Understanding the Flowing Atmospheric-Pressure Afterglow (FAPA) Ambient Ionization Source through Optical Means
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The advent of ambient desorption/ionization mass spectrometry (ADI-MS) has led to the development of a large number of atmospheric-pressure ionization sources. The largest group of such sources is based on electrical discharges; yet, the desorption and ionization processes that they employ remain largely uncharacterized. Here, the atmospheric-pressure glow discharge (APGD) and afterglow of a helium flowing atmospheric-pressure afterglow (FAPA) ionization source were examined by optical emission spectroscopy. Spatial emission profiles of species created in the APGD and afterglow were recorded under a variety of operating conditions, including discharge current, electrode polarity, and plasma-gas flow rate. From these studies, it was found that an appreciable amount of atmospheric H(2)O vapor, N(2), and O(2) diffuses through the hole in the plate electrode into the discharge to become a major source of reagent ions in ADI-MS analyses. Spatially resolved plasma parameters, such as OH rotational temperature (T(rot)) and electron number density (n(e)), were also measured in the APGD. Maximum values for T(rot) and n(e) were found to be ~1100 K and ~4×10(19) m(-3), respectively, and were both located at the pin cathode. In the afterglow, rotational temperatures from OH and N(2)(+) yielded drastically different values, with OH temperatures matching those obtained from infrared thermography measurements. The higher N(2)(+) temperature is believed to be caused by charge-transfer ionization of N(2) by He(2)(+). These findings are discussed in the context of previously reported ADI-MS analyses with the FAPA source.Keywords:
Glow discharge
An Experimental Study on the Implementation and Stabilization of Atmospheric Pressure Glow Discharge
Ionizers are essential in various areas of manufacturing industries to protect electrostatic hazards and to reduce inferior products. For ion sources used in the charge neutralizers, there are corona discharge, soft X-ray, ultraviolet and glow discharge. Glow discharge has lots of attractive properties, such as lower discharge sustaining voltage, no generation of ozone, and so on. In this paper, we did an experimental study to trace the mechanism and stabilization of atmospheric pressure glow discharge using the several size and shape of electrodes. As an experimental result, to sustain conditions of atmospheric pressure glow discharge is that discharge voltage is 360V, discharge current is 12mA, apply frequency is 1kHz between electrodes when positive electrode is molybdenum(Mo) and negative electrode is copper(Cu). We confirmed that the mechanism and stabilization of atmospheric glow discharge is deeply concerned with the shape and material of electrode for discharge. Especially, glow discharge in atmospheric pressure was well generated and sustained according with the physical properties used electrode materials, example melting point, thermal conductivity, and etc.
Glow discharge
Brush discharge
Discharge pressure
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The fundamental requirements for the optimum mechanical interface between a glow discharge ion source and a mass spectrometer are described in this paper. Specifically, the properties of a typical glow discharge ion source are compared and contrasted to those of a typical inductively coupled plasma ion source. The critical parameters and theoretical considerations of glow discharge and inductively coupled plasma ion source interfaces are reviewed, and the results of experiments using both quadrupole and time-of-flight mass spectrometers with a glow discharge source are presented. The experimental results clarify several important problems in the glow discharge ion sampling process. Our findings indicate that a shock wave structure does not occur in the supersonic expansion of the glow discharge ion source. Ions of different masses have similar initial kinetic energies in the glow discharge; thus, the angle of the skimmer cone is not a critical parameter for efficient ion beam extraction. Another consquence is that space charge effects in glow discharge ion sources repel heavy ions farther off axis than light ions. Thus, there are distinct and fundamental differences between glow discharge and inductively coupled plasma ion sources which are relevant to both ion sampling and ion extraction processes.
Glow discharge
Ion gun
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A glow discharge has been experimentally investigated in air at atmospheric pressure using two different electrode configurations of a perforated aluminium sheet and stainless steel wire mesh. The observations of the Lissajous figure of voltage-electric charges is used as a method of distinguishing between the glow discharge produced by perforated aluminium sheet and stainless steel wire mesh. The perforated material shows a better glow discharge stabilization than that of stainless steel wire mesh.
Glow discharge
Lissajous curve
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Usually, the electrical breakdown of dielectric barrier discharge (DBD) at atmospheric pressure leads to a filamentary non-homogeneous discharge. However, it is also possible to obtain a diffuse DBD in homogeneous form, called atmospheric pressure glow discharge (APGD). We obtained a uniform APGD in helium and in the mixture of argon with alcohol, and studied the electrical characteristics of helium APGD. It is found that the relationship between discharge current and source frequency is different depending on the difference in gas gap when the applied voltage is kept constant. The discharge current shows an increasing trend with the increased frequency when gas gap is 0.8 cm, but the discharge current tends to decrease with the increased frequency when the gas gap increases. The discharge current always increases with the increased applied voltage when the source frequency is kept constant. We also observed a glow-like discharge in nitrogen at atmospheric pressure.
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This paper introduces the research states, diagnose methods and discharge mechanics of atmospheric pressure glow discharge. The possibility to achieve the glow discharge in air gap more than 2mm at atmospheric pressure is demonstrated based on a numerical simulation of an electron avalanche developing in an air gap and the experiments of creating a discharge at a low electrical strength.
Glow discharge
Electron avalanche
Atmospheric air
Air gap (plumbing)
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The atmospheric pressure glow discharge (APGD)is a new kind of plasma source that has been recently developed. It has wider industrial application prospects compared with low-pressure glow discharge. A stable, homogeneous glow discharge plasma device produced in our laboratory and controlled by dielectric barrier at 1atm is introduced in detail. It is capable of operating by using 10/20KHz-power supply, a parallel plate configuration with electrodes being covered by insulating surfaces, 2mm of gap distance and many kinds of working gases. The measurements of the discharge current pulse shapes and lissajous figure of voltage-electric charges provide sufficient evidence that this is really a uniform glow discharge at atmospheric pressure.
Glow discharge
Lissajous curve
Brush discharge
Discharge pressure
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Glow discharge
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Recently the authors developed an atmospheric-pressure glow discharge plasma method which can be applied to surface treatment and deposition on insulating surfaces for purposes of large-scale system treatment. However, this method was not able to treat metallic substrates. Consequently, they have improved the upper electrode to enable metal substrates to be treated. Some organic films were polymerised by the atmospheric-pressure method. Comparison of results from the atmospheric-pressure glow plasma method with those obtained by the low-pressure glow plasma method showed no differences in the chemical structures of plasma-polymerised films.
Glow discharge
Deposition
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Glow discharge
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