Comparative Studies of Double Dielectric Barrier Discharge and Microwave Argon Plasma Jets at Atmospheric Pressure for Biomedical Applications

Two low-temperature plasma jets using argon carrier gas at atmospheric pressure have been experimentally characterized using optical emission diagnostics. The first one is a double dielectric barrier discharge (DBD) plasma jet generated by a pulsed power supply (9 kV , 9.69 kHz, duty cycle: 1%) and the second one is a microwave (MW) induced plasma jet (2.45 GHz, 40 W ). The argon gas (4.5 purity) flowing through the quartz tube used to launch the plasma in open air is kept at 1 L/min for both plasma devices. Some thermodynamic parameters such as rotation (Trot) and excitation (Texc) temperatures have been determined as well as some plasma active species such as electron density, ultraviolet C (UVC) irradiance, and atomic oxygen concentrations. Most of these plasma parameters are spatially resolved along the plasma jet axis using the spectra of atomic lines (Ar and O) in the visible range and molecular bands (N₂ and OH) in the UV range.

At the tube outlet, the electron density and atomic oxygen concentration are one decade higher in the case of the dielectric barrier discharges (DBDs) plasma jet while Trot is higher in the case of the MW plasma jet. These differences are mainly due to the way of plasma generation. Indeed, the guided-ionization waves generated by the DBD setup cause higher nonequilibrium phenomena since the difference between Trot and Texc is shown to be much larger in the DBD case. Furthermore, at the tube outlet, it is shown that UVC irradiance produced by the MW plasma jet is about twice as large as that of the DBD plasma jet. However, at 1.7 cm away from the tube outlet, the differences between the two plasma setups on temperatures and active species production become less significant. For instance, the plasma gas temperature measured with a thermocouple becomes the same (320 K) showing the ability of both plasma setups to be used inbiomedical applications without inducing a significant thermal effect.

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