Stuttgart 2012 – scientific programme

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P: Fachverband Plasmaphysik

P 20: Poster: Diagnostik

P 20.10: Poster

Thursday, March 15, 2012, 16:30–19:00, Poster.III

Electron density measurement in cc-rf argon plasma by 160 GHz microwave interferometer and electric probe — •Thomas Wegner, Christian Küllig, Kristian Dittmann, and Jürgen Meichsner — Institute of Physics, University of Greifswald

The applied non-invasive Gaussian beam microwave interferometry (mwi) at 160 GHz (beam waist 5 mm, confocal length of about 10 cm) provides immediately line integrated electron density in cc-rf plasma at 13.56 MHz. On the other hand, the cylindrical Langmuir probe (passive rf-compensated, platinum, r=125 µ m, l=8 mm) immersed in the rf plasma reveals the local plasma parameters. But probe measurements are combined with a disturbance of the plasma and specific assumptions for determination of electron density and electron energy distribution function. For an argon plasma both diagnostics are used for the deconvolution of the line integrated electron density of the mwi by spatially resolved electron density by means of probe measurement. Vice versa, it is possible to calculate the line integrated electron density from the probe data. It is shown that both diagnostics provides comparable results within the limit of factor two. Moreover, it was measured the ion saturation current in the whole plasma volume for selected rf power and total gas pressure. Thereby, it could be shown that the mean sheath thickness s in front of the powered rf electrode depends on the pressure p according to s∝ p^−κ. Whereby, κ is in the range of 0.27 to 0.40 which is in good agreement with standard collisional sheath models. // Funded by the DFG Collaborative Research Centre TRR24 "Fundamentals of Complex Plasmas", project B5.