Development of the CMS Magnetic Field Map

Abstract

This article focuses on pioneering work on the performance of the three-dimensional (3D) magnetic field map in the entire volume of the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider at CERN. In the CMS heterogeneous magnetic system, the magnetic flux is created by a superconducting solenoid coil enclosed in a steel flux-return yoke. To describe the CMS magnetic flux distribution, a system of the primitive 3D volumes containing the values of the magnetic flux density measured inside the superconducting coil inner volume and modelled outside the coil across a special mesh of reference nodes was developed. This system, called the CMS magnetic field map, follows the geometric features of the yoke and allows the interpolation of the magnetic flux density between the nodes to obtain the magnetic field values at any spatial point inside a cylinder of 18 m in diameter and 48 m in length, where all the CMS sub-detectors are located. The geometry of the volumes is described inside one 30° azimuthal sector of the CMS magnet. To obtain the values of the magnetic flux density components across the entire azimuth angle of the CMS detector, rotational symmetry is applied.