A dielectric barrier discharge (DBD) reactor producing cold plasma at atmospheric pressure has been used to treat seeds of eight different species and investigate their responses in term of germination. The device is made of nine cylindrical DBDs organized in a 3 × 3 array and partially immersed in water. O 2 , N 2 , and air were flown in the device; the cold plasma from such gas is formed in the bubbles and touch liquid surface. Seeds were either located inside the water during plasma treatment process (direct treatment) or were watered by the water exposed to cold plasma beforehand (indirect treatment). Such plasma activated water contains reactive oxygen species and reactive nitrogen species. The statistical analysis shows that the probability of germinating of treated mung bean, mustard and radish is significantly higher than in control groups (p < 0.05) for indirect treatments. A comparison of different treatment modalities (direct versus indirect treatment and gas composition) on germination boost has been completed on mung bean seeds. It is shown that direct plasma treatment using different gas (O 2 , N 2 , and air) give a strong enhancement of the mung bean germination probability compared to the control group; in the case of indirect treatment, only plasma air-treated water lead to a significant germination boost compared to the control group; this effect is still smaller than the one obtained using a direct treatment.
Abstract:The triggering and guiding of electric discharges produced in atmospheric air by a compact 100 kV Marx generator is realized in laboratory using an intense femtosecond laser pulse undergoing filamentation. We describe here an approach allowing extending the lifetime of the discharges by injecting a current with an additional circuit. Laser guiding discharges with a length of 8.5 cm and duration of 130 µs were obtained.In the last decade femtosecond laser filaments has proved to be a powerful tool to trigger and guide electric discharges in atmospheric air 1 with gap length of a few meters [2][3][4][5][6] . The weakly ionized plasma column and subsequent low density channel generated by laser filaments allow the precise triggering and guiding of electric discharges between two electrodes with a significant reduction of the breakdown voltage [7][8][9] . This effect is potentially useful for the development of laser lightning rod 4, 10-11 , high-voltage, high-current switches 12 , or virtual plasma antennas [13][14] .For applications such as plasma antennas, extension of the filament plasma lifetime is needed, since the plasma from the filament recombines in a few nanoseconds, seriously limiting the bandwidth of antennas to frequencies v> 10 9 Hz. This can be done using additional femtosecond or nanosecond laser pulses 15-17 but this technique is particularly complex and the resulting plasma is limited to a few µs. Injection of electric current through guided discharges appears to be a more promising way. The duration of the guided discharge mostly depends on the high voltage (HV) source, with a typical duration on the order of 100 ns [2][3][4]14 . In several publications, a Marx generator was used as the HV source to produce meter scale guided discharges. In this case, the discharge duration is defined by the product of the Marx "stack" capacitance C marx and a discharge load R load . In Ref. 18, a compact Marx generator was used to create a ~ 21 cm guided discharge of duration about 600 ns due to the mentioned Marx capacitance C max ~ 2 nF and the discharge load resistance R d ~ 300 Ω. In this letter we describe a method, which allows prolonging this parameter up to 130 µs. The experiment setup is presented in Fig. 1. The circuit is composed of two parts. The first part is a Marx generator described in 18. For this experiment the generator was composed of 5 stages charged up to 20 kV DC, resulting in 100 kV output pulse with a negative polarity. An inductance L 1 was connected to the generator output electrode and served as a load up to the moment when the Marx pulse produces a breakdown in the inter-electrode gap. The Marx output electrode has a cylinder form with an axial hole allowing the laser beam to enter in the generator and to trigger it. The second electrode is a round finger with a 5 mm radius. As described in Ref. 18, a chirped pulse amplified laser system emitting at a wavelength of 800 nm is used to produce the filaments between the two electrodes and inside the Marx generator. The laser pul...
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