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The pulse-modulated radio frequency (RF) and kHz sinusoidal voltages are used for the excitation of two plasma jets, for which the reactive species in the plasma plumes and in the treated water are comparatively studied. With the same discharge power, it is found that concentrations of aqueous reactive species generated by the kHz sinusoidal plasma jet are higher than that of the pulse-modulated RF plasma jet, especially for the short-lived species OH. In addition, the comparison between the bacterial inactivation results is in accordance with that for the concentrations of aqueous reactive species for the two types of plasma jets. On the contrary, the emission spectra indicate that the gaseous reactive species such as OH(A) and O(3p5P) have much higher densities for the pulse-modulated RF plasma jet, which should ascribe to its higher electron density and electron temperature. Moreover, the concentrations of the aqueous reactive species and the emission intensities of the gaseous reactive species have similar variation trends for each of the plasma jets, as a function of the discharge power and the gap width. These results imply that the emission intensity could not reflect the relative concentration of an aqueous reactive species between these two plasma jets, but it could be used as an indicator of the concentration variation of an aqueous reactive species for each of the plasma jets. In addition, the phenomenon of electron trapping effect also indicates that the aqueous reactive species can be effectively generated only when more electrons act on the water sample.

In this paper, in order to obtain an atmospheric-pressure plasma jet with high activity and safe performance, the plasma jets generated with three distinct needle–ring electrodes, i.e., completely covered needle with insulating dielectric, partially covered needle (PCN) with insulating dielectric, and noncovered needle with any insulating dielectric, are studied and compared. Corresponding characteristics of three types of plasma jets are diagnosed and compared under the same excitation conditions. The results show that the PCN electrode is the best optimized one of three electrodes and presents the best cost performance among them in terms of discharge morphology, safety performance, propagation speed, and concentration of reactive species. It is mainly attributed to the addition of the partial insulating dielectric between the needle electrode and the ring electrode, which would not only effectively limit current rapid growth and prevent the rapid transformation of discharge mode, but also promote the charge overflow and strengthen the chemical activity of the plasma jet.

A new surface dielectric barrier discharge source containing a matrix of holes in the dielectric slice is put forward in this paper, for which the plasma characteristics and the delivery of reactive species to the downstream sample are studied for three experimental conditions, i.e., EC1 with a helium gas flow of 1 SLM through the holes, EC2 with an artificial air flow of 1 SLM, and EC3 without any gas flow. All the other conditions are kept the same. For the same discharge power of 2 W, it is found that the surface plasma in EC1 is comparatively more homogeneous, the discharge voltage is lower by ~12%, and the densities of reactive species are much higher, since the emission spectral lines of N2(C), N2+(B), He(3s3S), and O(3p5P) are stronger by at least sixfold. A petri dish of deionized water is put 5-mm downstream the surface discharge, in which the concentrations of nitrite, nitrate, H2O2, and NO are measured after the plasma treatment of 3 min. Compared with EC1, EC2, and EC3, it is found that the gas flow can increase the concentration of H2O2 by ~1.4-fold, but when helium is participated, a further increase of sixfold is achieved. Similarly, further increase is also found for the other three reactive species, which may be ascribed to the higher densities of gaseous reactive oxygen and nitrogen species in the helium-participated plasma and their larger diffusion coefficients in helium compared with that in air.

A new plasma jet array source is reported, which has two plasma regions: a cylindrical bottle in which plasmas are generated to deposit charged species on the inner wall, and the outside atmosphere in which plasma jets are generated between the small holes in the underside of the bottle and the grounded sample underneath the bottle. Four temporal regions of discharge are found to exist during a voltage cycle, in which the first one has maximal amount of charge transfer but minimal discharge energy. The surface charges supply the seed charge to initiate and sustain the plasma jets, while restricting the intensity of each plasma jet because their amount is limited. Only the surface charges near the underside hole of the cylindrical bottle are possible to participate in the discharge. Therefore, the plasma jets have a good jet-to-jet homogeneity relatively independent of the number of jets and their relative positions, indicating that the plasma jets can be arbitrarily arranged to a large extent. This is an application advantage but with a limitation, i.e., two plasma jets cannot be closer than 2.5 mm, because the surface charge between them will be shunted, and therefore, the plasma jets will be weakened.

A new method for the interneedle-distance optimization of a multineedle-to-plane barrier discharge reactor is presented. As we know, there is gas breakdown when, in some regions between electrodes, the electric field is higher than the breakdown field; hence, the region may play a dominant role for the discharge, and the enhancement of its volume ratio in the reactor will allow an increase in discharge energy density. This can be achieved by structure optimization. With the finite-element method, the 3-D profiles of an electrostatic field in the reactor are acquired for a series of interneedle distances, thereby the one-to-one relationship between the volume ratio and interneedle distance is obtained. This allows the optimal interneedle distance for power input efficiency to be identified, as related to the maximal volume ratio. The optimal distance is between 7.2 and 8.4 mm in our simulation range, decreasing with the increase of operating voltages from 16 to 26 kV. The simulation results are experimentally validated by discharge energy measurement as well as the performance of SO2 removal from indoor air. This structure optimization method leads to a simple way to obtain the optimal interneedle distance for energy input efficiency and hence benefits commercial use.

Endoscopy is an important tool that can be used to identify and treat diseases and is essential to avoid cross infection when used on different people. Cold atmospheric-pressure plasmas (CAPs) offer the prospect of a future basic technology for decontaminating and sterilizing of endoscope. In this paper, we intend to design an endoscope sterilization device based on CAPs. The various lengths of gap between electrodes and electrodes themselves are considered, and the plasma distribution and its evolution are investigated.

Stratification of negatively charged species in electronegative discharges is a well-known phenomenon that can lead to various double-layer structures. Here, we report on the separation of electrons and anions in atmospheric-pressure electronegative microdischarges. In these discharges, electrons oscillate between the electrodes, moving across and beyond an electronegative core. As a result of this motion, positively charged regions form between the oscillating electron ensemble and the central electronegative discharge.

Dielectric barrier discharge is attractive for air pollution control, except for its low energy efficiency and high operating voltage. For the sake of commercial use, multineedle to plane electrodes is investigated in this paper, and its optimization is achieved both by simulation and experiments.