Micrometric Propagation of Error Using Overlapping Streched Wires for the CLIC Pre-Alignment

The geodetic network for the Compact LInear collider (CLIC) will consist of a combination of overlapping wires stretched in parallel and Wire Positioning Sensors (WPS). Such a configuration will limit the propagation of errors (maximum deviation w.r.t. a fit line) below 10 micrometres over 200 metres. These first results were obtained through simulations in 2009, with hypotheses remaining to be validated. New experimental results have been obtained allowing to reconsider the precision and accuracy of WPS sensors and the knowledge of stretched wires. This paper presents the experimental results obtained on dedicated calibration benches and on a facility made of three overlapping stretched wires over a length of 140 metres including WPS sensors measurements. It confirms the possibility to have a propagation of error below 10 micrometres using overlapping stretched wires combined with WPS sensors

CLIC pre-alignment - Status and remaining challenges

The Compact Linear Collider (CLIC) is a study of a 3 TeV linear electron-positron (e+e-) accelerator and is a successor candidate for CERN's Large Hadron Collider. The CLIC luminosity target is 5.9 1034 cm-2 s-1, which causes unprecedented pre-alignment requirements of its main linear accelerator (main linac). Along the 50 km long tunnel, the main components of any 200 m long section have to be positioned within 10 µm from a straight reference line. The pre-alignment challenge has been studied at CERN since the 1990s, and the main technical challenges have been solved. This article summarizes the positioning strategy and presents it to an audience outside the particle accelerator community. The methods can be of interest especially in the field of large-scale metrology. The positioning strategy consists of several steps or subsystems. The development of a straight reference line over tens of kilometers allows absolute positioning of accelerator components, while a process called fiducialization defines component reference axes with regard to alignment targets. Emphasis is on a support pre-alignment network that acts as a link between the straight reference line and fiducialization. The subsystems and remaining challenges in their development are presented. The chosen strategy's potential is demonstrated experimentally by building a short test setup.publishedVersionPeer reviewe

Alignment Methods Developed for the Validation of the Thermal and Mechanical Behaviour of the Two Beam Test Modules for the CLIC Project

CLIC project will consist of more than 20 000 two meters long modules. A test setup made of three modules is being built at CERN to validate the assembly and integration of all components and technical systems and to validate the short range strategy of pre-alignment. The test setup has been installed in a room equipped with a sophisticated system of ventilation able to reproduce the environmental conditions of the CLIC tunnel. Some of the components have been equipped with electrical heaters to simulate the power dissipation, combined with a water cooling system integrated in the RF components. Using these installations, to have a better understanding of the thermal and mechanical behaviour of a module under different operation modes, machine cycles have been simulated; the misalignment of the components and their supports has been observed. This paper describes the measurements methods developed for such a project and the results obtained

Position Monitoring System for HL-LHC Crab Cavities

The high luminosity upgrade for the LHC at CERN (HL-LHC project) will extend the discovery potential of the LHC by a factor 10. It relies on key innovative technologies like superconducting cavities for beam rotation, named 'crab cavities'. Two crab cavities will be hosted in a superconducting cryostat working at a cold (<3 K). The position of each cavity will be monitored during the cool-down and the operation in order to comply with the tight alignment tolerances: the misalignment of a cavity axis w.r.t. the other will have to be lower than 0.5 mm and each cavity roll w.r.t. the cryostat axis will have to be lower than 1 mrad. Moreover, the monitoring system will have to be radiation hard (up to 10 MGy) and maintenance free. We propose a solution based on the Frequency Scanning Interferometry to provide the position monitoring of the crab cavities. This paper describes the design and study of such a solution, including the engineering approach, the issues encountered and the lessons learnt

Drive Beam Quadrupoles for the CLIC Project: a Novel Method of Fiducialisation and a New Micrometric Adjustment System

This paper presents a new method of fiducialisation applied to determine the magnetic axis of the Drive Beam quadrupole of the CLIC project with respect to external alignment fiducials, within a micrometric accuracy and precision. It introduces also a new micrometric adjustment system along 5 Degrees of Freedom, developed for the same Drive Beam quadrupole. The combination of both developments opens very interesting perspectives to get a more simple and accurate alignment of the quadrupoles

Robust Optical Instrumentation for Accelerator Alignment Using Frequency Scanning Interferometry

The precise alignment of components inside particle accelerators is an important engineering challenge in high-energy physics. Optical interferometry, being a precise, optical distance measurement technique, is often a method of choice in such applications. However, classical fringe-counting interferometers present several drawbacks in terms of system complexity. Due to the increasing availability of broadband, high-speed, sweeping laser sources, Frequency Scanning Interferometry (FSI) based systems, using Fourier analysis of the interference signal, are becoming a subject of growing interest. In the framework of the High-Luminosity LHC project at CERN, a range of FSI-based sensor solutions have been developed and tested. It includes the optical equipment for monitoring the position of cryogenic components inside their cryostats and FSI instrumentation like inclinometers and water-based levelling sensors. This paper presents the results of preliminary tests of these components

Study of the Dynamic Response of CLIC Accelerating Structures

CLIC is a linear electron-positron collider, 48 km long, consisting of more than 20000 repetitive modules. The target beam size of 1 nm dictates very tight alignment tolerances for the accelerating structures (AS). In order to assess the effect of short-term RF power interruptions (breakdowns or failure modes) on the alignment, the dynamic behaviour of the AS was investigated on the prototype two-beam module. On a dedicated experimental setup, the thermal and mechanical time constant (TC) was monitored as a function of ambient temperature, water flow and power. The experimental results showed that the thermal TC ranged between 4 and 11 minutes and presented strong correlation with the cooling water flow. These results were in very good agreement with the theoretical expectations. The displacement dynamics were found to be comparable with the thermal ones. The study indicates that temperature measurement, which is a fast and easy process, can be used as an indicator of the AS displacement. Moreover, it is shown than the transient response can be efficiently controlled through appropriate regulation of the cooling water flow

The New CLIC Main Linac Installation and Alignment Strategy

A complete solution has been proposed for the pre-alignment of the CLIC main linac in 2012 for the Conceptual Design Report. Two recent studies provide new perspectives for such a pre-alignment. First in a study on Particle Accelerator Components' Metrology and Alignment to the Nanometre scale (PACMAN), new solutions to fiducialise and align different types of components within a micrometric accuracy on the same support were proposed and validated, using a stretched wire. Secondly, a 5 degree of freedom adjustment platform with plug-in motors showed a very accurate and efficient way to adjust remotely components. By combining the results of both studies, two scenarios of installation and alignment for the CLIC main linac are proposed, providing micrometric and automatized solutions of micrometric assembly, fiducialisation and alignment in metrological labs or in the tunnel. In this paper, the outcome of the two studies are presented; the two scenarios of installation and alignment are then detailed and discussed.A complete solution was proposed for the pre-alignment of the CLIC main linac in 2012 for the Conceptual Design Report. Two recent studies provide new perspectives for such a pre-alignment. First, in a study on Particle Acceler- ator Components Metrology and Alignment to the Nano- metre scale (PACMAN), new solutions to fiducialise and align different types of components within a micrometric accuracy on the same support were proposed and validated, using a stretched wire. Second, 5 degrees of freedom ad- justment platform with plug-in motors showed a very ac- curate and efficient way of remotely adjusting components. By combining both, we propose a new strategy for the in- stallation and alignment of the CLIC main linac, object of this paper

3D calculation for the alignment of LHC low-beta quadrupoles

The low beta triplet quadrupoles magnets of the Large Hadron Collider (LHC) are located on both sides of the ATLAS, CMS, ALICE and LHCb experiments. The alignment tolerances of these components are particularly stringent with ±0.5 mm at 3σ and are tracked by an alignment system consisting of micrometric sensors and motorized jacks used for components remote adjustment. The system has been installed in 2008 with the purpose of monitoring the triplets relative displacements with respect to their nominal position. After the development of appropriate calibration benches, the first absolute calibrations of the sensors have been performed in 2016, allowing a determination of the magnet positions in an absolute reference frame. The radial and vertical (plus roll) data were separated in two different calculations steps. During the LHC Long Shutdown 2 (LS2, 2019- 2021), consolidation works have been carried out on all triplets allowing to perform absolute calculation in 3D, and significantly increasing the position determination accuracy. This paper gives an overview of the 3D calculations used currently for the alignment of low beta quadrupoles magnets and summarizes their positions change since LS2