Stef Janssens

Review of Active Vibration Isolation Strategies

This paper reviews recent patented developments in active vibration isolation. First of all, the fundamental limitations of passive vibration isolations are established, to understand the motivations to introduce active control in vibration isolation. Then, the main different active strategies are presented using simple systems and compared. Finally, several specific issues are listed and briefly discussed.

Active vibration isolation of high precision machines

This paper provides a review of active control strategies used to isolate high-precisionmachines (e.g. telescopes, particle colliders, interferometers, lithography machines or atomic force microscopes) from external disturbances. The objective of this review is to provide tools to develop the best strategy for a given application. Firstly, the main strategies are presented and compared, using single degree of freedom models. Secondly, the case of huge structures constituted of a large number of elements, like particle colliders or segmented telescopes, is considered.

Study of the electronics architecture for the mechanical stabilisation of the quadrupoles of the CLIC linear accelerator

To reach a sufficient luminosity, the transverse beam sizes and emittances in future linear particle accelerators should be reduced to the nanometer level. Mechanical stabilisation of the quadrupole magnets is of the utmost importance for this. The piezo actuators used for this purpose can also be used to make fast incremental orientation adjustments with a nanometer resolution. The main requirements for the CLIC stabilisation electronics is a robust, low noise, low delay, high accuracy and resolution, low band and radiation resistant feedback control loop. Due to the high number of controllers (about 4000) a cost optimization should also be made. Different architectures are evaluated for a magnet stabilisation prototype, including the sensors type and configuration, partition between software and hardware for control algorithms, and optimization of the ADC/DAC converters. The controllers will be distributed along the 50 km long accelerator and a communication bus should allow external control. Furthermore, one might allow for an adaptive method to increase the S/N ratio of vibration measurements by combining seismometer measurements of adjacent magnets. Finally a list of open topics, the current limitations and the plans to overcome them will be presented.

Study of the hybrid controller electronics for the nano-stabilization of mechanical vibrations of CLIC quadrupoles

In order to achieve the required levels of luminosity in the CLIC linear collider, mechanical stabilization of quadrupoles to the nanometre level is required. The paper describes a design of hybrid electronics combining an analogue controller and digital communication with the main machine controller. The choice of local analogue control ensures the required low latency while still keeping sufficiently low noise level. Furthermore, it reduces the power consumption, rack space and cost. Sensitivity to radiation single events upsets is reduced compared to a digital controller. The digital part is required for fine tuning and real time monitoring via digitization of critical parameters.