Editorial announcements and information — ICFA Beam Dynamics Newsletter No. 85

This is a general information article of the ICFA Beam Dynamics Newsletter No. 85. It contains foreword from the Editor-in-Chief and the issue editor, a workshop and conference report section, a recent Ph.D. thesis section, a forthcoming beam dynamics events section, and a section of announcements from the beam dynamics panel.

I would like to thank Maria Enrica Biagini as the issue editor for coordinating and collecting nearly twenty articles that cover the circular  +  − colliders: SuperKEKB, FCC-ee, CEPC, and Tau/charm factories.In particular, the FCC-ee is considered a cost-effective Higgs factory and is gaining momentum to become a project in the coming decade for the High Energy Physics.I believe that this issue will lay a solid foundation to resolve the accelerator challenges to design and build the Higgs Factory.
In the workshop and conference reports section, we will have the summaries for one ICFA Advanced Beam Dynamics Workshop and one ICFA Beam Dynamics Mini-Workshop.I would like to thank Georg Hoffstaetter and Christopher Prior for writing the excellent reports.

Maria Enrica Biagini, INFN Frascati National Laboratories, Italy
The quest for New Physics and the need to better characterize the Higgs boson properties and also achieve precise measurements of the Z, W, as well as the top quark, demand for pushing e + e − colliders towards higher and higher energies.At the same time, precision measurements in Tau/charm and B decays demand for very high luminosity to collect a huge data sample in a reasonable time.This two different topics need two very different approach to accelerator design.The two high energy colliders planned for the future (FCC-ee at CERN and CEPC in China) both require a large circumference, a booster to be able to inject and operate for a large range of energies, different RF layouts.Still we can say that the level of technology needed is quite standard, while the engineering aspects can be challenging.Moreover the required luminosity at each energy is of the order of that already achieved in previous colliders.
On the other hand, the two smaller Tau/charm projects (SCTF at BINP and STCF at USTC) seem simpler in design, but require a luminosity of about 10 35 cm −2 s −1 in a range of low-to-medium (2-7 GeV) energies, which is above the present worldwide peak luminosity record of 4.7 × 10 34 cm −2 s −1 achieved by SuperKEKB in Japan at the B energy (10.5 GeV).These accelerators require a most careful design and modelling effort.The detector physicists wish to have for some measurements longitudinally polarized beams (electrons or both beams) adds a further challenge to the design.
It is clear that these two categories of storage rings face, besides common issues, some very different challenges.The low energy rings have to cope with the short Touschek lifetime and small dynamic aperture, while the high energy ones have issues related to their large size, such as tunnel engineering and machine alignments.Luckily, the operational experience of SuperKEKB, the present only high luminosity e + e − collider, can guide future accelerators designs and help to identify crucial aspects which can impact their actual performances.
To summarize progresses and challenges of future e + e − colliders, this issue is devoted to some of the studies performed for the four standing proposals for both high-energy and high-precision categories.In order to understand what is the present state-of-the-art, we will start with reviewing some of the SuperKEKB unresolved issues which at present prevent a further increase in luminosity.

SuperKEKB
Since April 2020, SuperKEKB has been operating with the Crab Waist (CW) scheme with a large Piwinski angle.This scheme was not implemented in the original design, but later on adapted to the present lattices in both the Low Energy Ring (LER) and High Energy Ring (HER), therefore it is not perfectly matched to the optics.Moreover in the CW operation scheme there is a clear reduction of dynamical aperture and lifetime, for off-energy particles.Luminosity performances are limited by the vertical beam blow-up caused by the beam-beam interaction.The beam-beam issues from the viewpoint of luminosity tuning are presented in the first paper on SuperKEKB, by D. Zhou et al. [1].
One of the major issues in SuperKEKB is the inadequate stability and reproducibility of the beam orbit and optics.A paper by H. Sugimoto et al. [2] discusses optics distortion caused by orbit deviation near the strong sextupole magnets: even a horizontal orbit deviation of a few tens of micro-meters induces a sizable distortion of the optical functions at the Interaction Point (IP).The orbit fluctuation at the sextupoles causes beta-beating and makes stable operation at high beam currents more difficult.Orbit tuning with a feedback at the sextupoles improves both the injection efficiency and the detector background level.
Collective instabilities are another issue in SuperKEKB.A review of the impedance model of has been carried out by T. Ishibashi et al. [3] for both rings.In particular, the longitudinal wake potential including Coherent Synchrotron Radiation (CSR) and Coherent Wiggler Radiation (CWR), in addition to the transverse one, was implemented to estimate the threshold of the Transverse Mode Coupling Instability (TMCI), and the vertical tune shift.In the LER, vertical beam-size blow-ups are observed at a bunch current of about 1.0 mA/bunch in single-beam operation.Machine studies have revealed that also the vertical bunch-by-bunch feedback systems play an important role in this instability.Further investigation are needed on the influence of the feedback on the collective instabilities in the transverse direction.
A possible limitation of SuperKEKB maximum beam currents and luminosity could come by the beam injection in the near future.This problem is addressed in the paper by Y. Funakoshi et al. [4].An estimation of beam injection requirements to achieve the next target luminosity with  *  = 1 mm and 0.8 mm was carried out.Simulations show that to meet the requirement with  *  = 1 mm the emittance growth of the injecting positron beam in the beam transport line needs to be reduced down to its design value.For  *  = 0.8 mm the LER dynamic aperture also needs improvements.Several measures to suppress the emittance growth are under considerations.

The FCCee and CEPC
The Future Circular Collider (FCC) Feasibility Study was launched by CERN Council in 2021.It will prepare the ground for an implementation of the first stage of the FCC integrated project, including tunnel construction, technical infrastructure, and the electron-positron collider (FCC-ee), plus the development of financing and organization models.It will also ensure compatibility with a subsequent hadron collider (FCC-hh) and define R&D directions and time schedule for the high-field magnets required for the latter.For the FCC-ee review in this issue, several papers are devoted to the studies of collimation system, impedance modelling, civil construction challenges for the 90 km long tunnel, survey and alignment, circumference choice, booster configuration and optics.A description and summary of the papers presented in this issue is given by F. Zimmermann in the section 3 below.
-3 -The Circular Electron-Positron Collider (CEPC) was proposed in China, shortly after the observation of Higgs (2012).After some years of pre-studies, the CEPC study group completed the Conceptual Design Report (CDR) in 2018.Since then a series of key technology R&D was carried out, and the accelerator design has been kept optimizing as well.The Technical Design Report (TDR) will be published in May 2023.The accelerator design can meet the scientific objectives by allowing the operation in different energies for W/Z, Higgs and ttbar with high luminosity.Key technologies required for the mass production have been or are being developed, such as the superconducting accelerating cavities, high efficiency RF power sources, magnets and vacuum systems etc.The selected key technology R&D accomplishments and the updated accelerator key parameters are presented in the paper by Y. Li [5] The beam coupling impedance and the collective effects that are triggered by the impedance are important subjects for CEPC.A robust impedance model is required for the instability evaluations as well as to investigate their possible mitigation.Meanwhile, a thorough investigation on the collective effects is essential to identify the critical issues on the beam instabilities.In the paper by N. Wang et al. [6], a detailed description of the impedance model built for the collider ring and of the identification of dominant impedance contributors by evaluating the effective impedance, is reported.The potential collective instabilities driven by the impedance are also discussed.
For a large size accelerator such as CEPC, the survey and alignment are challenging.Several key issues need to be considered: the measurement and data processing method, the error accumulation control, the global and relative accuracy, the measurement efficiency, the component alignment method and the deformation problem.An overall survey and alignment scheme was made, as described in the paper by X. Wang et al. [7].A multi-level control network will be built for the global and relative position control, and measurement method are introduced and the accuracy was estimated.The schemes of fiducialization, pre-alignment and tunnel alignment are introduced, the deformation problem was analyzed and monitor equipment will be applied.To improve the measurement efficiency a new kind of instrument was designed, the prototype has been fabricated and some experiments have been carried out.

The Super Tau/charm
To build a large, complex, and expensive project with extreme parameters like a Super Tau/charm factory, where the implementation of the Crab Waist collision scheme seems the only way to reach high luminosity, is a risky business, since this approach has strong demands on beam dynamics and technical collider design, which are very difficult to satisfy.The creation of a test facility at the old collider VEPP-4M for comprehensive study of the CW collision scheme is being considered at BINP, as well as building a small collider (an order of magnitude cheaper than the foreseen Super Tau/charm factory) for prototyping technologies and studying physical and technical peculiarities of this collision scheme.A double ring collider to conduct experiments between VEPP-2000 and VEPP-4M, with beam energy from 0.5 GeV to 1.6 GeV, could cover poorly studied area from the -meson to the -meson with higher luminosity.These plans are described in the paper by E. Levichev et al. [8].
An e + e − Super Tau/charm Factory (SCTF) is planned to be built in the National Center for Physics and Mathematics at Sarov, Russia.The double ring collider with CW collision scheme will operate in a wide beam energy range from 1.5 GeV to 3.5 GeV with a peak luminosity of 10 35 cm −2 s −1 .A polarized electrons source and three siberian snakes will provide an about 80% longitudinally polarized electron beam at 2 GeV.Superconducting wigglers will be used to decrease -4 -the damping times and the effects of intra-beam scattering, and to increase the Touschek beam lifetime, in particular at low energy.The paper by A. Bogomyagkov et al. presents the status of collider design and the studies for the optimization of the luminosity and beam lifetime.
Finally, a Super Tau/Charm Facility (STCF) has also been proposed at USTC, Hefei, China.The STCF aims at a luminosity greater than 0.5 × 10 35 cm −2 s −1 with a center-of-mass energy range of 2 to 7 GeV.Two topics of this project will be discussed in detail.
To meet the high quality and stability of the beam, a digital low-level RF (LLRF) system, working in the S-band (2856 MHz) as required by the STCF Linac, has been designed and is reported in the paper by C. Xie et al. [10].The system architecture and hardware design as well as the control algorithms and software design are discussed and tested.The results summarized in the paper prove that the LLRF system meets the requirement of the STCF.
An efficient injector complex is an essential component of the STCF accelerator, in particular the positron generating system is challenging.The proposed STCF Linac, accelerates both electrons and positrons from 1.0 GeV up to 3.5 GeV with a high intensity of 1.5 nC per bunch.An injector with a highenergy electron-target positron production system was designed.The design baseline of the STCF injector with Linac, positron source, and damping ring are described in the paper by A. Zhang et al. [11].
The editors wish to thank all the authors, from KEK, CERN, IHEP, BINP and USTC, for their effort to describe and explain many of the challenges encountered when designing a high luminosity e + e − collider.We hope readers will enjoy and appreciate this issue.

Communication on the FCC status
Frank Zimmermann, CERN, Switzerland

FCC feasibility study
We are now two years into the FCC Feasibility Study, which was launched by CERN Council in 2021.This Feasibility Study will prepare the ground for an implementation of the first stage of the FCC integrated project, including tunnel construction, technical infra-structure, and the electron-positron collider (FCC-ee), plus the development of financing and organization models.It will also ensure compatibility with a subsequent hadron collider (FCC-hh) and define R&D directions and time schedule for the high-field magnets required for the latter.In greater detail, the FCC Feasibility Study pursues the following high-level objectives [12]: to demonstrate the geological, technical, environmental and administrative feasibility of the tunnel and surface areas and optimization of placement and layout of the ring and related infrastructure; (2) to pursue, together with the Host States, the preparatory administrative processes required for a potential project approval to identify and remove any showstopper; (3) to optimize the design of the colliders and their injector chains, support-ed by R&D to develop the needed key technologies; (4) to elaborate a sustainable operational model for the colliders and experiments in terms of human and financial resource needs, as well as environmental aspects and energy efficiency; (5) to develop a consolidated cost estimate, as well as the funding and organizational models needed to enable the project's technical design completion, implementation and operation; (6) to identify substantial resources from outside CERN's budget for the implementation of the first stage of a possible future project (tunnel and FCC-ee); and (7) to consolidate the physics case and detector concepts for both colliders.The results, together -5 -with an updated cost estimate, will be summarized in a Feasibility Study Report to be released at the end of 2025, which will serve as an input to the next update of the European Strategy for Particle Physics.

Recent changes and time line
As one of the first deliverables for the upcoming Feasibility-Study "mid-term review" scheduled for autumn 2023, the placement of the FCC tunnel and surface sites has been optimized for lowest risk [13].The resulting optimized layout features only 8 (instead of previously 12) surface sites, with a 4-fold super-periodicity (which would allow for up to four collision points), and it has a reduced circumference of 90.6 km, compared with 97.76 km for the earlier FCC conceptual design, published in 2019.The next update of the European Strategy for Particle Physics is expected to occur around the year 2027.Assuming this update lends support to the first stage of the FCC integrated project, approval could be obtained in 2028.Tunnel groundbreaking and civil engineering may then begin in 2032, accelerator installation in 2040, and FCC-ee accelerator commissioning in 2045.

FCC articles in this newsletter
The present issue of the ICFA Newsletter includes six articles that elucidate important recent developments and achievements from various areas of the FCC Feasibility Study.First, L. Bromiley and R. Cunningham [14] are setting the scene by reporting on the ongoing civil engineering studies.The next article [15], by F. Carra et al., explores how the accelerators in the arc tunnels will look like.In particular, it describes the design effort towards an arc half-cell mock-up, and the development of supporting structures for both the booster and the collider rings.The following article [16], by L.H. Zhang, H. Damerau, I. Karpov and A.L. Vanel, describes the limited possible choices for the FCC ring circumference.It is assumed that either a modified LHC or a new superconducting SPS in the existing SPS tunnel is used as the injector for the FCC-hh hadron collider.The requirements for the RF synchronization between injector and collider then yield only a few favourable values of the circumference. A. Chance, B. Dalena and co-authors present a status update for the de-sign of the high energy booster [17], whose layout had to be matched to the new tunnel placement, as for the collider.The booster design studies currently underway focus on longitudinal stability and robustness with respect to errors.An alternate arc optics is also being considered.The last two articles related to FCC-ee, by A. Abramov and R. Bruce [18], and by M. Behtouei, E. Carideo, M. Zobov and M. Migliorati [19], respectively, cover the evolving design of the FCC-ee collimation system and a first assessment of the collimators' impedance.Finally, a summary of the geodetic, survey and alignment challenges is given in the paper by H. Mainaud Durand [20], reviewing the evolution of the required new techniques needed to ensure that the 91Km-long accelerator components are best aligned for providing the expected performances.

Workshop and conference reports 4.1 The 9 th ICFA Beam Dynamics Workshop on Energy-Recovery Linacs (Cornell University, October 3-6, 2022)
Georg Hoffstaetter, Cornell University and BNL (Georg.Hoffstaetter@Cornell.edu) From October 3-6 th , 110 participants from around the world met at Cornell University, Ithaca, New York for the ICFA Beam Dynamics Workshop #66, the 9 th international ERL workshop.This bi-annual workshop series had skipped one year because of the COVID pandemic and was now held entirely in-person.The location was particularly suitable, as the Cornell-BNL ERL Test Accelerator (CBETA) is located on the Cornell campus and, just before the pandemic, became the first multi-turn SRF ERL when 4-turn operation was established.The meeting was co-organized by Cornell University, Brookhaven National Laboratory, and Thomas Jefferson National Accelerator Laboratory, which all have a strong history in ERL research.Details of the workshop can be found at https://www.classe.cornell.edu/NewsAndEvents/ERL2022/.The fruitful discussions in a creative atmosphere was a reminder of 2009, when the 3 rd ERL workshop had also gathered at Cornell.This made ERL'22 an excellent time to connect with old colleagues and friends and to contemplate the progress our field has made in the interim years.
The need for energy efficiency has become ever more apparent.ERL applications in hadron cooling have become much more urgent with plans for the EIC cooler, and several large collider ideas contain ERLs; also industrial applications like ERL-based EUV lithography have drawn increased attention.A growing focus on ERLs therefore lead to very active working groups for Sources, SRF, Beam dynamics, applications, and ERL facilities.During the four days, plenary talks from each of the working groups were discussed in public and were concluded by a plenary summary by each working-group's conveners.The full program can be viewed at https://indico.classe.cornell.edu/event/2018/contributions/.
Many discussions happened also outside the meeting room, during tours of CBETA and of Cornell's SRF and bright-beams lab, and during a reception, a grill party, and a hike along scenic waterfalls.
The workshop started with an overview of ERL-facility programs: CBETA (Cornell), CEBAF-5pass (Jlab), cERL (KEK), bERLinPro(HZB), MESA (Mainz), PERLE (Orsay), S-DALINAC (TUD), the EIC ERL cooler (BNL), and an e-Linac upgrade at TRIUMF.Presentations on applications touched areas as divergent as High Energy Physics in the FCC-era, hadron-beam cooling, compact x-ray sources, medical isotopes, and computer-chip production.All focused on green acceleration and energy efficiency.Because most ERLs harvest their advantage only at large beam currents, high brightness electron sources were one of the working groups.While photo-emission DC sources have become stable at several 10 mA, also RF and SRF sources were covered.Because the beam energy is recovered in superconducting cavities, a working group on SRF was a critical, as in any previous ERL workshop.The beam-dynamics working group covered much basic research in areas from Coherent Synchrotron Radiation to space charge dynamics, scattering, halo creation, and radiation background.
It was announced that the next ERL workshop, in 2024, will be at KEK in Japan, at a beautiful location that will remind our community of a similar workshop in 2011.The workshop was considered extremely stimulating and successful.

The 2022 Workshop on Fixed Field Alternating Gradient Accelerators (September 25-30, 2022)
C.R. Prior, RAL, U.K. (chris.prior@stfc.ac.uk) The latest in the series of annual workshops devoted to the study of Fixed Field, alternating gradient Accelerators (FFAs) took place from 25 th to 30 th September 2022.The meeting was organised by members of the ISIS Neutron and Muon Source at the UK's Rutherford Appleton Laboratory and held at The Cosener's House in Abingdon, near Oxford.Support was provided by the ICFA Beam Dynamics Panel, which granted the event ICFA mini-workshop status.
After two years of virtual meetings, it was encouraging that 33 scientists were able to attend in-person.A further 28, who could not be present mostly because of Covid-related travel restrictions in their own countries, took part via video link, coping staunchly with time zone inconvenience.For those in Abingdon, it was a pleasure to be able to interact with colleagues again in the informal and scientifically productive way that characterised FFA meetings in the past.
The workshop was preceded by a two-day FFA school in line with the group's commitment to education and the training of people new to the field.Up to 25 participants heard lectures on transverse and longitudinal beam dynamics, the varied range of applications of FFA accelerators, RF and magnet hardware.The school concluded with practical sessions using the two codes Zgoubi and OPAL to model aspects of FFA design.The lectures were recorded and are available at https://indico.stfc.ac.uk/event/487/timetable/#20220925.detailed.
The programme of talks for the workshop proper was presented under the headings: Applications, Novel Designs, Hardware, Theory, and Present and Future Projects.Five invited talks were interspersed throughout the week on selected topics not generally associated with FFAs but intended to widen the scope of the community and identify new areas in which FFA studies might contribute.From an overview of the muon collider, opportunities for the use of FFAs for the main stages of muon acceleration were revealed.A talk on FLASH radiotherapy, with the emphasis on requirements from the medical side, clarified the demands from the accelerator and underlined why fixed-field machines can be particularly useful in cancer therapy.Superconducting magnet technology, a topic often mentioned at FFA workshops but without a great deal of understanding, was addressed in an invited talk by an expert from RAL.
In between, participants heard talks related to therapy and research, including the design of gantries with large momentum acceptance, and ideas for FFAs with fixed tunes, possibly fast cycling, exhibiting isochronicity and/or with non-linear, non-scaling beam optics.There were also talks on magnet technology and RF, including the control of emittance growth and theory of adiabatic trapping.
As befits the host laboratory, a full day was devoted to the program of FFA work at RAL to design a future spallation neutron and muon source, referred to as ISIS-II.An invited overview of the aims and scope of the project by the Head of the ISIS Accelerator Division was followed by detailed talks on options for the FFA ring design, injection studies, magnet design, diagnostics and modelling.Work is focused on a small (25 m circumference) prototype FFA to be built in the next few years as a machine to test features of the main accumulator/accelerating ring.FFAs with vertical orbit excursion have been extensively studied, though presently a more conventional design with horizontal excursion is preferred.The group was then taken on a tour of the injector that will drive the prototype ring at RAL and also saw some other, related, low energy hardware developments.
-8 -Our colleagues in Japan have been strong erstwhile supporters of FFA workshops in the past and while few were able to attend FFA2022 in person, there were several presentations given online describing the status and recent developments at Kyushu University and KURNS (Kyoto University Institute for Integrated Radiation and Nuclear Science).At the present time, these represent the only operating FFAs and many of the group have in the past been grateful for opportunities to engage in experimental studies of beam dynamics there.
Deliberately left to last in this report is the exciting idea to involve fixed-field permanent magnets in the upgrade plans for the CEBAF Nuclear Physics facility at J-Lab, Virginia.Participants at FFA2022 heard a comprehensive talk covering the history of CEBAF, the development of its accelerators and its path to a peak energy of 12 GeV, completed in 2017.The present plans are embodied in a feasibility study for an additional FFA racetrack accelerator in the existing CEBAF tunnel enabling the machine to reach a top energy of about 22 GeV.
The FFA International Advisory Committee subsequently accepted a proposal from CEBAF to host the next FFA workshop at J-Lab.FFA2023 will therefore be held in Newport News, Virginia, September 10-15, 2023.
Details of FFA2022, including the presentations and lectures, are available on the workshop website https://indico.stfc.ac.uk/event/487/, and further enquiries can be addressed to the organisers at FFA2022@stfc.ac.uk.Preliminary details of FFA2023 can be found at https://www.bnl.gov/ffaworkshop/.The work presented in this thesis is driven by the motivation of improving the understanding the beam optics of existing circular colliders at the energy and luminosity frontier and aims to define parameters required for improving the measurement quality, the energy reach and the understanding of performance limitations of the next generation synchrotron storage rings.This question is addressed, on one hand, by performing Turn-by-Turn (TbT) optics measurements at the Large Hadron Collider (LHC) and at SuperKEKB, where the latter also allows understanding optics challenges of the FCC-ee.On the other hand, lattice and optics design concepts applicable for Future Circular Collider options (FCC) aiming to be built in an existing tunnel infrastructure are developed using the High Energy LHC (HE-LHC) as an example.Complementary simulations presented here show the impact of increased particle burn-off on the collider performance.To improve the understanding of the LHC optics TbT measurements of run 2 are used to measure the second-order dispersion and the momentum compaction factor for the first time, where the latter allows for novel insights on the average arc BPM calibration.To confirm these findings a novel LHC injection optics with an arc cell phase advance of 60 • is proposed.Although the LHC is continuously being improved this collider and its successor, the High Luminosity LHC (HL-LHC), are limited in energy reach.

Recent Doctoral Theses
-9 -Thus, lattice and optics options for possible energy upgrades are studied, which would replace one third or two thirds of installed arc dipoles, and could increase the beam energy up to 9.5 TeV and 11.5 TeV, respectively.In addition to such partial energy upgrades, lattice and optics options for a new collider in the LHC tunnel infrastructure are presented here, achieving a beam energy of up to 13.5 TeV, which is also known as the HE-LHC.Presented strategies for lattice optimization and beam stay clear improvement are also applicable for other possible future projects, such as the integrated FCC program.As novel higher energy hadron colliders also aim at pushing the luminosity record for hadrons further, a large fraction of the initial bunch is burned, leading to an emittance growth over the physics fills.The luminosity loss due to luminosity production is therefore analyzed here for the three future hadron colliders HL-LHC, HE-LHC and the hadron FCC.A new collider demands optics commissioning to achieve its design goals.Although SuperKEKB holds the record for luminosity production, its design goals include a 20 times higher instantaneous luminosity.This demands improving the beam life time, smaller -functions at the interaction point and an exceptionally good knowledge and control of the beam optics.TbT optics measurements, recorded at four different machine settings, are performed during this commissioning phase and suggest unexpected sextupoles, octupoles and decapoles as larger than expected chromaticity up to third order and amplitude detuning is found.Measurement data obtained at various bunch currents reveal intensity dependent effects, estimate the head-tail damping time and show a larger than expected tune shift with intensity than the used impedance model, suggesting unexpected wake-field sources.Here presented studies also aim at showing techniques for improving the quality of TbT measurements at SuperKEKB using single kicks and a continuous excitation and benchmark results with closed orbit distortion measurements.Gained experience from SuperKEKB will also influence the design of future projects, such as the FCC-ee.The Compact Linear Collider (CLIC) could provide e e + e − collisions in two detectors simultaneously at a bunch train frequency in the linac twice the baseline design value.In this thesis, a novel dual Beam Delivery System (BDS) design is presented in order to serve two Interaction Regions (IR1 and IR2) including optics designs and the evaluation of luminosity performance with synchrotron radiation (SR) and solenoid effects for both energy stages of CLIC, 380 GeV and 3 TeV.IR2 features a larger crossing angle than the current baseline.The luminosity performance of the novel CLIC scheme was evaluated by comparing the different BDS designs with and without the detector solenoid field effects.It has to be highlighted that the impact of the detector solenoid on luminosity had not been evaluated for the current CLIC baseline, which amounts to a loss of about 4% that corresponds to the same value of the old baseline design.At 380 GeV the 2 IRs of the novel dual BDS design feature same luminosities than the current baseline.However, at 3 TeV the luminosity performance -10 -is reduced by 2% from the baseline design for the IR1 and by 33% for the IR2.The dual CLIC BDS design provides adequate luminosities to two detectors and proves to be a viable candidate for future linear collider projects.One of the main requests for future linear colliders is to achieve a nanometer vertical beam size at the Interaction Point (IP).Accelerator Test Facility 2 (ATF2) represents a scale down implementation of the Final Focus System (FFS) to test the novel local chromaticity correction scheme that is implemented in the International Linear Collider (ILC) and the Compact Linear Collider (CLIC) designs.After several years of operations and commissioning,  *  = 41 ± 3 nm was measured at ATF2 with the nominal  *  optics in 2016.This thesis reports the experimental tuning study done with the ultra-low  *  during March 2019 beam operation.This optics has a level of chromaticity comparable with CLIC one and it is expected to  *  below 40 nm.The e + e − collider is considered as one of the most suitable accelerator to precisely measure the Standard Model parameters at Higgs energies.Currently, there are two kinds of e + e − colliders proposed: the circular and the linear colliders.The e + e − circular colliders projects under study are: the Future Circular Collider (FCCee) and the Circular electron-positron Collider (CEPC).Alternatively, the two e + e − linear colliders projects are: the International Linear Collider (ILC) and the Compact Linear Collider (CLIC).This PhD is focused in the e + e − linear colliders.Both e + e − linear colliders projects are conceptually similar and composed of similar sub-systems.Starting from the particles source to the Interaction Point (IP) the main sub-systems are: the positron and the electron sources, the Damping Ring (DR), the Ring to Main Linac transport (RTML), the Main Linac (ML), and the Beam Delivery System (BDS).In particular the BDS is composed of: a diagnostic section, an energy and a betatron collimation sections, and a Final Focus System (FFS) where the beam is strongly focused down to several nanometers by means of a Final Doublet (FD) of quadrupoles.The design of the FFS of both ILC and CLIC is based on the local chromaticity correction scheme.It uses an interleaved pairs of sextupole magnets to simultaneously correct the horizontal and vertical chromaticities.The Accelerator Test Facility 2 (ATF2) at KEK (Japan) is an energy-scaled down implementation of a linear collider BDS like the ILC or CLIC ones, including a FFS system.During the last years the unique and outstanding ATF2 achievements have already verified the minimum technical feasibility of the FFS of linear colliders such as ILC or CLIC.This thesis focuses on the optimization of the CLIC FFS system for the first energy stage with a center-of-mass energy of 380 GeV.In the first part the study of shortening the FD to reduce chromaticity and an alternative optics design with a novel dispersion profile in the FFS is presented.In the second part the analytical and experimental tunability studies of a CLIC-like FFS optics for ATF2, called "ultra-low  * optics" is reported.These studies include: new alignment technique for the octupoles, new set of ultra-low  * tuning knobs to better control the aberrations and new alternative tuning strategy including the static errors performed during the ATF2 experimental campaigns in June 2019, December 2019, and March 2020.

Optimization of CLIC Final
and experimental activities towards more powerful and efficient RF power sources, reports on the existing test benches and plans for new ones, and much more.It is a unique opportunity to sketch a comprehensive landscape of a truly global activity, with many pulsing research sites spread all over the continents.Registration to the workshop and abstract submission are open via the HG2023 Indico page (https://agenda.infn.it/event/34253/).

5 Recent Doctoral Theses 5 . 1 6 Forthcoming Beam Dynamics Events 6 . 1 1 - 1
Beam optics design, measurement and correction strategies for circular colliders at the energy and luminosity frontier 5.2 Optics Design of a novel Beam Delivery System (BDS) for CLIC: the case of two Interaction Regions (IR).First experiments for the validation of the ultra-low  *  nanometer beam size at ATF2 5.3 Optimization of CLIC Final Focus System (FFS) at 380 GeV and implementation studies for ultra-low  *  at ATF2 Optics tuning and corrections for future colliders workshop (CERN, 26-28 June 2023) 6.2 68 th ICFA Advanced Beam Dynamics Workshop on High-intensity and Highbrightness Hadron Beams (CERN, 9-13 October 2023) 6.3 International Workshop on Beam Cooling and Related Topics, COOL'23 (Montreux, 8-13 October 2023) 6.4 15 th Workshop on Breakdown Science and High Gradient Technology (HG2023) -From the Panel Chair (Editor-in-Chief) Yunhai Cai, SLAC National Accelerator Laboratory, U.S.A.