Analysis of homogenous nanosecond discharge at moderate pressure: dissociation of oxygen for plasma assisted detonation

International audienceThe present study is a preliminary step toward producing a non-equilibrium plasma capable of enhancing deflagration and detonation processes. Experiments show that single shot nanosecond discharges can produce an homogeneous plasma in O2:Ar:Air mixtures. The measurement of the deposited energy was used as an input to ZDplaskin calculation of the O/O2 dissociation ratio. The result indicates that these ratio are very small compared with those that are achived by shock processes in non-dissociated mixtures

Fast pulsed discharges

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Effect of non-equilibrium plasma on decreasing the detonation cell size

International audienceThe effect of a volumetric nanosecond discharge on detonation cell size was demonstrated experimentally in a detonation tube test rig. The experiments were performed in CH 4 :O 2 :Ar=1:2:2 mixture, at initial pressure 180 mbar and ambient temperature. The plasma was generated by two consecutive pulses of −50 and −32 kV amplitude on the high-voltage electrode and 25 ns pulse duration. The analysis of the detonation cell size with and without plasma generation was performed via sootedplate technique. The detonation cell size was reduced by a factor of 1.5 − 2, while passing through the region of the discharge

Characterization of an Optical Pulse Slicer for Gas-Phase Electric Field Measurements Using Field-Induced Second Harmonic Generation

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A comparative experimental kinetic study of spontaneous and plasma-assisted cool flames in a rapid compression machine

International audiencePlasma-assisted cool flames of n- heptane were generated in the combustion chamber of a rapid compression machine coupled with a nanosecond dielectric barrier discharge, at a pressure of 1.5 bar and temperature T = 650 K. Increasing of the voltage pulse amplitude at the electrode resulted in a transition from no reactivity to induced cool flame and then to fast ignition. Sampling of the reacting mixture was performed at selected times during the experiments to draw mole fraction profiles of the fuel and major low temperature stable intermediates, showing a gradual increase in the mole fraction of these species after the discharge. Comparison with a spontaneous cool flame case at a slightly higher pressure shows that no new species are formed in the plasma-assisted case, and that after the initiation of reactivity by the discharge at the nanosecond timescale, the distribution and relative importance of the main reaction pathways is conserved at the millisecond timescale. Differences in the shape of the mole fraction and light emission profiles however suggest that the plasma-assisted cool flame is propagative

Cell death induced on cell cultures and nude mouse skin by non-thermal, nanosecond-pulsed generated plasma.

Non-thermal plasmas are gaseous mixtures of molecules, radicals, and excited species with a small proportion of ions and energetic electrons. Non-thermal plasmas can be generated with any high electro-magnetic field. We studied here the pathological effects, and in particular cell death, induced by nanosecond-pulsed high voltage generated plasmas homogeneously applied on cell cultures and nude mouse skin. In vitro, Jurkat cells and HMEC exhibited apoptosis and necrosis, in dose-dependent manner. In vivo, on nude mouse skin, cell death occurred for doses above 113 J/cm(2) for the epidermis, 281 J/cm(2) for the dermis, and 394 J/cm(2) for the hypodermis. Using electron microscopy, we characterized apoptosis for low doses and necrosis for high doses. We demonstrated that these effects were not related to thermal, photonic or pH variations, and were due to the production of free radicals. The ability of cold plasmas to generate apoptosis on cells in suspension and, without any sensitizer, on precise skin areas, opens new fields of application in dermatology for extracorporeal blood cell treatment and the eradication of superficial skin lesions

Hematoxylin Eosin sections of nude mouse skin after plasma treatment.

<p>Epidermis, dermis, hypodermis and muscle are affected for doses higher than 113 J/cm², 281 J/cm² and 394 J/cm² respectively. In the diagram in the lower quadrant, the doses necessary to produce mild lesions for each layer of the skin are shown.</p

Oxydative stress assay (A-D), Electroporation assay (E-F).

<p>For both tests, nucleuses were labelled with NucBlue, images were taken with the same parameters as for the negative control. Oxydative stress assay: Cells were incubated one hour after treatment by plasma or menadione 100µM with Cellrox deep green, an intracytoplasmic fluorescent marker of oxidative stress. A, negative control, almost no fluorescence is apparent. B, Menadione, a strong cytoplasmic red fluorescence is present. C and D, medium and intense fluorescence depending on the plasma dose, 169 and 508 J/cm² respectively. Electroporation assay: Cells were incubated just before plasma treatment with Sytox green, a fluorescent marker of membrane impairment. E, negative control, almost no fluorescence is visible. F, high-dose plasma treatment (506 J/cm²), a strong green fluorescence is present.</p