Sub-nanometer active seismic isolator control

Ambitious projects such as the design of the future Compact Linear Collider require challenging parameters and technologies. Stabilization of the Compact Linear Collider particle beam is one of these challenges. Ground motion is the main source of beam misalignment. Beam dynamics controls are, however, efficient only at low frequency (<4 Hz), due to the sampling of the beam at 50 Hz. Hence, ground motion mitigation techniques such as active stabilization are required. This article shows a dedicated prototype able to manage vibration at a sub-nanometer scale. The use of cutting edge sensor technology is, however, very challenging for control applications as they are usually used for measurement purposes. Limiting factors such as sensor dynamics and noise lead to a performance optimization problem. The current state of the art in ground motion measurement and ground motion mitigation techniques is pointed out and shows limits of the technologies. The proposed active device is then described, and a realistic model of the process has been established. A dedicated controller design combining feedforward and feedback techniques is presented, and theoretical results in terms of power spectral density of displacement are compared to real-time experimental results obtained with a rapid control prototyping tool.