The ac-coupling between a Langmuir probe and a plasma and its effect on the plasma density measurement in the afterglow

The ac-coupling between a Langmuir probe and a plasma is commonly enhanced by using a large-area compensation electrode (CE) in rf discharges in order to reduce the rf distortion on the probe I-V curves. However, in the early afterglow of pulsed discharges the ac-coupling induces a spurious electron...

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Bibliographic Details
Published in:Journal of physics. D, Applied physics Applied physics, 2014-02, Vol.47 (7), p.75201-9
Main Authors: Liu, Fei-Xiang, Wang, Zhen-Bin, Pu, Yi-Kang
Format: Article
Language:English
Subjects:
ac-coupling
Afterglows
Argon plasma
compensation electrode
diagnostics
Distortion
Electrodes
langmuir probe
low temperature plasmas
Plasma (physics)
Plasma density
Plasma potentials
Volt-ampere characteristics
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Summary:The ac-coupling between a Langmuir probe and a plasma is commonly enhanced by using a large-area compensation electrode (CE) in rf discharges in order to reduce the rf distortion on the probe I-V curves. However, in the early afterglow of pulsed discharges the ac-coupling induces a spurious electron current which prevents obtaining the correct values of the plasma parameters if conventional methods are used. In this work, the ac-coupling effect is investigated experimentally in a pulsed rf capacitively coupled argon plasma at 20 mTorr. An equivalent circuit model is also developed to simulate this effect. Both results show that the strong ac-coupling can lead to a significant misestimate of the plasma density in the early afterglow. However, the determination of the effective electron temperature and the plasma potential is not significantly affected by the ac-coupling if the Druyvesteyn method is used. In the last part of this work, two methods are proposed to estimate the correct value of the plasma density, using the data collected from a probe with a CE.
ISSN:0022-3727
1361-6463
DOI:10.1088/0022-3727/47/7/075201