Organisation européenne pour la recherche nucléaire

L’Organisation européenne pour la recherche nucléaire, aussi appelée laboratoire européen pour la physique des particules et couramment désignée sous l'acronyme CERN ou Cern (du nom du Conseil européen pour la recherche nucléaire, organe provisoire institué en 1952), est le plus grand centre de physique des particules du monde. Il se situe à quelques kilomètres de Genève, en Suisse, à cheval sur la frontière franco-suisse, sur les communes de Meyrin, Prévessin-Moëns et Saint-Genis-Pouilly. Les anneaux des accélérateurs s'étendent notamment sous les communes françaises de Saint-Genis-Pouilly et Ferney-Voltaire (département de l'Ain). Histoire Création Au lendemain de la Seconde Guerre mondiale, la recherche européenne en physique est quasi inexistante, alors qu'elle était au sommet de sa gloire quelques années auparavant. C'est dans ces conditions que le Français Louis de Broglie, prix Nobel de physique en 1929, lance l'idée, lors de la conférence européenne d

Accurate Profile Measurement of the low Intensity Secondary Beams in the CERN Experimental Areas

Inaki Ortega Ruiz

The CERN accelerators deliver a wide spectrum of secondary beams to the Experimental Areas. These beams are composed of hadrons, leptons, and heavy ions that can vary greatly in momentum (1 GeV/c to 400 GeV/c) and intensity (10^2 to 10^8 particles per second). The profile, position, and intensity of these beams are measured utilising particle detectors. However, the current systems show several problems that limit the quality of this kind of monitoring. The aim of this doctoral thesis is to investigate the best detector technology that could replace the existing monitors and build a first prototype of it. A review of the existing detection techniques has led to the choice of Scintillating Fibres (SciFi) read-out with Silicon Photomultipliers (SiPM). This detection technology has the potential to perform better in terms of material budget, range of intensities measured, and active area size. In addition, it has particle counting capabilities, which could extend its application to momentum spectrometry or Time-of-Flight (ToF) measurements. Its resistance to radiation damage offers good potential for longevity of use. A first prototype of a SciFi-SiPM monitor has been successfully tested with different particle beams at CERN, giving accurate profile measurements over a wide range of energies and intensities. It has only shown problems during use with lead ion beams, whose origin is believed to be crosstalk between the fibres. A Geant4 simulation of a single scintillating fibre has been performed to estimate its signal generation. This simulation is verified by real measurements of the light yield of scintillating fibres. Similarly, another Geant4 simulation of a full SciFi monitor has been developed to characterise the perturbation of the beam by the monitor. The future beam instrumentation for the Neutrino Platform at CERN is also described here, which is being developed as a continuation of the work conducted during this thesis.

EPFL2018

Radiation protection studies for CERN Linac4/SPL accelerator complex

Egidio Mauro

CERN is presently designing a new chain of accelerators to replace the present Proton Synchrotron (PS) complex: a 160 MeV room-temperature H- linac (Linac4) to replace the present 50 MeV proton linac injector, a 3.5 GeV Superconducting Proton Linac (SPL) to replace the 1.4 GeV PS booster (PSB) and a 50 GeV synchrotron (named PS2) to replace the 26 GeV PS. Linac4 has been funded and the civil engineering work started in October 2008, whilst the SPL is in an advanced stage of design. Beyond injecting into the future 50 GeV PS, the ultimate goal of the SPL is to generate a 4 MW beam for the production of intense neutrino beams. The radiation protection design is driven by the latter requirement. This thesis summarizes the radiation protection studies conducted for Linac4. FLUKA Monte Carlo simulations, complemented by analytical estimates, were performed 1) to evaluate the propagation of neutrons through the waveguide, ventilation and cable ducts placed along the accelerator, 2) to estimate the radiological impact of the accelerator in its low energy section, where the access area is located, and 3) to calculate the induced radioactivity in the air and in the components of the accelerator. The latter study is particularly important for maintenance interventions and final disposal of radioactive waste. Two possible layouts for the CCDTL section of the machine were considered in order to evaluate the feasibility, from the radiological standpoint, of replacing electromagnetic quadrupoles with permanent magnet quadrupoles with high content of cobalt. The present work provides complete information on beam loss assumptions, accelerator structure and duct and maze design, in order to make the present results of sufficiently general interest and provide guidelines for similar studies for intermediate energy proton accelerators. In addition to the Linac4-specific studies, this thesis also discusses FLUKA simulations performed to test the capability of the code, in a proton therapy application, in predicting induced radioactivity from intermediate energy protons. The thesis also reviews the analytical models mostly used for the calculation of neutron streaming through penetration traversing shielding barriers, discusses the FLUKA simulations performed to test the reliability of these models and, on the basis of the simulations, derives a universal expression that can be used to estimate the neutron transmission through a straight duct in direct view of the source, model missing so far in the literature.

EPFL2009

Possible Mitigations of Longitudinal Intensity Limitations for HL-LHC Beam in the CERN SPS

Joël Repond

The Super Proton Synchrotron (SPS) at CERN is the injector of the Large Hadron Collider (LHC), the world's largest particle collider. The High-Luminosity LHC (HL-LHC) project is a major step forward in the improvement of the LHC performances and it requires a doubling of the nominal bunch intensity of the current LHC beam. In the SPS, multi-bunch instabilities and particle losses limit the beam intensity that can be accelerated to 450 GeV/c and transferred to the LHC. Without mitigation measures, the bunch intensity threshold for longitudinal instabilities is three times below the nominal intensity of the LHC beam. Moreover, the present limited RF power is not sufficient to accelerate beams with intensities well above nominal without substantial particle losses and a reduction of the RF voltage available for the beam at the flat top energy. The SPS will undergo significant upgrades but they may not be sufficient to ensure the stability of the HL-LHC beam. The objectives of this doctoral research are to study the longitudinal intensity limitations of the LHC proton beam in the SPS and to find possible mitigation measures to ensure the beam stability and quality at HL-LHC intensity. Beam measurements and particle simulations are used in conjunction with analytical estimations to study the multi-bunch instabilities during the cycle in the SPS. This work attempts to identify the main sources of instabilities and beam quality degradation. Possible scenarios of mitigation measures are investigated to explore the future beam parameters achievable after upgrades. The effects on beam stability of the foreseen RF upgrade, the double RF operation and the reduction of various longitudinal beam-coupling impedances are analysed in detail. The scenario of a lower-harmonic RF system in the SPS, for particle losses reduction, is also studied.

EPFL2019