Ionization coefficients for argon in a micro-discharge

Kuschel, Thomas; Stefanović, Ilija; Malović, Gordana; Marić, Dragana; Petrović, Zoran Lj.

doi:10.1088/0963-0252/22/4/045001

Cited by 11 publications

(13 citation statements)

References 23 publications

(44 reference statements)

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“…Since the Townsend discharge is usually produced at low pressure, almost all the measurements of the ionization coefficient were carried out in the gases at a pressure much lower than the atmospheric pressure. Thus, the values of the α coefficient obtained by the measurements at low gas pressure are sometimes useless in the gas discharges at atmospheric pressure [11].…”

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confidence: 99%

A semi-empirical expression for the first Townsend coefficient in strong electric fields

Radmilović-Radjenović¹,

Radjenović²,

Klas³

et al. 2014

EPL

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The ionization coefficients for argon, nitrogen, hydrogen, oxygen and air are determined from the measured breakdown voltage curves in microgaps. The obtained values agree very well with the data for the standard size discharges indicating that the Townsend phenomenology does not need extension to describe microdischarges and that the ionization coefficients for such discharges obey the similarity law . In addition, an analytical expression for the ionization coefficients has been derived based on the generalized theory. The appropriate constants in derived expression have been modified by fitting the ionization coefficients obtained from the measured breakdown voltage curves.

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confidence: 99%

A semi-empirical expression for the first Townsend coefficient in strong electric fields

Radmilović-Radjenović¹,

Radjenović²,

Klas³

et al. 2014

EPL

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“…Exponential growth is best observed if plotted in a semi-logarithmic scale and the slope corresponds to the effective ionization coefficient α eff /N (Fig. 2), once equilibrium with the local field is reached [31,35,43]. The use of emission profiles recorded at high values of reduced electron fields to determine the α eff /N is limited due to emission in front of the cathode, coming from heavyparticle excitation, that masks the part of profile connected to electron-induced ionization and excitation [44,45].…”

Section: Resultsmentioning

confidence: 99%

Effective ionization coefficients for low current dc discharges in alcohol vapours at low pressure

et al. 2021

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This paper presents results for effective ionisation coefficients ($$\alpha _{\mathrm {eff}}/N$$ α eff / N , N—gas density) obtained from the breakdown voltage and emission profile measurements in low-pressure dc discharges in vapours of alcohols: methanol, ethanol, isopropanol, and n-butanol. Our results for $$\alpha _{\mathrm {eff}}/N$$ α eff / N are determined from the axial emission profiles in low-current Townsend discharge and lay in the interval of reduced electric field E/N (E—electric field, N—gas density), from 1 kTd to 8.8 kTd. We also give a comparison of our experimental results with those from the available literature. Our data cover the high E/N range of the standard operating conditions and in the region where other data are available we have a good agreement. Graphic abstract

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“…The biggest uncertainty lies in the gas amplification coefficient α. For low reduced field strengths this coefficient has large gradients and can yield strong variations depending on the quality of the fit or experimental results [22,23]. The fit parameters A and B are here only valid for reduced field strengths around E/p ≈ 7.6 V hPa −1 mm −1 .…”

Section: Discussionmentioning

confidence: 99%

Scaling and laws of DC discharges as pointers for HiPIMS plasmas

Maszl¹,

Laimer²,

Keudell³

et al. 2015

Preprint

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Scaling or smiliarity laws of plasmas are of interest if lab size plasma sources are to be scaled for industrial processes. In the case of direct current (DC) magnetron sputtering the scales can range from few centimeters in the lab to several meters if one takes the flat glass industry as one example. Ideally, the discharge parameters of the scaled plasmas are predictable and the fundamental physical processes are unaltered. Naturally, there are limitations and ranges of validity. Scaling laws for direct current glow discharges are well known. If a well diagnosed discharge is scaled, the field strength in the positive column, the gas amplification and the normal current density can easily be estimated. For non-stationary high power discharges like high power impulse magnetron sputtering (HiPIMS) plasmas, scaling is not as straight forward. Here, one deals with a non-stationary complex system with strong changes in plasma chemistry and symmetry breaks during the pulses. Because of the huge parameter space no good parameters are available to define these kind of discharges unambiguous at the moment. In this contribution we will discuss the scaling laws for DC glow discharges briefly and present experimental results for a discharge with copper electrodes and helium as plasma forming gas. This discharge was operated in a pressure range from 200 to 1600 hPa with three different electrode diameters (D = 2.1, 3.0 and 4.3 mm). Results from breakdown voltage measurements indicate that the pressure and electrode distance cannot be varied independently. Also limitations of the theoretical Paschen curves will be adressed. Effects of the scaling on the reduced normal current density, the reduced normal electric field in the positive column and discharge temperature will be discussed and limitations highlighted. Compared with these results the added complexity of HiPIMS plasmas will be described. Suggestions in the community how to obtain experimental finger prints of the plasmas will be reviewed and implications from the experiences with DC discharges on the development of similarity laws for HiPIMS plasmas will be discussed.

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Ionization coefficients for argon in a micro-discharge

Cited by 11 publications

References 23 publications

A semi-empirical expression for the first Townsend coefficient in strong electric fields

A semi-empirical expression for the first Townsend coefficient in strong electric fields

Effective ionization coefficients for low current dc discharges in alcohol vapours at low pressure

Scaling and laws of DC discharges as pointers for HiPIMS plasmas

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