A source of a tubular beam of ions comprising a cylindrical shell with one butt end having an axial hole in it and the other butt end solid. It is provided with a rod having one end fixed to the solid butt end of the cylindrical shell and arranged coaxially to the latter. The free end of the rod carries a disc placed in the axial hole of the butt end of the cylindrical shell so as to obtain a circular gap confined by the side wall of the hole. A hollow annular shell is arranged coaxially within the cylindrical shell so that a circular gap made in the butt end of the annular shell faces the circular gap in the butt end of the cylindrical shell. An annular cathode and an anode are arranged coaxially inside the annular shell. A thermoelectronic cathode is placed outside the cylindrical shell near to its butt end with the circular gap. An electromagnet coil is arranged coaxially inside the cylindrical shell. A device for ion acceleration is placed on the path of emission of the ions. The cylindrical shell and its butt ends, and the rod are made of magnetically soft material, whereas the annular shell is made of non-magnetic material.
