Search

The Large Hadron electron Collider (LHeC) is a proposed future particle physics project colliding 60 GeV electrons from a six-pass recirculating energy-recovery linac (ERL) with 7 TeV protons stored in the LHC. The ERL technology allows for much higher beam current and, therefore, higher luminosity than a traditional linac. The high-current, high-energy electron beam can also be used to drive a free electron laser (FEL). In this contribution, we examine how the LHeC ERL can serve as a source of high-energy photons for studies in nuclear physics, high-energy physics, Axion detection, dark energy, and protein crystallography. In the first section, we discuss the performance of the LHeC-based FEL, operated in the SASE mode for generating photon pulses at wavelengths ranging from 200 keV to 600 keV. In the second section, we investigate photon production via Laser Compton scattering (LCS)., 4

We report on the Future Circular Collider (FCC) Feasibility Study, the mid-term review in autumn 2023, and the longer term timeline., Invited contribution to ICFA Newsletter no. 85

One of the major upcoming challenges in particle physics is achieving precise measurements of the Z, W, and H bosons, as well as the top quark. To meet these targets, the next e\textsuperscript{+}e\textsuperscript{-} collider complex, FCC-ee, will need to achieve unprecedented luminosities. The FCC-IS European Study is investigating the feasibility of these challenges, with a cornerstone of the study being the design and optimization of the high-energy booster (HEB). This paper provides an update on the status of the HEB of FCC-ee in light of recent developments in the injector and collider survey, as well as an overview of ongoing work on longitudinal stability and design robustness in relation to field, alignment, and diagnostics errors. Constraints and effects related to the design frequency of the accelerating cavities, as well as collective effects, are also highlighted. Lastly, the paper presents an investigation into an alternative arcs cell design., Comment: pre-print of ICFA Newsletter 2023

The LHC infrastructure, i.e. the tunnel itself as well as the services associated with power, cooling, ventilation, network and access (among others), represent a considerable asset, and may be considered for hosting and supporting future versions of an “LHC” beyond its present configuration and the HL- LHC upgrade. In this chapter, we provide an overview of possible machine parameters and energy reach of a future higher-energy hadron collider in the LHC tunnel. We sketch four options with arc dipole magnetic fields in the range of 12 T to 24 T, each of which represents a well-defined discrete step in future accelerator magnet technology. We discuss the corresponding main machine and magnet parameters, and describe readiness, challenges and opportunities.

Charged-particle colliders have proven key instruments of discovery in high-energy physics. Pushing the frontiers of our knowledge ever further has relied on, and still keeps calling for, ever better performance and novel techniques. During more than four decades, Swapan Chattopadhyay has made numerous essential contributions to this endeavour. Often far ahead of his time, he helped advance many areas of collider development, notably in the domains of stochastic cooling, the development of asymmetric B factories, the design of next- and next-next-generation of high-energy colliders, and the harnessing of energy-recovery for particle colliders., Invited Contribution to Swapan Chattopadhyay Retirement Symposium, 30 April 2021. To be published in a special volume of IJMPA

Plasmonic modes offer the potential to achieve PetaVolts per meter fields, that would transform the current paradigm in collider development in addition to non-collider searches in fundamental physics. PetaVolts per meter plasmonics relies on collective oscillations of the free electron Fermi gas inherent in the conduction band of materials that have a suitable combination of constituent atoms and ionic lattice structure. As the conduction band free electron density, at equilibrium, can be as high as $\rm 10^{24}cm^{-3}$, electromagnetic fields of the order of $\rm 0.1 \sqrt{\rm n_0(10^{24}cm^{-3})} ~ PVm^{-1}$ can be sustained by plasmonic modes. Engineered materials not only allow highly tunable material properties but quite critically make it possible to overcome disruptive instabilities that dominate the interactions in bulk media. Due to rapid shielding by the free electron Fermi gas, dielectric effects are strongly suppressed. Because the ionic lattice, the corresponding electronic energy bands and the free electron gas are governed by quantum mechanical effects, comparisons with plasmas are merely notional. Based on this framework, it is critical to address various challenges that underlie PetaVolts per meter plasmonics including stable excitation of plasmonic modes while accounting for their effects on the ionic lattice and the electronic energy band structure over femtosecond timescales. We summarize the ongoing theoretical and experimental efforts as well as map out strategies for the future. Extreme plasmonic fields can shape the future by not only bringing tens of TeV to multi-PeV center-of-mass-energies within reach but also by opening novel pathways in non-collider HEP. In view of this promise, we invite the scientific community to help realize the immense potential of PV/m plasmonics and call for significant expansion of the US and international R\&D program., contribution to Snowmass 2021

A large circular e$^+$e$^-$ collider followed by a highest-energy hadron collider in the same tunnel promises the most far-reaching physics program for the post-LHC era, and such a facility could well serve the particle physics community through the end of the 21st century. Two such projects are presently proposed: The Future Circular Collider, in a global collaboration hosted by CERN, and the combination of Circular Electron Positron Collider and Super Proton-Proton Collider, advanced by IHEP Beijing. Over the centre-of-mass energy range from 90 to about 365 GeV, covering all known heavy elements of the Standard Model, from the Z resonance to the top-quark threshold, the circular e$^+$e$^-$ collider offers a high luminosity and exquisite energy efficiency. The high luminosity is maintained by top-up injection from a full-energy booster synchrotron. On the Z pole and at the WW threshold resonant depolarisation will allow for a precision energy calibration at the ppm level. This article summarizes and compares the designs of FCC-ee and CEPC, covering the latest accelerator layouts and beam parameters, R&D; plans, ongoing prototyping of key technologies, such as for the SRF system, and possible implementation schedules.

Possible circular colliders for the post-LHC era at CERN are being explored within the framework of the Future Circular Collider (FCC) feasibility study. The first stage of the FCC integrated project is the FCC-ee, an ambitious electron-positron collider with a circumference of approximately 100 km. Certain key concepts of the FCC-ee design can be demonstrated and tested at existing facilities, such as at SuperKEKB at KEK, DA$\Phi$NE at INFN, KARA at KIT, PETRA III at DESY, VEPP-4M at BINP, and the SwissFEL at PSI. The test of a prototype positron source at PSI, understanding the crab-waist collision scheme at SuperKEKB and DA$\Phi$NE, testing optics control and emittance tuning techniques at SuperKEKB and PETRA III, and precise beam energy calibration at VEPP-4M will offer invaluable insights for the FCC-ee design optimization and its operational procedures. The results of these beam tests will be an essential input to the FCC Feasibility Study Report. This article will give an overview of possible experimental tests for FCC-ee and highlight already successfully performed studies.

The current injector complex design of the FCC-e⁺e⁻ project consists of e⁺/e⁻ linacs, which accelerate the beams up to 6 GeV, a damping ring at 1.54 GeV, a pre-booster ring, accelerating the beam up to 16 GeV and a booster synchrotron ring integrated in the collider tunnel accelerating the beams up to the collision energies. The purpose of the damping ring is to accept the 1.54 GeV beam coming from the linac-1, damp the positron/electron beams and provide the required beam characteristics for the injection into the linac-2. In this presentation the current damping ring design is introduced and analytical calculations on various collective effect such as space charge, intra-beam scattering, longitudinal micro-wave instability, transverse mode coupling instability, ion effects, electron cloud and coherent synchrotron radiation, are presented., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The Future Circular electron-positron Collider (FCC-ee) is aimed at studying the Z and W bosons, the Higgs, and top quark with extremely high luminosity and good energy efficiency. Responding to a request from the 2020 Update of the European Strategy for Particle Physics, in 2021 the CERN Council has launched the FCC Feasibility Study to examine the detailed implementation of such a collider. This FCC Feasibility Study will be completed by the end of 2025 and its results be presented to the next Update of the European Strategy for Particle Physics expected in 2026/27., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA

Innovative new magnets with longitudinally varying dipole field are being produced for installation in a few modern light-source storage rings. We investigate some of the associated beam-dynamics issues, in particular the photon spectrum and quantum fluctuation associated with such magnets, and we study whether the resulting equilibrium emittance may deviate from the value expected in the long-magnet limit., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The Future Circular electron-positron Collider (FCC-ee) is designed for high precision particle physics experiments. This demands a precise knowledge of the beam energies, obtained by resonant depolarization, and from which the center-of-mass energy and possible boosts at all interaction points are then determined. At the highest beam energy mode of 182.5 GeV, the energy loss due to synchrotron radiation is about 10 GeV per revolution. Hence, not only the location of the RF cavities, but also a precise control of the optics and understanding of beam dynamics, are crucial. In the studies presented here, different possible locations of the RF-cavities are considered, when calculating the beam energies over the machine circumference, including energy losses from crossing angles, a non-homogeneous dipole distribution, and an estimate of the beamstrahlung effect at the collision point., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

In particle accelerators that operate with positrons, an electron cloud may occur due to several mechanisms. This work reports preliminary studies on electron cloud build-up for the arc sextupole sections of the positron ring of the FCCe⁺e⁻ using the code PyECLOUD. We compute the electron cloud evolution while varying strategic parameters and consider three simulation scenarios. We report the values of the central density just before the bunch passage, which is related to the single-bunch instability threshold and the electron density threshold for the three scenarios. In addition, we compare the simulated electron distribution across the central circular cross-section for a chamber with and without winglets., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The FCC-ee collider baseline foresees four different energy operation modes: Z, WW, H(ZH) and ttbar. An optional fifth mode, called s-channel Higgs production mode, could allow the measurement of the electron Yukawa coupling, in dedicated runs at 125 GeV centre-of-mass energy, provided that the centre-of-mass energy spread, can be reduced by at least an order of magnitude (5-10 MeV). The use of a special collision technique: a monochromatization scheme is one way to accomplish it. There are several methods to implement a monochromatization scheme. One method, named transverse monochromatization scheme, consists of introducing a dispersion different from zero but opposite sign for the two colliding beams at the Interaction Point (IP); In this paper we will report about the first attempt to design a new optics to implement a transverse monochromatic scheme for the FCC-ee Higgs production totally compatible with the standard mode of operation without dispersion at the IP., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The international FCC study group published in 2019 a Conceptual Design Report for an electron-positron collider with a centre-of-mass energy from 90 to 365 GeV with a beam currents of up to 1.4 A per beam. The high beam current of this collider create challenging requirements on the injection chain and all aspects of the linac need to be carefully reconsidered and revisited, including the injection time structure. The entire beam dynamics studies for the full linac, damping ring and transfer lines are major activities of the injector complex design. A key point is that any increase of positron production and capture efficiency reduces the cost and complexity of the driver linac, the heat and radiation load of the converter system, and increases the operational margin. In this paper we will give an overview of the status of the injector complex design and introduce the new layout that has been proposed by the study group working in the context of the CHART collaboration. In this framework, furthermore, we also present the preliminary studies of the FCC-ee positron source highlighting the main requirements and constraints., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The design parameters of the FCC-ee foresee operation with a total stored beam energy of about 20 MJ, exceeding those of previous lepton colliders by almost two orders of magnitude. Given the inherent damage potential, a halo collimation system is studied to protect the machine hardware, in particular superconducting equipment such as the final focus quadrupoles, from sudden beam loss. The different constraints that led to dedicating one straight section to collimation will be outlined. In addition, a preliminary layout and optics for a collimation insertion are presented., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

In order to maximize the luminosity production time in the FCC-ee, top-up injection will be employed. The positron and electron beams will be accelerated to the collision energy in the booster ring before being injected with either a small transverse or longitudinal separation to the stored beam. Using this scheme essentially keeps the beam current constant and, apart from a brief period during the injection process, collision data can be continuously acquired. Two top-up injection schemes, each with on- and off-momentum sub-schemes, viable for FCC-ee have been identified in the past and are studied in further detail to find a suitable design for each of the four operation modes of the FCC-ee. In this paper, injection straight optics, initial injection tracking studies and the effect on the stored beam are presented. Additionally, a basic proxy error lattice is introduced as a first step to studying injection into an imperfect machine., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Within the framework of the Future Circular Collider Feasibility Study, the design of the electron-positron collider FCC-ee is optimised, as a possible future double collider ring, currently foreseen to start operation during the 2040s. With close to 100 km of circumference and strong synchrotron radiation damping at highest beam energy, adequate beam measurements are needed to control the optics at the desired level. Various possible techniques to measure the optics in FCC-ee are explored, including the option of turn-by-turn measurements in combination with an AC-dipole., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The LEMMA-type muon collider generates muon pairs by the annihilation of 45 GeV positrons with electrons at rest. Due to the small cross section, an extremely high rate of positrons is required, which could be achieved by a ’Gamma factory’ based on the LHC. Other challenges with the LEMMA-type muon production scheme include the emittance preservation of muons and muon-generating positrons upon multiple traversals through a target, and the merging of many separate muon bunchlets. These two challenges may potentially be overcome by (1) operating the FCC-ee booster with a barrier bucket and induction acceleration, so that all positrons of a production cycle are merged into one single superbunch instead of storing ~10,000 separate bunches; and (2) sending the positron superbunch into a plasma target. During the passage of the positron superbunch, the electron density is enhanced 100–1000 fold without any increase in the density of nuclei, so that beamstrahlung and Coulomb scattering are essentially absent. We investigate prospects and difficulties of this approach, including emittance growth due to filamentation in the nonlinear plasma channel and due to positron self-modulation., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Since the Higgs boson discovery at CERN, precision measurement of its properties has become the first priority in the field of High Energy Physics. Two laboratories, CERN from Europe and IHEP from China, have proposed large scale circular electron-positron colliders, namely FCC-ee and CEPC. Record luminosities are expected in the center of mass energy range from 90 to about 365 GeV. In this talk the statuses of both projects are reviewed: Following the publication of the first CDR FCC-ee and CEPC entering the phase of consolidation and feasibility study. Special focus will be put on R plans, prototyping and key technologies., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

In the future circular electron-positron collider "FCC-ee", the intensity of colliding bunches must be tightly controlled, with a maximum charge imbalance between collision partner bunches of less than 3-5%. Laser Compton back scattering could be used to adjust and fine-tune the bunch intensity. We discuss a possible implementation and suitable laser parameters., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The FCC-e⁺e⁻ injector complex needs to produce and to transport high-intensity e⁺ and e⁻ beams at a fast repetition rate for topping up the collider at its collision energy. Two different options are under consideration as pre-accelerator before the bunches are transferred to the high-energy booster: either using the existing SPS machine or designing a completely new ring. The purpose of this paper is to present the studies of collective effects with analytical estimates for both the pre-booster ring design options including space charge (SC), longitudinal micro-wave instability (LMI), transverse mode coupling instability (TMCI), ion effects, electron cloud (e-cloud), coherent synchrotron radiation (CSR), and intra-beam scattering (IBS)., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The alignment strategy of the FCC-ee has a large impact on its luminosity. Larger alignment tolerances result in increased coupling and a subsequently higher vertical emittance. At the same time, tighter alignment tolerances around the 100 km ring are a major cost driver. This paper applies analytical emittance estimate methods to the FCC-ee and compares their predictions to data from simulations with different alignment tolerances. These methods can be used to help understand the impact of misalignments of certain magnet groups and to come up with an efficient alignment strategy., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Ultra-high gradients which are critical for future advances in high-energy physics, have so far relied on plasma and dielectric accelerating structures. While bulk crystals were predicted to offer unparalleled TV/m gradients that are at least two orders of magnitude higher than gaseous plasmas, crystal-based acceleration has not been realized in practice. We have developed the concept of nanoplasmonic crunch-in surface modes which utilizes the tunability of collective oscillations in nanomaterials to open up unprecedented tens of TV/m gradients. Particle beams interacting with nanomaterials that have vacuum-like core regions, experience minimal disruptive effects such as filamentation and collisions, while the beam-driven crunch-in modes sustain tens of TV/m gradients. Moreover, as the effective apertures for transverse and longitudinal crunch-in wakes are different, the limitation of traditional scaling of structure wakefields to smaller dimensions is significantly relaxed. The SLAC FACET-II experiment of the nano2WA collaboration will utilize ultra-short, high-current electron beams to excite nonlinear plasmonic modes and demonstrate this possibility., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Improving the accuracy of the impedance model of an accelerator is important for keeping beam instabilities and power loss under control. Here, by means of the PyHEAD- TAIL tracking code, we first review the longitudinal mi- crowave instability threshold for FCC-ee by taking into ac- count the longitudinal impedance model evaluated so far. Moreover, we present the results of beam dynamics simula- tions, including both the longitudinal and transverse wake- fields due to the resistive wall, in order to evaluate the influ- ence of the bunch length on the transverse mode coupling instability. The results of the transverse beam dynamics are also compared with the Vlasov solver DELPHI., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The FCC-ee is a proposed future high-energy, high-intensity and high precision lepton collider. Here, we present the latest developments for the FCC-ee interaction regions, which shall ensure optimum conditions for the particle physics experiments. We discuss measures of background reduction and a revised interaction region layout including a low impedance compact beam chamber design. We also discuss the possible impact of the radiation generated in the interaction region including beamstrahlung., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The FCC-ee project studies the design of a future 100 km e+/e circular collider for precision studies and rare decay observations in the range of 90 to 350 GeV center of mass energy with luminosities in the order of 10³⁵ cm⁻² s⁻¹. To achieve ultra-low vertical emittance a highly effective emittance tuning scheme is required. In this paper, we describe a comprehensive correction strategy used for the low emittance tuning. The strategy includes Dispersion Free Steering, linear coupling compensation based on Resonant Driving Terms and beta beat correction utilising response matrices., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

"Flakes" of neutral water or oxygen molecules carrying an electric or magnetic dipole moment can be attracted and trapped by the electromagnetic field of the circulating LHC proton beam. The possible presence of such flakes in the vacuum system could explain beam losses and beam instabilities encountered during the 2017 and 2018 LHC runs, and the observed effect of an external magnetic field., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

SuperKEKB has recently achieved the world record instantaneous luminosity of 2.8 × 10³⁴ \si{cm⁻²s⁻¹} and aims at reaching a target luminosity of about 6 × 10³⁵ \si{cm⁻²s⁻¹}. To accomplish this goal it is planned to increase beam currents up to §I{3.6}{A} and §I{2.6}{A} for the positron and the electron ring, respectively. Increasing the beam currents and, in particular, the number of leptons per bunch, can impact the optics parameters obtained by turn-by-turn measurements, such as the betatron tune or phase advance. Optics measurements performed at various bunch currents can give first indications of possible intensity dependent effects. In this paper, the effect of varying bunch current on optics measurements at SuperKEKB is explored., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Various physical and technology-dependent limits are encountered for key performance parameters of accelerators such as high-gradient acceleration, high-field bending, beam size, beam brightness, beam intensity and luminosity. This paper will review these limits and the associated challenges. Possible figures-of-merit and pathways to ultimate colliders will also be explored., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The Future Circular Collider study is exploring possible designs of circular colliders for the post-LHC era, as recommended by the European Strategy Group for High Energy Physics. One such option is FCC-hh, a proton-proton collider with a centre-of-mass energy of 100 TeV. The experimental insertion regions are key areas defining the performance of the collider. This paper presents the first insertion region designs with a complete assessment of the main challenges, as collision debris with two orders of magnitude larger power than current colliders, beam-beam interactions in long insertions, dynamic aperture for optics with peak $\beta$ functions one order of magnitude above current colliders, photon background from synchrotron radiation and cross talk between the insertion regions. An alternative design avoiding the use of crab cavities with a small impact on performance is also presented., Comment: 74 pages

At the end of 2018, a large worldwide collaboration, with contributors from more than 350 institutes completed the conceptual design of the Future Circular Collider (FCC), a ~100 km accelerator infrastructure linked to the existing CERN complex, that would open up the way to the post-LHC era in particle physics. We present an overview of the two main accelerator options considered in the design study, namely the lepton collider (FCC-ee), serving as highest-luminosity Higgs and electroweak factory, and the 100-TeV energy-frontier hadron collider (FCC-hh), along with the ongoing technological R efforts and the planned next steps. A recently approved EU co-funded project, the FCC Innovation Study (FCCIS), will refine the design of the lepton collider and prepare the actual implementation of the FCC, in collaboration with European and global partners, and with the local authorities., Proceedings of the 11th International Particle Accelerator Conference, IPAC2020, Caen, France

The proposed integrated program of the Future Circular Collider(FCC) takes a huge step beyond LEP and LHC. The FCC consists, in a first stage, of an energy- and luminosity-frontier electron-positron collider, which will operate at center-of-mass (c.m.) energies from about 90 to 365 GeV, and serve as electroweak factory. The second stage of the FCC will be a 100 TeV proton collider based on novel high-field magnets. A similar project is being proposed in China. In parallel to the development of future colliders, also the field of publications is undergoing profound changes. Physical Review Accelerators and Beams (PRAB) was founded in 1997 as a pioneering all-electronic diamond open-access journal, far ahead of its time. For many years PRAB was the fastest growing journal in the Physical Review family. Authors, editors and referees are highly internationalized. In this paper, on the occasion of the acceptance of the 2019 USPAS Prize for Achievement in Accelerator Science and Technology, I sketch the history, status, and challenges of FCC and PRAB., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

We report the design of the pre-injector chain for the Future Circular e⁺ e⁻ Collider (FCC-ee) system. The electron beam from a low-emittance RF gun is accelerated by an S-band linac up to 6 GeV. A damping ring at 1.54 GeV is required for emittance cooling of the positron beam. The intermediate energy step from the exit of the S-band linac at 6 GeV to the 20 GeV injection energy of the top-up booster can be provided by the modified Super Proton Synchrotron (SPS), serving as a pre-booster ring (PBR). An alternative option to reach 20 GeV energy would be to extend the S-band linac with a C- or X-band linac. An overall cost optimisation will determine the choice of the final configuration. Beam loss and emittance dilution in the linac due to space charge effects, wakefields, and misalignment of accelerator components can be mitigated by RF phasing and orbit steering. Start-to-end simulations examine the beam transport through the linac up to either 6 GeV or 20 GeV. The results indicate large design margins. Simulations of the beam dynamics in the damping ring (DR) demonstrate a sufficiently large momentum acceptance. Effects of intrabeam scattering and electron cloud instability in the DR are also studied., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The FCC-ee is a high-luminosity, high-precision circular collider to be constructed in a new 100 km tunnel in the Geneva area. The physics case is well established and the FCC-ee operation is foreseen at 91 GeV (Z-pole), 160 GeV (W pair production threshold), 240 GeV (Higgs resonance) and 365 GeV (t-tbar threshold). Due to the large 6D production emittance and important thermal load in the production target, the positron injector, in particular the positron source, is one of the key elements of the FCC-ee, requiring special attention. To ensure high reliability of the positron source, conventional and hybrid targets are currently under study. The final choice of the positron target will be made based on the estimated performances. In this framework, we present a preliminary design of the FCC-ee positron source, with detailed simulation studies of positron production, capture and primary acceleration., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

This milestone documents the gaps between the results of the particle collider conceptual design study and the level of detail required to enter a project construction preparatory phase. This document establishes a portfolio of suggested R&D topics related to the domain of particle collider design and associated technologies that need to be addressed with high priority in a follow-up project in order to come to a consistent and coherent design on which a project construction preparation can be based.

FCC-ee, the lepton version of the Future Circular Collider (FCC), is a 100 Km future machine under study to be built at CERN. It acquires two experiments with a highest beam energy of 182.5 GeV. FCC-ee aims to operate at four different energies, with different luminosities to fulfill physics requirements. Beam-beam effects at such a high energy/luminosity machine are very challenging and require a deep understanding, especially in the presence of x-y coupling sources. Beam-beam effects include the beamstrahlung process, which limits the beam lifetime at high energies, as well as dynamic effects at the Interaction point (IP) which include changes in the beta functions and emittances. In this report, we will define the beam-beam effects and their behaviours in the FCC-ee highest energy lattice after introducing x-y coupling in the ring., Proceedings of the 62th ICFA ABDW on High Luminosity Circular e$^+$e$^-$ Colliders, eeFACT2018, Hong Kong, China

The advantage of the linac-ring type electron proton collider is that it allows for the straightforward construction of $\gamma$p collider. In a $\gamma$p collider high energy photons can be generated from Compton backscattering of laser photons off electrons from a linear accelerator. In this study main parameters of photon-proton colliders based on some future electron linear accelerator projects and protons supplied form LHC or FCC are evaluated., Comment: 11 pages, 13 figures

This report describes a novel research infrastructure, based on a hadron collider with centre-of-mass collision energy of 100 TeV, collecting an integrated luminosity a factor of 5 or more 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 a 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. Thermal dark matter WIMP candidates will be discovered, or ruled out. Heavy ion and ep collisions will contribute to the breadth of the programme. As a single project, this particle collider infrastructure will serve the world-wide physics community for about 25 years and, in combination with a highest-luminosity energy frontier lepton collider (FCC-ee, see FCC conceptual design report volume 2), will provide a research tool until the end of the 21st century.

This report contains the description of a novel research infrastructure based on a highest-luminosity energy frontier electron-positron collider (FCC-ee) to address the open questions of modern physics. It will be a general precision instrument for the continued in-depth exploration of nature at the smallest scales, optimised to study with high precision the Z, W, Higgs and top particles, with samples of 5·10^12 Z bosons, 10^8 W pairs, 10^6 Higgs bosons and 10^6 top quark pairs. FCC-ee offers unprecedented sensitivity to signs of new physics, appearing in the form of small deviations from the Standard Model, of forbidden decay processes or of production of new particles with very small couplings. This collider will be implemented in stages, successively spanning the entire energy range from the Z pole over the WW threshold and H production peak to the tt ̅threshold. Most of the infrastructure (e.g. underground structures, surface sites, electrical distribution, cooling & ventilation, RF systems) can be directly reused for a subsequent energy-frontier hadron collider (FCC-hh, see FCC conceptual design report volume 3), serving the world-wide particle-physics community in a highly synergetic and cost-effective manner throughout the 21st century.

This report contains the description of a novel research infrastructure based on a high-energy hadron collider, which extends the current energy frontier by almost a factor 2 (27 TeV collision energy) and an integrated luminosity of at least a factor of 3 larger than the HL-LHC. In connection with four experimental detectors, this infrastructure will deepen our understanding of the origin of the electroweak symmetry breaking, allow a first measurement of the Higgs self-coupling, double the HL-LHC discovery reach and allow for in-depth studies of new physics signals arising from future LHC measurements. This collider would directly produce particles at significant rates at scales up to 12 TeV. The project re-uses the existing LHC underground infrastructure and large parts of the injector chain at CERN. This particle collider would succeed the HL-LHC directly and serve the world-wide physics community for about 20 years beyond the middle of the 21st century.

The most effective and comprehensive approach to thoroughly explore the open questions in modern particle physics is a staged research programme, integrating in sequence lepton (FCC-ee) and hadron (FCC-hh) collision programmes, to achieve an exhaustive understanding of the Standard Model and of electroweak symmetry breaking, and to maximize the potential for the discovery of phenomena beyond the Standard Model. The project would rely on a shared and cost effective technical and organizational infrastructure, as was the case with LEP followed by LHC. This integrated programme is complementary to other ongoing research activities and leverages cross-disciplinary synergies to expand our understanding of the universe. It cements and enlarges Europe’s leadership in particle and high-energy physics for decades to come. This document provides an overview of the physics potential of the integrated FCC programme and outlines its implementation scenario.

The first stage of the FCC (Future Circular Collider) is a high-luminosity electron-positron collider (FCC-ee) with centre-of-mass energy ranging from 88 to 365 GeV, to study with high precision the Z, W, Higgs and top particles, with samples of $5 \times 10^{12}$ Z bosons, $10^8$ W pairs, $10^6$ Higgs bosons and $10^6$ top quark pairs. A cornerstone of the physics program lays in the precise (ppm) measurements of the W and Z masses and widths, as well as forward-backward asymmetries. To this effect the centre-of-mass energy distribution should be determined with the high precision. This document describes the capacity offered by FCC-ee, starting with transverse polarization of the beams around the Z pole and the W pair threshold. A running scheme based on regular measurements of the beam energy by resonant depolarization of pilot bunches, during physics data taking, is proposed. The design for polarization wigglers, polarimeter and depolarizer is outlined. The $e^\pm$ beam energies will be monitored with a relative precision of $10^{-6}$. The centre-of-mass energy is derived subject to further corrections, related to the beam acceleration, synchrotron radiation and beamstrahlung; these effects are identified and evaluated. Dimuon events $e^+e^- \to ��^+ ��^-$, recorded in the detectors, provide with great precision the beam crossing angle, the centre-of-mass energy spread, and the $e^+$ and $e^-$ energy difference. Monitoring methods to minimize absolute error and relative uncertainties are discussed. The impact on the physics measurements is given. A programme of further simulations, design, monitoring and R&D is outlined., 107 pages, 15 tables, 58 figures

This document discusses the machine parameters and expected luminosity performance for the proposed future circular lepton collider FCC-ee. Particular emphasis is put on availability, physics run time, and efficiency. Key performance assumptions are compared with the operational experience of several past and present colliders including their injectors - LHC, LEP/LEP-2, PEP-II, KEKB, BEPCII, DAΦNE, SLC and the SPS complex., Proceedings of the 62th ICFA ABDW on High Luminosity Circular e$^+$e$^-$ Colliders, eeFACT2018, Hong Kong, China

As part of the Future Circular Collider study, the High Energy LHC (HE-LHC) is a proposed hadron collider situated in the already existing LHC tunnel. It aims at achieving a center of mass energy of 27 TeV, almost doubling the design c.o.m. energy of the LHC. This increase in energy relies on the use of 16 T Nb₃Sn dipoles to be developed for the FCC-hh. The field quality of these dipoles is expected to have a big impact on the Dynamic Aperture (DA) at injection energy and subsequently tracking studies are conducted to evaluate the impact of magnetic field errors on the beam dynamics. In the following the results of these studies for the different injection energies considered for the HE-LHC are presented and a possible strategy for increasing the DA are discussed., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Non-invasive diagnostics is essential to get important information about intense hadron beams, e.g. the transverse beam profile, which is indispensable in order to attain high brilliance and luminosity for upgrades on present machines and for future projects. Furthermore, it can be used to optimise parameter settings in environment of the running machine. An electron beam probe (EBP) is a beam diagnostics instrument which scans a low energy, low current electron beam through a hadron beam and obtains information from the detected response. The electrons are shot perpendicular through the hadron beam to be examined, which causes deflection in the beam potential of the intense hadron bunch, that needs to be detected and further analysed. We propose to build the EBP scanning apparatus for synchrotrons under ultra-high vacuum condition. The results of multi particle simulations evaluating limitations the expected measurement potential and limitations are presented. This work will be performed in collaboration with CERN., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

FCC-ee (Future Circular Collider) is a 100 km electron-positron circular collider with two foreseen experiments, aiming to run at four energies for precision studies of the Z, W, and Higgs boson and the top quark. The FCC-ee is a challenging machine from different points of view. In particular the beam-beam effects are of great importance. For the FCC-ee high-luminosity operation, the beam-beam effects impose profound constraints on the operating point in betatron tune space. In addition, taking into account different sources of machine nonlinearities, a tracking simulation with beam-beam elements revealed a strong beam blowup, especially in the vertical plane. Such a blowup is a potential obstacle to achieving and maintaining a high luminosity; therefore it needs to be carefully studied. In this paper, we present a general overview of simulation results on the FCC-ee beam-beam blowup with realistic machine errors., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The Gamma Factory (GF) initiative proposes to create novel research tools at CERN by producing, accelerating and storing highly relativistic partially stripped ion beams in the LHC rings and by exciting their atomic degrees of freedom by lasers, to produce high-energy photon beams. Their intensity would be several orders of magnitude higher than those of the presently operating light sources in the particularly interesting gamma-ray energy domain reaching up to 400 MeV. In this energy domain, the high-intensity photon beams can be used to produce secondary beams of polarized electrons, polarized positrons, polarized muons, neutrinos, neutrons and radioactive ions. Over the years 2017-2018 we have demonstrated that these partially stripped ion beams can be successfully produced, accelerated and stored in the CERN accelerator complex, including the LHC. The next step of the project is to build a proof of principle experiment in the SPS to validate the principal GF concepts. This contribution will present the initial conceptual design of this experiment along with its main challenge - the demonstration of the fast cooling method of partially stripped ion beams., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

In the FCC-ee pre-injector complex, a slightly modified SPS can serve as pre-booster. The baseline design foresees injecting the low-emittance electron and positron bunches off-axis into the SPS, and deploying strong wigglers to greatly enhance the radiation damping at the injection energy. We here compare the damping of large injection oscillations by means of radiation damping with the effect of other possible damping mechanisms such as a fast bunch-by-bunch feedback system and/or head-tail damping via nonzero chromaticity. As a by-product, we investigate the transverse beam stability., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia