Erlangen 2026 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 16: Poster Session Plasma Physics

P 16.41: Poster

Donnerstag, 19. März 2026, 13:45–15:45, Redoutensaal

Probing Ion Drag and Electric Field Forces in CCRF Plasmas with Optical Tweezers — •Jessica Niemann, Viktor Schneider, and Holger Kersten — Institute of Experimental and Applied Physics, Christian-Albrechts-University Kiel, Germany

Many different diagnostics can be used to measure the spatial distribution and temporal evolution of plasma parameters. Over the past decade, the concept of utilizing externally injected microparticles as non-invasive probes, influenced by various forces and energy fluxes in plasmas, has been implemented. Information about local electric fields, energy fluxes, and momentum transfer by ions to the particles can be obtained based on their behavior in the plasma. Especially, the manipulation of microparticles by an optical tweezer is of interest, as it enables the microprobe to be positioned in areas of the plasma typically inaccessible to conventional diagnostic methods, such as the plasma sheath. In this study, optically trapped microparticles in a highly focused laser beam are used to investigate both the electrostatic field force in the sheath and the ion drag force in the presheath of a capacitively coupled radio-frequency discharge. These forces differ by roughly one order of magnitude, requiring adjustments of the trapping laser power to control the sensitivity of the optical trap accordingly. By observing the displacement of the trapped particle under varying gas pressure and phase angle in dual-frequency discharges, the spatial structure and parameter dependence of both forces are resolved. These measurements allow the experimental reconstruction of the fundamental plasma structure comprising bulk, presheath, and sheath.

Keywords: Capacitively coupled RF discharges (CCRF); Optical tweezers diagnostics; Sheath and presheath forces; Ion drag force; Electric field force