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Journal of Instrumentation 17(05), P05042 (2022). doi:10.1088/1748-0221/17/05/P05042 special issue: "ICFA Beam Dynamics Newsletter 83", The Beam Delivery System (BDS) is a critical component of a high-energy linear collider. It transports the beam from the accelerator and brings it to a focus at the Interaction Point. The BDS system includes diagnostic sections for measuring the beam energy, emittance, and polarization, as well as collimators for machine protection. The length of the BDS increases with collision energy. Higher collision energies also require higher luminosities, and this is a significant constraint on the design for energy-frontier machines. Here, we review BDS designs based on traditional quadrupole magnets and examine the challenges involved in extending these to the Multi-TeV regime consistent with requirements for advanced accelerator concepts., Published by Inst. of Physics, London

International audience; Momentum bandwidth is an important characteristic for final focus systems (FFS) of future high-energy colliders. A large momentum bandwidth is a notable feature of the novel local-chromaticity-correction FFS, being demonstrated at the KEK Accelerator Test Facility 2 (ATF2), owing to the locality of chromaticity correction. In this article, analytical estimations and simulations of momentum bandwidth for various optics of ATF2 are presented. Possible deviations of the momentum bandwidth due to realistic machine imperfections are studied. Experimental measurements at ATF2 following successful tuning of small vertical beam size at the interaction point (IP) are also described, which agree well with numerical predictions and further verify the robustness of the local chromaticity correction scheme.

The main goal of the Accelerator Test Facility 2 (ATF2) is to demonstrate the feasibility of future linear colliders’ final focus systems. The Ultra-low β^{*} optics of ATF2 is designed to have the same chromaticity level as CLIC. To ease the tuning procedure, a pair of octupoles was installed in ATF2 in 2017. This paper reports the optimizations performed to the octupoles’ setup for Ultra-low β^{*} optics including the new alignment technique, based on the waist shift and the new tunning knobs constructed for this optics. The full tuning procedure including the static errors is simulated for this setup., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The first stage of the Compact Linear Collider (CLIC) is planned to be at the center-of-mass energy of 380 GeV. The final focus system (FFS) was re-optimized for this energy and for L* of 6 m (distance between the Interaction Point (IP) and the last quadrupole, QD0). Furthermore, the FFS optics was optimized for the vertical beta-function of 70 microns to approach the Hourglass effect limit. This paper reports the exploration of shortening the Final Doublet (FD) within the FFS to reduce the chromaticity. In addition, an alternative optics design is investigated with a different dispersion profile along the FFS, which outperforms the previous optics with the same β^{*}, increasing luminosity by 5 %., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The ATF2 beam line at KEK was built to validate the operating principle of a novel final-focus scheme devised to demagnify high-energy beams in future linear lepton colliders; to date vertical beam sizes as small as 41 nm have been demonstrated. However, this could only be achieved with an electron bunch intensity $\ensuremath{\sim}10%$ of nominal, and it has been found that wakefield effects limit the beam size for bunch charges approaching the design value of ${10}^{10}{e}^{\ensuremath{-}}$. We present studies of the impact of wakefields on the production of ``nanobeams'' at the ATF2. Wake potentials were evaluated for the ATF2 beam line elements and incorporated into a realistic transport simulation of the beam. The effects of both static (component misalignments and rolls, magnet strength errors and beam position monitor resolution) and dynamic (position and angle jitter) imperfections were included and their effects on the beam size evaluated. Mitigation techniques were developed and applied, including orbit correction, dispersion-free steering, wakefield-free steering, and interaction point tuning knobs. Explicit correction knobs to compensate for wakefield effects were studied and applied, and found to significantly decrease the intensity dependence of the beam size.

For future linear colliders, a nanometer-scale beam size at the interaction point (IP) is one of the most challenging technical aspects. To explore the feasibility of a final focus system with a high chromaticity level, comparable to that of the Compact Linear Collider, the ultralow ${\ensuremath{\beta}}^{*}$ optics has been proposed and tuned at the KEK Accelerator Test Facility 2. In this paper, the recent experimental results are presented, which demonstrate the capability of achieving and stabilizing a vertical average beam size of 60 nm and below at the virtual IP. The observed vertical beam size is about 20 nm above the numerical predictions in the presence of static and dynamic imperfections. We interpret this discrepancy as beam size growth due to multipole fields, beam jitters and wakefield effects, and diagnostic errors.

International audience; The computation of analytic and numerical beam based quantities are derived for full 3D representation of the quadrupoles magnetic field, which can be computed by finite element code or measured. The impact of this more accurate description of the non homogeneity of the field is estimated on beam based observables and non linear correctors strengths, and compared with the less accurate models in the case of HL-LHC.

Mit der Entdeckung des Higgs-Bosons hat ein Messprogramm begonnen, bei dem die Eigenschaften dieses neuen Teilchens mit der höchstmöglichen Präzision untersucht werden soll um die Gültigkeit des Standardmodells der Teilchenphysik zu prüfen und nach neuer Physik jenseits des Standardmodells zu suchen. Für dieses Ziel wird der Large Hadron Collider (LHC) und sein Upgrade, der High Luminosity-LHC bis etwa zum Jahr 2035 laufen und Daten produzieren. Um an der Spitze der Teilchenphysik zu bleiben, hat die “European Strategy Group for Particle Physics” empfohlen, ambitionierte Nachfolgeprojekte für die Zeit nach dem LHC zu entwickeln. Entsprechend dieser Empfehlung hat das CERN die “Future Circular Collider” (FCC) -Studie gestartet, die die Machbarkeit neuer Speicherringe für Teilchenkollisionen (Collider) untersucht. In dieser Arbeit wird die Entwicklung der Wechselwirkungszonen für FCC-hh, einem Proton-Proton-Speicherring mit einer Schwerpunktsenergie von 100 TeV und einem Umfang von 100 km, beschrieben. Die Wechselwirkungszone ist das Herzstück eines Colliders, da sie die erreichbare Luminosität bestimmt. Es ist daher entscheidend, schon früh im Entwicklungsprozess eine möglichst hohe Kollisionsrate anzustreben. Ausgehend von der optische Struktur der Wechselwirkungszonen des LHC und dem geplanten High Luminosity-LHC (HL-LHC) werden Strategien zur Skalierung hergeleitet um der höheren Strahlenergie gerecht zu werden. Bereits früh im Entwicklungsprozess wird die Strahlungsbelastung durch Teilchentrümmer vom Wechselwirkungspunkt als entscheidender Faktor für das Layout der Wechselwirkungszone identifiziert und eine allgemeine Design-Strategie, die den Schutz der supraleitenden Endfokussierungsmagnete mit einer hohen Luminosität verbindet, wird formuliert und implementiert. Aufgrund des deutlichen Spielraums in Bezug auf beta* wurde die resultierende Magnetstruktur zum Referenzdesign für das FCC-hh-Projekt., The discovery of the Higgs boson is the start of a measurement program that aims to study the properties of this new particle with the highest possible precision in order to test the validity or the Standard Model of particle physics and to search for new physics beyond the Standard Model. For that purpose, the Large Hadron Collider (LHC) and its upgrade, the High Luminosity-LHC, will operate and produce data until 2035. Following the recommendations of the European Strategy Group for Particle Physics, CERN launched the Future Circular Collider (FCC) study to design large scale particle colliders for high energy physics research in the post-LHC era. This thesis presents the development of the interaction region for FCC-hh, a proton-proton collider operating at 100 TeV center-of-mass energy. The interaction region is the centerpiece of a collider as it determines the achievable luminosity. It is therefore crucial to aim for maximum production rates from the beginning of the design process. Starting from the lattices of LHC and its proposed upgrade, the High Luminosity LHC (HL-LHC), scaling strategies are derived to account for the increased beam rigidity. After identifying energy deposition from debris of the collision events as a driving factor for the layout, a general design strategy is drafted and implemented, unifying protection of the superconducting final focus magnets from radiation with a high luminosity performance. The resulting FCC-hh lattice has significant margins to the performance goals in terms of beta*. Protecting the final focus magnets from radiation with thick shielding limits the minimum beta* and therefore the luminosity. An alternative strategy to increase the magnet lifetime by distributing the radiation load more evenly is developed. A proof of principle of this method, the so-called Q1 split, is provided. In order to demonstrate the feasibility of the derived interaction region lattices, first dynamic aperture studies are conducted.

Accelerator physics needs advanced modeling and simulation techniques, in particular for beam stability studies. A deeper understanding of the effects of magnetic fields non-linearities will greatly help in the improvement of future colliders design and performance. In *, a new tracking method was proposed to study the effect of the longitudinal dependency of the harmonics on the beam dynamics. In this paper, the study will focus on the effects on observable quantities in beam based measurements, for the case of HL-LHC Inner Triplet and with possible tests in LHC., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The Accelerator Test Facility 2 (ATF2) at KEK is a prototype for the Final Focus Systems of the future e⁺e⁻ linear colliders, the International Linear Collider (ILC) and the Compact Linear Collider (CLIC). In this paper both simulation and experimental results are presented with special emphasis on intensity-dependent effects. The importance of these effects is shown using the PLACET code and realistic ATF2 machine simulations (including beam jitter, misalignment, wakefield, Beam Based Alignment (BBA) correction, …). The latest experimental results are also presented, in particular the impact of the beam intensity on the beam size at the IP., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

International audience; NICA (Nuclotron-based Ion Collider fAcility) [1] is a heavy-ion collider for studying the properties of hot and dense baryonic matter to be constructed at JINR (Dubna). A major restricting factor on the NICA’s transverse dynamic aperture is the nonlinear fringe field of final-focus quadrupole lenses. We propose to enhance the NICA dynamic aperture with a set of multipole lenses whose characteristics and configuration are optimized using a genetic algorithm.

International audience; Aiming to simplify the machine detector interface of the Compact Linear Collider (CLIC), a new detector model has been designed allowing the last quadrupole QD0 of the final focus system (FFS) to be located outside of the experiment with a distance L* from the interaction point of 6 m. In this paper, the beam delivery system (BDS) has been reoptimized, offering a luminosity performance that exceeds the design requirements by 11% for the total luminosity and by 7% in the energy peak. A simulation campaign has been carried out and has proved the feasibility of recovering the luminosity under realistic transverse misalignments of the FFS optics, by means of different orbit and aberration correction techniques, making this long L* design a realistic candidate for the future CLIC BDS.

International audience; The European Strategy Group for High Energy Physics recommends to study collider designs for the post-LHC era. Among the suggested projects there is the circular 100 TeV proton-proton collider FCC-hh. Starting from LHC and its proposed upgrade HL-LHC, this paper outlines the development of the interaction region design for FCC-hh. We identify energy deposition from debris of the collision events as a driving factor for the layout and draft the guiding principles to unify protection of the superconducting final focus magnets from radiation with a high luminosity performance. Furthermore, we offer a novel strategy to mitigate the lifetime limitation of the first final focus magnet due to radiation load, the Q1 split.

Mitigation of static imperfections for emittance preservation is one of the most important and challenging tasks faced by the Compact Linear Collider (CLIC) beam delivery system. A simulation campaign has been performed to recover the nominal luminosity by means of different alignment procedures. The state of the art of the tuning studies is drawn up. Comparative studies of the tuning performances and a tuning-based final focus system design optimization for two L options are presented. The effectiveness of the tuning techniques applied to these different lattices will be decisive for the final layout of the CLIC final focus system at √s = 380 GeV., CERN Proceedings, Vol 1 (2017): CERN-BINP Workshop for Young Scientists in e+e- Colliders

International audience; The Compact Linear Collider (CLIC) project is right in the development phase. In this prospect, the main objective of the final focus stabilization is to succeed in damping ground motion vibration at the sub-nanometer scale to avoid any unwanted motion of the two last final focus magnets. Active vibration control using high-resolution industrial seismic sensors has already shown its limits in the desired range of attenuation [4-100] Hz. Hence, a dedicated inertial sensor has been designed, tuned to fit CLIC requirements. It doesn't contain any feedback or coil which would linearize its dynamic in its bandwidth [0.1-100] Hz, avoiding electrical noise or thermal noise, and when used for active control, enhancing its performances thanks to the internal resonance. An analytical modeling of the sensor dynamic behavior also shown experimentally gives a first internal resonance around 11 Hz. This paper is complemented by a comparative measurement with high precision industrial sensors. A noise level 2.5 times better (0.04 nm at 4 Hz) has been achieved. This sensor has also been tested in the context of vibration rejection with a sub-nanometer active vibration rejection support. Experimental results have been compared with the one obtained with the state-of-the-art industrial sensors. Vertical seismic motion attenuation results have shown unprecedented performances. A damping ratio of 8.5 has been achieved at 4 Hz, leading to an rms displacement of the support of 0.25 nm thanks to the active support prototype and the dedicated sensor.

The Compact LInear Collider (CLIC) [1] luminosity requires extremely low beam emittances. Therefore, high beam position stability is needed to provide cen-tral collisions of the opposing bunches. Since ground motion (GM) amplitudes are likely to be larger than the required tolerances, an Active Vibration Control (AVC) system is required to damp quadrupole motion to the desired value of 0.2 nm RMS at 4 Hz. This paper focuses on the vertical final focus quadrupoles (QD0, QF1) stabilization and demonstrates its feasibility. An AVC system to be installed under QD0 and QF1 has been developed and successfully tested at LAPP. Based on a dedicated homemade sensor with an ex-tremely low internal noise level of 0.05 nm at 4 Hz, it damps GM in the frequency range [3;70] Hz by up to 30 dB, leading to RMS values of approximately 0.25 nm at 4 Hz. Simulations based on GM measured in the Compact Muon Solenoid (CMS) experimental hall [2] show that with such a GM level, the specifications would only be achieved with a Passive Insulation (PI) system, which would filter ground motion starting at ~ 25 Hz, Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The tuning aims to mitigate static imperfections of the Final Focus System (FFS) for emittance preservation at the Interaction Point (IP). A simulation campaign on the nominal CLIC FFS at 3 TeV have shown the need of rethink the design in order to ease the tuning of the machine. The goal is to optimize the lattice in order to make the FFS more tolerant to misalignments by reducing the strength of the sextupoles. The tuning efficiency is promoted as figure of merit to find the optimal layout of the FFS. A comparative study of the tuning performances have been performed for two L* options., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

In the framework of the CLIC rebaselining, the Beam Delivery System (BDS) have been re-optimized for its initial stage at 380 GeV. Two BDS designs with L*=4.3 meters and L*=6 meters have been investigated. The optimization of the lattices and the beam parameters at the interaction point (IP) have been performed by taking into account their energy upgrade to 3 TeV and the tuning feasibility of the BDS in presence of static imperfections., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The SuperKEKB B-Factory at KEK (Japan), after few years of shutdown for the construction and renovation, has finally come to the Phase-1 commissioning of the LER and HER rings, without the final focus system and the Belle II detector. Vacuum scrubbing, optics tuning and beam related background measurements were performed in this phase. Low emittance tuning techniques have also been applied in order to set up the rings for Phase-2 with colliding beams next year. An update of the final focus system construction, as well as the status of the injection system with the new positron damping ring and high current/low emittance electron gun is also presented., Proceedings of the North American Particle Accelerator Conf., NAPAC2016, Chicago, IL, USA

In this brief overview we will reflect on the process of the design of the linear collider (LC) final focus (FF) optics, and will also describe the theoretical and experimental efforts on design and practical realisation of a prototype of the LC FF optics implemented in the ATF2 facility at KEK, Japan, presently being commissioned and operated. In this brief overview we will reflect on the process of the design of the linear collider (LC) final focus (FF) optics, and will also describe the theoretical and experimental efforts on design and practical realisation of a prototype of the LC FF optics implemented in the ATF2 facility at KEK, Japan, presently being commissioned and operated.

One of the options considered for the ECFA-CERNNuPECC design study for a Large Hadron electron Collider (LHeC) based on the LHC is adding a recirculating energy-recovery linac tangential to the LHC. First designs of the electron Final Focus System have shown the need to correct the chromatic aberrations. Two designs using different approaches for the chromaticity correction are compared, namely, the local chromaticity correction and the traditional approach using dedicated sections.