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Title: Analysis of uncompensated Langmuir probe characteristics in radio-frequency discharges revisited

Abstract

Measurements of the electron temperature, plasma density, and floating and plasma potentials with Langmuir probes in radio-frequency discharges often represent a challenge due to rf oscillations of the plasma potential. These oscillations distort the probe characteristic, resulting in wrong estimates of the plasma parameters. Both active and passive rf compensation methods have previously been used to eliminate rf fluctuation effects on the electron current drawn by an electrostatic probe. These effects on an uncompensated probe have been theoretically and experimentally studied by Garscadden and Emeleus [Proc. Phys. Soc. London 79, 535 (1962)], Boschi and Magistrelli [Nuovo Cimento 29, 487 (1963)], and Crawford [J. Appl. Phys. 34, 1897 (1963)]. They have shown theoretically that, assuming a Maxwellian distribution and sinusoidal plasma-potential oscillation, the electron temperature can be deduced directly from an uncompensated Langmuir probe trace, by taking the natural logarithm of the electron current. It is the purpose of this paper to bring back the attention onto this result, which shows that under certain discharge conditions it is not necessary to build any rf compensation in a Langmuir probe system. Here we present and reference experimental data found on the literature which support this result. Also computational data are presented.

Authors:
; ;  [1]
  1. National Centre for Plasma Science and Technology, School of Physical Sciences, Dublin City University, Collins Avenue, Glasnevin, Dublin 9 (Ireland)
Publication Date:
OSTI Identifier:
20787778
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 99; Journal Issue: 1; Other Information: DOI: 10.1063/1.2158496; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CHARGED-PARTICLE TRANSPORT; ELECTRON TEMPERATURE; ELECTRONS; ELECTROSTATIC PROBES; EXPERIMENTAL DATA; FLUCTUATIONS; HIGH-FREQUENCY DISCHARGES; LANGMUIR PROBE; OSCILLATIONS; PLASMA; PLASMA DENSITY; PLASMA POTENTIAL; PLASMA WAVES; RADIOWAVE RADIATION

Citation Formats

Oksuz, L., Soberon, F., and Ellingboe, A.R. Analysis of uncompensated Langmuir probe characteristics in radio-frequency discharges revisited. United States: N. p., 2006. Web. doi:10.1063/1.2158496.
Oksuz, L., Soberon, F., & Ellingboe, A.R. Analysis of uncompensated Langmuir probe characteristics in radio-frequency discharges revisited. United States. doi:10.1063/1.2158496.
Oksuz, L., Soberon, F., and Ellingboe, A.R. Sun . "Analysis of uncompensated Langmuir probe characteristics in radio-frequency discharges revisited". United States. doi:10.1063/1.2158496.
@article{osti_20787778,
title = {Analysis of uncompensated Langmuir probe characteristics in radio-frequency discharges revisited},
author = {Oksuz, L. and Soberon, F. and Ellingboe, A.R.},
abstractNote = {Measurements of the electron temperature, plasma density, and floating and plasma potentials with Langmuir probes in radio-frequency discharges often represent a challenge due to rf oscillations of the plasma potential. These oscillations distort the probe characteristic, resulting in wrong estimates of the plasma parameters. Both active and passive rf compensation methods have previously been used to eliminate rf fluctuation effects on the electron current drawn by an electrostatic probe. These effects on an uncompensated probe have been theoretically and experimentally studied by Garscadden and Emeleus [Proc. Phys. Soc. London 79, 535 (1962)], Boschi and Magistrelli [Nuovo Cimento 29, 487 (1963)], and Crawford [J. Appl. Phys. 34, 1897 (1963)]. They have shown theoretically that, assuming a Maxwellian distribution and sinusoidal plasma-potential oscillation, the electron temperature can be deduced directly from an uncompensated Langmuir probe trace, by taking the natural logarithm of the electron current. It is the purpose of this paper to bring back the attention onto this result, which shows that under certain discharge conditions it is not necessary to build any rf compensation in a Langmuir probe system. Here we present and reference experimental data found on the literature which support this result. Also computational data are presented.},
doi = {10.1063/1.2158496},
journal = {Journal of Applied Physics},
number = 1,
volume = 99,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • The properties of an inductively coupled argon plasma in a uniform magnetic field, at pressures of the order of 0.1 Pa, in the presence of a weak current-free electric double layer, are measured with a plane Langmuir probe. The static current-voltage probe characteristics, recorded on the symmetry axis of the experimental device, both in the plasma source and in the main chamber of the setup, showed the existence of two electron populations with different temperatures. The axial profiles of plasma parameters, such as the plasma potential and the cold and hot electron temperatures, offered a new insight into such amore » complex system. However, both the external magnetic field and the two electron populations contribute to the difficulty of calculation of the local plasma density. A method for solving this problem, involving the definition of an effective electron temperature, is also presented.« less
  • The double-probe has been used successfully in radio-frequency discharges. However, in low-frequency discharges, the double-probe I-V curve is so much seriously distorted by the strong plasma potential fluctuations that the I-V curve may lead to a large estimate error of plasma parameters. To suppress the distortion, we investigate the double-probe characteristics in low-frequency gas discharge based on an equivalent circuit model, taking both the plasma sheath and probe circuit into account. We discovered that there are two primary interferences to the I-V curve distortion: the voltage fluctuation between two probe tips caused by the filter difference voltage and the currentmore » peak at the negative edge of the plasma potential. Consequently, we propose a modified passive filter to reduce the two types of interference simultaneously. Experiments are conducted in a glow-discharge plasma (f = 30 kHz) to test the performance of the improved double probe. The results show that the electron density error is reduced from more than 100% to less than 10%. The proposed improved method is also suitable in cases where intensive potential fluctuations exist.« less
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