Kurt Artoos

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.

Review: Inertial sensors for low-frequency seismic vibration measurement

The objective of this paper is to review recent advances in the sensors used to measure seismic linear vibrations at low frequencies. The main types of inertial sensors are reviewed: absolute displacement sensors, geophones, accelerometers, and seismometers. The working principle of each of them is explained, along with the general strategies to extend their bandwidth. Finally, the principle fundamental limitations of all inertial sensors are reviewed: tilt‐to‐horizontal coupling, zero‐length springs, and sources of noise.

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.

Mechanical dynamic analysis of the LHC arc cryo-magnets

The arcs of the Large Hadron Collider (LHC) will contain around 1700 main superconducting dipoles and quadrupoles. The long and heavy magnets are placed on fragile composite support posts inside a cryostat to reduce the heat in-leak to the magnets super fluid helium bath. The presence of such fragile components like the support posts, the beam position monitors and the corrector magnets make the cryo-magnets very difficult to handle and transport. Furthermore, keeping the geometry of the cryo-magnets unchanged (in the range of 0.1 mm) throughout the various transports and handling is essential for the good functioning of the future LHC. A detailed dynamic analysis was performed to determine the behavior of the cryo-magnets under all the handling and transport conditions and to choose the related optimum parameters. The results of finite element modal calculations as well as experimental modal analyses are presented and compared. The maximum accelerations admissible during transport with several types of vehicle were computed. The accelerations experienced by both types of cryo-magnets were measured during real transport with different vehicles. The dynamic deformation of the support posts in the cryo-dipole was also measured. The methodologies of these analyses and their results are reported as well as the resulting specification for the transport during the LHC installation.

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.

Transport and installation of the LHC cryo-magnets

Eleven years have passed between the beginning of transport and handling studies in 1996 and the completion of the LHC cryo-magnets installation in 2007. More than 1700 heavy, long and fragile cryo-magnets had to be transported and installed in the 27 km long LHC tunnel with very restricted available space. The size and complexity of the project involved challenges in the field of equipment design and manufacturing, maintenance, training and follow-up of operators and logistics. The paper presents the milestones, problems to be overcome and lessons learned during this project.

The measurement of friction coefficient down to 1.8 K for LHC magnets

The Large Hadron Collider (LHC) proposed for construction at CERN consists of a series of high field superconducting dipole magnets operating at 1.8 K. The mechanical structure of these magnets contains many components in close contact. A knowledge of the friction coefficient between these components is required. Indeed, during assembly and cool down of the magnets, prestresses must be transferred to the superconducting coils. During operation, frictional heating may provoke loss of superconductivity. A machine has been built at CERN to measure the coefficient of friction from room temperature down to 1.8 K. This paper describes the cryogenic tribometer and the results collected to date.

The crab cavities cryomodule for SPS test

RF Crab Cavities are an essential part of the HL-LHC upgrade. Two concepts of such systems are being developed: the Double Quarter Wave (DQW) and the RF Dipole (RFD). A cryomodule with two DQW cavities is in advanced fabrication stage for the tests with protons in the SPS. The cavities must be operated at 2 K, without excessive heat loads, in a low magnetic environment and in compliance with CERN safety guidelines on pressure and vacuum systems. A large set of components, such as a thermal shield, a two layers magnetic shield, RF lines, helium tank and tuner are required for the successful and safe operation of the cavities. The sum of all these components with the cavities and their couplers forms the cryomodule. An overview of the design and fabrication strategy of this cryomodule is presented. The main components are described along with the present status of cavity fabrication and processing and cryomodule assembly. The lesson learned from the prototypes and first manufactured systems are also included.

Sensors applications within the research framework of the PACMAN project on metrology for particle accelerators at CERN

Within the framework of the Compact Linear Collider Study (CLIC) [1] at CERN, new sensing and actuators technologies must be developed in order to achieve the required performance. An ITN Marie Curie Skowoska project funded by the European Union was launched in 2013. This project is a study on Particle Accelerator Components Metrology and Alignment to the Nanometre Scale, named PACMAN [2]. The project team consists of ten early stage researchers, divided in four work packages focusing on different tasks. Each of them is developing innovative transducers overperforming the current state of the art. Their main tasks are high-precision metrology and fiducialization, magnets prequalification and determination of magnetic axis under the constraint of small aperture (below 10 mm), determination of electrical center of a 15 GHz Radio Frequency-Beam Position Monitor (RF-BPM) and the electro-magnetic axis of an accelerating cavity, improvement of an existing seismic sensor to guarantee an optimized alignment process. The project has now been running for two years at CERN, resulting in dramatic progress for each of the early stage researchers. Their work already lead to building new experiments and proofs of concepts that are to be assembled in a unique, flexible, and compact test bench.