Active Vibration Isolation System for CLIC Final Focus

With pinpoint accuracy, the next generation of Linear Collider such as CLIC will collide electron and positron beams at a centre of mass energy of 3 TeV with a desired peak luminosity of 2*1034 cm⁻²s^{−1}. One of the many challenging features of CLIC is its ability to collide beams at the sub-nanometer scale at the Interaction Point (IP). Such a high level of accuracy could only be achieved by integrating Active Vibration Isolation system (AVI) upstream the collision to prevent the main source of vibration; Ground Motion (GM). Complementary control systems downstream the collision (Interaction Point FeedBack (IPFB), Orbit FeedBack(OFB)) allow low frequency vibration rejection. This paper focus on a dedicated AVI table designed for the last focusing quadrupole QD0 where the specifications are the most stringent. Combining FeedForward (FF) and FeedBack (FB) techniques, the prototype is able to reduce GM down to 0.6 nm RMS(4Hz) experimentally without load. These performances couldn’t be achieved without cutting edge-technology such as sub-nanometer piezo actuator, ultra-low noise accelerometer and seismometers and an accurate guidance system. The whole AVI system is described in detail.