Field Quality and Mechanical Analysis of the Beam Separation Dipole for HL-LHC Upgrade

High luminosity upgrade of the Large Hadron Collider (HL-LHC) project has been launched to attain a ten times higher integrated luminosity than the current LHC that has been in operation for over ten years. For this goal, the quadruple and dipole magnets around two interaction points, the ATLAS and the CMS, will be upgraded. High Energy Accelerator Research Organization (KEK) is in charge of developing the new superconducting beam separation dipole magnet (D1). The main dipole field of 5.6 T in a large aperture of 150 mm is generated using a cos-theta coil wound with Nb-Ti cables at nominal operating current of 12.0 kA at 1.9 K corresponding to 75% of the load line ratio. The main challenges for the D1 are larger aperture, a high level of iron saturation, radiation resistance, and tight constraints on field quality. This article summarizes the results of a detailed analysis on field error. Electromagnetic simulation with ROXIE was carried out for the 2-D model of the new D1. As possible design changes, a diameter and position of heat exchanger holes in the iron yoke, and shape of the cryostat were considered. To reveal the influence on systematic error, packing factor of iron yoke, relative permeability of the stainless steel collar, and coil deformation during yoking were reflected to the baseline design. In addition, random geometric error was also estimated. Based on these results, contribution of each factor to field quality is studied.

I. Introduction

THE high Luminosity upgrade of the Large Hadron Collider (HL-LHC) project has been in progress, aiming at increasing the LHC peak luminosity up to and the integrated luminosity up to 3000 fb , that is, ten times more data with respect to what was planned for the LHC [1]. One of the paths to attain higher luminosity is to reduce the beams to smaller size at the interaction point. This requires quadrupole magnets with larger aperture, and therefore, the beam separation dipole magnet located after the triplet also should have larger aperture. High Energy Accelerator Research Organization (KEK) is in charge of design study including the short model development of the beam separation dipole magnet (D1).