Comparison of electron-density measurements made using a Langmuir probe and microwave interferometer in the Gaseous Electronics Conference reference reactor

Abstract

A Langmuir probe and a microwave interferometer have been combined to measure the electron density of argon glow discharges in the Gaseous Electronics Conference reference reactor [Bull. Am. Phys. Soc. 36, 207 (1991)]. The two techniques indicate the same charge density at 100 mTorr to within 30%. This 30% difference is easily explained by the experimental peculiarities. While the predicted charge densities obtained from the two techniques track one another as the applied rf voltage is varied at constant pressure, they do not track one another as the pressure is varied at constant rf voltage. In fact, the charge densities predicted from the Langmuir probe using Laframboise’s theory (Tech. Rep. 100, Univ. Toronto Inst. Aerospace Study, 1966) are factors of 2 and 4 times lower than those from the interferometer at 250 and 500 mTorr, respectively. It appears that the probe alters the charge density in its vicinity when the probe radius becomes greater than the ion mean free path. The interferometer has also been used to investigate the macroscopic perturbation of the plasma electron density caused by the Langmuir probe. It was found that presence of the probe in a radio-frequency discharge does not appreciably alter the electron density measured by the interferometer at a set rf voltage irrespective of the potential placed upon it. This was not the case for dc discharges in the same apparatus where the volume-averaged electron density could be depleted by as much as 70% when the probe was biased even a few volts above plasma potential.

Microwave Diagnostics of the Electron Density in Molecular Mixture Plasmas

“…For its measurement the Langmuir probe technique and microwave diagnostics are often used [1,2,3]. By inserting a metal probe into a discharge plasma electric probe measurements allow to determine spatially resolved the energy distribution and thus the absolute density of the electrons.…”

Microcalorimetry of dust particles in a radio-frequency plasma

“…9 Many other researchers, e.g., Olthoff, Hebner, Anderson, Overzet, and McMillin, have used GEC cells to study the behavior of plasmas. [10][11][12][13][14] In our GEC cell we use argon and oxygen as feed gases and we operate between 5 and 60 Pa with a typical flow rate of 1 sccm. The supplied rf power is in the range of 2-45 W. The plasma is created with a frequency generator ͑Hewlett-Packard 33120A, 13.56 MHz͒, a wideband rf amplifier ͑Kalmus 150 C͒, and a homebuilt T-type matching network.…”

“…In order to calculate J e , J i , and J rec the internal plasma parameters obtained by Langmuir probe measurements ͑see Fig. 2͒ and/or typical literature values for a GEC cell under comparable experimental conditions, 13,26,27 respectively, have been taken. In Fig.…”

Electron density measurements in an atmospheric pressure argon discharge by means of plasma radiation

“…[1][2][3] The electron density as a key parameter plays an important role in the understanding of plasma sources and plasma processing. Typical methods to measure the electron density include Langmuir probe, 4,5 microwave interferometer, [6][7][8] laser Thomson scattering, 9 and Stark broadening. 10 The plasma oscillation probe ͑POP͒ was developed by Shirakawa and Sugai 11 as a plasma diagnostic method usable even in contaminated conditions.…”