it is contact with the cavity walls of both blades 10 10 u2032 regardless of the operating condition of turbomachine 1 both side surfaces 21 21 u2032 of damper 2 have a first zone having a first radius of curvature r 1 a second zone having a second radius of curvature r 2 and a third zone having a third radius of curvature r 3 moreover in both side surfaces 21 21 u2032 the second zone having the second radius of curvature r 2 is disposed between the first zone and the third zone and is longer than the first zone and the third zone third radius of curvature r 3 has a smaller value than first radius of curvature r 1 and second radius of curvature r 2 moreover first radius of curvature r 1 has a smaller value than second radius of curvature r 2 in first side surface 21 the first zone having the first radius of curvature r 1 is disposed at the end of side surface 21 that is radially proximal to the rotor axis the third zone having the third radius of curvature r 3 is disposed at the end of side surface 21 that is radially distal from the rotor axis and is in frictional contact with the respective cavity wall in a region of frictional contact 22 in second side surface 21 u2032 the first zone having the first.