Erlangen 2018 – scientific programme
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P: Fachverband Plasmaphysik
P 13: Low Pressure Plasmas - Poster
P 13.9: Poster
Tuesday, March 6, 2018, 16:15–18:15, Redoutensaal
Application of an AC method for measuring the EEDF in low pressure plasmas by a Langmuir probe — •Adrian Heiler1, Roland Friedl1, and Ursel Fantz1,2 — 1AG Experimentelle Plasmaphysik, Universität Augsburg, 86135 Augsburg — 2Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching
The electron energy distribution function (EEDF) in low pressure low temperature plasmas is often non-Maxwellian and therefore needs to be measured in experiment. The most straightforward approach to determining the EEDF is to measure the I-V characteristic of a Langmuir probe and numerically differentiate it twice (Druyvesteyn correlation). However, numerical differentiation requires data smoothing techniques and leads to inevitable numerical errors. Therefore, a Langmuir probe method first proposed in the 1930s by Sloane and MacGregor (1934 Phil. Mag. 18, 193) was adopted to directly measure d2I/dV2. This is done by superimposing a sinusoidal AC voltage on the probe DC bias and Fourier transformation of the corresponding probe current. Besides avoiding numerical errors, the AC method provides access to a higher dynamic range of the EEDF due to better signal-to-noise ratio.
The system is implemented for a sinus frequency of 13 kHz and a variable amplitude in the range of 1 V. Moreover, it is also capable of measuring and analysing the probe I-V characteristic. The system is tested in an ICP discharge (planar coil, RF 2 MHz, power up to 2 kW) in the 1−10 Pa pressure range and compared to a conventional Langmuir probe system.