A radiant tube (4) for guiding a charged particle stream (10) has a hollow cylindrical isolation core (6) directly encompassing a beam-guiding hollow volume (8). The isolation core (6) is formed from a dielectrically acting carrier substrate (14) and an electrical conductor (16) held therein. The conductor (16) is divided into a plurality of conductor loops (20) completely encompassing the circumference of the isolation core (6) at different axial positions of the isolation core (6). The conductor loops (20) are galvanically connected to each other.