Measurement of the Neutral Particle Density in an Electron Cyclotron Resonance Plasma by Rayleigh Scattering

Abstract

The neutral atom density in an electron cyclotron resonance plasma has been directly measured for the first time using a combination of Rayleigh and Thomson scattering. The measurements were made in the source region of a 3 mTorr argon discharge, and indicated that the neutral atom density was at least 50% less than would be expected at a gas pressure of 3 mTorr. The decrease in the neutral atom density is attributed to the effect of ion-neutral charge exchange collisions in the plasma. The accuracy of the measurement was found to depend on the contribution of metastable atoms to the measured scattered signal.

Concepts, Capabilities, and Limitations of Global Models: A Review

“…In particular, cases where there is a significant modulation of reaction rates in space, such as the aforementioned case of high pressure CCPs, [122,123] require some consideration of this. The effect of neutral dynamics is also of concern for high pressure systems, where gas temperatures may be elevated, [136,137] and high density plasmas where the high degrees of ionization lead to neutral gas depletion [138][139][140] through a variety of effects.…”

Laser-scattering instrument for fundamental studies on a glow discharge

“…For instance, the argon atom Rayleigh-scattering cross-section is 500 times lower than that of the argon metastable. 15,24 According to Muraoka et al, 25 there should be less than one argon metastable per one thousand argon atoms so that the atom number-density measurement should be affected by less than 10% because of scattering from excitedstate argon. The argon metastable population was not measured in the present study.…”

Diagnostics of low-density glow discharge plasmas using Thomson scattering

“…It has already been mentioned that the scattered spectrum which is measured from the discharge contains a Rayleigh scattered component from the neutral particles in the discharge, as well as a Thomson scattered component. This Rayleigh scattered component can be measured and so the density of neutral particles in the discharge can also be determined [15]. For this measurement, the Thomson spectrum must be measured, so that the Thomson component of the spectrum can be determined, and the stray light must also be measured.…”