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

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

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

Linear & Nonl. optics checks diring LHC injection tests

In early LHC commissioning, linear and “higher-order” polarity checks were performed for one octant per beam, by launching suitable free betatron oscillations and then inverting a magnet-circuit polarity or strength. Circuits tested included trim quadrupoles, skew quadrupoles, lattice sextupoles, sextupole spool-pieces, Landau octupoles, and skew sextupoles. A nonzero momentum offset was introduced to enhance the measurement quality. The lowintensity single-pass measurements proved sufficiently sensitive to verify the polarity and the amplitude of (almost) all circuits under investigation, as well as the alignment of some individual trim quadrupoles. A systematic polarity inversion detected by this measurement helped to pin down the origin of observed dispersion errors. Later, the periodic “ring dispersion” was reconstructed from the full first-turn trajectory of an injected off-momentum beam, by removing, at each location, the large incoming dispersion mismatch, forward-propagated via the optics model. Various combinations of inverted trim quadrupoles were considered in this model until reaching a good agreement of reconstructed dispersion and prediction

Impact of CMS Stray Field on the Large Hadron Collider Beam Dynamics and Thin Solenoid in the SixTrack Code

The impact of the CMS main solenoid field and stray field on the coupling and on the dynamic aperture is evaluated for both LHC collision (7 TeV) and injection optics (450 GeV). To study the impact of CMS solenoid field on the LHC dynamic aperture, a new element ‘solenoid’ has been added in the SixTrack code and debugged. In Appendix B and C the analytical formulae applied on the solenoid are presented

Determination of the Chromaticity of the TI 8 Transfer Line Based on Kick Response Measurements

The 3 km long TI 8 transfer line is used to transfer 450 GeV proton and ion beams from the SPS to LHC collider. As part of a detailed optics investigation program the chromaticity of the transfer line was measured. Kick response data of the transfer line was recorded for various extraction energy offsets in the SPS. The quadrupolar and sextupolar field errors (b2 and b3, respectively) over the whole transfer line dipoles, a systematic error of the main quadrupole strengths and the initial momentum error were estimated by a fit. Using the updated model, the chromaticity of the line was then calculated

First β-beating measurement and optics analysis for the CERN Large Hadron Collider

Proton beams were successfully steered through the entire ring of the CERN Large Hadron Collider (LHC) on September the 10th of 2008. A reasonable lifetime was achieved for the counterclockwise beam, namely beam 2, after the radiofrequency capture of the particle bunch was established. This provided the unique opportunity of acquiring turn-by-turn betatron oscillations for a maximum of 90 turns right at injection. Transverse coupling was not corrected and chromaticity was estimated to be large. Despite this largely constrained scenario, reliable optics measurements have been accomplished. These measurements together with the application of new algorithms for the reconstruction of optics errors have led to the identification of a dominant error source

First beta-beating measurement in the LHC

In 2008 beam successfully circulated in the LHC. Thanks to an excellent functioning of the beam position monitor (BPM) system and the related software, injection oscillations were recorded for the first 90 turns at all BPMs. The analysis of these data gives the unique opportunity of evaluating the periodic optics and inferring possible error sources

Field quality of the LHC dipole magnets in operating conditions

We report here the main results of the field measurements performed so far on the pre-series LHC superconducting dipoles at superfluid helium temperature. After discussing the results at injection and collision conditions, we focus on the non-linear contributions at high field, on the contribution of superconductor magnetization at injection, and on ramp rate effects. The statistics accumulated on the first magnets of the production verify the hypotheses that have been used to design the correctors scheme for the LHC. In particular high field saturation is in line with the expectations, although a small systematic deformation due to Lorentz forces affects both sextupole and decapole terms. The decay at injection and snap-back at beginning of beam acceleration require careful characterization

Analysis of Optical Layouts for the Phase 1 upgrade of the CERN Large Hadron Collider Insertion Regions

In the framework of the studies for the upgrade of the insertions of the CERN Large Hadron Collider, four optical layouts were proposed with the aim of reducing the beta-function at the collision point down to 25 cm. The different candidate layouts are presented. Results from the studies performed on mechanical and dynamic aperture are summarized, together with the evaluation of beam-beam effects. Particular emphasis is given to the comparison of the optics performance, which led to retain the most promising layouts for further development