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Accelerator Test Facility (ATF) is R facility to evaluate final focus technology for small beam required by ILC. The final focus beamline(ATF2) sets the goal to achieve 37 nm vertical beam size and 41 nm beam size had been demonstrated. Moreover, a significant intensity dependence on a nanometer beam size was observed and several studies of the wakefield had been conducted [*,**,***]. ATF2 is a proper beamline for wakefield studies with low emittance beam and nanometer resolution cavity BPMs and a nanometer beam size monitor. The simulation results were qualitatively cross-checked with experimental results and showed that the effects of some vacuum components and BPMs were significant. Further analysis of the wakefield will be done for flexible components (e.g. bellows). An upgrade of the ATF2 beamline is proposed by including minimization of the wakefield sources, to establish technologies for stable nanometer beam., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

During the preparatory phase of the International Linear Collider (ILC) project, all technical development and engineering design needed for the start of ILC construction must be completed, in parallel with intergovernmental discussion of governance and sharing of responsibilities and cost. The ILC Preparatory Laboratory (Pre-lab) is conceived to execute the technical and engineering work and to assist the intergovernmental discussion by providing relevant information upon request. It will be based on a worldwide partnership among laboratories with a headquarters hosted in Japan. This proposal, prepared by the ILC International Development Team and endorsed by the International Committee for Future Accelerators, describes an organisational framework and work plan for the Pre-lab. Elaboration, modification and adjustment should be introduced for its implementation, in order to incorporate requirements arising from the physics community, laboratories, and governmental authorities interested in the ILC., 48 pages, 5 figures

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

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) concept based 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, σy∗ of 41 ± 3 nm was measured at ATF2 with the nominal βy∗ optics in 2016. This paper reports the experimental tuning study done with the ultra-low βy∗ during March 2019 beam operation. This optics has a level of chromaticity comparable with CLIC one and it is expected to reduce σy∗ below 40 nm.

A high-precision intra-bunch-train beam orbit feedback correction system has been developed and tested in the ATF2 beamline of the Accelerator Test Facility at the High Energy Accelerator Research Organization in Japan. The system uses the vertical position of the bunch measured at two beam position monitors (BPMs) to calculate a pair of kicks which are applied to the next bunch using two upstream kickers, thereby correcting both the vertical position and trajectory angle. Using trains of two electron bunches separated in time by 187.6~ns, the system was optimised so as to stabilize the beam offset at the feedback BPMs to better than 350~nm, yielding a local trajectory angle correction to within 250~nrad. The quality of the correction was verified using three downstream witness BPMs and the results were found to be in agreement with the predictions of a linear lattice model used to propagate the beam trajectory from the feedback region. This same model predicts a corrected beam jitter of c.~1~nm at the focal point of the accelerator. Measurements with a beam size monitor at this location demonstrate that reducing the trajectory jitter of the beam by a factor of 4 also reduces the increase in the measured beam size as a function of beam charge by a factor of c.~1.6., Comment: 16 pages, 10 figures

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

The high luminosity requirement for a future linear collider sets a demanding limit on the beam quality at the Interation Point (IP). Even the natural motion of the ground could misalign the quadrupole magnets to such an extent that the resulting dipole kicks would require compensation. The novel technique described in this paper uses seismometers to measure the positions of the quadrupole magnets in real time and a kicker to counteract the effect of their misalignment. The prototype system deployed at the Accelerator Test Facility (ATF) at KEK in Japan has already demonstrated a reduction in the pulse-to-pulse vertical position jitter of the beam by about 10%. Based on the observed correlation of the beam position to the quadrupole positions the maximum possible jitter reduction from such a system is estimated to be about 25%. This paper details the latest improvements made to the system with the aim of achieving this limit., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

A single vertical beam halo collimation system has been installed in ATF2 in March 2016 to reduce the background in the IP and Post-IP region. In this paper, we present the results of an experimental program carried out during 2016 in order to demonstrate the efficiency of the vertical collimation system and measure the wakefields induced by such a system. Furthermore, a comparison of the measurements of the collimation system wakefield impact with CST PS numerical simulations and analytical calculations is also presented., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

In order to reduce the background that could limit the precision of the diagnostics located in the ATF2 post-IP beamline, a single vertical beam halo collimation system was installed in March 2016. In this paper we present the measurements done in March and May 2016 in order to characterize the collimation system performance. Furthermore, the collimator wakefield impact has also been measured and compared with theoretical calculations and numerical simulations in order to determine the most efficient operation mode of the collimation system in terms of halo cleaning and negligible wakefield impact., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

A nanometer beam size in the interaction point (IP) is required in case of future linear colliders for achieving the desired rate of particle collisions. KEK Accelerator Test Facility (ATF2), a scaled down implementation of the beam delivery system (BDS), serves for investigating the limits of electron beam focusing at the interaction point. The goal of the ultra-low beta∗ study is to lower the IP vertical beam size by lowering the beta_{y}∗ value while keeping the beta_{x}∗ value unchanged. Good control over the beam optics is therefore required. The first experience with low beta∗ optics revealed a mismatch between the optics designed in the model with respect to the beam parameters observed in the experiment. Additionally, existing methods of beam parameters characterization at the IP were biased with high uncertainties making it difficult to set the desired optics. In this paper we report on the new method introduced in ATF2 for IP beam parameters characterization which gives a good control over the applied optics and makes the ultra-low beta∗ study possible to conduct. It can be also used for verifying the performance of some of the existing beam instrumentation devices., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

A single vertical beam halo collimation system has been installed in the ATF2 beamline to reduce the background that could limit the precision of the diagnostics located in the post-IP beamline. On this paper the commissioning and first performance studies of a single vertical beam halo collimation system are reported. Furthermore realistic efficiency studies have been done using the simulation code BDSIM and compared with the first experimental tests., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

A primary goal of ATF2 (Accelerator Test Facility) is to demonstrate a low vertical beam size at the interaction point (IP) of about 37 nm. Measurements over the past years indicate that the ATF2 vertical beam size strongly rises with bunch intensity. Several different origins of this increase are considered, e.g. wakefields occurring between the ATF damping ring and the IP, and/or intrabeam scattering (IBS) causing the increase of transverse emittances and energy spread in the damping ring with the increase of the bunch intensity. In this paper we address the second possibility. Past measurements and simulations of the IBS effects in the ATF are used to model the intensity-dependent initial emittances and energy spread at the entrance of the final focus. Particle tracking simulations predict the IP vertical beam size growth expected from the known optical aberrations for initial beam parameters corresponding to varying bunch intensities. Comparing simulation results with emittance measurements at different locations allows us to draw some conclusions about the impact of IBS in the damping ring on the IP spot size, and about possible single-bunch wakefields in the ATF2., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

The Accelerator Test Facility 2 (ATF2) has already demonstrated the feasibility of Final Focus Systems based on the local chromaticity correction scheme and its focusing capabilities by reaching a vertical beam size at the virtual Interaction Point (IP) of less than 50 nm. The value of the chromaticity in ATF2 is comparable with the expected chromaticity in ILC, but 4 times lower than in a design of CLIC. ATF2 gives the unique possibility to test operation at CLIC chromaticity values by reducing the vertical beta function at the IP by a factor of 4 (the inverse proportionality of chromaticity with beta function value at IP is assumed). The experience collected in this way would be beneficial for both ILC and CLIC projects. Simulations show that the multipolar errors and Final Doublet fringe fields spoil the IP beam sizes at ATF2. Either increasing a value of the horizontal beta function or installing a pair of octupole magnets mitigate the impact of these aberrations. This paper summarizes the studies towards the realization of the ultra-low β^{*} optics in ATF2 and reports on the progress of the construction of the octupoles., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

The efforts during the second half of 2014 towards nano-metric beam position measurement and stabilization at the Interaction Point (IP) section of the Accelerator Test Facility (ATF) at KEK are presented. Recent improvements to the beam position monitor (BPM) data analysis and processing electronics, as well as the installation of a new set of C-Band BPMs, are reviewed., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

This paper presents the design of a halo collimation system for the ATF2 beamline. The main objective is the reduction of background noise that limits the performance of key diagnostic devices around the final focal point (IP), especially the Shintake Monitor (IPBSM) used for measuring the nanometer level vertical beam sizes and the future Diamond Sensor (DS) for measuring the beam halo. Beam tracking simulations have been performed to optimize the position and characteristics of the halo collimation devices. Furthermore the collimator wakefield-induced effect is being studied., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

For linear colliders, realizing extremely small and stable beam is essentially important. At ILC (International Linear Collider), designed vertical beam size and required position stability at the interaction point is nanometer level. In ATF (Accelerator Test Facility) at KEK, study of the final focus system has been performed using small emittance beams extracted from the damping ring. The project is called ATF2. The ATF2 beam line is designed as a prototype of the final focus system of ILC, with basically the same optics, similar beam energy spread, natural chromaticity and tolerances of magnetic field errors. Its design, construction and operation have been performed as an international collaboration. We have demonstrated the local chromatic correction method, which will be used in ILC, and observed the vertical beam size about 55 nm. Test and demonstration of intra-pulse orbit feedback has been successfully performed in the middle of the ATF2 beam line. For demonstration of nm level stable beam, high resolution beam position monitors were installed around the focal point. Here, we report our achievement, status and future plans., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

The International Linear Collider Technical Design Report (TDR) describes in four volumes the physics case and the design of a 500 GeV centre-of-mass energy linear electron-positron collider based on superconducting radio-frequency technology using Niobium cavities as the accelerating structures. The accelerator can be extended to 1 TeV and also run as a Higgs factory at around 250 GeV and on the Z0 pole. A comprehensive value estimate of the accelerator is give, together with associated uncertainties. It is shown that no significant technical issues remain to be solved. Once a site is selected and the necessary site-dependent engineering is carried out, construction can begin immediately. The TDR also gives baseline documentation for two high-performance detectors that can share the ILC luminosity by being moved into and out of the beam line in a "push-pull" configuration. These detectors, ILD and SiD, are described in detail. They form the basis for a world-class experimental programme that promises to increase significantly our understanding of the fundamental processes that govern the evolution of the Universe.

The primary aim of the ATF2 research accelerator is to test a scaled version of the final focus optics planned for use in next-generation linear lepton colliders. ATF2 consists of a 1.3 GeV linac, damping ring providing low-emittance electron beams (12pm in the vertical plane), extraction line and final focus optics. The design details of the final focus optics and implementation at ATF2 are presented elsewhere* . The ATF2 accelerator is currently being commissioned, with a staged approach to achieving the design IP spot size. It is expected that as we implement more demanding optics and reduce the vertical beta function at the IP, the tuning becomes more difficult and takes longer. We present here a description of the implementation of the overall tuning algorithm and describe operational experiences and performances, Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The KEK ATF2 facility, with a well instrumented beam line and Final Focus (FF), is a proving ground for linear collider (LC) technology to demonstrate the extreme beam demagnification and spot stability needed for a LC FF*. ATF2 uses water cooled magnets but the baseline ILC calls for a superconducting FF**. Thus we plan to replace some ATF2 FF magnets with superconducting ones made via direct wind construction as planned for the ILC. With no cryogenic supply at ATF2, we look to cool magnets and current leads with a few cryocoolers. ATF2 FF coil winding is underway at BNL and production warm magnetic measurements indicate good field quality. Having FF magnets with larger aperture and better field quality than present FF might allow reducing the beta function at the FF for study of focusing regimes relevant to CLIC. Our ATF2 magnet cryostat will have laser view ports for cold mass movement measurement and FF support and stabilization requirements under study. We plan to make stability measurements at BNL and KEK to relate ATF2 FF magnet performance to that of a full length ILC R prototype at BNL. We want to be able to predict LC FF performance with confidence., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

For preserving low emittance beam in the ILC (International Linear Collider) main linacs, Dispersion Matching Steering (DMS) is planed to be used as a main correction method. The linacs are following the earth¿s curvature and the designed vertical dispersion in the linacs should not be zero. For this reason, the orbit difference due to beam energy difference will have to be measured accurately and tolerance of scale error of beam position monitors (BPM) can be tight. Here, the tolerance of the scale error are estimated by tracking simulations. Choice of optics design for relaxing the tolerance is also discussed., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

In order to establish an evaluation method of creep crack growth in the structural components of high temperature engineering plant, it is necessary to clarify the effect of specimen size on creep crack growth behaviour. However, experimental investigation using large specimens concerning specimen size effect on creep crack growth has been little conducted. We conducted creep crack growth tests using CT specimens of various sizes, including ultra-large CT specimens of 254 mm in width and 63.5 mm in thickness which had never been investigated. Creep crack growth rate was characterized in terms of C ∗ parameter. Correlation of creep crack growth rate with C ∗ parameter was independent of specimen width, but dependent on specimen thickness. As the specimen thickness increased, the creep crack growth rate increased. It was considered that the effect of specimen thickness on creep crack growth rate was due to constraints of deformation during creep crack propagation.

Since the ICFA decision on the choice of technology, a world-wide collaboration on the design of the ILC has rapidly progressed. The formation of the GDE will accelerate the work towards a final design. An important technical challenge is obviously the high gradient acceleration but what is similarly challenging is the collision of extremely small beams of a few nanometer size. The latter challenge has three distinct issues: creating small emittance beams, preserving the emittance during acceleration and transport, and focusing the beams to nanometers. Most studies have been done using computer simulations but many issues still remain that require experimental verification. KEK-ATF was built to create small emittance beams, and succeeded in obtaining an emittance that almost satisfies the ILC requirements. In this proposal we present a project, ATF2, which addresses the third issue, namely the focusing of the beam into nanometer spot.ybr> In the longer term, the ATF2 project would also provide invaluable input for the CLIC design of a future multi-TeV collider. The ATF2 project will extend the extraction beamline of the ATF with an ILC-type final focus system to create a tightly focused, stable beam by making use of the small emittance of the ATF.