Transient Spark Research Articles

Special issue: Plasma and Liquids

Special issue: Plasma and Liquids

Specificity of detection methods of nitrites and ozone in aqueous solutions activated by air plasma

Air transient spark (TS) discharge generates cold plasma, which is a rich source of reactive oxygen and nitrogen species (RONS). The gaseous products both in ambient air and air humidified by water electrospray (ES) are nitrogen oxides (NO and NO2). The rotational and vibrational temperatures determined by optical emission spectroscopy (OES) are lower with water ES through the discharge than in ambient air, which reduces the formation of NOx. The investigation of the specificity of Griess colorimetric assay for the detection of long‐lived nitrites in plasma activated solutions confirms its accuracy by comparison with ion chromatography (IC) and excludes possible interferences with hydrogen peroxide by using the enzyme catalase. Examination of the specificity of the Indigo blue assay for ozone detection shows strong interferences with the peroxynitrite chemistry. Phenol as the chemical probe confirms that the TS air discharge produces no aqueous ozone.

Effect Of Plasma Pen Treatment And Plasma Activated Medium (PAM) On Cancer And Normal Cells

Non-thermal atmospheric pressure plasma has recently found an ever growing use in medicine; including development of new cancer treatments. The most significant factor, produced by plasma that influence cancer cells are reactive oxygen and nitrogen species (RONS). RONS react with the surrounding air, cellular aqueous media and with cells themselves; however, the exact mechanism of their interaction with the cells is not yet fully understood. Some of the studies suggest that plasma is able to induce apoptosis in cancer cells and has a potential to selectively kill cancer cells without causing a major destruction of normal cells [1]. Plasma can be applied both directly on cell or tissues or indirectly – by plasma-activated medium (PAM). It is a cellular medium, which was treated by plasma and then applied onto the cells, so the cells interact only with RONS produced in PAM [2]. The aim of this study was to test in vitro the effect of plasma on cancer cells A375 (human melanoma epithelial cells) and normal cells HEK293T (human embryonic kidney cells). As a medium we used DMEM with 10% FBS. The first part focuses on direct treatment of cells by our design of air corona plasma pen [3,4]. In the second part, we evaluated the effect of PAM on the cells. We used discharges generated in atmospheric air, unlike the majority of plasma jets used for biomedical application that use rare gases (He, Ar). Cell viability was measured using the MTT test. In the first setup, cells were treated with the corona plasma multipen. The cells were placed in 96-well plate with 100μl of medium and the corona discharge operated in between the 8 pen needles and steel wire above the medium surface. Medium temperature did not exceed 34°C. The cell viability was measured after 24-hour incubation and it was evaluated in dependence on time of plasma treatment. Viability of both types of cells decreased with the time of plasma treatment with no selectivity on cancer cells. After 5 minutes of plasma treatment almost all cells were dead (> 95 %). In the second setup, the effect of PAM on cells was tested in various experimental setups aiming to find the most effective way of PAM production. We used transient spark or streamer corona discharges with different parameters in combination with electro-spraying of the used medium. The discharges were operated in between the high voltage needle and a grounded mesh. The cells viability was evaluated after 24- and 48-hour incubation. We investigated the cell viability dependence on time of plasma treatment, on the used discharge regime, treatment before and after FBS was added, and on the amount of PAM added to the cells. To conclude, cold plasma has the potential to be used in cancer treatment, because it can be used on live cells and tissues. The use of direct plasma is more technically demanding and still possible mainly in surface in vivo procedures, because endoscopic plasma application into the organism is more difficult to implement. Therefore the use of PAM seems to be perspective, since PAM can be prepared before and its in vivo application by injections is relatively easy.

Contribution to the Chemistry of Plasma-Activated Water

Plasma-activated water (PAW) was prepared by exposure to nonthermal plasma produced by a positive dc corona discharge in a transient spark regime. The activation of water was performed in atmosphere of various surrounding gases (air, nitrogen, carbon dioxide, and argon). This PAW retains its biological activity, measured on the mouse neuroblastoma cells culture, even after storage for more than one year. The highest hydrogen peroxide content was found for PAWs prepared in the atmospheres of argon or carbon dioxide, whereas the PAWs prepared in air and nitrogen exhibited lower hydrogen peroxide content. The acidity of PAWs mediated by nitric and nitrous acid formation displayed an opposite trend. It is concluded that the long-lasting biological effect of PAW is mediated by hydrogen peroxide in acid milieu only, whereas other possible active components decompose rapidly.

Comparing the biocidal properties of non-thermal plasma sources by reference protocol

The previously proposed reference protocol enabling easy comparison of biocidal properties of different non-thermal plasma sources has been followed and discussed. For inactivation tests the reference protocol has used spores of Gram positive bacterium Bacillus subtilis (ATCC 6633) deposited on a polycarbonate membrane as reference sample. In this work, biocidal properties of a negative glow corona, positive streamer corona, positive transient spark and cometary discharges are being compared in both open air and closed apparatus. Despite the total number of bacteria surviving 1 h exposure has decreased by up to 7 orders in closed apparatus, in open one, only weak inhibition bactericidal effect has been observed.

Influence of repetition frequency on streamer-to-spark breakdown mechanism in transient spark discharge

Streamer-to-spark transition in a self-pulsing positive transient spark (TS) discharge was investigated at different repetition frequencies. The temporal evolution of the TS was recorded, showing the primary streamer and the secondary streamer phases. A streak camera-like images were obtained using spatio-temporal reconstruction of the discharge emission detected by a photomultiplier tube with light collection system placed on a micrometric translation stage. With increasing TS repetition frequency f (from ~1 to 6 kHz), the increase of the propagation velocity of both the primary and the secondary streamer was observed. Acceleration of the primary and secondary streamers, and shortening of streamer-to-spark transition time τ with increasing f was attributed to the memory effect composed of pre-heating and gas composition changes induced by the previous TS pulses. Fast propagation of the secondary streamer through the entire gap and fast gas heating could explain the short τ (~100 ns) at f above ~3 kHz.

Nanosecond pulsed humid Ar plasma jet in air: shielding, discharge characteristics and atomic hydrogen production

Gas phase non-equilibrium plasmas jets containing water vapor are of growing interest for many applications. In this manuscript, we report a detailed study of an atmospheric pressure nanosecond pulsed Ar + 0.26% H2O plasma jet.The plasma jet operates in an atmospheric pressure air surrounding but is shielded with a coaxial argon flow to limit the air diffusion into the jet effluent core. The jet impinges on a metal plate electrode and produces a stable plasma filament (transient spark) between the needle electrode in the jet and the metal plate. The stable plasma filament is characterized by spatially and time resolved electrical and optical diagnostics. This includes Rayleigh scattering, Stark broadening of the hydrogen Balmer lines and two-photon absorption laser induced fluorescence (TaLIF) to obtain the gas temperature, the electron density and the atomic hydrogen density respectively. Electron densities and atomic hydrogen densities up to and have been measured. This shows that atomic hydrogen is one of the main species in high density Ar-H2O plasmas. The gas temperature does not exceed 550 K in the core of the plasma.To enable in situ calibration of the H TaLIF at atmospheric pressure a previously published O density calibration scheme is extended to include a correction for the line profiles by including overlap integrals as required by H TaLIF. The line width of H TaLIF, due to collision broadening has the same trend as the neutral density obtained by Rayleigh scattering. This suggests the possibility to use this technique to in situ probe neutral gas densities.

Cross-correlation spectroscopy study of the transient spark discharge in atmospheric pressure air

A streamer-to-spark transition in a self-pulsing transient spark (TS) discharge of positive polarity in air was investigated using cross-correlation spectroscopy. The entire temporal evolution of the TS was recorded for several spectral bands and lines: the second positive system of N2 (337.1 nm), the first negative system of (391.4 nm), and atomic oxygen (777.1 nm). The results enable the visualization of the different phases of discharge development including the primary streamer, the secondary streamer, and the transition to the spark. The spatio-temporal distribution of the reduced electric field strength during the primary streamer phase of the TS was determined and discussed. The transition from the streamer to the spark proceeds very fast within about 10 ns for the TS with a current pulse repetition rate in the range 8–10 kHz. This is attributed to memory effects, leading to a low net electron attachment rate and faster propagation of the secondary streamer. Gas heating, accumulation of species such as oxygen atoms from the previous TS pulses, as well as generation of charged particles by stepwise ionization seem to play important roles contributing to this fast streamer-to-spark transition.

Performance of Copper Electrode for Machining En-19 and Nickel Plated En-19 Alloy Steel by EDM

Electric discharge machining (EDM) is non-conventional machining processes that involves a transient spark discharges through the fluid due to the potential difference between the electrode and the work piece. The aim of this project is to determine the proper machining conditions for machining EN-19 and Nickel Plated EN-19 work pieces using electrical discharge machining (EDM). Basically, improper choice of parameter in EDM machine may result a few problems like the machine may cause of poor machining performance and it will decrease the accuracy of the products and incurs a lot of cost. The aim of this project is to determine the optimal machining parameters for machining work pieces using electrical discharge machining (EDM). Intensity of current, pulse on time and pulse of time were used as process parameters. This paper explores the characteristic of electric discharge machine (EDM) that is tool wear rate (TWR) and material removal rate (MRR) by using different workpiece materials namely En-19 and Nickel Plated En-19 alloy steel and copper as a tool material in order to increase the understanding of EDM processes. To achieve this project objective, an experimentation was done where the approach used was response surface methodology in which a well-designed experimental scheme named box behnken design was used to reduce the total number of experiments into 15 for each workpiece material. A second order empirical model is developed to predict the MRR and TWR. Finally ANOVA analysis is done to validate the model developed.

Surface chemistry of water-dispersed detonation nanodiamonds modified by atmospheric DC plasma afterglow

DC discharge afterglow cause rearrangement of oxygen and carbon moieties on asrec-DNDs while maintaining zeta-potential and opposite trend on O-DNDs.

Simulation of a spark ignited hydrogen engine for minimization of NOx emissions

A global kinetics based model is developed for a spark ignited single cylinder H2 engine for prediction of NO emissions, using mass and energy conservation equations. Based on literature experimental data, a transient spark energy delivery model is developed. A comprehensive heat transfer model is used which considers the heat losses by a combination of forced convection, conduction and natural convection using extended surfaces. It is shown that the major resistance to heat transfer in our setup is because of convective heat transfer from the cylinder to the coolant, with the in-cylinder heat transfer playing a relatively minor role. The model predicts the temporal variation of pressure and temperature profiles during the various strokes of the engine operation and their effect on the transient NO concentrations. It is shown that the exhaust NO concentrations depend not only on the peak in-cylinder temperatures, but also on the temporal variation of the in-cylinder temperature. A thermodynamically consistent rate expression for NO formation is used, which predicts a maximum in the in-cylinder NO concentration with time due to the decrease in temperatures during the power stroke and the reversible nature of NO formation. Using a kinetics based approach, the effect of various operating variables such as engine speed, equivalence ratio, compression ratio and spark advance on the NO emissions is predicted by the model, with results consistent with reported trends. It is shown that the NO emissions go through a maximum with engine speed and the range of engine speeds for which the NO emissions increase is broader for high equivalence ratios. The maximum in NO emissions with equivalence ratio and the increase in NO emissions with spark advance and compression ratio is predicted, which is in agreement with the literature. It is found that the equivalence ratio strongly affects the peak in-cylinder temperature, whereas the engine speed governs the amount of time available for NO formation. Consistent with reported data, the phenomenon of back-fire is predicted at high equivalence ratios. It is found that NO emissions are sensitive to compression ratio at high values of the compression ratio. Optimum values of the equivalence ratio and compression ratio are suggested to optimize the power output and NO emissions.

Study of transient spark discharge focused at NOx generation for biomedical applications

The paper is focused at nitrogen oxides generation by transient spark (TS) in atmospheric pressure air. The TS is a DC-driven self-pulsing discharge with short duration (∼⃒10-100 ns) high current pulses (>1A), with the repetition frequency 1-10 kHz. Thanks to the short spark duration, highly reactive non-equilibrium plasma is generated, producing ∼⃒300 ppm of NOx per input energy density 100 J.l-1. Further optimization of NO/NO2 production to improve the biomedical/antimicrobial effects is possible by modifying the electric circuit generating the TS.

Transient liquid phase spark plasma sintering of B4C-based ceramics using Ti-Al intermetallics as sintering aid

Fully-dense B4C-based ceramics were fabricated using Ti-Al intermetallics as sintering aid by Spark Plasma Sintering at a low temperature of 1700°C whilst applying 32MPa uniaxial pressure. The influence of the intermetallic additions on the phase composition, morphology and mechanical properties of the ceramics were investigated. The intermetallics flowed and react with B4C to form a three-phase composite containing B4C, TiB2 and Al4C3 during the transient liquid phase sintering process. The TiB2 and Al4C3 particles were located on the boundaries between B4C grains and effectively inhibited the growth of B4C, which improved the mechanical properties. Good bonding between B4C and the phases formed was confirmed by TEM analysis. The specimens with 5wt.% Ti-Al provide an attractive combination of homogeneous morphology and excellent mechanical properties, including a Vickers hardness of 33.5±0.4GPa, a flexural strength of 506±16MPa and a fracture toughness of 5.5±0.1MPam0.5.

Generation of Antimicrobial NOx by Atmospheric Air Transient Spark Discharge

Atmospheric pressure air plasma discharges generate potential antimicrobial agents, such as nitrogen oxides and ozone. Generation of nitrogen oxides was studied in a DC-driven self-pulsing (1–10 kHz) transient spark (TS) discharge. The precursors of NOx production and the TS characteristics were studied by nanosecond time-resolved optical diagnostics: a photomultiplier module and a spectrometer coupled with fast intensified camera. Thanks to the short (~10–100 ns) high current (>1 A) spark current pulses, highly reactive non-equilibrium plasma is generated. Ozone was not detectable in the TS, probably due to higher gas temperature after the short spark current pulses, but the NOx production rate of ~7 × 1016 molecules/J was achieved. The NO2/NO ratio decreased with increasing TS repetition frequency, which is related to the complex frequency-dependent discharge properties and thus changing NO2/NO generating mechanisms. Further optimization of NO2 and NO production to improve the biomedical and antimicrobial effects is possible by modifying the electric circuit generating the TS discharge.

Study of Transient Spark Discharge Properties Using Kinetic Modeling

The kinetic model simulating plasma chemistry induced by Transient Spark (TS) discharge in air is presented in this paper. TS is a dc-driven self-pulsing discharge of streamer-to-spark transition type. The presented kinetic model defines the temporal evolution of reduced electric field strength $E/N$ , gas temperature, and density of neutrals $N$ during the evolution of TS discharge, so that calculated electron density is in agreement with experimental results. We studied the mechanism of the streamer-to-spark transition and breakdown in TS using this model. We assume that the breakdown mechanism in TS is based on the gas density decrease and can be summarized as follows: heating of the channel $\rightarrow $ increase in the pressure $\rightarrow $ hydrodynamic expansion $\rightarrow $ decrease in $N$ in the core of the channel $\rightarrow $ increase in $E/N~\rightarrow $ 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. A lower density of O2 means a lower rate of electron attachment, while accumulated atomic oxygen atoms lead to acceleration of electron detachment processes.

Effects of air transient spark discharge and helium plasma jet on water, bacteria, cells, and biomolecules.

Atmospheric pressure DC-driven self-pulsing transient spark (TS) discharge operated in air and pulse-driven dielectric barrier discharge plasma jet (PJ) operated in helium in contact with water solutions were used for inducing chemical effects in water solutions, and the treatment of bacteria (Escherichia coli), mammalian cells (Vero line normal cells, HeLa line cancerous cells), deoxyribonucleic acid (dsDNA), and protein (bovine serum albumin). Two different methods of water solution supply were used in the TS: water electrode system and water spray system. The effects of both TS systems and the PJ were compared, as well as a direct exposure of the solution to the discharge with an indirect exposure to the discharge activated gas flow. The chemical analysis of water solutions was performed by using colorimetric methods of UV-VIS absorption spectrophotometry. The bactericidal effects of the discharges on bacteria were evaluated by standard microbiological plate count method. Viability, apoptosis and cell cycle were assessed in normal and cancerous cells. Viability of cells was evaluated by trypan blue exclusion test, apoptosis by Annexin V-FITC/propidium iodide assay, and cell cycle progression by propidium iodide/RNase test. The effect of the discharges on deoxyribonucleic acid and protein were evaluated by fluorescence and UV absorption spectroscopy. The results of bacterial and mammalian cell viability, apoptosis, and cell cycle clearly show that cold plasma can inactivate bacteria and selectively target cancerous cells, which is very important for possible future development of new plasma therapeutic strategies in biomedicine. The authors found that all investigated bio-effects were stronger with the air TS discharge than with the He PJ, even in indirect exposure.

Self-pulsing discharges in pre-heated air at atmospheric pressure

The paper presents investigations of self-pulsing discharges in atmospheric pressure air pre-heated to 300–1000 K. Despite using a direct-current power supply, two self-pulsing discharge regimes, a repetitive transient spark (TS) and a repetitive streamer (RS) were generated. The pulse repetition frequency, on the order of a few kHz, can be controlled by adjusting the generator voltage. The TS is a discharge initiated by a streamer, followed by a short (tens of ns) spark current pulse (∼ 1 A), associated with the total discharging of the internal capacity of the electric circuit. The TS is suitable for the study of ‘memory’ effects (pre-heating, pre-ionization) on the mechanisms of streamer-to-spark transition and electrical breakdown in atmospheric pressure air. The TS regime was stable below ∼600 K. Above ∼600 K, a stable repetitive streamer (RS) regime was observed. In this regime, the breakdown and spark did not occur. After the initial streamer, the internal capacity of the electrical circuit discharged partially. With further pre-heating of the gas, the stable TS appeared again at ∼1000 K.

Measurement of the electron density in Transient Spark discharge

This paper presents our measurements of the electron density in a streamer-to-spark transition discharge, which is named transient spark (TS), in atmospheric pressure air. Despite the dc applied voltage, TS has a pulsed character with short (∼10–100 ns) high current (>1 A) pulses, with a repetition frequency on the order of kHz. The electron density ne ∼ 1017 cm−3 at maximum is reached in TS with repetition frequencies below ∼3 kHz, using relatively low power delivered to the plasma (0.2–3 W).The temporal evolution of ne was estimated from the resistance of the plasma discharge, which was obtained by a detailed analysis of the electric circuit representing the TS and the discharge diameter measurements using a fast intensified charge-coupled device (iCCD) camera. This estimate was compared with ne calculated from the measured Stark broadening of several atomic lines: Hα, N at 746 nm, and O triplet at 777 nm. Good agreement was obtained, although the method based on the plasma resistance is sensitive to an accurate determination of the discharge diameter. We have found that this method is also limited for strongly ionized plasmas. On the other hand, a lower ne detection limit can be obtained by this method than from the Stark broadening of atomic lines.

Abstract 321: Obesity Causes Enhanced Sensitivity Of The Mitochondrial Permeability Transition Pore

Several mechanisms have been implicated in heart failure (HF) development due to obesity, including altered Ca2+ homeostasis and mitochondrial increased reactive oxygen species (ROS). Besides their metabolic role, mitochondria are important cell death regulators, since their disruption induces apoptosis. The mitochondrial permeability transition pore (MPTP) formation is key in this process. Ca2+ and ROS are known inducers of MPTP, and mitochondria are the main ROS generators. However, it has not been demonstrated that MPTP formation is involved in cardiac cell death due to obesity. Therefore, the aim of this work was to determine whether Ca2+ alterations and/or MPTP opening underlie cardiac dysfunction. We used obese Zucker fa/fa rats (32 weeks old), displaying concentric hypertrophy and cardiac dysfunction. We measured: i) Systolic and diastolic Ca2+ signaling in isolated myocytes, in basal conditions and upon β-adrenergic stimulation (β-AS), and ii) in vitro mitochondrial function: respiration, ROS production and MPTP opening. We found that the main alteration in Ca2+ signaling in fa/fa myocytes was a decrease in SERCA Ca2+ removal capacity, since Ca2+ transient amplitude and spark frequency were unchanged. Furthermore, in fa/fa myocytes, β-AS response was preserved. On the other hand, fa/fa mitochondria respiration, in state 3 decreased, but was unchanged in state 4, when glutamate/malate were used as substrate, resulting in an small decrease in respiratory control. In addition, fa/fa mitochondria were more sensitive to MPTP opening, induced by Ca2+ and carboxyatractiloside (CAT). Moreover, fa/fa mitochondria showed increased H2O2 production, and in exposed thiol groups in the adenine nucleotide translocase, a regulatory MPTP component. Since Ca2+ signaling is relatively normal in fa/fa cells, it does not seem to be the main contributor to the cardiac contractile dysfunction. However, given that fa/fa mitochondria showed decrease respiratory performance, were more susceptible to MPTP opening, and showed enhanced H2O2 production. We conclude that fa/fa mitochondria were more vulnerable to enhanced oxidative stress, causing MPTP opening, which could be exacerbated by SERCA slower Ca2+ removal capacity, leading to myocyte apoptosis.

Time-resolved ion density determination by electrical current measurements in an atmospheric-pressure argon plasma

High-resolution current signal measurements of a self-pulsing transient spark discharge revealed oscillations in the pulse decay phase. These oscillations appear with decreasing frequency between 250 MHz and 50 MHz for a specific gas flow range. The frequencies are well within the range of the plasma ion frequency. Consequently, ion acoustic waves are discussed as a possible reason. Considering molecular argon ions as the dominant ion, densities are found to decrease from to . Evaluation of the plasma ion frequency creates a new possibility to determine ion densities.