In this paper, dielectric columns with different dielectric constants are employed as dielectric materials in the packed bed reactor to investigate the dynamic behaviors of plasma interaction processes. The effects of the dielectric constants (zirconia: ε = 25 and PTFE: ε = 2.5) on the production of reactive species are studied for plasma catalysis applications. Comparison studies of discharge images, electrical characteristics, discharge dynamic evolution and spatial-temporal resolved optical emission spectroscopy are carried on when zirconia and PTFE columns are employed. The results show that there are four discharge processes existing in the packed bed reactor: surface streamer on the dielectric column, local discharge at the contact point, surface discharge on the grounded dielectric plate, and the volume discharge. The production of reactive species such as N 2 (C 3 Π u ), N + 2 (B 2 Σ + u ) and O(3p 5 P) depend on the discharge processes to a great extent. The production of the N + 2 (B 2 Σ + u ) always accompanies the formation of the streamer by electrons direct impact process to excite the ground state nitrogen molecules to N + 2 (B 2 Σ + u ). The O(3p 5 P) is generated in two different ways, which plays a major role during the voltage pulse raising and falling time, respectively. The rst way is the direct and fast one-step ionization and excitation by high energy electrons with O 2 . The second way is the energy transfer from the nitrogen metastable N 2 (A 3 Σ + u ) and energetic electrons, in which the O is rst ionized from O 2 and then excited to O(3p 5 P). Furthermore, compared with a zirconia column, a PTFE column is more conductive to the generation of reactive species.

An underwater Ar bubble discharge is excited by nanosecond pulsed power, and the effects of adding N2/O2 in Ar discharge on products are investigated. This work focus on regulating species concentration in plasma activated water (PAW), and then seeking specific concentrations for future application. The optical emission spectra (OES) and colorimetric chemical probes are used to diagnose and measure active species in plasma region or liquid phase. The H2O2 energy yield with Ar bubble can be up to 3.04 g kWh−1. The emission intensity characteristics of Ar (4p‐4s), OH (A‐X), Hα, and O (3p‐3s) in plasma region, and the concentrations of H2O2, NnormalO3−, and NnormalO2− in liquid are investigated with adding varying N2/O2 proportion in Ar bubble discharge.

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In this paper, a capacitor assisted AC high-voltage was employed to generate a gas–liquid discharge in pure oxygen at atmospheric pressure. The discharge images, waveforms of voltage and discharge current, and optical emission spectra of plasma were diagnosed for the purpose of investigating the discharge modes. The gas temperature (Tg), excitation temperature of hydrogen (Texc), and electron density (ne) were calculated by the spectra of OH (A2Σ–X2Π), the intensity ratio of Hα and Hβ, and the Stark broadening of Hβ, respectively. The effects of applied voltage and capacitance value on the mode transition of discharge were also discussed. It is found that due to the presence of capacitor, not only is the unlimited growth of discharge current restrained, but the transition of discharge mode is also controllable. There are three discharge modes of gas–liquid discharge oxygen plasma (GLDOP), and with the increase of applied voltage or capacitance value, discharge modes are transited from the streamer mode, to the glow-like mode, and to the abnormal glow/arc mode. With the mode transition, the Tg and Texc of GLDOP increase and the ne decreases. In contrast, the change of Tg and ne is negligible when GLDOP maintains one kind of discharge mode.

In this Letter, atmospheric pressure glow discharge based on a small discharge gap is excited by sine AC voltage in air on purpose of detecting trace heavy metal elements in solid samples, which makes the detection limits of trace heavy metal elements reach tens μg/kg. The waveforms of voltage and discharge current, discharge images, plasma gas temperature, and optical emission spectra are obtained to discuss the feasibility of atmospheric pressure glow discharge on detection of trace heavy metals. The formation mechanism of optical emission spectra and the strong emission intensity of heavy metal elements show that energetic electrons and excited metal atoms are easily generated by atmospheric pressure glow discharge. The effects of applied voltage and discharge gap on atmospheric pressure glow discharge are discussed to acquire the optimal experimental conditions. And a smaller discharge gap and applied voltage can restrain the transition from glow discharge to arc discharge. Besides, the limits of detections of Cu and Cd are about 0.0241 and 0.0318 μg/g, respectively, by using atmospheric pressure glow discharge with an applied voltage of 3.8 kV, discharge gap of 3.5 mm, and driving frequency of 10 kHz.

In this paper, a pulsed electrolyte cathode discharge is generated for the purpose of detecting metal elements by atomic emission spectrometry in atmospheric air. The discharge image, and the waveforms of voltage and current are obtained for studying the discharge mode. To understand the mechanisms of metal atomic excitation, the plasma temperature and the electron density of discharge are obtained by the spectra of N2 (C-B, Δν = −2) and Hβ (486.1 nm), respectively. Also, the effects of the solution pH, solution flow rate, discharge gap, and discharge voltage on the emission intensities of Cu and Fe are discussed to acquire the optimal experimental conditions. It is found that the pulsed electrolyte cathode discharge is a kind of atmospheric pressure glow discharge, and it can analyze metal elements accurately and sensitively. The gas temperature and electron density play important roles in the improvement of emission intensities of metal elements.

Two modes of the atmospheric-pressure plasma discharge, distinguished by the dominant O3 and NO x species are studied numerically and experimentally. To investigate the mode transition mechanisms, here we develop a global chemical kinetics model for the atmospheric-pressure dielectric barrier discharge involving 63 species and 750 reactions. Validated by the experimental results, the model accurately describes the mode transition. The N, O, O2(a), and O2(b) are the essential transient intermediate species for the O3 and NO x production and loss reactions.The individual and synergistic effects of the specific discharge energy and the gas temperature on the species density and the relative contributions of the dominant reactions are quantified under the increasing discharge voltage conditions. The modeling results indicate that the gas temperature and specific discharge energy both contributed to the discharge mode transition, while the decisive factors affecting the change of the O3 and NO x density are different in the respective modes. These insights contribute to diverse plasma applications in biomedicine, agriculture, food, and other fields where selective and controlled production of O3 and NO x species is the key for the desired plasma performance.

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