For PIV diagnostics, a laser (Coherent Verdi V6, 532 nm) with an output power of 6 W is used. The laser beam is shaped using a slit aperture and subsequently guided through the reactor by means of a mirror before being terminated in a beam dump. The slit is adjusted such that the laser sheet has a width of approximately 0.5 mm in the x-direction and a height of approximately 2.5mm in the z-direction. The laser is operated with active cooling (Coherent ThermoTek T255P). A high speed camera (Phantom Veo 410L) is used for image acquisition and is equipped with a long-distance microscope (KX InfiniMax, MX-6), enabling high resolution imaging of the seeded flow. The camera is positioned to view the region between the metal grid and the quartz cover from the side, and it is aligned at a right angle to the laser sheet. Based on the camera’s field of view (FOV), the position of the laser sheet, and the seeding distribution, an elliptically shaped region of interest is defined for the PIV evaluation. The spatial resolution is approximately 5.76µm\pixel and is calibrated using a millimeter scale placed at the position of the laser sheet plane, when the laser was turned off. The effective measurement region is thus restricted to the illuminated section of the flow, with its extent defined by the intersection of the laser sheet and the camera field of view. The final vector field resolution depends on the chosen interrogation window size and overlap during PIV processing, while the minimum feasible window size is mainly constrained by the seeding density and the frame rate. In Particle Image Velocimetry, the displacement of particle patterns between two consecutive images is determined by applying cross-correlation on small interrogation windows to obtain the local velocity field. The temporal separation between the image pairs was set to Delta t = 118.8µs (8420 fps) for a flow rate of 2000sccm and Delta t = 188.79 µs (5297 fps) for all lower gas flow rates. Operating the camera at the high frame rate of 8420fps leads to a reduction of the image resolution from 1280 x 800 pixel to 1152x 552 pixel. Under discharge operation, the resulting particle image displacements satisfied in this way for all flow rates the so-called one-quarter criterion, i.e., the particle displacement between consecutive frames remained approximately four times smaller than the corresponding interrogation window size. Fulfilling this condition reduces in-plane loss of particle pairs and thereby improves the robustness and accuracy of the cross-correlation analysis. The PIV evaluation was conducted using the software DaVis (Version~10, LaVision GmbH, Germany). Spatial calibration was performed at the beginning of each measurement series by placing a millimeter scale in the plane of the laser light sheet, enabling the determination of the calibration factor.