Mitigation of the line start effect in PLATO normal camera CCDs for accurate read-out noise characterization

PLATO is ESA's M3 mission to detect and characterise exoplanets around bright solar-type stars using high-precision space photometry. The payload includes 26 cameras: 24 Normal Cameras (N-CAMs) for photometry and 2 Fast Cameras for bright targets and guidance. Each N-CAM hosts four CCDs, each read out on two sides. During thermal-vacuum tests, bias and dark frames are acquired to characterise the read-out noise (RON) of each side. The CCD bias exhibits a Line Start Effect (LSE), a column-dependent offset at line start that leads to a systematic overestimation of pixel-to-pixel noise and can cause RON to exceed its requirement. For each side, an LSE profile is derived by averaging bias frames along rows and subtracted before recomputing RON maps. After presenting the general framework and the analysis concept, in this presentation, we show how the LSE mitigation reducing high-noise tails and restoring compliance with the N-CAM noise requirement.