Barbara Dalena

Overview of Arc Optics of FCC-hh

The FCC-hh (Future Hadron-Hadron Circular Collider) is one of the options considered for the next generation accelerator in high-energy physics as recommended by the European Strategy Group. In this overview the status and the evolution of the design of optics integration of FCC-hh are described, focusing on design of the arcs, alternatives, and tuning procedures. LAYOUT OF THE FCC-hh The layout of the FCC-hh ring is shown in Fig. 1. It has only slightly changed compared to the one shown in Ref. [1]. The total circumference of the FCC-hh ring is 97.75 km. The FCC-hh ring is made of 4 short arcs (SAR), 4 long arcs (LAR), 6 long straight sections of 1.4 km (LSS) and 2 extended straight sections of 2.8 km (ESS). The parameters of the ring are given in Table 1. Figure 1: Layout of the FCC-hh ring. The high luminosity interaction points (IPs) are located in the sections LSS-PA and LSS-PG. The value of L∗ in the experimental insertion region (EIR) has been shortened from 45 m to 40 m [2–4], giving a greater flexibility to the optics and reducing the chromaticity generated into the triplet. Two additional IPs (with lower luminosity) are located in the sections LSS-PB and LSS-PL. These sections host the injection as well, which gives additional constraints [2, 4, 5]. The beam H1, which runs in the clockwise direction, is injected into the section LSS-PB and the other one H2 into the section LSS-PL. The RF cavities are located into the section LSS-PH with a beam separation enlarged from 204 mm ∗ Corresponding author: antoine.chance@cea.fr Table 1: Parameters of the FCC-hh Ring Parameter Value Unit Baseline Ultimate Energy 50 TeV Circumference 97.75 km LSS and ESS length 1.4 and 2.8 km SAR and LAR length 3.4 and 16 km β∗ 1.1 0.3 m L∗ 40 m Normalized emittance 2.2 μm γtr 98.806 98.802 Qx/Qy 110.31/ 107.32 Qx/Q y 2/2 Beam separation 204 mm Beam separation (RF) 420 mm to 420 mm. This section is currently made of FODO cells. The extraction section is located in the section ESS-PD and enables the extraction of both beams in the same section [5]. The betatron cleaning section is located in the section ESS-PJ for both beams. The momentum cleaning section is located in the section LSS-PF for both beams [6–8]. UPDATES OF THE ARC CELLS To reduce the cost and to enable the compatibility between FCC-hh and HE-LHC, the beam separation is 204 mm [9,10]. Because of the strong magnetic field in the dipoles, the yoke saturates at collision energy and creates a quadrupole component. The dipoles have then a systematic b2 component, which increases from injection (near 0) to collision energy (near 50 units). Moreover, the sign of b2 is inverted between the inner and outer sides of the arcs for the cos θ or block designs. For the beam H1, we consider then b2 = 50 from PA to PB and from PG to PL and b2 = −50 in the other sections. For the beam H2, the signs are inverted. The integrated quadrupole component in a dipole is given by: b2Ld ρRref ≈ 0.4 × 10−3 (1) where Ld and ρ are respectively the length and the curvature radius of the dipole, Rref = 17 mm is the reference radius. For comparison, the integrated gradient in one arc quadrupole is about 14×10−3. Since there are 12 dipoles and 2 quadrupoles per cell, the integrated gradient in the dipoles is equal to 17% of the one in the main quadrupoles, which is not negligible. That is why the b2 component of the dipoles is not considered as a perturbation and is taken into account 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-MOPMF025 01 Circular and Linear Colliders A01 Hadron Colliders MOPMF025 141 Co nt en tf ro m th is w or k m ay be us ed un de rt he te rm so ft he CC BY 3. 0 lic en ce (© 20 18 ). A ny di str ib ut io n of th is w or k m us tm ai nt ai n at tri bu tio n to th e au th or (s ), tit le of th e w or k, pu bl ish er ,a nd D O I.

Progress on the Optics Corrections of FCC-hh

The FCC-hh (Future Hadron-Hadron Circular Collider) is one of the three options considered for the next generation accelerator in high-energy physics as recommended by the European Strategy Group, and the natural evolution of existing LHC. Studies are ongoing about the evaluation of the various magnets mechanical errors and field errors tolerances in the arc sections of FCC-hh, as well as an estimation of the correctors strengths necessary to perform the corrections of the errors. In this study advanced correction schemes for the residual orbit, the linear coupling and the ring tune are described. The impact of magnet tolerances on the residual errors, on the correctors technological choice and on the beam screen design are discussed. In particular the effect of the dipole a2 error is emphasized.

Residual Orbit Correction Studies for the FCC-hh

The FCC-hh (Future Hadron-Hadron Circular Collider) is one of the three options considered for the next generation accelerator in high-energy physics as recommended by the European Strategy Group [1]. Preliminary studies have started to estimate the design parameters of FCC-hh. One of these studies is the calculation of the residual orbit in the arcs of the collider. This is very important for the evaluation of the alignment tolerances of the quadrupoles used in the arcs, the dimensioning of the correctors and of the beam screen. Moreover it has an impact on the dynamic aperture of the ring and the field tolerances of the arc multipoles. To perform the simulations, the beam transport code MADX has been used. Systematic studies of the residual orbit and of the correctors’ strength dependence on the magnets misalignment or field errors are presented and discussed. THE FCC-HH RING FCC-hh is the hadron-hadron option considered for the Future Circular Collider accelerator facility that will come after the LHC. The circumference of the ring will be around 100 km and the proton beam energy at collision 50 TeV. The general layout of FCC-hh and its optics are described in [2]. The ring has several long and short arc sections amounting to about 80% of the total ring circumference. One of the studies concerning the arc sections is the correction of the beam residual orbit created by magnet errors. The goal of this study is to find a good correction scheme and to estimate which tolerances on the magnets errors can lead to acceptable results for the corrector strengths, residual orbit and related variables. ERRORS AND CORRECTION SCHEME Error Description There are several error contributions that can affect the closed orbit of the particles in the arcs of the FCC-hh ring:  Quadrupole alignment errors  Dipole field errors (random b1)  Quadrupole roll angle errors  Dipole roll angle errors  BPM readout errors For the present study only the first two contributions are studied. The errors are considered as static. Also the incoming beam errors are currently not taken into account. Correction scheme Next to each of the quadrupoles of the arcs (‘MQ’ type) and of the neighbouring dispersion suppression regions (DIS, ‘MQ’ and ‘MQB’ type), there are a BPM (Beam Profile Monitor) and an orbit corrector (0.647-meter-long) made with Nb-Ti technology (as well as a sextupole), both located after the quadrupole. Figure 1 shows the structure of an arc cell around a ‘MQ’ quadrupole unit. Figure 1: Structure of a quadrupole unit in the arc sections, with from left to right, the quadrupole itself (QP), a BPM, a sextupole (SX), and an orbit corrector (COR). The following correction scheme has been defined: all BPMs and all correctors are used, the polarity of each corrector and the plane in which each BPM is measuring the beam position, corresponds to the plane in which the neighbouring quadrupole is focusing (a BPM next to a quadrupole focusing in the horizontal plane will only measure the horizontal orbit). This scheme means that a residual orbit measured by a BPM will be compensated by an orbit corrector placed in the second next quadrupole (located at a phase advance of 90° downstream). With this scheme the horizontal and vertical orbit corrections are made with a separate set of BPMs and correctors. The orbit correction optimization was performed with the MADX [3] code. The complete FCC lattice has been used for the simulations with a tuning at collision energy. The alignment error was defined only for the ‘MQ’ type quadrupoles. The field error was defined for the all the dipoles present in arcs and in DIS sections. A systematic study on each of the error contributions was investigated, within the following ranges of RMS values:  0 < σδx,y < 0.5 mm for quadrupole alignment errors  0 < σδB/B < 0.5 % for relative dipole field errors ___________________________________________ * This Research and Innovation Action project submitted to call H2020INFRADEV-1-2014-1 receives funding from the European Union’s H2020 Framework Program under grant agreement no. 654305. † email address: david.boutin@cea.fr THPMB042 Proceedings of IPAC2016, Busan, Korea ISBN 978-3-95450-147-2 3332 C op yr ig ht