Stabilization and positioning of CLIC quadrupole magnets with sub-nanometre resolution

To reach the required luminosity at the CLIC interaction point, about 2000 quadrupoles along each linear collider are needed to obtain a vertical beam size of 1 nm at the interaction point. Active mechanical stabilization is required to limit the vibrations of the magnetic axis to the nanometre level in a frequency range from 1 to 100 Hz. The approach of a stiff actuator support was chosen to isolate from ground motion and technical vibrations acting directly on the quadrupoles. The actuators can also reposition the quadrupoles between beam pulses with nanometre resolution. A first conceptual design of the active stabilization and nano positioning based on the stiff support and seismometers was validated in models and experimentally demonstrated on test benches. Lessons learnt from the test benches and information from integrated luminosity simulations using measured stabilization transfer functions lead to improvements of the actuating support, the sensors used and the system controller. The controller electronics were customized to improve performance and to reduce cost, size and power consumption. The outcome of this R&D is implemented in the design of the first prototype of a stabilized CLIC quadrupole magnet.