The effects of cold atmospheric-pressure plasma jet (CAPPJ) were investigated on germination and early seedling growth of fenugreek (Trigonella foenum-graecum L) seeds. A two-electrode argon CAPPJ system with and without an additional grounded electrode [accelerating grounded (AG) electrode] was used at different exposure times. After 16 h of observation, the germination rates increased by 4 and 7 times, without and with using an AG electrode, respectively, for 1 min of plasma exposure. An increase in shoot fresh weight was observed, especially at 10 min exposure time. A high dry weight of root and shoot at 1 min-AG exposure time was observed. The root:shoot ratio was lower in plasma-treated seedlings, compared with the control plants. The study found that the O-radical emission line (777.4 nm) enhanced 5 times, due to the presence of an AG electrode, which increased the axial electric field and led to the formation of more streamers. The three stated effects (O-radicals, enhancement of the electric field and streamers) could be the cause for the stimulation of seed germination and seedling growth parameters when using the CAPPJ. The scanning electron microscope images showed the etching of the seed surface layers, which was more pronounced when an AG electrode was applied. The results of the current study indicate that the germination rates increased due to the increase of O-radical concentration and the etching of the seed surfaces.

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Nonthermal equilibrium atmospheric pressure plasma jet gained great interest due to its multidisciplinary applications. This work is focused on studying the characteristics of an argon atmospheric pressure plasma jet and the laminarto-turbulent flow mode transition. By increasing the applied voltage from 10 to 25 kV, the plasma can run in four operational modes depending on the number of current pulses per half a cycle of the applied voltage. The plasma jet gas temperature increases from 310 to 370 K and the laminar-to-turbulent transition value shifts toward lower flow rate values from 3.75 to 2.6 slpm as a result of increasing the applied voltage. A clear border between the laminar and the turbulent regions has been resolved at different applied voltages and flow rates at a fixed applied frequency of 24 kHz.