Greifswald 2009 – scientific programme
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P: Fachverband Plasmaphysik
P 9: Poster: Niedertemperaturplasmen
P 9.20: Poster
Tuesday, March 31, 2009, 17:30–19:30, Foyer des IfP
160 GHz microwave interferometry for oxygen rf plasma (CCP) diagnostics — •Kristian Dittmann, Christian Küllig, and Jürgen Meichsner — University of Greifswald, Institute of Physics, Greifswald, Germany
The microwave interferometry compared with probe diagnostics is a non-invasive method which affords a direct measurement of the line integrated electron density by the phase shift of the microwave due to the change of electron density without any model assumptions. The
electron density is directly coupled with the plasma frequency and therefore with the refractive index of the plasma.
The interferometer consists of a frequency stabilized (PLL) heterodyne system operating at a frequency of 160 GHz (λ = 1.87 mm). Therefore, a quasi-optical setup is assumed, whereas it has to be considered special designed horn antennas and elliptical mirrors as well as the limiting apertures (windows of the plasma chamber) in relation to the beam waist for optimal coupling and focussing the microwave into the plasma centre. Assuming typical electron densities of rf plasmas (CCP) in the range from 1015 to 1016 m−3 the corresponding phase shifts are expected of between 0.03∘ and 0.3∘.
First measurements of line integrated electron densities were performed in dependence on oxygen total pressure and rf power. Using a simplified de-convolution method of the line-integrated signal the determined electron densities correspond to the expected values in rf plasmas.