Experimental investigations on the propagation of the plasma jet in the open air

Abstract

The fundamental of the generation and propagation of the atmospheric pressure nonequilibrium plasma jets has recently attracted significant interests. In this paper, investigations on the effects of the parameters of the pulsed dc voltages on the optical emission intensity of the plasma jet and the bullet propagation behavior are carried out based on the temporal-spatial resolved optical emission spectroscopy measurements and the high-speed photography. It is found that, with the increase in the applied voltage, the bullet propagates out from the nozzle earlier and accelerates to higher peak-velocities. The increase in the pulse frequency exerts no significant influences on the optical emission of the plasma jet and the bullet propagation velocity. But it can induce the bullet propagates out from the nozzle earlier. Besides, it is interesting to notice that, with the increase in the pulse width in the beginning, the bullet propagates out from the nozzle with longer delay time. However, when the pulse width is increased to be more than 100 μs, the delay time of the bullet propagating out from the nozzle becomes much shorter. On the other hand, with the increase in the pulse width, the optical emission intensity of the plasma jet drops and the maximum bullet velocity decreases too. Detailed analysis shows that it may be due to the accumulation of the charges and radicals, which can shorten the prebreakdown of the discharge inside the syringe and result in the bullet propagating out earlier from the nozzle.

Electrical, Thermal and Optical Parametric Study of Guided Ionization Waves Produced with a Compact μs-Pulsed DBD-Based Reactor

“…The rising slopes of the fitting curves are not the same, which implies different production mechanisms of these species. These variations are in quite good agreement with the ones that were obtained in Figure 5, where I Peak and Q main grew also linearly with the voltage amplitude and other published works concerning identical [16,25] and different [43] GIWs setups. This increase of I Peak and Q main was attributed to the higher electrical energy delivered in the reactor at elevated voltage amplitudes.…”

“…Depending on the duty cycle value, ∆t GIWs decreases from 250 ns at V p = 6 kV to~100 ns at V p = 8 kV, values that are in the range of the ones published in the bibliography [16,25]. These results demonstrate also clearly that low duty cycle values highly favorize the fast development of the discharge, which correlates with [43,45] even if they refer to different electrode setup and operating gas. Figure 6 illustrates the effect of V p on L GIWs for different duty cycles at f = 15 kHz.…”

“…Towards this direction, an effective control of the above parameters, and especially the temperature and the reactive species formation in the free-GIW case, appears to be crucial for better understanding the GIWs performance on various specimens (mostly biomedical). As it was shown by different groups, the latter can be tuned (free-GIWs case) by varying the system parameters [6,15,16,25,43]. In this section, effective production of emissive reactive species is achieved even at the lower voltage amplitude of 4.5 kV (L GIWs = 0.5 cm), which is demonstrated below via optical emission spectroscopy measurements (see Figure 11).…”

“…Although, these results are not linked with the ones reported in [44], where L GIWs appeared significantly longer at 20 kHz (~4.8 cm) in respect to 5 kHz (~3.5 cm), for V p = 4.6 kV and a pulse width of 2 µs. Besides, in the work of Xiong et al [43], L GIWs did not depend on frequency at all. The differences that were observed between these three DBD systems could be related to the dissimilar electrode configurations and dielectric materials used, while for a better understanding of these behaviors, more experimental/theoretical works are necessary.…”

“…These are indirectly associated with the plasma current in the inter-electrode region. The positive impulse refers to a primary discharge that is formed in the reactor, with characteristics depending strongly on the system operating parameters [16,25,43,44]. It is now well known that this primary discharge is due to the development of a guided ionization wave or guided streamer [3,4]; it is formed in the DBD region once the space charge electric field becomes comparable to the external one, and it propagates fast (velocities up to some 100 s km/s) outside the reactor, being confined in the noble gas channel.…”