München 2019 – scientific programme

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P: Fachverband Plasmaphysik

P 18: Postersitzung

P 18.20: Poster

Thursday, March 21, 2019, 16:30–18:30, Foyer Audimax

Measurement of photophoretic forces in binary complex plasmas — •Frank Wieben and Dietmar Block — Institute of Experimental and Applied Physics, Kiel University, Kiel, Germany

Lasers are widely used in complex plasma research to manipulate micron sized dust particles embedded in a plasma without affecting the plasma itself. The particles experience a significant force when irradiated with laser light that is used to excite single or collective particle motion. The radiation force on the particles comprises two contributions: The first contribution is a force resulting from radiation pressure, i.e. momentum transfer from collisions with photons. The second contribution is a photophoretic force which results from interaction with the surrounding gas. Depending on how the particle absorbs energy from the electromagnetic radiation the particle surface can be non-uniformly heated causing an anisotropic net-momentum-transfer from the gas atoms. This complex interplay of particle properties, Mie scattering and interaction with neutral gas usually inhibits a separate measurement of the photophoretic force component. In this contribution a method to measure both forces for melamine-formaldehyde and silica particles in a binary mixture is presented. Forces are determined from the kinetic temperatures the particles attain in a laser heating scenario and results are compared to a model. Obtained efficiency factors are compared to Lorenz-Mie theory computations. This work has been supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of SFB TR24, Project A3b and Research Grant BL555/3-1.