Xi-Ming Zhu

A simple collisional?radiative model for low-temperature argon discharges with pressure ranging from 1?Pa to atmospheric pressure: kinetics of Paschen 1s and 2p levels

A simple collisional?radiative model for the Paschen 1s and 2p levels is proposed for low-temperature argon discharges. This model can predict the population distribution of 1s and 2p levels over a wide discharge pressure range 1?105?Pa and ionization ratio range 10?6?10?3. The modelling results are found to be in good agreement with observed optical emissions from several different types of argon discharges at 1, 100 and 105?Pa. By using the model, the dominant kinetic processes of 1s and 2p levels are investigated for an electron beam plasma, an inductively coupled plasma, a capacitively coupled plasma and a microwave microplasma. A kinetic diagram is given, which can be used to identify the kinetic state of 1s and 2p levels in many low-temperature argon discharges reported in the literature. This model is also useful for obtaining discharge parameters from optical emissions in low-temperature argon discharges.

Characteristics of atmospheric pressure plasma jets emerging into ambient air and helium

An investigation of atmospheric pressure helium plasma jets emerging into ambient air and helium was carried out with the aim of shedding light on the mechanism for the formation of extended plasma plumes. By electron multiplying charge coupled device imaging, it is shown that the geometrical shape of the jet in ambient helium is not an arrow-like shape as that in ambient air, but a diffusive one. In ambient helium, the jet length increased continuously with the applied voltage. For ambient air, the jet length was determined by both the helium flow rate and the applied voltage. In addition, the N2 (C–B) band and the lines dominate the emission spectra of the jet in ambient air. The Penning ionization between metastable He atoms and N2 molecular may be the main source of .

Effects of gas flow rate on the length of atmospheric pressure nonequilibrium plasma jets

Effects of gas flow rate on the length of atmospheric pressure plasma jets have been investigated using a capillary dielectric barrier discharge configuration. For the discharge in only downstream region, three distinguishable modes of plasma jet length versus argon gas flow rate, namely, laminar, transition, and turbulent jet mode, have been identified. For the case of discharge in both downstream and upstream regions, the curve of length versus flow rate has significant “dent” in the laminar jet mode for pure helium, neon, and argon flow gas spraying into air ambient.

Gas temperature, electron density and electron temperature measurement in a microwave excited microplasma

Gas temperature, electron density and electron temperature of a microwave excited microplasma are measured by optical emission spectroscopy. This microplasma is generated in the small gap of a microstrip split-ring resonator in argon at near atmospheric pressure. When less than 100 ppm of water is present in the plasma, the gas temperature can be obtained from the rotational temperature of the hydroxyl molecule (A 2Σ+, v = 0) and the electron density can be measured by the Stark broadening of the hydrogen Balmer β line. According to a collisional–radiative model, the electron temperature can be estimated from the measured excitation temperature of argon 4p and 5p levels. It is found that the values of these parameters (gas temperature, electron density and temperature) increase when the gap width of the resonator is reduced. However, when the microwave power increases, these parameters, especially the electron density, do not vary significantly. Discussions on this phenomenon, being very different from that in the low-pressure bounded discharges, are provided.

Optical emission spectroscopy in low-temperature plasmas containing argon and nitrogen: determination of the electron temperature and density by the line-ratio method

This article reviews a variety of methods to obtain the electron temperature and density by the emission line ratios for low-temperature plasmas containing argon or nitrogen gas. Based on the collisional–radiative model of excited particles, the underlying principle of each of these methods is described, along with the criterion on how to select an appropriate line-ratio method according to the discharge conditions. Limitations on the application of each line-ratio technique are also discussed.

Measurement of the electron density in atmospheric-pressure low-temperature argon discharges by line-ratio method of optical emission spectroscopy

A new collisional–radiative model for atmospheric-pressure low-temperature argon discharges is proposed, which illustrates the significant effect of electron density on the excited atom population distribution. This makes it possible to determine the electron density from the intensity ratio of emission lines of excited atoms. Results of this new method in several types of atmospheric-pressure discharges are found to be in agreement with those of the Stark broadening method and the electric model over a wide electron density range 10 11 –10 16 cm −3 . (Some figures in this article are in colour only in the electronic version)

Using OES to determine electron temperature and density in low-pressure nitrogen and argon plasmas

A summary of the methods of electron temperature and electron density measurement in low-pressure nitrogen and argon discharges using optical emission spectroscopy (OES) is given. This paper describes recently developed simple kinetic models for nitrogen and argon discharges and their applications in establishing the relationship between the electron parameters (temperature and density) and the OES line ratios from the discharges. In particular, the assumptions and applicability of these models in different kinds of discharges (capacitively coupled and inductively coupled discharges, discharges with different gas mixtures, etc) are discussed in detail.

Influence of operating pressure on surface dielectric barrier discharge plasma aerodynamic actuation characteristics

This letter reports an experimental study of surface dielectric barrier discharge plasma aerodynamic actuation characteristics’ dependence on operating pressure. As the pressure decreases, the N2(CПu3) rotational temperature decreases, while its vibrational temperature decreases initially and then increases. In addition, the discharge mode changes from a filamentary type to a glow type at 45Torr. In the filamentary mode, the electron density decreases with pressure, while the electron temperature remains almost unchanged. In the glow mode, however, both the electron density and the electron temperature increase while the pressure decreases. The induced velocity shows a maximum value at 445Torr.

Role of metastable atoms in the propagation of atmospheric pressure dielectric barrier discharge jets

In the experiment of plasma jets generated in a tube dielectric barrier discharge configuration, three distinguishable modes, namely, laminar, transition, and turbulent jet modes, have been identified. Flows of helium, neon, and argon gases shared the hydrodynamic law when their plasma jets spraying into ambient air of atmospheric pressure and room temperature. Aiming to reveal the basic processes, we propose that plasma jet length is mainly determined by reactions involving metastable atoms. These processes are responsible for the variation in plasma jet length versus gas flow rate and working gas species. To investigate this proposal in detail, we have obtained three significant experimental results, i.e., (1) the plasma jet lengths of helium, neon, and argon are different; (2) the plasma jet length of krypton slightly changes with gas flow rate, with three modes indistinguishable; and (3) there are large differences between optical emission spectra of helium, neon, argon, and krypton flow gases. These ...

Effects of Penning ionization on the discharge patterns of atmospheric pressure plasma jets

Atmospheric pressure plasma jets, generated in a coaxial dielectric barrier discharge configuration, have been investigated with different flowing gases. Discharge patterns in different tube regions were compared in the flowing gases of helium, neon and krypton. To explain the difference of these discharge patterns, a theoretical analysis is presented to reveal the possible basic processes. A comparison of experimental and theoretical results identifies that Penning ionization is mainly responsible for the discharge patterns of helium and neon plasma jets.