COMPASS - RICH - Alignment of the Mirrors

Precise alignment of the 116 mirrors of the RICH detector of the COMPASS Physics experiment using a theodolite based metho

REMOTE: Geodetic metrology for future accelerators - Facing the future challenges in the domain of accelerator alignment

Abstract In particle accelerators, high radiation levels, ultra-high vacuum, cryogenic temperatures of the measured components and high electro-magnetic noise push accelerator surveyors to look for more robust,&nbsp;safe&nbsp;and accurate solutions of alignment. For example, for the High-Luminosity LHC project at CERN, a range of new and cost-optimized solutions using Fourier&nbsp;analysis-based&nbsp;Frequency Sweeping Interferometry (FSI) and capacitive technologies are under development. Moreover, the safe and easy&nbsp;alignment of components located in radioactive areas, requires easy,&nbsp;low-cost,&nbsp;and fast adjustment&nbsp;of&nbsp;the components. Two presentations during this&nbsp;lecture&nbsp;will illustrate some axes of research and development related to this domain.&nbsp;The first presentation will&nbsp;present the status of development of&nbsp;such robust and low-cost, micrometric alignment systems.&nbsp;The second one will focus on the structured laser beam (SLB). The SLB is a new&nbsp;solution in the creation of pseudo-non-diffractive optical beams. Among its properties, it can, for example, propagate over extremely long distances with a very low central core divergence. These beams seem interesting to create optical alignment systems and are being studied to be used as reference for very precise alignments and positioning of optical elements, or objects such as physics detectors, particle accelerator components, etc. This presentation will give an overview of some of the SLB properties and of potential applications. Short Bio&nbsp;Mateusz Sosin Mateusz Sosin is&nbsp;head of the&nbsp;High Precision Alignment Section,&nbsp;inside the BE-GM group at CERN. The Section provides 3D, micrometric alignment solutions for specific accelerator components and is involved in research &amp; development works to improve alignment techniques for HL-LHC and future colliders.&nbsp;Since&nbsp;the beginning of his career at CERN, Mateusz&nbsp;has been&nbsp;working&nbsp;as a mechatronic engineer, focusing on development of micrometric alignment systems for use in harsh accelerator environment. Short Bio&nbsp;Jean-Christophe Gayde Jean-Christophe Gayde is head of the Experiment Survey and Alignment section and deputy group leader of the&nbsp;BE-GM&nbsp;group. The section provides the Geodetic Metrology for the physics experiments at CERN and for the HIE-ISOLDE and ISOLDE facilities. The section is also in charge of the development of specific integrated alignment and monitoring systems for the experiments, and in charge of the R&amp;D related to the Structured Laser Beam project.</p

Evaluation of Frequency Scanning Interferometer Performances for Surveying, Alignment and Monitoring of Physics Instrumentation

During the last three years, the performance of Frequency Scanning Interferometry, accurate to a few micrometres, has been evaluated at CERN in the frame of the PACMAN project. Improvements have been studied and tested to make it better suited for typical alignment and survey conditions in accelerators and experiments. The results of these developments and tests, coupled with the multi-channel capability of the system, and its compactness which eases its integration in the area to be surveyed, offer a wide scope of possible applications for in-situ large scale metrology for physics equipment and facility elements. Furthermore, the fact that the system electronics can be placed far away from the position to be measured, allows the system to be used in confined and hazardous spaces. This paper briefly describes the system and its improvements. It gives the precision obtained for distance measurements and for the 3D point reconstruction based on FSI observations in the case of CLIC component fiducialisation

Low Divergence Structured Beam In View Of Precise Long-Range Alignment

A new method of generation of a Structured Laser Beam (SLB) with non-diverging central core was proposed and is promising for creating long distance multipoint alignment systems. This beam is generated by a set-up consisting of two convex lenses in Kepler telescope arrangement. The first one is a high refractive index ball lens, second one is a standard lens. The beam, in cross-section consisting of light and dark concentric circles, propagates over a large distance. The central core of the SLB has a very small divergence which can be tuned. A divergence of 10 μrad was proven experimentally. In this experiment, the small initial beam core diameter of 10 μm, and its diameter of 1.5 mm at a distance of 150 m, show its ability for use as a multipoint fiducial reference line. This small beam divergence seemingly lies beyond the diffraction limit for laser beams

Structured laser beam in non-homogeneous environment

This article summarizes part of the research related to the structured laser beam (SLB) properties focused on align- ment. The SLB has the potential to be used as a reference line. This is due to SLB features such as a very clear spot in the center of the beam, a sharp boundary of the central spot, low divergence of the central spot (practically mea- sured value 10 µrad) and theoretically infinite range (tested over several hundred meters). However, the environment (the non-homogeneous distribution of the refractive index) affects the trajectory of the SLB, which is then a general curve. A new approach based on numerical simulations was used to investigate this phenomenon. A method gen- eralizing the diffraction integral was developed to trace ac- curately any optical beam in a non-homogeneous environ- ment. This solution offers in principle a better accuracy than the Eikonal equation used for ray tracing because it allows evaluating the position of the optical beam center with methods based on the analysis of the optical intensity transverse distribution. The propagation of the complex amplitude in the longitudinal direction can generally not be described by the Eikonal equation, but the generalized diffraction integral attains this goal. The article compares the trajectories of a SLB calculated using both the Eikonal equation and the generalized diffraction integral. It de- scribes the differences between these two approaches and identifies conditions under which these differences are neg- ligible in an inhomogeneous environment. Furthermore, the influences of different types of environmental non ho- mogeneities on the SLB trajectory are discussed

Mathis software for controlling BCAM-based monitoring and alignment systems

The MATHIS Software (Monitoring and Alignment Tracking for HIE-Isolde Software) aims at providing 3D positions of physical components of the HIE-Isolde superconducting modules, accurately and permanently measured by well-designed networks of BCAM devices (Brandeis Camera Angle Monitoring). Although it is originally intended for the HIE-Isolde project, its architecture and its use cases have been extended and optimized for more general setups. Most of the configuration data are stored either within XML-formatted files or within databases. The adaptation of MATHIS for different BCAM monitoring systems therefore does not require any further code rewriting. Moreover, the software is fully cross-platform and can either be run on the specific Linux machines driving the accelerator electronic devices, or be used on independent Windows workstations as a stand-alone software. In the first case, the software mainly relies on FESA (Front End Software Architecture) which is an object-oriented real-time framework that ensures equipment software portability across CERN accelerators. Through this standardized module, MATHIS communicates with dedicated servers networks and publishes in real-time the computed positions to any workstation, and more specifically to the concerned control room operators. This paper describes the main features and explains the modular architecture of the software

11T dipole short model coil metrology at cold and measurement of its thermal contraction

The main objective of the HL-LHC project at CERN is to increase the LHC peak luminosity by a factor of five and the integrated luminosity by a factor of ten. The increased integrated and peak luminosity requires to improve the cleaning efficiency of the collimation system with the installation of new collimators in the cold section of the machine. In order to create the space for such equipment a set of two new high field magnet (here referred as 11T dipole) will replace one standard LHC dipole leaving free space in middle for the new equipment. The metrology tests of one of the 11T dipole short model coils (1.97 m long) have been performed at CERN, using close range photogrammetric techniques, in order to evaluate the mechanical behaviour of the coil. For this measurement, the coil has been immersed and completely covered by nitrogen gas for the thermal cycling (ΔT ≈ 178 Κ). In this paper, some of the environmental constraints are highlighted. These constraints have been: a thin vapour cloud on the top of the cryostat, a small ice layer that has been formed a few minutes after the opening of the cryostat cap and the high temperature gradient for measurement rays. As result, it can be concluded that the short model coil of the 11T dipole is a flexible structure that contracts and bends (bending of 4.85 mm between warm and cold state of the coil). In addition, the best estimate for the coefficient of thermal expansion of the coil is 12.8 μm/m/K what is probably not enough to characterize the short model coil as a composite structure

HIE-Isolde: Commissioning and first results of the Mathilde system monitoring the positions of cavities and solenoids inside cryomodules

The new superconducting HIE-ISOLDE Linac replaced most of pre-existing REX ISOLDE facility at CERN. This upgrade involves the design, construction, installation and commissioning of 4 high-β cryomodules. Each high-β cryomodule houses five superconducting cavities and one superconducting solenoid. Beam-physics simulations show that the optimum linac working conditions are obtained when the main axes of the active components, located inside the cryostats, are aligned and permanently monitored on the REX Nominal Beam Line (NBL) within a precision of 0.3 mm for the cavities and 0.15 mm for the solenoids at one sigma level along directions perpendicular to the beam axis. The Monitoring and Alignment Tracking for HIE-ISOLDE (MATHILDE) system has been developed to fulfil the alignment and monitoring needs for components exposed to non-standard environmental conditions such as high vacuum or cryogenic temperatures. MATHILDE is based on opto-electronic sensors (HBCAM) observing, through high quality viewports, spherical retroreflectors made of high index (~2) glass. Precise mechanical parts, metrological tables and the, so called, MATHIS software were designed to be able to reconstruct the position of the active elements within a precision of 0.1 mm. The commissioning of MATHILDE and its first results to monitor the cavity and solenoid positions, especially during the installation and tests of the two first cryomodules on the HIE-ISOLDE Linac, are reviewed in this contribution

Introduction to Structured laser beam for alignment and status of the R&D

A new method of generating a Structured Laser Beam (SLB) has been proposed recently. The SLB is a pseudo- non-diffractive optical beam. Its transverse optical intensity profile looks similar to that of a quasi Bessel beam and shows a narrow central core of high intensity surrounded by concentric circles. The SLB has the ability to propagate over very long distances, theoretically to infinity with a low divergence of the central core beam. It has been tested up to 200 m and during the experiments a divergence of typically 0.01 mrad has been measured, the diameter of the central spot at start being about 0.01 mm. The SLB properties open potential applications in different domains, comprising geodetic and large scale metrology. Even if the SLB is still at a research stage it appears as a promising candidate for the development of optical long range reference lines for alignment systems. This article is an introduction to the SLB, to its generation principle and to some of its characteristics, in particular the ones interesting for alignment. It relates the status of some aspects of the on-going research. It summarizes some SLB study results, among them the creation of SLBs at long distances, the study and simulations of beam straightness, or the creation of SLB with non-classical polarization

Deformation measurement the ATLAS cavern at CERN

Caverns for large physics detectors as the one for the Large Hadron Collider experiments sit nearly 100 m underground and measure several tens of meters in length, width and height. The deformation of the cavern base slab over decades has a direct influence on the relative alignment of detectors to the accelerator. The expected long-term movements are larger than the fine adjustment of detectors and accelerators. In this paper, the measured deformations of the ATLAS experiment main cavern floor and lateral walls over nearly 20 years have been analysed. The measurement series have been performed in various time intervals getting down to half a year. The measurement techniques such as polar method (total station and laser tracker) and precise levelling allow to obtain sub-millimetre precision. The measured deformation reaches values up to 5.0 mm for the base slab and it is significantly (four times) lower compared to the predictions of the civil engineering consultants at the moment of the cavern construction. For the lateral walls, they reach up to 14.7 mm