A reactor for the conversion of biomass material includes an elongate annular chamber with an inner wall and an outer casing. A screw conveyor extends from one end into the chamber to feed biomass material. A heat source is provided within the inner wall of the chamber, and may be comprised of a series of permanent magnet assemblies mounted for rotation within a sleeve of electrically conductive material. The sleeve also serves as the inner wall of the chamber. Each magnet assembly includes a series of magnets spaced apart on a periphery of a circular support. A layer of insulating material is provided between the magnet assemblies and the sleeve. A rotatable shaft adapted for connection to a driving power source provides a mounting for the magnet assemblies.