Low-Beta Insertions inducing Chromatic Aberrations in Storage Rings and their Local and Global Correction

The chromatic aberrations induced by low-β insertions can seriously limit the performance of circular colliders. The impact is twofold: (1) a substantial off-momentum beta-beating wave traveling around the ring and leading to a net reduction of the mechanical aperture of the low-beta quadrupoles but also impacting on the hierarchy of the collimator and protection devices of the machine, (2) a huge non-linear chromaticity which, when combined with the magnetic imperfections of the machine, could substantially reduce the momentum acceptance of the ring by pushing slightly off-momentum particles towards non-linear resonances. These effects will be analyzed and illustrated in the framework of the LHC insertions upgrade Phase I [1] and a strategy for correction will be developed, requiring a deep modification of the LHC overall optics

LSS magnet aperture requirements for the LHC insertion upgrade, a first estimate

A significant reduction of B* will be determinant to push the LHC luminosity by a factor 2 to 10. Beyond the obvious implications this has on the need of designing brand new low-b quadrupole magnets with increased aperture and possibly higher peak field depending on the choice of the technology, this report investigates the various modifications to bring to the matching section magnets Q4 and Q5 and the separation/recombination dipoles D1 and D2. The aim on this report is essentially to activate an R&D effort on the development of moderate gradient (<~ 120 T/m) two-in-one quadrupoles with increased aperture 90 mm diameter) and negligible cross-talk between apertures, but also, based on the ultimate aperture requirements obtained for the D1/Db2 (a gap height of about 120-130 mm for a normal conducting D1 and an inner coil diameter of almost 100 mm for a two-in-one cold D2, assuming a B* of 15 cm), to help in the decision of keeping or not these two magnets warm and cold, respectively

Linear Imperfections and Operational Aspects Induced by the D1 Multipole Errors for the LHC Upgrade Phase I

In addition to the dynamic aperture as a general machine parameter that has to be optimized in the LHC upgrade machine, strong lower order multipoles will lead to a series of problems for the operation of the machine. A direct influence on the linear beam optics (beta beating, tune shift and coupling) from the a2, b2 multipoles is evident. Equally important however are the multipole coefficients of the next higher order n=3 via the feed down effect. The foreseen half crossing angle of about 205 µrad at the IP creates large offsets in the D1 magnet that finally lead again to a strong a2, b2 errors. The estimates presented in this paper show a distortion in the order of several percent for the beta beat and a considerable shift of the working point. Even after compensation of these effects an influence on the machine performance is expected during machine operation and a further reduction of the multipole coefficients, especially in the case of the D1 magnet, might be needed

Specification of the closed orbit corrector magnets for the new LHC inner triplet

Various orbit correction schemes are studied for the new inner triplets of the SLHC. The figures of merit used to compare the different schemes are the peak orbit after correction, the loss of beam-beam separation at the parasitic encounters and the required integrated Corrector strength. The flexibility of the crossing bump generation is also used as a key parameter to compare the different schemes

Baseline LHC machine parameters and configuration of the 2015 proton run

This paper shows the baseline LHC machine parameters for the 2015 start-up. Many systems have been upgraded during LS1 and in 2015 the LHC will operate at a higher energy than before and with a tighter filling scheme. Therefore, the 2015 commissioning phase risks to be less smooth than in 2012. The proposed starting configuration puts the focus on feasibility rather than peak performance and includes margins for operational uncertainties. Instead, once beam experience and a better machine knowledge has been obtained, a push in $\beta^*$ and performance can be envisaged. In this paper, the focus is on collimation settings and reach in $\beta^*$---other parameters are covered in greater depth by other papers in these proceedings.Comment: submitted for publication in a CERN yellow report (Proceedings of the LHC Performance Workshop - Chamonix 2014

Reliable Operation of the AC Dipole in the LHC

The AC dipole in the LHC will not only provide transverse oscillations without emittance growth but also with a safety guarantee. These two features are due to the adiabaticity of the excitation. However chromaticity and nonlinear fields spoil this adiabaticity. This paper assesses the margins of the relevant beam observables for a reliable and safe operation of AC dipoles in the LHC

Optimization of the LHC separation bumps including beam-beam effects

The LHC beams will cross each other and experience perturbations as a result of the beam-beam effect at the interaction points, which can result in emittance growth and halo creation. The beam-beam force is approximately linear for small offsets and highly non-linear for larger offsets with peaks in growth close to 0.3 and 1.5 σ separation. We present a study of the process of going into collisions in the LHC and use simulations to investigate on possible emittance blow-up. We analyze how the crossing scheme can be optimized to minimize the collapsing time of the separation bumps for given hardware constraints

A semi-analytical method to generate an arbitrary 2D magnetic field and determine the associated current distribution

This reports describes a novel method based on polynomial algebra techniques which aims to determine the transverse position of N current wires perpendicular to a plane in which the induced 2D magnetic field map shall exhibit a given multipole expansion at one or several specified locations. Rather than a case-by-case comparative study of the method with other existing ones, we will insist on the details of the method itself and then illustrate its potential to the design of many magnet classes, from very pure 2n-pole magnets to more exotic components producing a magnetic field with more complex characteristics, such as FFAG magnets, mass-less septa or magnetic collimators

Optics Flexibility in the LHC at Top Energy

Flexibility of the LHC optics at top energy has been studied, in terms of betatron tune tunability, mainly for the high-beta optics that requires tunability of the order of half a unit. It has been shown that the tunability at top energy is good enough for the high-beta optics. The results obtained in this study could be useful for other optics and operation modes

Optics studies based on V6.503 nominal configuration

Optics studies based on the V6.503 nominal optics have been performed, aiming at improving the collimation efficiency by adjusting the phase advance from IP1 to IP5 to be π/2 off a multiple of 2π such that the off-momentum beta-beating is localized to the left side of the LHC ring. The off-momentum beta-beating in IR7 (betatron collimation section) is suppressed as expected. In addition to this main point, IR2 and IR8 injection optics are studied to improve the apertures of the inner triplet magnets. The aperture could be increased by either increasing beta* or improving the crossing scheme as proposed or bot