The attenuation chain of single-wir

The attenuation chain of single-wire suspensions forms a multi-stage torsion pendulum with very low resonant frequencies (in the order of 10 mHz). Although the yaw motions of the attenuation chain are isolated well in this configuration, these modes naturally have long decay time due to their high quality factors (100) and thus the filters will keep oscillating once these modes are excited. So as not to disturb the interferometer operation by these motions, the torsion modes are passively damped by eddy-current dampers. The conceptual design of the torsion mode damper is illustrated in figure 4.12. A disc with a number of permanent magnets is suspended from the pre-isolation stage by three wires and placed just above the first standard filter (written as F1). A conductive plate attached to F1 and the permanent magnets attached to the damper produce breaking torque between the damper and F1.