A gasification reactor including a gasifier having a tubular gastight wall with a discharge channel or dip tube at its lower end leading into a lower slag collection bath. The gastight wall and the slag collection bath are arranged within a pressure vessel. An annular space between the pressure vessel and the gasifier with the discharge channel is separated in a high pressure top section and a low pressure lower section by a sealing arrangement having a damper. The damper can for instance be a hydraulic lock, or a lower seal at a distance below an upper seal.