Machine learning models are proposed to successfully detect heating from pressure measurements in synchrotron colliders. These models allow to analyze all the pressure measurements in the time ...available between two consecutive machine runs. The limits of simple heuristic-based algorithms arsing from noise and non-reproducibility are overcome by the proposed machine learning models. These models were trained, tested, and compared with an heuristic-based base-line approach. In particular, for the case of the CERN Large Hadron Collider (LHC), they reached better performance than base-line algorithms, both in precision and recall scores.
Machine learning entails a broad range of techniques that have been widely used in Science and Engineering since decades. High-energy physics has also profited from the power of these tools for ...advanced analysis of colliders data. It is only up until recently that Machine Learning has started to be applied successfully in the domain of Accelerator Physics, which is testified by intense efforts deployed in this domain by several laboratories worldwide. This is also the case of CERN, where recently focused efforts have been devoted to the application of Machine Learning techniques to beam dynamics studies at the Large Hadron Collider (LHC). This implies a wide spectrum of applications from beam measurements and machine performance optimisation to analysis of numerical data from tracking simulations of non-linear beam dynamics. In this paper, the LHC-related applications that are currently pursued are presented and discussed in detail, paying also attention to future developments.
A method for a first-order approximation estimation of the longitudinal impedance of a synchrotron component, starting from power loss measurements on the device, is proposed. This method also ...estimates the resonance frequency and the quality factor of the impedance after the execution of several machine runs, without disconnecting the device. After a detailed description of the method, its suitability is demonstrated through a practical case study using power loss measurements of the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN).
The crystal-based primary collimators installed in the Large Hadron Collider (LHC) at CERN use the channelling process in bent crystals to steer halo particles efficiently onto downstream ...collimators. This scheme, called crystal collimation, is also considered for applications of fixed-target implementations in the context of the Physics Beyond Collider at the LHC. Crystal collimation uses 4 mm-long silicon crystals that need to be approached very close to the high-intensity circulating beams, posing obvious concerns for machine impedance. A complex mechanical assembly was developed for this purpose. The setup includes also a system to control with sub-μrad accuracy the angular orientation of the crystal, which is done with a high-precision interferometric system. In order to prevent possible beam-induced instabilities and/or damage of the device components from excessive RF-heating, the electromagnetic (EM) characterization of this device is essential prior to its usage with high-intensity beams. In this article, the longitudinal impedance of the crystal primary collimator is studied extensively and estimations of power loss inside the device are provided for the different beam types planned at the LHC and at its High-Luminosity upgrade (HL-LHC). Electromagnetic simulations are performed on a realistic model that includes all the relevant components. The model is described in detail and computational challenges coming from its complexity are discussed. Care is taken to characterize the materials of each relevant sub-component. In particular, the lossy properties of silicon, whose complex permittivity is also evaluated through RF rectangular-cavity perturbation measurements, are taken into account. Numerical results are then compared with dedicated RF measurements performed on a prototype built for the LHC.
The High Luminosity (HL) upgrade of the Large Hadron Collider (LHC) will increase the peak luminosity at the experiments by more than a factor of 5 with respect to the LHC design value. To achieve ...this goal, among the upgrade of several beam and machine parameters, the beam intensity will nearly double with respect to the operational LHC value, and the transverse beam emittance will decrease by 50% compared to the LHC design value. Past operational experience showed that coherent beam instabilities may occur for low, positive values of chromaticity, and a higher tune spread than predicted from simulations is required from the dedicated octupole magnets to provide enough Landau damping. With the HL-LHC brighter beams, stability margins will become tighter, and coherent instabilities become stronger if no dedicated mitigation measures are taken. An impedance reduction plan is therefore taking place targeting the collimation system, and the main contributor to the transverse beam coupling impedance at the flattop energy. New collimators with lower resistivity materials will replace the current LHC ones. In this work, we assess the benefits of this impedance reduction with respect to the transverse mode coupling instability threshold. This study quantifies the discrepancy between measured and predicted beam stability thresholds at low chromaticity. It also probes the expected gain of the impedance reduction plan of HL-LHC.
The accurate calculation of the beam coupling impedance for particle accelerators is necessary to carefully assess the machine stability against impedance-driven collective effects. A first order ...evaluation of the beam coupling impedance is often done by means of analytical formulas and/or 2D numerical codes. The infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be a less accurate approximation for segmented devices. In this work, we present the application of the mode matching method to the calculation of the transverse dipolar impedance of a cylindrical cavity loaded with a toroidal insert. By choosing different insert electromagnetic properties (permittivity, permeability, and conductivity) and dimensions, the model can represent a beam pipe, a thin insert, a lossy cavity, or a collimator for which the effect of the finite length is investigated. The method is successfully benchmarked against available analytical formulas, field-matching codes, and 3D commercial solvers. The proposed model allows for performing wide parametric scans and reaching accurate results, therefore becoming an essential tool for the impedance evaluation of accelerator devices.
Beam Instabilities in Hadron Synchrotrons Metral, E.; Argyropoulos, T.; Bartosik, H. ...
IEEE transactions on nuclear science,
04/2016, Letnik:
63, Številka:
2
Journal Article
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Beam instabilities cover a wide range of effects in particle accelerators and they have been the subjects of intense research for several decades. As the machines performance was pushed new ...mechanisms were revealed and nowadays the challenge consists in studying the interplays between all these intricate phenomena, as it is very often not possible to treat the different effects separately. The aim of this paper is to review the main mechanisms, discussing in particular the recent developments of beam instability theories and simulations.
Since 2015 the LHC has been operating at 6.5 TeV. In 2016 the β -functions at the interaction points of ATLAS and CMS were squeezed to 0.4 m. This is below the design β*=0.55m at 7 TeV, and has been ...instrumental to surpass the design luminosity of 1034cm−2s−1 . Achieving a lower than nominal β* has been possible thanks to the extraordinary performance of the LHC, in which the control of the optics has played a fundamental role. Even though the β -beating for the virgin machine was above 100%, corrections reduced the rms β -beating below 1% at the two main experiments and below 2% rms around the ring. This guarantees a safe operation as well as providing equal amount of luminosity for the two experiments. In this article we describe the recent improvements to the measurement, correction algorithms and technical equipment which allowed this unprecedented control of the optics for a high-energy hadron collider.
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