ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.

/pdf/performance-of-the-alice-experiment-at-the-cern-lhc-3v531yoy85.pdf

Performance of the ALICE experiment at the CERN LHC

In response to the 2013 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) study was launched, as an international collaboration hosted by CERN. This study covers a highest-luminosity high-energy lepton collider (FCC-ee) and an energy-frontier hadron collider (FCC-hh), which could, successively, be installed in the same 100 km tunnel. The scientific capabilities of the integrated FCC programme would serve the worldwide community throughout the 21st century. The FCC study also investigates an LHC energy upgrade, using FCC-hh technology. This document constitutes the second volume of the FCC Conceptual Design Report, devoted to the electron-positron collider FCC-ee. After summarizing the physics discovery opportunities, it presents the accelerator design, performance reach, a staged operation scenario, the underlying technologies, civil engineering, technical infrastructure, and an implementation plan. FCC-ee can be built with today’s technology. Most of the FCC-ee infrastructure could be reused for FCC-hh. Combining concepts from past and present lepton colliders and adding a few novel elements, the FCC-ee design promises outstandingly high luminosity. This will make the FCC-ee a unique precision instrument to study the heaviest known particles (Z, W and H bosons and the top quark), offering great direct and indirect sensitivity to new physics.

/pdf/fcc-ee-the-lepton-collider-future-circular-collider-61xh2cg09w.pdf

FCC-ee: The Lepton Collider: Future Circular Collider Conceptual Design Report Volume 2

https://hal.archives-ouvertes.fr/jpa-00239583/document

Il nuovo cimento

Particle physics has arrived at an important moment of its history. The discovery of the Higgs boson, with a mass of 125 GeV, completes the matrix of particles and interactions that has constituted the “Standard Model” for several decades. This model is a consistent and predictive theory, which has so far proven successful at describing all phenomena accessible to collider experiments. However, several experimental facts do require the extension of the Standard Model and explanations are needed for observations such as the abundance of matter over antimatter, the striking evidence for dark matter and the non-zero neutrino masses. Theoretical issues such as the hierarchy problem, and, more in general, the dynamical origin of the Higgs mechanism, do likewise point to the existence of physics beyond the Standard Model. This report contains the description of a novel research infrastructure based on a highest-energy hadron collider with a centre-of-mass collision energy of 100 TeV and an integrated luminosity of at least a factor of 5 larger than the HL-LHC. It will extend the current energy frontier by almost an order of magnitude. The mass reach for direct discovery will reach several tens of TeV, and allow, for example, to produce new particles whose existence could be indirectly exposed by precision measurements during the earlier preceding e+e– collider phase. This collider will also precisely measure the Higgs self-coupling and thoroughly explore the dynamics of electroweak symmetry breaking at the TeV scale, to elucidate the nature of the electroweak phase transition. WIMPs as thermal dark matter candidates will be discovered, or ruled out. As a single project, this particle collider infrastructure will serve the world-wide physics community for about 25 years and, in combination with a lepton collider (see FCC conceptual design report volume 2), will provide a research tool until the end of the 21st century. Collision energies beyond 100 TeV can be considered when using high-temperature superconductors. The European Strategy for Particle Physics (ESPP) update 2013 stated “To stay at the forefront of particle physics, Europe needs to be in a position to propose an ambitious post-LHC accelerator project at CERN by the time of the next Strategy update”. The FCC study has implemented the ESPP recommendation by developing a long-term vision for an “accelerator project in a global context”. This document describes the detailed design and preparation of a construction project for a post-LHC circular energy frontier collider “in collaboration with national institutes, laboratories and universities worldwide”, and enhanced by a strong participation of industrial partners. Now, a coordinated preparation effort can be based on a core of an ever-growing consortium of already more than 135 institutes worldwide. The technology for constructing a high-energy circular hadron collider can be brought to the technology readiness level required for constructing within the coming ten years through a focused R&D programme. The FCC-hh concept comprises in the baseline scenario a power-saving, low-temperature superconducting magnet system based on an evolution of the Nb3Sn technology pioneered at the HL-LHC, an energy-efficient cryogenic refrigeration infrastructure based on a neon-helium (Nelium) light gas mixture, a high-reliability and low loss cryogen distribution infrastructure based on Invar, high-power distributed beam transfer using superconducting elements and local magnet energy recovery and re-use technologies that are already gradually introduced at other CERN accelerators. On a longer timescale, high-temperature superconductors can be developed together with industrial partners to achieve an even more energy efficient particle collider or to reach even higher collision energies.The re-use of the LHC and its injector chain, which also serve for a concurrently running physics programme, is an essential lever to come to an overall sustainable research infrastructure at the energy frontier. Strategic R&D for FCC-hh aims at minimising construction cost and energy consumption, while maximising the socio-economic impact. It will mitigate technology-related risks and ensure that industry can benefit from an acceptable utility. Concerning the implementation, a preparatory phase of about eight years is both necessary and adequate to establish the project governance and organisation structures, to build the international machine and experiment consortia, to develop a territorial implantation plan in agreement with the host-states’ requirements, to optimise the disposal of land and underground volumes, and to prepare the civil engineering project. Such a large-scale, international fundamental research infrastructure, tightly involving industrial partners and providing training at all education levels, will be a strong motor of economic and societal development in all participating nations. The FCC study has implemented a set of actions towards a coherent vision for the world-wide high-energy and particle physics community, providing a collaborative framework for topically complementary and geographically well-balanced contributions. This conceptual design report lays the foundation for a subsequent infrastructure preparatory and technical design phase.

/pdf/fcc-hh-the-hadron-collider-3zjqrxf0o5.pdf

FCC-hh: The Hadron Collider

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.

/pdf/machine-learning-for-beam-dynamics-studies-at-the-cern-large-3nrb3f5uq0.pdf

Machine learning for beam dynamics studies at the CERN Large Hadron Collider

The LHC Injectors Upgrade project (LIU) has been initiated to improve the performances of the existing injector complex at CERN to match the future requirements of the HL-LHC (High Luminosity LHC). In this framework, theProtonSynchrotron(PS) will undergofundamental changes for many of its main systems: the injection energy will be increased to reduce space-charge effects, the transverse damperwill be improvedto cope with transverse instabilities, and the RF systems will be upgraded to accelerate higherbeamintensityand brightness. Thesehardware improvements are triggered by a series of studies meant to identify the most critical performance bottlenecks, like space charge, impedances, longitudinal and transverse instabilities, as well as electron-cloud. Additionally, alternative production schemes for the LHC-type beams have been proposed and implemented to circumvent some of the present limitations. A summary of the most recent advances of the studies, as well as the proposed hardware improvements is given.

/pdf/the-ps-upgrade-programme-recent-advances-32q84zzmmd.pdf

The ps upgrade programme: recent advances

The impedance of the Finemet® loaded longitudinal damper cavity, installed in the CERN Proton Synchrotron straight section 02 during the Long Shutdown 2013-2014, has been evaluated [1]. Time domain simulations with CST Particle Studio have been performed in order to get the longitudinal and transverse impedance of the device and make a comparison with the longitudinal impedance that was measured for a single cell prototype.

/pdf/impedance-studies-for-the-ps-finemet-loaded-longitudinal-55po1ayvcf.pdf

Impedance Studies for the PS Finemet® Loaded Longitudinal Damper

A very important issue for the Future Circular Collider (FCC) is represented by collective effects due to the selfinduced electromagnetic fields, which, acting back on the beam, could produce dangerous instabilities. In this paper we will focus our work on the FCC electron-positron machine: in particular we will study some important sources of wake fields, their coupling impedances and the impact on the beam dynamics. We will also discuss longitudinal and transverse instability thresholds, both for single bunch and multibunch, and indicate some ways to mitigate such instabilities. INTRODUCTION The FCC-ee is an e+e− circular collider designed to cover the beam energy range from the Z pole (45.6 GeV) to the top pair threshold (175 GeV). It would be the first step towards the FCC-hh [1], a 100 TeV hadron collider in the same tunnel of 97.75 km. Collective effects represent a serious issue for such a kind of machine, since they can produce instabilities and limit its operation and performance. In this paper we will focus on single bunch and multi bunch instabilities for the Z pole caused by the resistive wall (RW) and describe other important impedance sources, i.e. Beam Positions Monitors (BPMs), tapers and bellows with RF fingers. For reference, Table 1 shows the FCC-ee beam parameter list used for these studies [2]. Table 1: FCC-ee Beam Parameter List Beam energy [GeV] 45.6 Circumference C [km] 97.75 Bunches/beam 73770 Bunch population [1011] 0.4 Beam current I [A] 1.45 Rf frequency fRF [MHz] 400 RF voltage VRF [MV] 88.8 Momentum compaction αc[10−5] 1.465 Bunch length σz [mm] 3.6 Energy spread σe [%] 0.037 Betatron tunes Qx\Qy 265.14\267.22 Synchrotron tune Qs 0.0234 RESISTIVE WALL WAKE FIELDS When the beam passes through the vacuum chamber, it induces currents on the pipe walls. If the beam pipe walls ∗ eleonora.belli@roma1.infn.it have a finite resistivity, these currents extend behind the position of the charges, creating electromagnetic fields which can act on the following particles and perturb their motion by increasing the amplitude of their oscillations. This instability can occur in both longitudinal and transverse directions [3,4]. In the following, we will focus on the main single bunch effects due to the RW on the beam dynamics, by considering a 35 mm radius vacuum chamber with three layers (a first layer of copper with 2 mm thickness [5], then 6 mm of dielectric and finally iron with resistivity ρ = 10−7Ωm) and different coatings of the pipe walls: • Amorphous Carbon (AC) thk = 200 nm, ρ = 10−4 Ωm [5] • Non-Evaporable Getter (NEG) thk = 1μm , ρ = 10−6 Ωm [6] • Titanium Nitride (TiN) thk = 200 nm, ρ = 0.5 · 10−6 Ωm [7, 8] All these materials are characterized by a low Secondary Electron Yield (SEY) and a low desorption yield that could reduce significantly the electron cloud build up in the machine [9, 10]. Figure 1 shows the real and imaginary part of the transverse and longitudinal impedances due to RW as a function of the frequency for all the cases mentioned above. These impedances have been obtained from the ImpedanceWake2D code [11] and will be used in the following to analyze the effects of the RW on the beam dynamics. Single Bunch Effects This section is focused on the most important effects of the RWon the single bunch dynamics: theMicrowave Instability (MI) and the Transverse Mode Coupling Instability (TMCI) in the longitudinal and transverse planes, respectively. These two kinds of instability can limit the bunch intensity in the accelerator: it is well known from the theory [12] that the frequencies of the intra-bunch modes depend on the bunch intensity and as it increases the mode frequencies shift and merge, giving rise to the instability. The instability threshold is localized in the point where there is the mode coupling. Above this threshold, the bunch is lost in the transverse case while in the longitudinal case there is an increase of the bunch length and the energy spread and sometimes bunch internal oscillations can be observed which could be particular harmful in beam-beam collisions. MI In order to evaluate the MI threshold, several simulations were performed by using the macroparticle tracking codes PyHEADTAIL [13] and SBSC [14, 15]. Figs. 2, 3 THPAB020 Proceedings of IPAC2017, Copenhagen, Denmark ISBN 978-3-95450-182-3 3734 Co py rig ht © 20 17 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs 05 Beam Dynamics and Electromagnetic Fields D05 Coherent and Incoherent Instabilities Theory, Simulations, Code Developments Figure 1: Real and imaginary part of the transverse (top) and longitudinal (bottom) RW impedances as a function of the frequency in the case of no coating, NEG coating, TiN coating and Carbon coating. show the bunch lengthening and the energy spread increase due to the RW wakes for all the coatings under study. The NEG coating gives a MI threshold around the nominal bunch population, while the threshold for TiN and AC coatings is about 1.6− 1.8 · 1011, i.e. four times larger than the nominal intensity. Figure 2: RMS bunch length as a function of the bunch intensity given by PyHEADTAIL by considering only the RW impedance in the case of no coating and NEG, TiN and AC coatings. TMCI As in the longitudinal case, the TMCI threshold has been evaluated with PyHEADTAIL, by including also the bunch lengthening due to the longitudinal wake of Fig. 2. All the coatings show a good margin of safety. As an exFigure 3: RMS energy spread as a function of the bunch intensity given by PyHEADTAIL by considering only the RW impedance in the case of no coating and NEG, TiN and AC coatings. ample, Fig. 4 shows the real part of the frequency shift of the first two radial modes for the first five azimuthal modes going from -2 to 2 as a function of the bunch population, in the case of Carbon coating. Figure 4: TMCI threshold evaluated with PyHEADTAIL by taking into account the bunch lengthening due to the longitudinal wake in the case of Carbon coating.

/pdf/jacow-coupling-impedances-and-collective-effects-for-fcc-ee-4xjfj2ynxo.pdf

JACoW : Coupling Impedances and Collective Effects for FCC-ee

/pdf/studies-and-implementation-of-the-ps-dummy-septum-to-zkxae2it8r.pdf

Studies and implementation of the PS dummy septum to mitigate irradiation of magnetic septum in straight section 16

The Future Circular Collider study, hosted by CERN to design post-LHC particle accelerator options in a worldwide context, represents a great challenge under several aspects, which require R&D on beam dynamics and new technologies. One very critical point is represented by collective effects, generated by the interaction of the beam with selfinduced electromagnetic fields, called wake fields, which could produce beam instabilities, thus reducing the machines performance and limiting the maximum stored current. It is therefore very important to be able to predict these effects and to study in detail potential solutions to counteract them. In this paper the resistive wall and some other important geometrical sources of impedance for the FCC electron-positron accelerator are identified and evaluated, and their impact on the beam dynamics, which could lead to unwanted instabilities, is discussed.

Collective Effects Issues for FCC-ee

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