A mechanical damper for the horizontal mode at 20 Hz of the North End bench has been built. It consists of a metallic mass (about 15 kg) suspended to a metallic frame by means of a wire and 4 VITON absorber rods connected both to the pendulum mass and to the bench . This damper has been conceived to reduce the amplitude of the annoying mode at 20 Hz visible also on the interferometer dark fringe.
In the plots here reported the effect of this mechanical damper mounted on the North End bench is visible. The plotted signals are those ones of a three-axial accelerometer and a second single axis accelerometer (Em_SEDBNE01) mounted on the optical bench. Comparing the accelerometer signals before (black curve) and after the damper installation (violet curve), the amplitude of the mode is reduced by a factor 4.
