Plasma sheath diagnostic using microscpic particle probes manipulated in laser tweezers

Low-temperature plasmas are important tools in industrial applications as well as in many basic research fields. Important plasma parameters such as density, temperature or composition are diagnosed using various established methods [1]. However, it is difficult to probe the extremely important sheath region, which is only a few millimeters thick and, thus, not accessible with macroscopic methods, as they themselves change the plasma. In recent years, microparticles have been used as probes for non-conventional plasma diagnostic purposes. Due to their size and behavior in the plasma, they are well suited for increasing the spatial resolution and, thus, providing information in addition to common diagnostics [2].

The presentation first gives a brief overview of some experiments in which microparticles were used as probes. For example, experiments on the momentum of test particles showed the importance of fast neutrals in an ion beam by charge exchange collisions [3]. With the help of temperature-dependent fluorescent particles, the temperature of the particles and, via modeling, the energy balance due to the surrounding plasma could be estimated [4]. Recently published studies with optically trapped microparticles [5, 6] showed for the first time the forces acting on the particles within the whole sheath of an rf plasma down to the electrode surface. Assuming a linear field increase in this space charge region, it is possible to estimate the spatial development of the particle charge from the bulk towards the electrode.



[1] Benedikt, J., et.al., Plasma Sources Sci. Technol. 30(2021), 033001.

[2] Maurer, H.R., et.al., Contrib. Plasma Phys. 51(2011), 218-227.

[3] Schneider, V., et.al., Rev. Sci. Instrum. 81(2010), 013503.

[4] Maurer, H.R., et.al., Phys. Plasmas 17(2010), 113707.

[5] Schneider, V., et.al., Rev. Sci. Instrum. 89(2018), 103505.

[6] Schleitzer, J., et.al., Phys. Plasmas 28(2021), 083506.