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 H 2 O 2 and O 3 production 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.
We here demonstrate the potentialities of pigtailed electrooptic probes to perform vectorial electric field characterizations of dielectric barrier discharges (DBDs). The analysis leads to the ...accurate determination of the breakdown voltage and the associated electric field in the vicinity of the discharge. A polarimetric analysis of the DBDs is proposed due to real-time measurement of longitudinal and radial components of the electric field vector. Moreover, the transition from capacitive to resistive behavior is characterized at the breakdown field.
This paper presents a combined 2D numerical and experimental study of the influence of N$_2$ admixture on the dynamics of a He–N$_2$ discharge in the 10 cm long dielectric tube of a plasma gun setup. ...First, the comparison between experiments and simulations is carried out on the ionization front propagation velocity in the tube. The importance of taking into account a detailed kinetic scheme for the He–N$_2$ mixture in the simulations to obtain a good agreement with the experiments is put forward. For the μs driven plasma gun, the two-and three-body Penning reactions occurring in the plasma column behind the ionization front, are shown to play a key role on the discharge dynamics. In the experiments and simulations, the significant influence of the amplitude of the applied voltage on the ionization front propagation velocity is observed. As the amount of N$_2$ varies, simulation results show that the ionization front velocity, depends on a complex coupling between the kinetics of the discharge, the photoionization and the 2D structure of the discharge in the tube. Finally, the time evolution of axial and radial components of the electric field measured by an electro-optic probe set outside the tube are compared with simulation results. A good agreement is obtained on both components of the electric field. In the tube, simulations show that the magnitude of the axial electric field on the discharge axis depends weakly on the amount of N 2 conversely to the magnitude of the off-axis peak electric field. Both, simulations and first measurements in the tube or within the plasma plume show peak electric fields of the order of 45 kV·cm$^{−1}$ .
Atmospheric pressure plasmas are widely used in research for biomedical or clinical applications. Reactive oxygen species and reactive nitrogen species (RNS) produced by plasmas are thought to be of ...major significance in plasma-cell interactions. Different applications, however, may demand for different plasma properties. Tailoring plasma devices by modulating the supply gas or the surrounding is a suitable way to alter reactive species composition, vacuum ultra violet emission, or temperature. Treatment regimens involving availability of oxygen or humidity may lead to increased hydrogen peroxide deposition in liquids and thus will be toxic to cells. Using an atmospheric pressure argon plasma jet, we applied a nitrogen gas curtain to its visible effluent during treatment of human immune cells. The curtain deprived the plasma of molecular oxygen. This excluded gas-phase oxygen plasma chemistry and led to generation of highly energetic metastables. Planar laser-induced fluorescence spectroscopy verified laminar gas flow and complete elimination of surrounding air by the gas curtain. We used human immune cells to monitor cytotoxic effects as they are highly relevant in potential clinical plasma applications, e.g., treatment of chronic wounds. Air curtain plasma treatment led to significantly higher cytotoxicity compared with nitrogen curtain plasma treatment. Scavenging of hydrogen peroxide abrogated cell death in both gas curtain conditions. This indicated a negligible contribution of highly energetic metastables or increased gas temperature to cytotoxicity. Finally, the results suggested an oxygen-independent generation of hydrogen peroxide pointing to an indirect role of UV or RNS in plasma-mediated cytotoxicity.
This paper focuses on the use of an electro-optic (EO) probe for the spatially and temporally resolved characterization of the electric field (E-field) associated with guided ionization waves—or ...guided streamers—propagating at atmospheric pressure. An AC high-voltage power supply (6 kV at 18 kHz) is used to generate guided ionization waves in helium with a cold atmospheric pressure plasma jet device (APPJ). The capabilities of this electro-optic technique are investigated with and without the discharge. This innovative technology will use to carry out the optical polarimetric analysis of the APPJ with simultaneous real-time measurement of longitudinal and radial components of the electric field vector. Last but not least, an application-based case study of the ionization waves propagating and interacting with the EO probe—being a solid dielectric target—is also reported. The results will bring realistic information on the potential perturbation induced by the EO probe itself on the E-field characterization at the macroscopic scale.
Graphic abstract
Parameter studies of plasma treatment are informative about the optimal use of this technology in biomedical applications such as the argon radio-frequency plasma jet kINPen. However, the ...interdependence of the plasma-dissipated power in relation to input current and feed gas modulation on the resulting biological consequences has not been studied so far. To this end, a parameter study is presented, and the effect on human immune cell viability was investigated across different input current power and argon with oxygen/nitrogen feed gas admixture settings. It was found that with both nitrogen and oxygen admixtures, a concentration-dependent change in plasma-dissipated power emerged, which converged at 27.5 and 26.5 mA, respectively. The extent of cytotoxicity in immune cells confirmed the relevance of these findings, which were in congruency with the plasma-dissipated powers identified. These findings underline the critical role and input parameter-dependent action of plasma sources for biomedical application.
Abstract
The electric field is a fundamental parameter for plasma sources and devices. Its knowledge is a dominant setscrew for many processes such as controllable fluxes and energies of charged ...particles onto surfaces and for the electron energy distribution function. However, experimental data of electric field strengths in micro-structured surface dielectric barrier discharges are rare. Due to geometric configurations and dimensions in micrometer scale, probe-based investigations are challenging. To tackle these issues, we exploit the optical access into micro cavities of a plasma array operated with pure helium to use the Stark effect of the allowed 492.19 nm
(
D
1
↦
P
0
1
)
and forbidden 492.06 nm helium line
(
F
0
1
↦
P
0
1
)
. Based on it, we present spatially-integrated and time-resolved electric field strengths in a range between 20 kV cm
−1
and 60 kV cm
−1
depending on various parameters such as cavity diameters in 100
μ
m range and excitation properties. The obtained electric fields can be controlled just by bipolarity of applied voltage and show a good agreement to previous simulated field strengths in pore and silicon-based devices. As expected from simulation dealing with discharges in pores, a smaller cavity dimension yields higher electric field strengths. Due to these high electric fields and the option of this plasma source to easily integrate a catalyst in the discharge volume, this micro cavity plasma array promises further insights into plasma-enhanced catalysis.
In this work, quantum cascade laser (QCL) absorption spectroscopy was used to investigate the nitric dioxide (NO2) production dynamics at ambient conditions. For the first time, QCL detection of NO2 ...and NO was used at ambient conditions in order to remain close to the conditions that are present in the application of plasma jets in open atmosphere. For the investigations, the plasma jet was placed inside an open multi-pass cell. The detection limit of the setup was 20 ppb for NO2 and similar for nitric oxide (NO). Since the effective production of NO was below the detection limit, further investigations of the NO density were performed with optical emission spectroscopy.
An open question in the research of the dynamics of non-equilibrium cold atmospheric pressure plasma jets is the influence of ambient species on streamer propagation pathways. In the present work, by ...means of planar laser-induced fluorescence (PLIF), an atmospheric pressure argon plasma jet is investigated in a laminar and turbulent gas flow regime. The flow pattern is investigated with plasma on and plasma off. It is shown that in turbulent mode, the streamer path changes according to the flow pattern changes and the resulting changes in air abundance. From a comparison of an analytical diffusion calculation and LIF measurements, the air impurity boundary is determined. Most importantly, the origin of the streamer pathway is investigated in detail, by recording the flow pattern from OH-PLIF measurements and simultaneously measuring the streamer path by an overlay technique through emission measurements. It is shown that the streamer path is correlated to the turbulent flow pattern.
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