Extruder (100; 100') for the viscosity-increasing preparation of meltable polymers, at least comprising a barrel (10; 10') having an inner barrel aperture in which an extruder screw (20; 20') having at least one extruder screw flight (31,32, 33, 34, 35) in the form of a helical coil is rotatably arranged, which extruder screw (20; 20') is divided in terms of its external diameter into a diameter start region, diameter middle region and diameter end region, wherein: - the diameter middle region has a greater external diameter D2 than at least one of the other diameter regions; - a respective transition cone (22, 24) is formed between regions of different diameter D1, D2 or D3; - at least one degassing zone (23.3) is formed in the diameter middle region and has a barrel aperture from which at least one suction-removal opening (15.2) extends to an outer side of the barrel (10; 10'), wherein, in the region of the degassing zone (23.3), a plurality of satellite screws which surround the extruder screw (20; 20'), which are driven in rotation and which each rotate individually about a satellite axis and jointly with the extruder screw (20; 20') are provided, characterized - in that at least two degassing zones (23.1, 23.3) are provided in the diameter middle region and each have at least one assigned suction-removal opening (15.1, 15.2) in the barrel (10; 10'), wherein a degassing zone (23.3) is formed in the region of the satellite screws and a further degassing zone (23.1) is formed upstream thereof in a flow direction, and - in that the channel depth of the screw channels (42, 43, 44) of the extruder screw (20; 20') which are formed between the extruder screw flights (32, 33, 34, 35) is greater in both degassing zones (23.1, 23.3) than in at least one sealing and compression portion (23.2) formed between the degassing zones (23.1, 23.3). at least comprising a barrel (10; 10') having an inner barrel aperture in which an extruder screw (20; 20') having at least one extruder screw flight (31,32, 33, 34, 35) in the form of a helical coil is rotatably arranged, which extruder screw (20; 20') is divided in terms of its external diameter into a diameter start region, diameter middle region and diameter end region, wherein: - the diameter middle region has a greater external diameter D2 than at least one of the other diameter regions; - a respective transition cone (22, 24) is formed between regions of different diameter D1, D2 or D3; - at least one degassing zone (23.3) is formed in the diameter middle region and has a barrel aperture from which at least one suction-removal opening (15.2) extends to an outer side of the barrel (10; 10'), wherein, in the region of the degassing zone (23.3), a plurality of satellite screws which surround the extruder screw (20; 20'), which are driven in rotation and which each rotate individually about a satellite axis and jointly with the extruder screw (20; 20') are provided, - the diameter middle region has a greater external diameter D2 than at least one of the other diameter regions; - a respective transition cone (22, 24) is formed between regions of different diameter D1, D2 or D3; - at least one degassing zone (23.3) is formed in the diameter middle region and has a barrel aperture from which at least one suction-removal opening (15.2) extends to an outer side of the barrel (10; 10'), wherein, in the region of the degassing zone (23.3), a plurality of satellite screws which surround the extruder screw (20; 20'), which are driven in rotation and which each rotate individually about a satellite axis and jointly with the extruder screw (20; 20') are provided, characterized - in that at least two degassing zones (23.1, 23.3) are provided in the diameter middle region and each have at least one assigned suction-removal opening (15.1, 15.2) in the barrel (10; 10'), wherein a degassing zone (23.3) is formed in the region of the satellite screws and a further degassing zone (23.1) is formed upstream thereof in a flow direction, and - in that the channel depth of the screw channels (42, 43, 44) of the extruder screw (20; 20') which are formed between the extruder screw flights (32, 33, 34, 35) is greater in both degassing zones (23.1, 23.3) than in at least one sealing and compression portion (23.2) formed between the degassing zones (23.1, 23.3). - in that at least two degassing zones (23.1, 23.3) are provided in the diameter middle region and each have at least one assigned suction-removal opening (15.1, 15.2) in the barrel (10; 10'), wherein a degassing zone (23.3) is formed in the region of the satellite screws and a further degassing zone (23.1) is formed upstream thereof in a flow direction, and - in that the channel depth of the screw channels (42, 43, 44) of the extruder screw (20; 20') which are formed between the extruder screw flights (32, 33, 34, 35) is greater in both degassing zones (23.1, 23.3) than in at least one sealing and compression portion (23.2) formed between the degassing zones (23.1, 23.3).