The aim of this paper is to determine the influence of the position of the electrodes on the range of a plasma jet, for specific experimental conditions, by using time-resolved optical emission spectroscopy. The optimal position of the electrodes is determined for a fixed gas flow rate and applied excitation voltage. We characterize the helium plasma jet for different distances from the end of the glass tube, showing detailed results for four different electrode positions from the jet nozzle (7, 15, 30 and 50 mm). It was found that at the distance of 15 mm, the length of the plasma jet is at its maximum. The highest speeds of the plasma package travelling outside the glass tube of the atmospheric plasma jet are obtained for the same electrode configuration (15 mm from the jet nozzle). With the electrodes positioned at smaller distances from the nozzle, the plasma plume was much shorter, and at the larger distances the plasma did not even leave the glass tube.

In this paper, we will present results of plasma treatments of meristematic cells of Daucus carota. Plasma needle was used as an atmospheric pressure/gas composition source of non-equilibrium plasma in all treatments. Activity of antioxidant enzymes superoxide dismutase and catalase was measured immediately after plasma treatment and after two weeks following the treatment. Superoxide dismutase activity was increased in samples immediately after the plasma treatment. On the other hand, catalase activity was much higher in treated samples when measured two weeks after plasma treatment. These results show that there is a direct proof of the triggering of signal transduction in the cells by two reactive oxygen species H2O2 and O2−, causing enzyme activity and short and long term effects even during the growth of calli, where the information is passed to newborn cells over the period of two weeks.

Atmospheric pressure plasma jets (APPJs) have been one of the most studied nonthermal discharges in the past decade. Recently, the use of multiple jets in order to cover larger areas has become desirable. However, the interaction between neighboring jets is a common phenomenon that can greatly modify plasma characteristics up to the point of merging several jets into a single one. The present study focus on bringing new insight on this phenomenon, named jet-to-jet coupling, investigating the discharge modes (coupled and uncoupled) of a plasma source composed of an array of seven plasma jets arranged adjacent to one another and driven by a sinusoidal excitation. The experimental results achieved by means of mass spectrometry, show a considerable increase in ion concentrations in the plasma, up to some orders of magnitude in the case of negative ions, as an effect of jet-to-jet coupling. Temporally resolved imaging of the discharge also shows how the evolution and intensity of the discharge are greatly affected by jet-to-jet interaction. Air/helium mole fraction and negative ions concentration are regarded as the main possible parameters affecting the coupling phenomenon. Moreover, experimental results suggest that the presence of remnant conductive channels behind the ionization fronts governs the propagation of the next ionization fronts, independently from the direction of propagation (from the source toward the target or vice versa). Furthermore, a parametrical investigation of the coupled mode discharge showed the presence of a critical value of the imposed voltage for which a drastic change in the electrical characteristics of the discharge is observed.

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