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The development of atmospheric pressure helium plasma jet from dielectric barrier discharge (DBD) under different ground electrodes and applied voltages is investigated by experiment and numerical simulation. The distribution of helium metastable atoms, electron density, electron temperature, surface charges, electric potential, and space charges during the development of the plasma jet are calculated. It is shown that the plasma jet can only form when the ground-electrode width is small enough so that the electric field outer side of the ground electrode is larger than a critical value. The length, the current peak, and the propagating velocity of the plasma jet decrease at increasing ground-electrode width, while the critical voltage for plasma jet forming outside the ground electrode and the current peak of the DBD increase. The time-resolved images of emission around 337.1 nm and 706.5 nm show that electrons of high energy exist in front of the discharge towards the cathode and of the outside plasma jet, while those of low energy exist in the whole discharge area. The formation and propagation of the plasma jet can be controlled by the operating conditions of the DBD. [ABSTRACT FROM AUTHOR]

Atmospheric pressure plasma jet (APPJ) has recently been the focus of cytoprotective research due to the physiological roles of ROS and RNS. In the current study, we investigated the effect of APPJ treatment on the hypoxia (1% oxygen) induced cell injuries. SH-SY5Y cells were treated by APPJ for different duration and incubated in normoxic condition (20% oxygen) for 5 h followed by 24 h hypoxia treatment. Cell viability was evaluated by lactate dehydrogenase (LDH) release and further monitored using the electric cell-substrate impedance sensing (ECIS) system after APPJ treatment. Results showed that APPJ could reduce cell injuries after 24 h hypoxia, which was consistent with the ECIS results. Furthermore, extracellular NO and H2O2 production was significantly increased with the APPJ treatment. It was also interesting to find that APPJ treatment reduced SH-SY5Y cells proliferation in the hypoxic microenvironment during the first 20 h of hypoxia. Although more work was still need to clarify whether the cell viability maintenance was related to the cell proliferation during hypoxia, our results provide the first evidence of real-time cell viability changes after APPJ treatment under both normoxic and hypoxic conditions, which could provide evidence for the neuroprotective applications of APPJ. [ABSTRACT FROM AUTHOR]

Conductive solid material sampling by micro-plasma under ambient atmosphere was studied experimentally. A high-voltage pulse generator was utilized to drive discharge between a tungsten needle and metal samples. The effects of pulse width on discharge, micro-plasma and sampling were investigated. The electrical results show that two discharge current pulses can be formed in one voltage pulse. The duration of the first current pulse is of the order of 100 ns. The duration of the second current pulse depends on the width of the voltage pulse. The electrical results also show that arc micro-plasma was generated during both current pulses. The results of the emission spectra of different sampled materials indicate that the relative emission intensity of elemental metal ions will increase with pulse width. The excitation temperature and electron density of the arc micro-plasmas increase with the voltage pulse width, which contributes to the increase of relative emission intensity of metal ions. The optical images and energy dispersive spectroscopy results of the sampling spots on metal surfaces indicate that discharge with a short voltage pulse can generate a small sputtering crater. [ABSTRACT FROM AUTHOR]

In this paper, we report on the investigation on filament interaction and pattern evolution in glow DBD regime by using a fluid model. The aim is to find the leading mechanism controlling the filamentary dynamic behaviors. Space-charge and voltage (or surface-charge) fluctuations are introduced into the discharge space to trigger initial non-uniformity of glow DBDs. Filamentary dynamic behaviors of generation and annihilation, merging and splitting, and attraction and repulsion are observed in interaction and evolution process under both kinds of fluctuations. It is found that, localized lateral electric field and its induced electron-focusing effect (EFE) should be the controlling mechanism, which is significantly influenced by discharge intensity, filament diameter and distance. If neighboring discharge channels connect or partially overlap with each other, they will attract and merge under the combined effect of lateral bi-diffusion and EFE. The fluid model and a dynamic model based on voltage transfer character are compared from basic physics and reach good unification. [ABSTRACT FROM AUTHOR]

Trichel pulse of negative corona discharge in atmospheric air is investigated numerically using a 2D fluid model. The model consists of a hyperbolic cathode tip and a plane anode, and considers 11 kinds of particles and the most important interactions among them. The spatio-temporal evolution of charged species and the electric field are evaluated during the pulse process. During the pulse rising edge, the positive ions accumulate ahead of the tip forming the temporal cathode sheath, significantly enhancing the local field. In the pulse decay edge, the temporal sheath collapses and the discharge falls back to a low-current mode. In the pulse interval, the discharge does not cease but sustains weakly until the next pulse. The location of the temporal sheath is independent of the averaged value during the Trichel pulse regime and also the same with that in a normal glow regime, which determines a nearly constant pulse rising time at given configurations. However, a smaller tip radius will lead to their decrease. The effect of negative ions on the pulse process is studied by adjusting the attachment rates. It indicates that the negative ions are actually not necessary in the Trichel pulse process, but will influence the pulse waveform significantly. [ABSTRACT FROM AUTHOR]

The modulation of absorption manner in helicon discharge by changing the profile of low axial magnetic field is explored experimentally in this work. The experiments are carried out in Boswell-type antenna driven by 13.56-MHz power source in 0.35-Pa argon environment. The peak of the external non-uniform magnetic field (Bex) along the axis is observed in a range from 0 Gs to 250 Gs (1 Gs = 10–4 T), where the electron density varies from 0.5 × 1016 m–3 to 9 × 1016 m–3. When Bex is located near the tube upper end sealed by a dielectric plate, or near the tube bottom end connected with a diffusion chamber, the plasmas are centralized in the tube in the former case while the strong luminance appears between the edge of the tube and the axial line in the latter case. When Bex is located in the middle of the antenna, moreover, an effective resistance (Reff) peak appears apparently with increasing magnetic field. The glow moves toward first the edge of the tube and then the two antenna legs as the magnetic field increases. The discharge in this case is caused by the absorption of Trivelpiece–Gould (TG) wave. It is suggested that Bex is located in the middle of the antenna to obtain a higher efficiency of power transfer. [ABSTRACT FROM AUTHOR]

Atmospheric pressure plasma jet (APPJ) can produce biological active species for biomedical applications. This work proves direct evidence of the protective effects of APPJ against oxidative stress. SH-SY5Y cells, a commonly used cell model for the study of neurotoxicity and neuroprotection, were treated with APPJ for different durations. Then, cells were exposed to 200 µM H2O2 for 24 h and cell viability was measured using a CCK-8 kit. Changes in cell apoptosis were further confirmed by calcein-AM fluorescence imaging and flow cytometry. Extracellular NO production was detected using the Griess method. The results showed that APPJ protected SH-SY5Y from H2O2-induced apoptosis in a time-dependent manner. Moreover, extracellular NO production was significantly increased with the APPJ treatment. The results show in vitro that APPJ treatment could protect SH-SY5Y cells from oxidative stress by reducing cell apoptosis, which might be related to the reactive nitrogen species induced by the APPJ treatment. Our results indicate that the APPJ may have therapeutic potential as a novel ‘NO donor drug’ in neuroprotection and in the treatment of neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

The spatio-temporal characteristics of microhollow cathode sustained discharge are investigated using a fully self-consistent fluid model. The evolutions of discharge current, electric potential, electron density, the axial and radial electric fields, and ionization rates are simulated at 100 Torr. The interaction between the microhollow cathode discharge (MHCD) and the microhollow cathode sustained discharge (MCSD) is also investigated. Results show that the mode transition is related to the distance d between the first anode and the second anode. When the distance is large (e.g. d  =  2 mm), a complete discharge process comprises five stages. These stages are Townsend mode, the transition from mainly axial electric field to mainly radial electric field, the formation of the hollow cathode effect, the formation of microcathode sustained discharge, and stable discharge. The influence of MHCD on MCSD is prior to the influence of MCSD on MHCD. By contrast, when d is very small (e.g. d  =  0.3 mm), the influence of MHCD on MCSD is posterior to the influence of MCSD on MHCD. [ABSTRACT FROM AUTHOR]

Trichel pulses of negative corona discharge in atmospheric air are investigated in a needle-to-plate configuration. Time-resolved images of the pulsed discharge are recorded by using an ICCD camera. Light emission spectra of N2 molecules and ions during the discharge are measured by optical diagnostics. The distributions of the positive ions and the reduced electric field along the discharge channel are analyzed accordingly. The results show that the positive ions that can accumulate in space and distort the electric field play an important role on the formation of the Trichel pulse. The Trichel pulse is a mode transition between low-current Townsend discharge and high-current glow discharge. The rising time of the pulse corresponds to the breakdown and formation of glow discharge, and the decay time is related to destroy the process of positive ion clouds and the quenching of glow discharge. The time interval between the pulses is determined by the re-accumulation of positive ions near the cathode in the low-current Townsend discharge to form the positive ion clouds as well as a strongly-distorted electric field. [ABSTRACT FROM AUTHOR]

In this paper, we present the images of planar dielectric-barrier discharge in neon. Various plasma patterns are observed at different voltage of square waveform. The discharge patterns may be in the forms of self-organized filaments, ring, and other shapes and are sensitive to the applied voltage. The wall charge on the dielectric surface plays an important role on the existence and stability of the patterns. [ABSTRACT FROM AUTHOR]

In this paper, we present images of light emission by the plasma in a planar dielectric-barrier glow discharge in pure neon. The images have been obtained using an intensified charge-coupled device digital camera at nanosecond exposure time. The time-dependence discharge images for lower and higher frequency at a constant voltage are presented. [ABSTRACT FROM AUTHOR]