CLIC quadrupole stabilization and nano-positioning

In the Compact LInear Collider (CLIC) currently under study, electrons and positrons will be accelerated in two linear accelerators to collide at the interaction point with an energy of 0.5- 3 TeV. This machine is constituted of a succession of accelerating structures, used to accelerate the beams of particles, and electromagnets (quadrupoles) used to focus the beams. In order to ensure good performances, the quadrupoles have to be extremely stable. Additionally, they should also have the capability to move by steps of some tens of nanometers every 20 ms with a precision of +/- 1nm. This paper proposes a holistic approach to fulfill alternatively both requirements using the same device. The concept is based on piezoelectric hard mounts to isolate the quadrupoles from the ground vibrations in the sensitive range between 1 and 20 Hz, and to provide nano-positioning capabilities. It is also shown that this strategy ensures robustness to external forces (acoustic noise, water flow for the cooling, air flow for the ventilation) directly acting on the quadrupoles. In the first part, the strategy adopted is presented, and its advantages compared to other stabilization strategies are discussed. In the second part, experimental validations are presented on two test benches. Both set-ups consist of a compact mass, supported by piezoelectric hard mounts. Isolation and nano-positioning performances are presented, and specific issues of sensor noise and resolution are addressed.