LHC Lattice Research Articles

Status of the 11 T $\hbox{Nb}_{3}\hbox{Sn}$ Dipole Project for the LHC

The planned upgrade of the LHC collimation system includes additional collimators in the LHC lattice. The longitudinal space for the collimators could be obtained by replacing some LHC main dipoles with shorter but stronger dipoles compatible with the LHC lattice and main systems. A joint development program with the goal of building a 5.5 m long two-in-one aperture Nb 3 Sn dipole prototype suitable for installation in the LHC is being conducted by FNAL and CERN magnet groups. As part of the first phase of the program, 1 m long and 2 m long single aperture models are being built and tested, and the collared coils from these magnets will be assembled and tested in two-in-one configuration in both laboratories. In parallel with the short model magnet activities, the work has started on the production line in view of the scale-up to 5.5 m long prototype magnet. The development of the final cryo-assembly comprising two 5.5 m long 11 T dipole cold masses and the warm collimator in the middle, fully compatible with the LHC main systems and the existing machine interfaces, has also started at CERN. This paper summarizes the progress made at CERN and FNAL towards the construction of 5.5 m long 11 T Nb 3 Sn dipole prototype and the present status of the activities related to the integration of the 11 T dipole and collimator in the LHC.

Design, Assembly, and Test of the CERN 2-m Long 11 T Dipole in Single Coil Configuration

The upgrade of the LHC collimation system includes additional collimators in the LHC lattice. The longitudinal space for the collimators can be obtained by replacing some LHC main dipoles with shorter but stronger dipoles compatible with the LHC lattice and the existing powering circuits, cryogenics, and beam vacuum. A joint development programme aiming at building a 5.5 m long two-in-one aperture Nb 3 Sn dipole prototype suitable for installation in the LHC is being conducted by FNAL and CERN. As part of the first phase of the programme, 1 m and 2 m long single aperture models are being built and tested. Later on, the collared coils from these models will be assembled and tested in a two-in-one aperture configuration in both laboratories. A 2 m long practice model made of a single coil wound with Nb 3 Sn cable, MBHSM101, was developed and constructed at CERN. It has been completed, and tested at both 4.3 K and 1.9 K. This practice model features collared coils based on removable pole concept, S2-glass cable insulation braided over a mica layer, and coil end spacers made of sintered stainless steel with springy legs. The paper describes the main features of this practice model, the main manufacturing steps and the results of the cold tests.

Chromatic coupling correction in the Large Hadron Collider

In this article we present the measurement and correction of the chromatic coupling in the LHC. The transverse coupling is calculated from turn-by-turn data, exciting the beam with an ac dipole. By adjusting the momentum relative to the reference energy and repeating the measurement, we obtain the transverse coupling dependency on momentum. The measurements are compared to the predictions from the magnetic model, and show good agreement. We describe the algorithm used to calculate the corrections, which are performed using skew sextupoles in the LHC lattice. A reduction in the chromatic coupling of a factor $2.5\ifmmode\pm\else\textpm\fi{}0.4$ for beam 1 and 1.6 $\ifmmode\pm\else\textpm\fi{}0.3$ for beam 2 was obtained after applying the corrections.

Development and Test of a Single-Aperture 11 T $ \hbox{Nb}_{3}\hbox{Sn}$ Demonstrator Dipole for LHC Upgrades

The upgrade of the LHC collimation system foresees installation of additional collimators around the LHC ring. The longitudinal space for the collimators could be provided by replacing some 8.33 T NbTi LHC main dipoles with shorter 11 T Nb3Sn dipoles compatible with the LHC lattice and main systems. To demonstrate this possibility, FNAL and CERN have started a joint program with the goal of building a 5.5 m long twin-aperture dipole prototype suitable for installation in the LHC. The first step of this program is the development of a 2 m long single-aperture demonstrator dipole with a nominal field of 11 T at the LHC nominal current of 11.85 kA and ~ 20% margin. This paper describes the design, construction, and test results of the first single-aperture Nb3Sn demonstrator dipole model.

Design and Fabrication of a Single-Aperture 11 T ${\rm Nb}_{3}{\rm Sn}$ Dipole Model for LHC Upgrades

The planned upgrade of the LHC collimation system includes additional collimators to be installed in the dispersion suppressor areas of points 2, 3 and 7. To provide the necessary longitudinal space for the collimators, a replacement of 8.33 T Nb-Ti LHC main dipoles with 11 T dipoles based on Nb3Sn superconductor compatible with the LHC lattice and main systems is being considered. To demonstrate this possibility FNAL and CERN have started a joint program to develop a 2 m long single-aperture dipole magnet with the nominal field of 11 T at ~11.85 kA current and 60 mm bore. This paper describes the demonstrator magnet magnetic and mechanical designs and analysis, coil fabrication procedure. The Nb3Sn strand and cable parameters and test results are also reported.

Strong–strong simulation study for the wire compensation of long-range beam–beam effect in LHC

The wire compensation of long-range beam–beam interactions in LHC was studied with numerical simulation of 10 6 macro-particles up to 10 5 turns. In the simulation, head-on beam–beam interactions at two high-luminosity interaction points of LHC were calculated self-consistently with the particle-in-cell (PIC) method and long-range beam–beam interactions calculated with the soft-Gaussian approximation. Including also the multipole field errors in the LHC lattice, the effectiveness of the compensation was evaluated in terms of the emittance growth. The robustness of the compensation to static and random errors in the electric currents on the wires was also investigated.

Deformations and Displacements of the LHC Superconducting Dipoles Induced by Standard and Non-Standard Operational Modes

A full-scale and fully-instrumented working model of the LHC lattice cell has been tested at CERN between March and December 2002. Aside of the current, pressure and temperature sensors controlled by an industrial supervision system, a novel device has been set to monitor magnet positions with respect to the surrounding cryostat. The series of operating modes to test cryogenics, current leads and quench recovery electronics offered the chance to investigate potentially harmful deformations of the superconducting structure. In this paper, we present a survey of displacements and deformations experienced by the LHC cell magnets during thermal cycles, current ramps and resistive transitions. Although the system complexity prevented from complete modeling, a preliminary phenomena explanation is given.

Accelerator related background in the CMS detector at LHC

Complete calculations of the accelerator related background in the muon spectrometer of the CMS detector at the Large Hadron Collider are presented. The simulations have been performed with the STRUCT multi-turn tracking code and the MARS and FLUKA cascade codes taking into account latest information of the LHC lattice, vacuum conditions, beam cleaning system and the shielding and layout of the CMS experiment. Beam loss distributions in the interaction regions and their vicinities and their contribution to the background levels in the muon spectrometer of CMS are analyzed. The studies show that hadronic and electromagnetic components of machine background are efficiently suppressed by the proposed CMS shielding. High energy muons penetrate through the shielding, but in positions of significance they do not contribute more than a few percent compared to the background generated by the pp-collisions. It is anticipated that the relative contribution of accelerator background will be higher during the first years of operation, but will drop down with the LHC performance evolution. The obtained results concerning the machine background and the efficiency of the proposed shielding are rather generic and can be directly applied to the ATLAS detector.