Interaction of Atmospheric Pressure Plasma Jets with Liquids

In this work, the interaction of atmospheric pressure plasmas with liquids is investigated. On the exampleof hydrogen peroxide, generation and transport mechanisms are studied from the plasma to the gas- andliquid phase. Interaction with the ambient surroundings is investigated and effects of nitrogen and oxygenspecies on the plasma dynamics a well as on the reactive species generation in the liquid phase arediscusse

The spatial distribution of HO2in an atmospheric pressure plasma jet investigated by cavity ring-down spectroscopy

Cold atmospheric pressure plasma jets make important contributions to a range of fields, such as materials processing and plasma medicine. In order to optimise the effect of those plasma sources, a detailed understanding of the chemical reaction networks is pivotal. However, the small diameter of plasma jets makes diagnostics challenging. A promising approach to obtain absolute number densities is the utilisation of cavity-enhanced absorption spectroscopy methods, by which line-of-sight averaged densities are determined. Here, we present first measurements on how the spatial distribution of HO2 in the effluent of a cold atmospheric pressure plasma jet can be obtained by cavity ring-down spectroscopy in an efficient way. Instead of recording fully wavelength resolved spectra, we will demonstrate that it is sufficient to measure the absorption coefficient at two wavelengths, corresponding to the laser being on and off the molecular resonance. By sampling the effluent from the 1.6 mm diameter nozzle in the radial direction at various axial positions, we determined that the distances over which the HO2 density was distributed were (3.9 ± 0.5) mm and (6.7 ± 0.1) mm at a distance of 2 mm and 10 mm below the nozzle of the plasma jet, respectively. We performed an Abel inversion in order to obtain the spatial distribution of HO2 that is presented along the symmetry axis of the effluent. Based on that localised density, which was (4.8 ± 0.6) ⋅ 1014 cm-3 at the maximum, we will discuss the importance of the plasma zone for the production of HO2

Reproducibility of `COST Reference Microplasma Jets'

Atmospheric pressure plasmas have been ground-breaking for plasma science and technologies, due to their significant application potential in many fields, including medicinal, biological, and environmental applications. This is predominantly due to their efficient production and delivery of chemically reactive species under ambient conditions. One of the challenges in progressing the field is comparing plasma sources and results across the community and the literature. To address this a reference plasma source was established during the `Biomedical Applications of Atmospheric Pressure Plasmas' EU COST Action MP1101. It is crucial that reference sources are reproducible. Here, we present the reproducibility and variance across multiple sources through examining various characteristics, including: absolute atomic oxygen densities, absolute ozone densities, electrical characteristics, optical emission spectroscopy, temperature measurements, and bactericidal activity. The measurements demonstrate that the tested COST jets are mainly reproducible within the intrinsic uncertainty of each measurement technique

Atmospheric pressure streamer follows the turbulent argon air boundary in a MHz argon plasma jet investigated by OH-tracer PLIF spectroscopy

International audienceAn open question in the research of the dynamics of non-equilibrium cold atmospheric pressure plasma\\n jets is the influence of ambient species on streamer propagation pathways. In the present work, by\\n means of planar laser-induced fluorescence (PLIF), an atmospheric pressure argon plasma jet is\\n investigated in a laminar and turbulent gas flow regime. The flow pattern is investigated with\\n plasma on and plasma off. It is shown that in turbulent mode, the streamer path changes according to\\n the flow pattern changes and the resulting changes in air abundance. From a comparison of an\\n analytical diffusion calculation and LIF measurements, the air impurity boundary is determined. Most\\n importantly, the origin of the streamer pathway is investigated in detail, by recording the flow\\n pattern from OH-PLIF measurements and simultaneously measuring the streamer path by an overlay\\n technique through emission measurements. It is shown that the streamer path is correlated to the\\n turbulent flow pattern

The Influence of Feed Gas Humidity Versus Ambient Humidity on Atmospheric Pressure Plasma Jet-Effluent Chemistry and Skin Cell Viability

The influence of ambient air species especially humidity is an ever-present challenge for atmospheric pressure plasma jet applications. Especially, where the plasma-induced effects are extremely sensitive to humidity, such as in the field of plasma medicine, an understanding of the influence of ambient species diffusion on plasma chemistry and on reactive component composition is crucial. In this paper, we investigate the influence of ambient humidity versus feed gas humidity on the production of reactive components by atmospheric pressure plasma jets. By the use of a shielding gas curtain, we control the surrounding atmosphere around the active effluent region of the investigated argon RF-plasma jet (kinpen) and control the gas humidity of the ambient gas. By quantum cascade laser absorption spectroscopy and by Fourier transformed infrared (IR) absorption spectroscopy, the effect of diffusing surrounding molecular species on the chemistry of the long-living reactive oxygen species is investigated. Mechanisms of H2O2and O3production are studied. In this paper, we have quantified the influence that ambient species, namely, water molecules, have on the reactive species' generation in the gas phase. It is shown that the effect of ambient humidity is important for the long-living species production, feed gas humidity, however, has the much stronger effect. Finally, with the focus of applications in plasma medicine, the cell viability of human skin cells (HaCaT keratinocytes) as a function of feed gas and ambient gas humidity is compared

Detection of ozone in a MHz argon plasma bullet jet

International audienceThis study for the first time confirms the presence of plasma bullets in a MHz argon atmospheric pressure plasma jet. Bullet characteristics are investigated by phase-resolved optical emission measurements. Regarding the jet's reactive component output, its ozone production rates are investigated by two independent diagnostic techniques yielding complementary results. The first method - UV-absorption spectroscopy in the Hartley band - determines space-resolved distribution of the ozone concentration in the jet effluent. The second method - quantum cascade laser-absorption spectroscopy in the mid-infrared spectral region - yields high sensitivity results of the average ozone concentration in a multipass cell, in which the effluent is directed. The results of both diagnostic techniques show excellent agreement. © 2012 IOP Publishing Ltd

Tracking plasma generated H2O2 from gas into liquid phase and revealing its dominant impact on human skin cells

The pathway of the biologically active molecule hydrogen peroxide (H 2O2) from the plasma generation in the gas phase by an atmospheric pressure argon plasma jet, to its transition into the liquid phase and finally to its inhibiting effect on human skin cells is investigated for different feed gas humidity settings. Gas phase diagnostics like Fourier transformed infrared spectroscopy and laser induced fluorescence spectroscopy on hydroxyl radicals (•OH) are combined with liquid analytics such as chemical assays and electron paramagnetic resonance spectroscopy. Furthermore, the viability of human skin cells is measured by Alamar Bluel assay. By comparing the gas phase results with chemical simulations in the far field, H2O2 generation and destruction processes are clearly identified. The net production rate of H2O2 in the gas phase is almost identical to the H2O2 net production rate in the liquid phase. Moreover, by mimicking the H2O2 generation of the plasma jet with the help of an H2O2 bubbler it is concluded that the solubility of gas phase H2O 2 plays a major role in generating hydrogen peroxide in the liquid. Furthermore, it is shown that H2O2 concentration correlates remarkably well with the cell viability. Other species in the liquid like •OH or superoxide anion radical do not vary significantly with feed gas humidity. © 2014 IOP Publishing Ltd