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Laser induced fluorescence (LIF) was applied at the B-X transition of the CH radical to measure absolute densities of the CH radicals in an electron cyclotron resonance (ECR) methane plasma. The absolute experimental uncertainty is only about 30 % due to a new calibration procedure. The central CH density rises from about 3 x 1.0 E9/cm3 at 14 mPa to about 1 x 1.0 E11/cm3 at 0.5 Pa and is in most cases independent of the absorbed microwave power. The CH density correlates well with optical emission from the CH A-X and B-X transitions over a wide pressure range. Furthermore, the electron temperature was estimated from optical emission spectroscopy. Additionally the line-integral of the electron density was measured by microwave interferometry. Atomic hydrogen density was determined by means of actinometry. The experimental results are in satisfactory agreement with predictions from a model based on rate equations for the electron-induced dissociation and ionisation of the parent methane gas. This model also includes the interaction of the plasma species with the surrounding walls and the particle transport due to pumping.

Additional information

Authors: ENGELHARD M, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 4/262 DE/EN (1993)
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