Simulation and experimental study of proton bunch self-modulation in plasma with linear density gradients

We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported [F. Braunmller, T. Nechaeva et al. (AWAKE Collaboration), Phys. Rev. Lett. 125, 264801 (2020)PRLTAO0031-900710.1103/PhysRevLett.125.264801]: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement

Development of the self-modulation instability of a relativistic proton bunch in plasma

Self-modulation is a beam–plasma instability that is useful to drive large-amplitude wakefields with bunches much longer than the plasma skin depth. We present experimental results showing that, when increasing the ratio between the initial transverse size of the bunch and the plasma skin depth, the instability occurs later along the bunch, or not at all, over a fixed plasma length because the amplitude of the initial wakefields decreases. We show cases for which self-modulation does not develop, and we introduce a simple model discussing the conditions for which it would not occur after any plasma length. Changing bunch size and plasma electron density also changes the growth rate of the instability. We discuss the impact of these results on the design of a particle accelerator based on the self-modulation instability seeded by a relativistic ionization front, such as the future upgrade of the Advanced WAKefield Experiment

Simulation and experimental study of proton bunch self-modulation in plasma with linear density gradients

We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported [F. Braunmller, T. Nechaeva et al. (AWAKE Collaboration), Phys. Rev. Lett. 125, 264801 (2020)]: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement

Hosing of a Long Relativistic Particle Bunch in Plasma

Experimental results show that hosing of a long particle bunch in plasma can be induced by wakefields driven by a short, misaligned preceding bunch. Hosing develops in the plane of misalignment, self-modulation in the perpendicular plane, at frequencies close to the plasma electron frequency, and are reproducible. Development of hosing depends on misalignment direction, its growth on misalignment extent and on proton bunch charge. Results have the main characteristics of a theoretical model, are relevant to other plasma-based accelerators and represent the first characterization of hosing

Transition between Instability and Seeded Self-Modulation of a Relativistic Particle Bunch in Plasma

We use a relativistic ionization front to provide various initial transverse wakefield amplitudes for the self-modulation of a long proton bunch in plasma. We show experimentally that, with sufticient initial amplitude [>= (4.1 +/- 0.4) MV/m], the phase of the modulation along the bunch is reproducible from event to event, with 3%-7% (of 2 pi) rms variations all along the bunch. The phase is not reproducible for lower initial amplitudes. We observe the transition between these two regimes. Phase reproducibility is essential for deterministic external injection of particles to be accelerated

Design and implementation of a Client-Server System for Acquiring Beam Intensity Data from High Energy Accelerators at CERN

The world’s largest research center in the domain of High Energy Physics (HEP) is the European Organization for Nuclear Research (CERN) whose main goal is to accelerate particles through a sequence of accelerators – accelerator complex – and bring them into collision in order to study the fundamental elements of matter and the forces acting between them. For controlling the accelerator complex, CERN needs several diagnostic tools to provide information about the beam’s attributes and one such system is the Fast Beam Current Transformer (FBCT) measuring system that provides bunch-by-bunch and total beam intensity information. The current hardware and firmware of the FBCT system has certain issues and lacks diagnostics as a lot of the calculations are done in an FPGA. In order to improve on this, the firmware was redesigned and simplified in order to increase its capabilities and provide the base of a unified FBCT measuring system that could be installed in several of CERN’s accelerator complex’s parts. Following the above changes, this Thesis proposes the implementation of an operational client-server software solution to control the FBCT installation in the Super Proton Synchrotron (SPS) accelerator, as well as studying the design and implementation of a unified client-server software scheme that can replace the operational ones in the Large Hadron Collider (LHC) and can eventually allow further installations of the FBCT measuring system, elsewhere in the CERN accelerator complex

The LHC Fast Beam Current change Monitor

The modularity of the Large Hadron Collider’s (LHC) machine protection system (MPS) allows for the integration of several beam diagnostic instruments. These instruments have not necessarily been designed to have protection functionality, but MPS can still use them to increase the redundancy and reliability of the machine. The LHC fast beam current change monitor (FBCCM) is an example. It is based on analogue signals from fast beam current transformers (FBCT) used nominally to measure the LHC bunch intensities. The FBCCM calculates the magnitude of the beam signal provided by the FBCT, looks for a change over specific time intervals, and triggers a beam dump interlock if losses exceed an energy-dependent threshold. The first prototype of the FBCCM was installed in the LHC during the 2012-2013 run. The aim of this article is to present the FBCCM system and the results obtained, analyse its current performance and provide an outlook for the final system which is expected to be operational after the long LHC shutdown

Adapted method to assess and map fire hazard in Wildland-urban interfaces

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVINThe report presents an original method for fire hazard assessment and for a total fire risk index assessment. The exposed method is based on spatial analysis of the territory. Results are also presented with maps.Le rapport expose une méthode originale d'évaluation de l'aléa d'une part et de l'évaluation d'un indice global du risque d'incendie d'autre part dans les interfaces habitat-forêt. Cette méthode s'appuie sur une analyse spatiale du territoire. Il présente également la représentation cartographique des résultats

Commissioning of ALPS, the New Beam Position Monitor System of CERN’s Super Proton Synchrotron

The Super Proton Synchrotron (SPS) is both, the final machine in the pre-accelerator chain of the Large Hadron Collider (LHC) at CERN, and a machine providing several experiments with proton and ion beams. In the framework of CERN’s LHC Injectors Upgrade (LIU) project, aimed at improving the performances of the pre-accelerators in view of the high-luminosity upgrade of the LHC, the Beam Position Monitor (BPM) system of the SPS was redesigned during Run 2 of the LHC and deployed during the subsequent Long Shutdown 2 (LS2). This new system is called ALPS (A Logarithmic Position System) and acquires the signals from some 240 BPMs. It is designed to improve the system’s reliability and reduce the required maintenance with respect to its predecessor. During the restart of the SPS in 2021, the BPM system was a key element of the fast recommissioning of the machine, proving the validity of the chosen design approach and pre-beam commissioning strategy. This paper aims to illustrate the design choices made for ALPS, the strategy for commissioning it with beam in parallel with the machine restart, the commissioning procedure and the results obtained

Method to characterize and to map wildland urban interface. Part1- State of the art on the methods to characterize and to map wildland urban interfaces

Le rapport fait un état de l'art sur la définition des interfaces habitat-forêts et leurs méthodes d'évaluation et de cartographie. La recherche bibliographique est internationale. Elle est le support du développement d'une méthode développée dans le cadre européen