NOVELTY - A gasification reactor comprises a ring gap (33), with the height and width, in a thermo-chemical reaction pipe that divides the pipe into upper and lower sections (31, 34). The upper section has different diameter than the lower section with a concentric parallel sections that overlap zone which defines the gap.    USE - Reactor (including downstream reactor, upstream reactor or horizontal tilted reactor) for gasification of solid fuels such as biofuels.    ADVANTAGE - The reactor is economical to operate and durable in use, and uniformly heats and distributes the material inside the reactive zone to improve efficiency and dynamic behavior.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a method for varying and manipulating the relative distance between the piston such as gate valve and the ring carrier device with the use of an actuator, to vary and manipulate the effective flow resistance for the oxidant through the ring gap, and the flow rate and the flow speed of the oxidant through the ring gap into the thermo-chemical gasification reactor;    (2) a method for controlling the temperature of the different heating zones of the thermo-chemical gasification reactor by controlling the electric energy provided to the heating elements, to generate an optimized temperature profile within the reactor, to maximize the thermodynamic efficiency of the gasification process in dependence of the specific physical and chemical properties of the inserted fuel type; and    (3) a method for controlling the oxidant flow rate to generate an optimized temperature profile of the chemical oxidation zone and the chemical reduction zone within the thermo-chemical gasification reactor, to maximize the thermodynamic efficiency of the gasification process in dependence of the specific physical and chemical properties of the inserted fuel type.    DESCRIPTION OF DRAWING(S) - The drawing shows a cut-away side view of the lower part of downdraft gasification reactor assembly.    Upper and lower sections (31, 34)    Gaps (33, 37)    Bed plate (35)