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The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) is the world’s largest and most powerful particle accelerator colliding beams of protons and lead ions at energies up to 7 TeV and 2.76 TeV, respectively. ALICE is one of the detector experiments optimised for heavy-ion collisions. A fixed-target experiment in ALICE is considered to collide a portion of the beam halo, split using a bent crystal, with an internal target placed a few meters upstream of the detector. Fixed-target collisions offer many physics opportunities related to hadronic matter and the quark-gluon plasma to extend the research potential of the CERN accelerator complex. Production of physics events depends on the particle flux on target. The machine layout for the fixed-target experiment is being developed to provide a flux of particles on a target high enough to exploit the full capabilities of the ALICE detector acquisition system. In this paper, we discuss a method of increasing the system’s performance by applying a local modification of optics to set the crystal at the optimal betatron phase., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) is the world largest and most powerful particle accelerator colliding beams of protons and lead ions at energies up to 7 TeV and 2.76 TeV, respectively. ALICE is one of the detector experiments optimised for heavy-ion collisions. A fixed-target experiment in ALICE is considered to collide a portion of the beam halo split by means of a bent crystal with an internal target placed a few meters upstream of the detector. Fixed-target collisions offer many physics opportunities related to hadronic matter and the quark-gluon plasma to extend the research potential of the CERN accelerator complex. This paper summarises our progress in preparing the fixed-target layout consisting of crystal assemblies, a target and downstream absorbers. We discuss the conceptual integration of these elements within the LHC ring, impact on ring losses, conditions for a parasitic operation and expected performance in terms of particle flux on target., Proceedings of the 64\textsuperscript{th} ICFA ABDW on High-Intensity and High-Brightness Hadron Beams, HB2021, Batavia, IL, USA

Annual high intensity requests of over 10¹⁹ protons on target (POT) from the CERN Super Proton Synchrotron (SPS) Fixed Target (FT) physics program continue, with the prospect of requests for even higher, unprecedented levels in the coming decade. A concerted and multifaceted R effort has been launched to understand and reduce the slow extraction induced radioactivation of the SPS and to anticipate future experimental proposals, such as SHiP* at the SPS Beam Dump Facility (BDF)**, which will request an additional 4·10¹⁹ POT per year. In this contribution, we report on operational improvements and recent advances that have been made to significantly reduce the slow extraction losses, by up to a factor of 3, with the deployment of new extraction concepts, including passive and active (thin, bent crystal) diffusers and extraction on the third-integer resonance with octupoles. In light of the successful tests of the prototype extraction loss reduction schemes, an outlook and implications for future SPS FT operation will be presented., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

In this MD, a beam scraping was performed using the momentum primary collimator in IR3 where dispersion is high. A second scraping was performed using a TCSG in IR7 where dispersion is almost negligible. In such a way, we aim to disentangle the contribution of off-momentum particles to halo population. These scrapings will provide useful information to better understand the usual off-momentum losses we see at the start of the ramp. The MD results would also be used to benchmark simulations of off-momentum beam losses in order to gain confidence in simulation models.

The Super Proton Synchrotron (SPS) is the last accelerator in the LHC Injectors Chain. Its performance is constantly being improved in frame of the LHC Injectors Upgrade (LIU) Project in order to prepare it for the future HL-LHC (High Luminosity LHC) operation. One of the LIU goals is to nearly double the intensity extracted from the SPS, up to 2.32×10¹¹ p/bunch. In recent years, nearly 10% of losses are observed for nominal intensity and LHC-type beams; they grow to about 20% for the intensity approaching the HL-LHC target. Beam losses imply activation and aging of the SPS hardware; the possibility to add a collimation system is being considered to mitigate this problem. In this paper we present studies of a collimation system design for the SPS. The concept is based on a primary horizontal collimator located in an available position with high enough dispersion, and a secondary collimator to intercept the particles leaking out from the primary collimator. Performance of the proposed collimation system is evaluated by means of numerical simulations., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

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 lepton linear collider is considered by the accelerator and particle physics communities as an appropriate machine to perform high precision particle physics research in the TeV energy regime. There are two proposals for the future e+e- linear collider: the Compact Linear Collider (CLIC) and the International Linear Collider (ILC), both developed by two wide international collaborations with strong overlap between them. Both designs satisfy the particle physics requirements. At the TeV energy regime the cross sections of many processes of interest are small, therefore large luminosities on the order of 10^{34} cm^{-2}s^{-1} at the interaction point (IP) are required to deliver the required event rates. The luminosity inversely depends on the transverse size of the colliding beams which restricts the beam sizes at the IP to the nanometer level. The strong focusing of the beams occurs in the final focus system (FFS), the most inner part of a linear collider, where the beams are focused at the IP by means of two strong quadrupole magnets called the final doublet (FD). The efficiency of the beam focusing is deteriorated by the chromatic effects of the FD quadrupoles meaning that off-momentum particles are not exactly focused at the focal point, leading to larger spot sizes at the IP. A novel design of the final focus system with a local compensation of the chromatic effects has been proposed in 2001 by P. Raimondi and A. Seryi. This design is being tested in the KEK Accelerator Test Facility 2 (ATF2) in Japan, a scaled down implementation of the linear collider beam delivery system. It has already been demonstrated that the IP vertical beam size in ATF2 decreases from some hundreds of nanometers to about 40 nm when the chromaticity is corrected. Therefore, the local chromaticity correction scheme is considered as a baseline for the ILC and a strong candidate for CLIC. However, for CLIC the expected level of chromaticity is higher by about a factor 5. The parameter describing the focusing strength is the IP value of the optical \beta function (\beta^{*}). In linear approximation, the IP beam size is proportional to the square root of the \beta^{*} value and chromaticity is inversely proportional to the \beta^{*} value. Therefore, decreasing the \beta^{*} value in ATF2 allows to reduce the IP beam size and to increase the level of chromaticity. The main objective of the study described in this thesis is to decrease the \beta^{*} value in the ATF2 in order to investigate the performance of more chromatic optics (close to the level of CLIC) and to study the limits of beam focusing at the IP. Understanding the tradeoffs between lowering \beta^{*} and increasing aberrations is of critical importance for future linear colliders. In Chapter 1, after a reminder of the Standard Model of elementary particles, the main differences of linear colliders with respect to circular colliders are discussed. The physics potential of linear colliders is also summarized. Linear colliders are discussed in more detail in Chapter 2. The most important tools of the linear and nonlinear beam dynamics are described first. Afterwards, the linear collider layout is presented with a special emphasis given to the final focus system. Finally, the two existing designs for a future linear collider are described, together with the test facilities. The Accelerator Test Facility serving for performing the experimental studies of this thesis is described in detail in Chapter 3. The feasibility studies of the low \beta^{*}_{y} optics in the ATF2 are presented in Chapter 4. The results of the nonlinear beamline optimisation for minimising the IP beam size are presented in the first section of this chapter. The impact of the quadrupole fringe fields on CLIC, the ILC and three lattices of the ATF2 are described in the second section. In the third section the contribution of optical aberrations to spot size increase with bunch intensity is investigated. Finally, the developed computer tools for performing the tuning simulations are described in the last section of this chapter. The experimental studies of the new ATF2 optics with the \beta^{*}_{y} value decreased by a factor 2 are described in Chapter 5. Completing this research required 11 visits in the High Energy Accelerator Research Organization (KEK) in Japan and spending 23 weeks working with the ATF2 accelerator. The optics control and implementation was achieved by introducing a new method of beam diagnostics at the IP based on precise beam size measurements and fine, well-controlled changes of the vertical beam waist position. The beam sizes measured after two complete tuning sessions were almost a factor three larger than the design values. Comparison with the nominal \beta^{*}_{y} optics suggests that the beam size growth due to machine imperfections for lower \beta^{*}_{y} values is much stronger than expected in the design. The experimental results are also compared with the tuning simulations. The realistic errors applied to the machine model are not sufficient to reproduce the experimental results. Simulation results get closer to the experiment for larger machine errors. Simulations also show that an accurate orbit correction can help in lowering the IP beam size. The main reasons for observing larger beam sizes than expected are identified: insufficient orbit control and sensitivity to machine drifts, contribution of wakefields combined with the beam orbit jitter, larger multipolar fields, larger magnet alignment errors, instrumentation errors and stability (especially Shintake monitor and beam position monitors). Addressing these issues is recommended for future experiments with low \beta^{*}_{y} optics in the ATF2.

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 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

For the commissioning and operation of modern particle accelerators, automated error detection and diagnostics methods are becoming increasingly important. In this paper, we present two such methods, which are capable of localising sources of beam offset jitter with a combination of correlation studies and so called degree of freedom plots. The methods were applied to the ATF2 beam line at KEK, where one of the major goals is the reduction of the beam offset jitter. Results of this localisation are shown in this paper. A big advantage of the presented method is its high robustness especially to varying optics parameters. Therefore, we believe that the developed beam offset jitter localisation methods can be easily applied to other accelerators., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Since July 2012 I had an honor to work in the European Organization for Nuclear Researc\n(CERN) as a member of the Technical Student Programme. This thesis presents the research concerning the electron transport in the Beam Gas Ionization (BGI) monitor in order to study the effects of the electrons interaction with a high energy particle beam.\nIn the first chapter the Beam Gas Ionization monitor is described together with its operating \nprinciple to give an overview of the analyzed detector. Chapter 2 contains the introduction to the \ntransverse beam dynamics in the particle accelerator which is the theoretical background for the \nemittance measurements. The analyzed BGI data are presented in chapter 3. As the research was based on the computer simulations, its description together with the results are given in the chapter 4. \nFinally the chapter 5 contains the investigation of the magnetic field threshold in the BGI \nelectron dynamics. In very short words the Beam Gas Ionization monitors installed in the CERN LHC make use of the ionization of a small volume of the injected neon gas by the circulating beam. The electrons produced are guided towards the readout system using a combination of electric and magnetic fields. In the presence of the beam field their tracks are modified and the resulting profile is distorted. The Geant4 particle simulation package is used to simulate the ionization process, while the CERN developed PyECLOUD code is used for tracking of the resulting ionized particles.\nIt turned out that the space charge effects of the beam strongly affect the electron distribution \nof the liberated electrons. The profile broadening and distortion therefore occur which causes the \nwrong indications of the BGI monitors. Those effects strongly depend on the beam density which is defined by the bunch intensity and the beam size. It is important to mention that those phenomena occur only for proton beam which is more intense than the ion beam.\nBy running the simulations it was found that the stronger magnetic field dumps the space charge \neffects. The simulations have shown that a magnetic field of 1 T is enough to reproduce the beam \nprofile correctly and obtain right value of the beam emittance. The further investiga- tion of this \nissue resulted in obtaining the empirical formula for magnetic field threshold needed to keep the \nspace charge effects at the expected level.\nThe performed research is a justification for possible BGI magnet exchange in order to\nensure the correct operation also for a proton beam.

The ionisation profile monitors installed in the CERN LHC and SPS make use of the ionisation of a small volume of the injected neon gas by the circulating beam. The electrons produced are guided towards the readout system using a combination of electric and magnetic fields. In the presence of the beam field their tracks are modified and the resulting profile is distorted. The Geant4 particle simulation package has been used to simulate the ionisation process, while the CERN developed PyECLOUD code has been used for tracking of the resulting ionised particles. In this paper the results of simulations are compared with observations and conclusions are presented concerning the accuracy of the reconstruction of high-intensity beam profiles.