A sensitiviy analysis for the stabilization of the CLIC main beam quadrupoles

In particle colliders (like the LHC), particles are highly accelerated in a circular beam pipe before the collision. However, due to the curved trajectory of the particles, they are also loosing energy because of the so-called Bremsstrahlung. In order to bypass this fundamental limitation imposed by circular beams, the next generation of particle colliders will accelerate two straight beams of particles before the collision. One of them, the Compact Linear Collider, is currently under study at CERN. The machine is constituted of a huge number of accelerating structures (used to accelerate the particles) and quadrupoles (electromagnets used to focus the particles). The latter ones are required to be stable at the nanometer level. This extreme stability has to be guaranteed by active vibration isolation from all types of disturbances like ground vibrations, ventilation, cooling system, or acoustic noise. Because of the huge number of quadrupoles (about 4000), it is critical that the strategy adopted for the active isolation is robust to any type of uncertainty: variations of the mechanical properties of the structure, variations of the level of the above mentioned disturbance sources, variations of the properties of the actuators and sensors, variations of the temperature, etc. In this paper, two active isolation strategies are investigated: one using soft supports and one using hard supports. These strategies are compared; their advantages and performances are discussed. Then, in order to quantify their robustness, a systematic sensitivity analysis against the different types of uncertainty is performed.