Active damping of suspension wire violin modes in gravitational wave detectors

A technique is described to actively damp the fundamental violin mode reson ances of the suspension wires used in the high-e multi-stage pendulum syste ms found in interferometric gravitational wave detectors. The damping proce dure utilises sensing signals and actuators that already exist in the contr ol topology for such interferometers, making for very convenient practical implementation. An experimental demonstration of the damping technique appl ied to the double pendulum suspensions used in the Glasgow 10 m prototype i nterferometer is presented. The decay times of the violin modes associated with these suspensions, which occured typically at around 400 Hz, were redu ced from of order 100 seconds to around 1 second or less without degrading the interferometer noise performance, (C) 1999 Elsevier Science B.V. All ri ghts reserved.