Analysis and filtering of the effect of tides on the hydrostatic levelling systems at CERN

Abstract

RESUMELes géomètres de la section Survey de l'Organisation Européenne pour la Recherche Nucléaire (CERN) utilisent le nivellement hydrostatique HLS pour effectuer des alignements verticaux précis. Le HLS atteint des précisions micrométriques, ce qui lui permet d'être utilisé pour les expériences à but de physique fondamentale comme le Large Hadron Collider (LHC).HLS mesure certes des déformations qui ont pour conséquence de désaligner tout accélérateur de particules lié au sol, mais il mesure également d'autres phénomènes aux caractéristiques bien particulières. Parmi ces phénomènes mesurés, les marées terrestres représentent une part très largement majoritaire du signal. Leur effet sur les mesures HLS est périodique et engendre une inclinaison longue base qui n'aboutit pas au désalignement relatif des aimants constitutifs d'un accélérateur. Ce doctorat est inspiré des travaux déjà réalisés sur les inclinomètres longue base et décrit les effets mesurés par HLS afin de classer ces phénomènes selon qu'ils désalignent ou non un accélérateur de particules. Enfin, les outils et modèles pour prédire les effets maitrisables sont utilisés pour anticiper les différents signaux mesurés par les HLS installés au CERN.Mots clefs : Hydrostatic Levelling System (HLS), nivellement hydrostatique, inclinomètre, CERN, LHC, CLIC, alignement vertical, marées terrestres, surcharges, effets locaux, effets de cavité. 3/184 ABSTRACTThe surveyors of the Large Scale Metrology section of the European Organization for Nuclear Research (CERN) use hydrostatic levelling systems (HLS) to perform precise vertical alignment measurements. The HLS achieves micrometer accuracy, which allows it to be used for the fundamental physics experiments such as the Large Hadron Collider (LHC).An HLS measures the deformations that lead to the misalignment of any particle accelerator linked to the ground, but it also measures other phenomena with very particular characteristics. Among these measured phenomena Earth tides form the main part of the signal. Their effect on HLS measurements is periodic and produces a long baseline tilt that does not lead to a relative misalignment of the magnets that constitute the accelerator.The objectives of this doctoral research are to be able to predict the effects which do not disturb the relative alignment of a particle accelerator and to remove these signals from the HLS measurements. Indeed, the horizontal and vertical positioning tolerances to be respected in the realm of particle accelerators are becoming tighter and tighter. For example, the Compact Linear Collider (CLIC), currently the object of a feasibility study, requires a 3σ alignment accuracy of 10 μm in a sliding window of 200 m, in both the transverse and vertical directions. The HLS is a candidate for measuring the vertical alignment but the amplitude of the tidal effect is approximately +/-20 μm over 200 m, making it necessary to take into account this long baseline phenomenon for the instrument to meet the CLIC requirements.This doctoral thesis is inspired ...

Geophysics From Terrestrial Time‐Variable Gravity Measurements

“…For completeness, let us mention that tides influence the alignment and, hence, the measurements of particle accelerators (Boerez et al, ; Xu et al, ), but this must be additionally monitored using strainmeters and tiltmeters, as deformations and tilts are of concern rather than gravity changes.…”

The Concept of Geodetic Analyses of the Measurement Results Obtained by Hydrostatic Leveling

“…Assuming that sensors are connected in series, as shown in Figure 2, concept II applies the height differences between individual sensors. Such a solution is often used in hydrostatic leveling systems, which is presented in [6,9,10]. If we consider the case with the controlled points equally spaced on the investigated object, then the implementation of either concept (I or II) is unrestricted.…”

“…Morishita and Ikegami [6] explained the slow-ground-motion monitoring system for the J-PARC (Japan Proton Accelerator Research Complex) linac, while Zhang et al [7] focused on processing the power transmission tower vertical displacements. Other examples of hydrostatic leveling systems address the European Synchrotron Radiation Facility (ESRF) [8] and the TT1 tunnel at CERN (European Organization for Nuclear Research) [9]. The review above shows an enormous variety of objects involving hydrostatic leveling for displacement study.…”

Technical Monitoring System for a New Part of Gdańsk Deepwater Container Terminal

“…In the technical monitoring systems for structures [12], [15], [18], [19] it is possible to apply various measuring technologies such as precise levelling, hydrostatic levelling, [2], [21], laser scanning [1], photogrammetric methods [24], advanced geodesic methods as well as specialty measurements of deformations, pressures, temperatures [23] etc, or also numerical simulation modules such as in [17], [22]. The technical monitoring system for micro-piles required to use technologies which make it possible to fulfill the task at relatively low costs.…”