Design and operation of the air-cooled beam dump for the extraction line of CERN's Proton Synchrotron Booster (PSB)

A new beam dump has been designed, built, installed and operated to withstand the future proton beam extracted from the Proton Synchrotron Booster (PSB) in the framework of the LHC Injector Upgrade (LIU) Project at CERN, consisting of up to 1E14 protons per pulse at 2 GeV, foreseen after the machine upgrades planned for CERN's Long Shutdown 2 (2019-2020). In order to be able to efficiently dissipate the heat deposited by the primary beam, the new dump was designed as a cylindrical block assembly, made out of a copper alloy and cooled by forced airflow. In order to determine the energy density distribution deposited by the beam in the dump, Monte Carlo simulations were performed using the FLUKA code, and thermo-mechanical analyses were carried out by importing the energy density into ANSYS. In addition, Computational Fluid Dynamics (CFD) simulations of the airflow were performed in order to accurately estimate the heat transfer convection coefficient on the surface of the dump. This paper describes the design process, highlights the constraints and challenges of integrating a new dump for increased beam power into the existing facility and provides data on the operation of the dump

Analysis on the mechanical effects induced by beam impedance heating on the HL-LHC target dump injection segmented (TDIS) absorber

The High Luminosity Large Hadron Collider (HL-LHC) Project at CERN calls for increasing beam brightness and intensity. In such a scenario, critical accelerator devices need to be redesigned and rebuilt. Impedance is among the design drivers, since its thermo-mechanical effects could lead to premature device failures. In this context, the current work reports the results of a multiphysics study to assess the electromagnetic and thermo-mechanical behaviour of the Target Dump Injection Segmented (TDIS). It first discusses the outcomes of the impedance analysis performed to characterise the resistive wall and the high order resonant modes (HOMs) trapped in the TDIS structures. Then, their RF-heating effects and the related temperature distribution are considered. Finally, mechanical stresses induced by thermal gradients are studied in order to give a final validation on the design qualit

Experimental results and strength model identification of pure iridium

Intense and high energy proton beams are impacted with fixed materials (targets) in order to produce new particles and secondary beams at CERN. In some of these targets, the requirement of reaching high yield production of secondary particles points out to the use of high density materials. The interaction of the beam with the atoms and nuclei of these materials produce extremely fast depositions of energy, highly soliciting them from thermo-structural point of view due to subsequent rise of temperature and pressure waves. Iridium is a good candidate material since exhibits very high density, high melting point, good strength and stability at high temperature, and resistance to thermal shock. The main goal of this study is the investigation of the mechanical behaviour at different temperatures and strain-rates in tensile loading condition of pure iridium. A series of tests at room temperature at different strain-rates (from 10-3 s-1 up to 104 s-1) was performed in order to obtain information about strain and strain-rate sensitivity of the material. In addition, a series of tests at different temperatures in both quasistatic and high strain-rate loading conditions was performed in order to obtain information about the thermal softening of the material (from room temperature up to 1250 °C). The experimental data were used to identify a strength model able to predict the material behaviour over wide ranges of variation of the variables of interest

CERN antiproton target: Hydrocode analysis of its core material dynamic response under proton beam impact

Antiprotons are produced at CERN by colliding a 26 GeV=c proton beam with a fixed target made of a3 mm diameter, 55 mm length iridium core. The inherent characteristics of antiproton production involveextremely high energy depositions i nside the target when impacted by each primary proton beam, making it one of the most dynamically demanding among high energy solid targets in the world, with a risetemperature above 2000 °C after each pulse impact and successive dynamic pressure waves of the order of GPa¿s. An optimized redesign of the current target is foreseen for the next 20 years of operation. As a first step in the design procedure, this numerical study delves into the fundamental phenomena present in the target material core under proton pulse impact and subsequent pressure wave propagation by the use of hydrocodes. Three major phenomena have been identified, (i) the dominance of a high frequency radial wave which produces destructive compressive-to-tensile pressure response (ii) The existence of end-ofpulse tensile waves and its relevance on the overall response (iii) A reduction of 44% in tensile pressure could be obtained by the use of a high density tantalum cladding.Torregrosa Martín, CL.; Perillo Marcone, A.; Calviani, M.; Muñoz-Cobo González, JL. (2016). CERN antiproton target: Hydrocode analysis of its core material dynamic response under proton beam impact. Physical Review Special Topics: Accelerators and Beams. 19(7):1-12. doi:10.1103/PhysRevAccelBeams.19.073402S11219

FIB-SEM investigation and uniaxial compression of flexible graphite

Flexible graphite (FG) with 1 - 1.2 g/cm$^3$ density is employed as beam energy absorber material in the CERN's Large Hadron Collider (LHC) beam dumping system. However, the increase of energy deposited expected for new HL-LHC (High-Luminosity LHC) design demanded for an improvement in reliability and safety of beam dumping devices, and the need for a calibrated material model suitable for high-level FE simulations has been prioritized. This work sets the basic knowledge to develop a material model for FG suitable to this aim. A review of the FG properties available in literature is first given, followed by FIB-SEM (Focused Ion Beam - Scanning Electron Microscopy) microstructure investigation and monotonic and cyclic uniaxial compression tests. Similarities with other well-known groups of materials such as crushable foams, crumpled materials and compacted powders have been discussed. A simple 1D phenomenological model has been used to fit the experimental stress-strain curves and the accuracy of the result supports the assumptions that the graphite-like microstructure and the crumpled meso-structure play the major role under out-of-plane uniaxial compression.Comment: Pre-print template, 57 pages, 14 figure

Finite Element Analysis of the Proximal implanted Tibea in relation to implant loosening

Tibial component alignment is one of the parameters that have most influence on implant loosening. The effect of varus-valgus and antero-posterior angles on the cancellous bone stress at the bone-implant interface was examined by means of finite element analysis. The lowest stress was obtained when the tibial tray was orientated in values. Moreover, the larger the valgus tilt was, the lower were the stresses within the cancellous bone. It was observed that higher stresses were produced with a posterior angle, as compared to a perfectly horizontal tibial cut. These findings were in line with clinical observations related to prosthesis orientations.In general, previously reported finite element models did not include patient specific data. Therefore, a comprehensive convergence study was performed in order to determine the finite element mesh characteristics (element size) and material property distribution (number of material groups) necessary to accurately describe the stress and risk ratio distributions at the bone-implant interface in patient-specific FE models. It was observed that with a logarithmic discretisation of the material properties within the bone convergence was reached with fewer material groups, as compared to the linear discretisation. Convergence was assessed at two levels, locally be examining variations at the nodal points and globally, by examining the mean and peak values within a pre-defined volume. This study has shown that accurate assignment of the material properties is critical in achieving convergence of other parameters such as stress and risk ratio. If convergence of the assigned material properties is not achieved, errors are then propagated through to other parameters of interest. There has been found no evidence of previous studies that show that the assigned material properties in models of bony structures are influenced by the mesh density, as was demonstrated here.In the final part of the thesis, based on the convergence study, a combined, prospective FE and RSA migration study was performed.</p

Electron cloud build-up simulations in the two-beam common chamber of the HL-LHC TDIS with non-uniform surface properties

The segmented injection protection absorber (TDIS) foreseen for the High-Luminosity Large Hadron Collider (HL-LHC) project is designed to protect the machine in case of injection kicker malfunctioning. Since the current LHC injection protection absorber has suffered from vacuum issues possibly induced by electron multipacting, numerical studies were done to estimate the electron flux expected on the internal surfaces of the TDIS. This device will consist of three pairs of movable absorbing blocks above and below one beam and a beam screen surrounding the second circulating beam. The build-up of electron cloud in the TDIS was simulated accounting for the presence of two counter-rotating beams, for the configuration of the jaws and for the different materials used for the different surfaces in the device. The simulation studies have also investigated the possibility of coating the most critical surfaces with amorphous carbon in order to mitigate the multipacting