Developing the Technique of Measurements of Magnetic Field in the CMS Steel Yoke Elements With Flux-Loops and Hall Probes

TL;DR

This paper presents a method for measuring the magnetic field in CMS steel yoke elements using flux-loops and Hall probes, including experimental validation with a test setup to ensure accurate magnetic characterization.

Contribution

It introduces an experimental approach combining flux-loops and Hall sensors for precise magnetic field measurement in large steel yoke components of the CMS detector.

Findings

Flux-loop voltages can be integrated to determine steel flux during solenoid discharges.

Hall sensors provide supplementary axial magnetic field data and remanent field estimation.

Experimental results validate the measurement technique for large ferromagnetic structures.

Abstract

Compact muon solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN large hadron collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in theCMSdetector, including the large ferromagnetic parts of the yoke, is required. To measure the field in and around ferromagnetic parts, a set of flux-loops and Hall probe sensors will be installed on several of the steel pieces. Fast discharges of the solenoid during system commissioning tests will be used to induce voltages in the flux-loops that can be integrated to measure the flux in the steel at full excitation of the solenoid. The Hall sensors will give supplementary information on the axial magnetic field and permit estimation of the remanent field in the steel after the fast discharge. An experimental R&D program has been undertaken, using a test flux-loop, two Hall sensors, and sample disks made from the same construction steel used for the CMS magnet yoke. A sample disc, assembled with the test flux-loop and the Hall sensors, was inserted between the pole tips of a dipole electromagnet equipped with a computer-controlled power supply to measure the excitation of the steel from full saturation to zero field. The results of the measurements are presented and discussed.