the cylindrical coolant liquid channels are all hollow channels with a certain inner diameter, and are symmetrically distributed with a neutron target as a center; a top end of the cylindrical coolant liquid channel is in communication with an internal coolant liquid passage of the upper cover plate, and is shunted via the internal coolant liquid passage of the upper cover plate and flows to internal cooling channels of the neutron target and a extraction electrode respectively, and a bottom end of the cylindrical coolant liquid channel is in communication with the lower cover plate and is provided with a design of a quick plug sealing joint, so as to facilitate plugging and unplugging of a coolant liquid pipeline at any time and ensure a sealing performance; and

the cylindrical high-voltage channel is a cylindrical channel having a certain inner diameter and being hollow, an upper end of the cylindrical high-voltage channel is in communication with the upper cover plate, a hole position at an outlet of the upper cover plate is located directly below the extraction electrode, such that a high-voltage line passes through the channel and contacts with a bottom of the extraction electrode to provide a high voltage for the extraction electrode, a lower end of the cylindrical high-voltage channel is in communication with the lower cover plate, and a plurality of high-voltage line fixing screw holes are distributed around an outlet connection position of the lower cover plate for fixing the high-voltage line.