Carbon-fibre composites are currently foreseen as material for the high heat load areas of the ITER divertor target plates. Erosion will largely determine both the lifetime of these components and the long term retention of fuel via the formation of hydrogen-rich carbon layers on the targets themselves and on remote areas. At JET the Horizontal Target plate (HT) in front of the pumping duct of the inner MKII-HD divertor leg was previously identified as the location with strongest carbon deposition on a plasma-facing area. Post mortem-analysis of MKII divertor tiles after the DT campaign discovered the thickest carbon layers with high fuel content in the louvre area of the inner divertor. The migration of carbon in the inner divertor was assumed to be stepwise; however, the key parameters and the exact mechanism remained unclear.