Santolo De Benedictis

Energy transfers by long-lived species in glows and afterglows

An overview of the current literature on diagnostics and modeling of energy transfers by long-lived species in N2CO, HeNO, HeN2O2, N2O2, and N2H2O plasma is given. Energy transfers by vibrationally excited ground-state long-lived species and by electronic molecular and atomic metastables will be highlighted.

2D Thermoluminescence imaging of dielectric surface long term charge memory of plasma surface interaction in DBD discharges

The charge trapping effect due to the exposure of alumina surfaces to plasma has been studied in a volume dielectric barrier discharge (DBD) in Ar and He noble gases. The long lasting charge trapping of alumina dielectric plates, used as barriers in DBDs, is evidenced by an ex situ thermoluminescence (TL) experiment performed with a standard and a custom two-dimensional (2D)-TL apparatus. The spatial density of trapped surface charges is found to be strongly correlated to the plasma morphology, and the surface spatial memory lasted for several minutes to hours after plasma exposure. In the case of Ar, the plasma channel impact signature on the surface shows a higher equivalent radiation dose with respect to the surface plasma wave and the post-discharge species signature. As a consequence, for the development of discharges, inside the dielectric surface the availability of lower energy trapped electrons is larger in the first region of plasma impact. The reported spatial memory increases the likelihood of the occurrence of plasma filaments in the same position in different runs. In He plasmas, the dielectric barrier shows an almost uniform distribution of trapped charges, meaning that there is no preferred region for the development of the discharge. In all cases a slight asymmetry was shown in the direction of the gas flow. This can be interpreted as being due to the long-living species moving in the direction of the gas flow, corresponding with the TL side experiment on the sample exposed to the plasma afterglow. The maximum values and the integral of the 2D-TL images showed a linear relation with the total charge per ac cycle, corresponding with findings for the TL glow curve. In conclusion, 2D-TL images allow the retrieval of information regarding the plasma surface interaction such as the plasma morphology, trap sites and their activation temperature.

Optical diagnostics in dielectric barrier discharges at atmospheric pressure

Our recent work on optical emission spectroscopy (OES) and laser-induced fluorescence (LIF) applied to dielectric barrier discharge (DBD) at atmospheric pressure (ATP) is reported. The interplay of discharge kinetics and diagnostic techniques features is evidenced, with emphasis on collision processes that, with their variety of state-to-state characteristics and rate constants, determine the observation of a peculiar collision-dominated non-equilibrium system.

Optical–optical double resonance LIF detection of in high pressure gas discharges

An optical?optical double resonance (OODR) laser induced fluorescence (LIF) for the detection of the metastable is described. OODR employs the double laser excitation of A?B and B?C nitrogen transitions. Here it is proposed as a sensitive approach to detect in high-pressure discharges. We have tested its sensitivity with respect to conventional single photon LIF by an excitation/detection scheme in which the two wavelengths required are generated by a provisional single laser setup. Other single laser configurations that might allow a sensitivity close to two orders of magnitude larger than that of conventional LIF are proposed. Such gain can be particularly useful for the detection of in non-equilibrium, high-pressure discharges.