Rogelio Tomás

Present status and first results of the final focus beam line at the KEK Accelerator Test Facility

ATF2 is a final-focus test beam line which aims to focus the low emittance beam from the ATF damping ring to a vertical size of about 37 nm and to demonstrate nanometer level beam stability. Several advanced beam diagnostics and feedback tools are used. In December 2008, construction and installation were completed and beam commissioning started, supported by an international team of Asian, European, and U. S. scientists. The present status and first results are described.

Small angle crab compensation for LHC IR upgrade

A small angle crab scheme is being considered for the LHC luminosity upgrade. In this paper we present a 400 MHz superconducting cavity design and discuss the pertinent RF challenges. We also present a study on the beam-beam performance and proton-beam emittance growth in the presence of crab compensation, with RF noise sources.

High Luminosity LHC: Challenges and plans

The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will undergo a major upgrade in the 2020s. This will increase its rate of collisions by a factor of five beyond the original design value and the integrated luminosity by a factor ten. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11–12 T superconducting magnets, including Nb3Sn-based magnets never used in accelerators before, compact superconducting cavities for longitudinal beam rotation, new technology and physical processes for beam collimation. The dynamics of the HL-LHC beams will be also particularly challenging and this aspect is the main focus of this paper.

Completion of the sextupole driving terms measurement at the SPS

This paper represents the completion of the series of sextupole driving terms measurements in the SPS which started in June 1998. The following two items have been missing from earlier reports on these studies: measuring two dimensional resonances and the resonance phase. The possible dependence of these terms on collective effects was studied. Lastly, the experiment was performed at two different energies of 26 and 80 GeV, to suppress energy dependencies. Comparisons to the tracking model show excellent agreement, proving that this technique is ready for other machines.

Experimental and theoretical progress of linear collider final focus design and ATF2 facility

Abstract 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.

Tuning of CLIC-Final Focus System 3 TeV Baseline Design Under Static and Dynamic Imperfections

In this paper we present the tuning study of the Compact Linear Collider - Final Focus System (CLIC-FFS) 3 TeV baseline design under static and dynamic imperfections for the first time. The motion of the FFS magnets due to ground motion and the impact of active and passive mechanisms envisaged to stabilize both e − and e + systems are described. It is found that the Pre-isolator required for stabilization of the Final Doublet drives the performance of the collider at the final stages of the tuning process. The obtained tuning performance depending on the stabilization techniques are discussed in detail.

High-Energy LHC design

In the frame of the FCC study we are designing a 27 TeV hadron collider in the LHC tunnel, called the High Energy LHC (HE-LHC). The HE-LHC can be realized by replacing the LHCs 8.33 T niobium-titanium dipole magnets with 16 T niobium-tin magnets developed for FCC-hh. A high-quality beam available from the upgraded LHC injector complex and significant radiation damping allow achieving the challenging target values for both peak and integrated luminosity required by particle physics. Tunnel integration determines the maximum outer size of the magnet cryAPCostat. The HE-LHC arc optics maximizes the dipole filling factor and optimizes the dynamic aperture, while limiting the field strengths of quadrupoles and sextupoles. The low-beta optics for the experimental insertions features a shielded quadrupole triplet even longer than the HL-LHCs, which can support an interaction-point beta function of 25 cm, and survive an integrated luminosity above 10/ab. Other challenges include collimation and extraction. The choice of injection energy and injector is another important element, and so are various collective effects. We here report the HE-LHC design status.

JACoW : Twiss Parameter Measurement and Application to Space Charge Dynamics

We are looking for feasible and quantitative method to evaluate space charge induced beam loss in J-PARC MR. One possible way is space charge simulation and theory based on measured Twiss parameter. Twiss parameter measurement using turn-by-turn monitors is presented. Resonance strengths of lattice magnets and space charge force are estimated by the measured Twiss parameters. Emittance growth and beam loss under the resonance strengths are discussed.

JACoW : Studies on Luminous Region, Pile-up and Performance for HL-LHC Scenarios

Studies on luminous region and pile-up density are of great interest for the experiments at the future High Luminosity LHC (HL-LHC) in order to optimize the detector performance. The evolution of these parameters at the two main interaction points of the HL-LHC along optimum physics fills is studied for the baseline and alternative operational scenarios with the latest set of parameters, including a refined description of the longitudinal bunch profile. Results are discussed in terms of a new figure-of-merit, the effective pile-up density.

Non-Linear Errors in the Experimental Insertions of the LHC

Correction of nonlinear magnetic errors in low-β insertions can be of critical significance for the operation of a collider. This is expected to be of particular relevance to LHC Run II and the HL-LHC upgrade, as well as to future colliders such as the FCC. Current correction strategies for these accelerators have assumed it will be possible to calculate optimized local corrections through the insertions using a magnetic model of the errors. To test this assumption the nonlinear errors in the LHC experimental insertions have been examined via feed-down and amplitude detuning. It will be shown that while in some cases the magnetic measurements provide a sufficient description of the errors, in others large discrepancies exist which will require beambased correction techniques. INTRODUCTION As the LHC progresses to more challenging β∗ regimes nonlinear errors in the low-β insertion regions (IRs) will play an increasing role in limiting the performance of the accelerator. In particular a ∼ 5σ reduction in dynamic aperture is expected in the HL-LHC due to these errors [1]. For this reason dedicated nonlinear correctors are provided in the common-beam regions left and right of the experimental insertions. A schematic of the corrector layout is shown in Fig. 1. Figure 1: Corrector layout in LHC experimental IRs [2]. Two correction strategies have been considered for the LHC and HL-LHC. The first method compensates magnetic errors in IR elements via local minimization of selected resonance driving terms [2]. The second method is based upon a direct compensation of the transverse map coefficients left and right of the interaction point (IP) [3]. For these strategies to be valid however, an accurate magnetic model of the insertions is required. Magnetic measurements performed on the LHC magnets during construction provide a foundation for such a model, but must be verified and refined through beam-based measurements to ensure the validity of the IR correction scheme. Strategies for nonlinear correction based upon feed-down to tune have previously been employed around the whole ring in SIS18 and CERN-SPS [4, 5], and in the RHIC experimental insertions [6]. In the RHIC method linear coupling was held constant during the feed-down scan, with correction attempted through minimization of observed tune shifts. At the LHC study of nonlinear multipoles in the IRs has been performed through feed-down to both tune and linear coupling. The focus of the studies in the LHC was also upon testing the magnetic model, rather than any beam-based minimization of the observable symptoms of the nonlinear errors. Table 1 summarizes the feed-down of normal and skew nonlinear multipoles, due to horizontal or vertical displacement from the magnetic axis, generating shifts in tune (ΔQ) and linear coupling (Δ|C−|). In Run I such studies were performed in the LHC by varying crossing angle bumps in the IRs, which are intended for prevention of collisions at parasitic crossing points either side of the IP (studies were performed with non-colliding probe bunches). More details of Run I studies may be found in [7, 8]. In 2015 feed-down scans were also performed [9], however new theoretical developments [10] also allowed use of an AC-dipole for measurement of amplitude detuning at top energy, providing an additional measure of normal octupole errors. MODEL VS MEASUREMENT Results from beam-based studies were compared to predictions of MAD-X simulations incorporating the best available knowledge of the magnetic errors in the IRs. This allowed for the validation of several components of the LHC magnetic model. Figure 2 shows an excellent agreement between modelled and measured variation of linear coupling with vertical crossing angle in the ALICE IR (IR2), dominated by the b3 component of the separation dipoles.