Instrumentation status of the low-b magnet systems at the Large Hadron Collider (LHC)

The low-beta magnet systems are located in the Large Hadron Collider (LHC) insertion regions around the four interaction points. They are the key elements in the beams focusing/defocusing process allowing proton collisions at luminosity up to 10**34/cm**2s. Those systems are a contribution of the US-LHC Accelerator project. The systems are mainly composed of the quadrupole magnets (triplets), the separation dipoles and their respective electrical feed-boxes (DFBX). The low-beta magnet systems operate in an environment of extreme radiation, high gradient magnetic field and high heat load to the cryogenic system due to the beam dynamic effect. Due to the severe environment, the robustness of the diagnostics is primordial for the operation of the triplets. The hardware commissioning phase of the LHC was completed in February 2010. In the sake of a safer and more user-friendly operation, several consolidations and instrumentation modifications were implemented during this commissioning phase. This paper presents the instrumentation used to optimize the engineering process and operation of the final focusing/defocusing quadrupole magnets for the first years of operation.Comment: 6 pp. ICEC 23 - ICMC 2010 International Cryogenic Engineering Conference 23 - International Cryogenic Materials Conference 2010. 19-23 Jul 2010. Wroclaw, Polan

LHC Beam Diffusion Dependence on RF Noise: Models and Measurements

Radio Frequency (RF) accelerating system noise and non-idealities can have detrimental impact on the LHC performance through longitudinal motion and longitudinal emittance growth. A theoretical formalism has been developed to relate the beam and RF loop dynamics with the bunch length growth [1]. Measurements were conducted at LHC to validate the formalism, determine the performance limiting RF components, and provide the foundation for beam diffusion estimates for higher energies and intensities. A brief summary of these results is presented in this work

Scenarios about the long-time damage of silicon as material and detectors operating beyond LHC collider conditions

For the new hadron collider LHC and some of its updates in luminosity and energy, as SLHC and VLHC, the silicon detectors could represent an important option, especially for the tracking system and calorimetry. The main goal of this paper is to analyse the expected long-time degradation in the bulk of the silicon as material and for silicon detectors, in continuous radiation field, in these hostile conditions. The behaviour of silicon in relation to various scenarios for upgrade in energy and luminosity is discussed in the frame a phenomenological model developed previously by the authors. Different silicon material parameters resulting from different technologies are considered to evaluate what materials are harder to radiation and consequently could minimise the degradation of device parameters in conditions of continuous long time operation.Comment: submitted to Physica Scripta Work in the frame of CERN RD-50 Collaboratio

The one-loop six-dimensional hexagon integral with three massive corners

We compute the six-dimensional hexagon integral with three non-adjacent external masses analytically. After a simple rescaling, it is given by a function of six dual conformally invariant cross-ratios. The result can be expressed as a sum of 24 terms involving only one basic function, which is a simple linear combination of logarithms, dilogarithms, and trilogarithms of uniform degree three transcendentality. Our method uses differential equations to determine the symbol of the function, and an algorithm to reconstruct the latter from its symbol. It is known that six-dimensional hexagon integrals are closely related to scattering amplitudes in N=4 super Yang-Mills theory, and we therefore expect our result to be helpful for understanding the structure of scattering amplitudes in this theory, in particular at two loops.Comment: 15 pages, 2 figure

Commissioning of the cryogenics of the LHC long straight sections

The LHC is made of eight circular arcs interspaced with eight Long Straight Sections (LSS). Most powering interfaces to the LHC are located in these sections where the particle beams are focused and shaped for collision, cleaning and acceleration. The LSSs are constituted of several unique cryogenic devices and systems like electrical feed-boxes, standalone superconducting magnets, superconducting links, RF cavities and final focusing superconducting magnets. This paper presents the cryogenic commissioning and the main results obtained during the first operation of the LHC Long Straight Sections.Comment: 8 pp. Cryogenic Engineering Conference and International Cryogenic Materials Conference, 28 Jun - 2 Jul 2009. Tucson, Arizon

A High Luminosity e+e- Collider to study the Higgs Boson

A strong candidate for the Standard Model Scalar boson, H(126), has been discovered by the Large Hadron Collider (LHC) experiments. In order to study this fundamental particle with unprecedented precision, and to perform precision tests of the closure of the Standard Model, we investigate the possibilities offered by An e+e- storage ring collider. We use a design inspired by the B-factories, taking into account the performance achieved at LEP2, and imposing a synchrotron radiation power limit of 100 MW. At the most relevant centre-of-mass energy of 240 GeV, near-constant luminosities of 10^34 cm^{-2}s^{-1} are possible in up to four collision points for a ring of 27km circumference. The achievable luminosity increases with the bending radius, and for 80km circumference, a luminosity of 5 10^34 cm^{-2}s^{-1} in four collision points appears feasible. Beamstrahlung becomes relevant at these high luminosities, leading to a design requirement of large momentum acceptance both in the accelerating system and in the optics. The larger machine could reach the top quark threshold, would yield luminosities per interaction point of 10^36 cm^{-2}s^{-1} at the Z pole (91 GeV) and 2 10^35 cm^{-2}s^{-1} at the W pair production threshold (80 GeV per beam). The energy spread is reduced in the larger ring with respect to what is was at LEP, giving confidence that beam polarization for energy calibration purposes should be available up to the W pair threshold. The capabilities in term of physics performance are outlined.Comment: Submitted to the European Strategy Preparatory Group 01-04-2013 new version as re-submitted to PRSTA

IMPLEMENTATION OF LUMINOSITY LEVELING BY BETATRON FUNCTION ADJUSTMENT AT THE LHC INTERACTION POINTS

Abstract Growing expectations for integrated luminosity during upcoming LHC runs introduce new challenges for LHC beam operation in the scope of online luminosity control. Because some LHC experiments are limited in the maximum event rates, their luminosity is leveled to a constant value. Various techniques may be used for luminosity leveling, changing the betatron function at the interaction point is one of them. This paper explains the main operational requirements of a betatron function leveling scheme for the upcoming LHC run. Issues concerning the beam optics, orbits and collimator settings are discussed. The proposed architecture for control system integration will be discussed. A few operational scenarios with different beam configurations foreseen for the next LHC run will be presented. LUMINOSITY An important parameter that affects the quality of the recorded luminosity at the LHC is the event pile-up, the number of simultaneous particle interactions during one bunch crossing. A high event pile-up complicates the physics analysis and degrades the data quality for certain types of physics channels. The event pile-up µ is directly proportional to the luminosity per bunch crossing L bb , µ = L bb × σ P , where σ P is the total cross section for pp interactions at the LHC, σ P = 70 − 85 mbarn. The total luminosity L p is given by L p = k L bb where k is the number of bunch crossings per turn. The bunch pair luminosity for round beams at an interaction point can be written as where N stands for number of particles in the bunch, ε N for the normalized emittance and β * for the betatron function at the interaction point. f is the revolution frequency and γ the relativistic factor. F is a correction factor for the crossing angle. For round beams ε N and β * are identical for both transverse planes. d is the transverse offset (separation) between the colliding beams. The transverse separation d and the betatron function β* can be seen as a way for control luminosity. LHC RUN 2 BEAM PROJECTIONS After the long shutdown the LHC will restart beam operation in 2015 at an energy of 6.5 TeV. The LHC has two high luminosity experiments ATLAS and CMS that are installed at interaction points 1 and 5 (IR1 and IR5). Those experiments can cope with a maximum average pile-up of 50 and a time-averaged pile-up of 30 to 40. The LHCb experiment in IR8 on the other hand will operate at a maximum pile-up of µ = 1.6. Luminosity leveling is required for the LHCb experiment for all scenarios, while for the high luminosity experiments only the 50 ns scenario definitely requires leveling. With 25 ns some leveling is required in IR1 and IR5 only for the brightest beams. For the LHC luminosity upgrade HL-LHC (from 2023) [1] luminosity leveling by β* is part of the operational baseline

Closed Orbit Response to Quadrupole Strength Variation

Abstract We derive two formulae relating the variation in closed orbit in a storage ring to variations in quadrupole strength, neglecting nonlinear and dispersive effects. These formulae correct results previously reporte