The turbine (1) has a rotor (2) with blades (4) arranged on a periphery of disks (5) in radial planes (3), and a tie rod (6) extending along slots (7) in the disks. An annular spacer (15, 15′) fixes a position of the tie rod relative to a center line (M) of the disks, and is arranged in a channel (10, 11). The spacer has through-openings, which are arranged radially relative to the tie rod or to its center line, and extend coaxially. The channel carries a cooling medium and is limited by a separating pipe (13, 14) radially outwards. The through-openings serve for flow of the medium.