within the range of solution conductivities 100-500 µS/cm. It was found that photon flux from the discharge may be directly related to the discharge pulse mean power Pp as J190-280 = 44.33 Pp2.11 (quanta/pulse). A significant role of UV radiation in the production of hydrogen peroxide and bacterial inactivation by the corona discharge in water has been identified. As the solution conductivity increased the yield of H2O2 produced by the discharge decreased due to increasing photolysis of H2O2 accounting for up to 14% of the total decomposition rate of H2O2. As regards bactericidal effects, it was estimated that the UV radiation contributes about 30% to the overall inactivation of Escherichia coli.

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Hydrogen Peroxide Production in Capillary Underwater Discharges

Czech. J. Phys. 56 (Suppl. B): B1132-B1139 (2006)
De Baerdemaeker F., Simek M., Clupek M., Lukes P., Leys C.

Abstract: Hydrogen peroxide production by an AC driven capillary underwater discharge was investigated quantitatively. Concentration of formed hydrogen peroxide was measured by a colorimetric method using a specific reaction between H2O2 and a titanium reagent. It comes out. that the amount of H2O2 increases linearly during the first hour of the discharge duration and is slightly higher at the high voltage side of the capillary. The initial rate of H2O2 formation by the capillary discharge was therefore determined for initial electrical conductivity of aqueous solution in the range of 100-500 µS/cm. The initial rate of H2O2 formation increases with applied power at fixed initial conductivity of aqueous solution. Experiments performed at fixed applied power indicate that the initial conductivity appears to have only negligible effect on the initial rate of H2O2 formation.

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Erosion of Needle Electrodes in Pulsed Corona Discharge in Water

Czech. J. Phys. 56 (Suppl. B): B916-B924 (2006)
Lukes P., Clupek M., Babicky V., Sunka P., Skalny J.D., Stefecka M., Novak J., Malkova Z.

Abstract: Erosion of needle electrodes in the pulsed corona discharge in water with a pulse energy of ≈ 2–3 J was investigated in dependence on the electrode material (platinum, tungsten and stainless–steel) and the solution conductivity (100 and 500 µS/cm). Erosion of electrodes remarkable increased with the higher solution conductivity for all three tested metals. The highest erosion rates were determined for tungsten while platinum was the least eroded material. In addition to the dominant melting effect, release of anode material by the electrolysis significantly contributed to the total erosion of needle electrodes. The highest contribution of electrolysis was determined for stainless-steel electrodes that released up to 40–50% of eroded metal in the form of iron ions. Peculiar protrusions were observed on the surface of eroded tungsten electrodes.

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Plasmachemical Oxidation Processes in Hybrid Gas-Liquid Electrical Discharge Reactor

J. Phys. D: Appl. Phys. 38 (22): 4074-4081 (2005)
Lukes P., Locke B. R.

Abstract: Oxidation processes induced in water by pulsed electrical discharges generated simultaneously in the gas phase in close proximity to the water surface and directly in the liquid were investigated in a hybrid series gas-liquid electrical discharge reactor. The mechanism of phenol degradation was studied through its dependence on the gas phase and liquid phase compositions using pure argon and oxygen atmospheres above the liquid and different initial pH values in the aqueous solution. Phenol degradation was significantly enhanced in the hybrid-series reactor compared to the phenol removal by the single-liquid phase discharge reactor. Under an argon atmosphere the mechanism of phenol degradation was mainly caused by the electrophilic attack of OH· radicals produced by the liquid phase discharge directly in water and OH· radicals produced by the gas phase discharge at the gas-liquid interface. Under an oxygen atmosphere the formation of gaseous ozone dominated over the formation of OH· radicals, and the contribution of the gas phase discharge in this case was determined mainly by the dissolution of gaseous ozone into the water and its subsequent interaction with phenol. At high pH phenol was degraded, in addition to the direct attack by ozone, also through indirect reactions of OH· radicals formed via Peroxone process by the decomposition of dissolved ozone by hydrogen peroxide produced by the liquid phase discharge. Such mechanism was proved by the detection of cis,cis-muconic acid and pH-dependent degradation of phenol, which resulted in significantly higher removal of phenol from alkaline solution observed under oxygen atmosphere than in argon.

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Degradation of Substituted Phenols in a Hybrid Gas-Liquid Electrical Discharge Reactor

Ind. Eng. Chem. Res. 44 (9): 2921-2930 (2005)
Lukes P., Locke B. R.

Abstract: Nonthermal plasma-induced decomposition of ortho, meta, and para isomers of hydroxy-, chloro-, and nitrophenols in water was investigated using the hybrid series gas-liquid electrical discharge reactor that generates gas-phase discharge above the water surface simultaneously with the electrical discharge directly in the liquid. Degradation of substituted phenols was evaluated for two gas-phase compositions, pure argon and pure oxygen, above the aqueous solution. Removal of all phenols was found to follow first-order kinetics. Hydroquinone was the most reactive among substituted phenols under an oxygen atmosphere, whereas in argon the most reactive were 4-chlorophenol and 2-nitrophenol. Electrophilic attack by hydroxyl radicals and ozone were determined to be the main oxidation pathways for degradation of phenols in the hybrid series reactor under argon and oxygen atmospheres, respectively. Hydroxylated aromatic byproducts were identified during degradation of all substituted phenols under both gas-phase compositions. In addition, cis,cis-muconic acid was detected during degradation of catechol under an oxygen atmosphere. An electrophilic substitution reaction mechanism was also proved by the significant correlation between the relative rates of oxidation of substituted phenols obtained in the hybrid series reactor and the Hammett substituent constants. Dechlorination and denitration of chlorophenols and nitrophenols, respectively, corresponded typically to about 50% of total conversion of parent compounds.

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Degradation of Phenol by Underwater Pulsed Corona Discharge in Combination with TiO2 Photocatalysis

Res. Chem. Intermediat. 31 (4-6): 285-294 (2005)
Lukes P., Clupek M., Sunka P., Peterka F., Sano T., Negishi N., Matsuzawa S., Takeuchi K.

Abstract: Non-thermal plasma induced degradation of phenol by pulsed high voltage discharge generated in water using point to plane geometry of electrodes was investigated in the presence of photocatalytically active TiO2. The phenol removal attributed directly to the effects of plasma chemical activity of the discharge was enhanced in the presence of TiO2. At the same time, higher formation of 1,4-benzoquinone as the main primary aromatic by-product, and increased accumulation of hydrogen peroxide in the solution were found. The main effect of TiO2 addition was in the utilizing of ultraviolet radiation from the plasma resulting in the photocatalytical formation of OH radicals on the surface of TiO2 particles and, thus, in the increase of the yield of OH radicals available for phenol degradation.

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Generation of Ozone by Pulsed Corona Discharge over Water Surface in Hybrid Gas-Liquid Electrical Discharge Reactor

J. Phys. D: Appl. Phys. 38 (3): 409-416 (2005)
Lukes P., Clupek M., Babicky V., Janda V., Sunka P.

Abstract: Ozone formation by a pulse positive corona discharge generated in the gas phase between a planar high voltage electrode made from reticulated vitreous carbon and a water surface with an immersed ground stainless steel plate electrode was investigated under various operating conditions. The effects of gas flow rate (0.5–3 litre min-1), discharge gap spacing (2.5–10 mm), applied input power (2–45 W) and gas composition (oxygen containing argon or nitrogen) on ozone production were determined. Ozone concentration increased with increasing power input and with increasing discharge gap. The production of ozone was significantly affected by the presence of water vapour formed through vaporization of water at the gas–liquid interface by the action of the gas phase discharge. The highest energy efficiency for ozone production was obtained using high voltage pulses of approximately 150 ns duration in Ar/O2 mixtures with the maximum efficiency (energy yield) of 23 g/kWh for 40% argon content.

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Ozone Formation by Gaseous Corona Discharge Generated above Aqueous Solution

Czech. J. Phys. 54 (Suppl. C): C909-C913 (2004)
Lukes P., Clupek M., Babicky V., Sunka P.

Abstract: Production of ozone generated in oxygen by the gas phase discharge above aqueous solution was Studied for different applied pulse high voltage and discharge gap heights between gas phase high voltage electrode and water surface. The ozone production increased with higher gap and higher applied voltage, while the efficiency decreased with higher voltage for fixed gap height and increased with higher gap height. The appearance of the gas phase discharge occurring above the water significantly differed with the change of discharge gap height. The formation of ozone was affected by the presence of water vapor formed through the vaporization of water surface by the gas phase discharge, which was in direct contact with aqueous solution.

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Hydrogen Peroxide and Ozone Formation in Hybrid Gas-Liquid Electrical Discharge Reactors

IEEE Trans. Ind. Appl. 40 (1): 60-67 (2004)
Lukes P., Appleton A. T., Locke B. R.

Abstract: Ozone in the gas phase and hydrogen peroxide in the liquid phase were simultaneously formed in hybrid electrical discharge reactors, known as the hybrid-series and hybrid-parallel reactors, which utilize both gas phase nonthermal plasma formed above the water surface and direct liquid phase corona-like discharge in the water. In the series configuration the high voltage needle-point electrode is submerged and the ground electrode is placed in the gas phase above the water surface. The parallel configuration employs a high voltage. electrode in the gas phase and a high voltage needle-point electrode in the liquid phase with the ground electrode placed at the gas-liquid interface. In both hybrid reactors the gas phase concentration of ozone reached a power-dependent steady state, whereas the hybrid-parallel reactor produced a substantially larger amount of ozone than the hybrid series. Hydrogen peroxide was produced in both hybrid reactors at a similar rate to that of a single-phase liquid electrical discharge reactor. The resulting,concentration of H2O2 in the hybrid reactors, however, depended on the pH of the solution and the gas phase ozone concentration since H2O2 was decomposed by dissolved ozone at high pH.

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Potential Applications of Pulse Electrical Discharges in Water

Acta Phys. Slovaca 54 (2): 135-145 (2004)
Sunka P., Babicky V., Clupek M., Fuciman M., Lukes P., Simek M., Benes J., Locke B. R., Majcherova Z.

Abstract: High voltage pulse electrical discharges in water solutions have been studied using different geometries of electrodes. It was demonstrated that discharges in all electrode configurations used (needle - plate, coaxial composite anode - tubular cathode and coaxial pinhole anode tubular cathode) produce plasmas with very similar parameters. Plasma electron density depends strongly on the solution conductivity. Discharges in water have no counterpart in gas phase ones. The main chemically active specie produced by corona-like discharges is hydrogen peroxide, other species as H, O and OH radicals play a minor role. Degradation of phenol and decolorizing of organic dye "reactive blue 137" by OH radicals have been demonstrated. Corona-like discharges may find some applications in solution of environmental problems. At very high solution conductivity (5 - 20 mS/cm) multi-channel discharge with the composite anode generates strong acoustic waves. Focusing of the cylindrical pressure wave by parabolic metallic reflector and generation of spherically convergent wave has been demonstrated. Strong shock waves that lead to cavitation are formed at the focus region. Interaction of focused shock waves with cellular scale structures have been demonstrated. We believe that the focused shock waves will find some applications in medicine.

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Non-Thermal Plasma Induced Decomposition of 2-Chlorophenol in Water

Acta Phys. Slovaca 53 (6): 423-430 (2003)
Lukes P., Clupek M., Sunka P., Babicky V., Winterova G., Janda V.

Abstract: Application of non-thermal plasma produced by pulsed corona discharge in water for degradation of 2-chlorophenol has been investigated in reactor with the needle-plate geometry of electrodes. It was shown that decomposition of 2-chlorophenol by the discharge can be referred essentially to the oxidation by hydroxyl radical and it can be described by the first order kinetics. The complete removal of 500 µmol.l-1 2-chlorophenol by the discharge was attained in the presence of ferrous ions with the energy efficiency of 3.5×10-3 µmol.J-1. Chlorohydroquinone, chlorobenzoquinone, 3-chlorocatechol and catechol were detected as the primary decomposition products.

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Effect of Ceramic Composition on Pulse Discharge Induced Processes in Water Using Ceramic-Coated Wire to Cylinder Electrode System

Czech. J. Phys. 52 (Suppl. D): D800-D806 (2002)
Lukes P., Clupek M., Sunka P., Babicky V., Janda V.

Abstract: The formation of hydrogen peroxide and degradation of phenol by the pulsed high voltage discharge in water using ceramic-coated wire to cylinder electrode system were investigated for three different ceramic compositions of the discharge electrode (corundum, almandine and olivine). For corundum composite electrode the determined yield of H2O2 production and the phenol removal were similar to those obtained for the needle-plate reactor. For almandine and olivine composite electrodes the surface reactions induced by the discharge on the ceramic coating, especially dissolution, had a significant effect on the H2O2 production and phenol removal by the discharge. Iron(II) released from the almandine coating and pH and solution conductivity significantly increased when olivine ceramic was used.

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Water Treatment by Pulsed Streamer Corona Discharge

Ph.D. Dissertation, Institute of Plasma Physics: Prague (2001) ISBN: 80-902724-6-0
Lukes P.

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Summary: The main objective of this thesis was to study the production of ultraviolet light and hydrogen peroxide by the pulsed streamer corona discharge in water and to investigate the corona-induced degradation processes using phenol, 2-, 3- and 4-chlorophenol as model organic compounds. The emphasis has been mainly laid on the determination of factors affecting the yield of UV radiation and hydrogen peroxide and the role of H2O2 and UV light in degradation processes of the pulsed corona discharge. The key parts of the corona-induced degradation processes were the mechanism of degradation, removal efficiency and identity of the oxidation products of model compounds. Reactor with the point to plane geometry of electrodes developed in Institute of Plasma Physics of Academy of Sciences of the Czech Republic has been used to generate corona discharge in water.

It has been demonstrated that pulsed electrical discharges in water provide a promising alternative technique for the water and wastewater treatment especially of a low level of organic pollutants. It was observed that the principle reactive species involved in the breakdown process is hydroxyl radical. However, apart from OH· radicals it was shown that H2O2 and ultraviolet light, both produced by the discharge play an important role in the oxidation processes of the discharge as well. The rate of breakdown was strongly increased in the presence of iron due to catalytic formation of OH· radicals from decomposition of H2O2 by ferrous ions. Consequently, in higher conductivities of the solution it was observed that the photolysis of H2O2 caused by UV radiation emitted from the discharge significantly contributes to the efficiency of the breakdown process. The ultraviolet radiation emitted from the corona discharge strongly increased with the increasing solution conductivity. The production of H2O2 by the discharge depended mainly on the power input and the conductivity of the solution. It was inferred that the production of H2O2 could be separated into two parts: hydrogen peroxide production at a constant rate by a zero order process and its decomposition by breakdown processes. Hydroquinone, 1,4-benzoquinone, catechol and resorcinol were detected as primary phenol decomposition products. The chlorinated dihydroxybenzenes and quinones were detected as the main primary decomposition byproducts of monochlorophenols. In addition, chlorine free aromatic byproducts have been identified in minor amounts. The presence and position of chlorine atom relatively to OH strongly influenced the decomposition process. The initial degradation rate of 3-chlorophenol was the fastest, followed by 2-chlorophenol, 4-chlorophenol and phenol. A comparison between the pulsed corona discharge in the presence of iron and Fenton's process showed a higher efficiency of discharge process. On the other hand, estimated operating costs of the pulsed corona discharge process were much higher than of the Fenton's process.


Generation of Chemically Active Species by Electrical Discharges in Water

Plasma Sources Sci. Technol. 8 (2): 258-265 (1999)
Sunka P., Babicky V., Clupek, Lukes P., Simek M., Schmidt J., Cernak M.

Abstract: Pulse positive streamer corona discharges in water solution with a different conductivity have been investigated in reactors with the needle-plate and coaxial electrode geometry. A special composite anode was used in the coaxial geometry. With such an anode hundreds of streamers were generated at each voltage pulse. Production of H, O and OH radicals by the discharge was proved by emission spectroscopy and formation of H2O2 and degradation of phenol was demonstrated by chemical methods. Assuming that the broadening of the H alpha line profile was caused by the dynamic Stark effect, plasma with an electron density over 1018 cm-3 was generated during the initial phase of voltage pulse in the both reactors in spite of the very different electrode geometry and wave-forms of voltage pulses. Production of OH radicals was most effective at solution conductivity below 100 µS.cm-1.

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