Physics of high-pressure helium and argon radio-frequency plasmas

Moravej, M.; Yang, Xian-Jie; Nowling, G R; Chang, Jane P.; Hicks, Robert F.; Babayan, S E

doi:10.1063/1.1815047

Cited by 133 publications

(101 citation statements)

References 53 publications

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“…In many atmospheric pressure plasmas being utilized in various industrial processes, gases such as argon or helium are often introduced for assisting stable plasma generation and/or for other particular processes. In general, helium has lower breakdown voltage characteristics in the Ͼ10 Torr cm range of the Paschen curve [1][2][3] and a lower gas temperature 4 than argon, which is consistent with our experimental results. The low breakdown voltage is beneficial because it helps by preventing arc production and system overloading.…”

Section: Introductionsupporting

confidence: 82%

Control of radio-frequency atmospheric pressure argon plasma characteristics by helium gas mixing

2006

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The control of plasma characteristics is one of the important issues in many atmospheric pressure plasma applications. In order to accomplish this control, a feasibility study was performed by investigating the role of helium gas in an argon glow plasma that were produced in ambient air by 13.56 MHz radio-frequency power. Optical emission spectroscopy was used to measure rotational temperature and emission spectra acquired between 300 and 840 nm. Based on electrical and optical measurements, parameters such as gas temperature, breakdown voltage, power coupling efficiency, spatial uniformity of rotational temperature, and the sum of the emission intensity were controlled by varying the argon and helium gas mixing ratio. The addition of helium gas ͑from 0 to 10 ᐉpm͒ to the argon flow ͑of 10 ᐉpm͒ lowered the breakdown voltage ͑from 430 to 300 V pk ͒ and the rotational temperature ͑from 465 to 360 K͒. However, an excessive addition of helium resulted in a reduction of the spatial uniformity and efficiency of power coupling. When the ratio of helium to argon flow was between 0.3 and 0.5, a high spatial uniformity with a relatively low gas temperature and breakdown voltage was achieved. This suggests that mixing of the supply gas is a useful way of controlling the plasma characteristics that may be utilized for applications with specific required discharge conditions.

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Section: Introductionsupporting

confidence: 82%

Control of radio-frequency atmospheric pressure argon plasma characteristics by helium gas mixing

2006

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“…[1][2][3] As the interpretation of the data obtained with electric probes at such pressures is not clear, 4 many experimental works have focused on the use of optical emission spectroscopy ͑OES͒ as a way of characterizing the fundamental parameters of the discharge, either calculating the broadening of the emission lines to obtain the electron density, 5 modeling emission bands of some species to get the gas temperature, 6 or simply by recording the emission of the different excited states in order to get the electron temperature assuming a Bolztmann-like distribution of the population of the emitting excited levels. 3 The determination of the electron mean kinetic energy through this method is based on the identification of the excitation temperature obtained with the electron temperature.…”

Section: Introductionmentioning

confidence: 99%

Measuring the electron temperature by optical emission spectroscopy in two temperature plasmas at atmospheric pressure: A critical approach

Yanguas‐Gil

Cotrino

González‐Elipe

2006

Journal of Applied Physics

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The measurement of the electron mean kinetic energy by identifying the electron temperature and the excitation temperature obtained by optical emission spectroscopy is theoretically studied for two temperature argon plasmas at atmospheric pressure. Using a 32-level collisional radiative model in which both electron impact and argon-impact inelastic collisions are taken into account, it has been found that under certain conditions the argon inelastic collisions may cause a decrease of the argon excitation temperature so that the relation T e Ͼ T exc Ͼ T 0 is satisfied. This inequality also appears when electron losses due to diffusion are important and the electron density is lower than its equilibrium value.

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“…Since we expect to generate plasmas in scales less than 1mm, at atmospheric pressure, the argon and helium curves from [Moravej et al, 2004] illustrate approximate voltages of 125V and 70V, both safely and easily achievable in laboratory conditions. That we have generated plasmas with characteristic scale of 800 µm in argon and oxygen already suggests feasibility in the scales of microchips (LozanoParada, 2007).…”

Section: §1 Introductionmentioning

confidence: 99%

The role of kinetics in the design of plasma microreactors

Lozano-Parada¹,

Zimmerman²

2010

Chemical Engineering Science

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Miniaturisation of plasma reactors has the potential of low power operation. In general, the electric field strength in the gap between two electrodes increases proportionate to inverse of the gap width, so that it is possible to Overcome the first ionization potential of the gas with a low voltage. However, plasmas are extinguished primarily by recombination at the walls. Wall collisions are enhanced by the greater surface area to volume ratio in microchannels, which also increases proportionate to the inverse of the gap width. If the plasma were well-mixed, then the plasma creation in the bulk would be balanced by extinction at the wall, providing no particular advantage with regard to low voltage / low power operation. However, the plasma is transferred from the bulk to the wall by ambipolar diffusion. If the operation of the plasma microreactor is essentially transient or batch, whether or not the reaction kinetics are comparable to or faster than ambipolar diffusion determines if there is a regime of operation in which a low voltage plasma discharge can generate a high yield of product. In this paper, this question is investigated with regards to the ozone formation reaction and a particular design of a microchannel plasma reactor, with parameters so chosen to arguably achieve low voltage operation. The focus of this paper is the simulation of the kinetics of the plasma reactions leading to ozone formation, which shows a time to completion that is comparable (10 -2 s) or faster than the estimate of ambipolar diffusion time at these length scales. Preliminary results of a microchip reactor are consistent with this prediction.

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Physics of high-pressure helium and argon radio-frequency plasmas

Cited by 133 publications

References 53 publications

Control of radio-frequency atmospheric pressure argon plasma characteristics by helium gas mixing

Control of radio-frequency atmospheric pressure argon plasma characteristics by helium gas mixing

Measuring the electron temperature by optical emission spectroscopy in two temperature plasmas at atmospheric pressure: A critical approach

The role of kinetics in the design of plasma microreactors

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