Compact muon solenoid (CMS) is a general-purpose detector designed to run atthe highest luminosity at the CERN large hadron collider (LHC). Its distinctivefeatures include a 4 T superconducting solenoid with 6 m diameter by 12.5 mlong free bore, enclosed inside a 10000-ton return yoke made of constructionsteel. Accurate characterization of the magnetic field everywhere intheCMSdetector, including the large ferromagnetic parts of the yoke, isrequired. To measure the field in and around ferromagnetic parts, a set offlux-loops and Hall probe sensors will be installed on several of the steelpieces. Fast discharges of the solenoid during system commissioning tests willbe used to induce voltages in the flux-loops that can be integrated to measurethe flux in the steel at full excitation of the solenoid. The Hall sensors willgive supplementary information on the axial magnetic field and permitestimation of the remanent field in the steel after the fast discharge. Anexperimental R&D program has been undertaken, using a test flux-loop, two Hallsensors, and sample disks made from the same construction steel used for theCMS magnet yoke. A sample disc, assembled with the test flux-loop and the Hallsensors, was inserted between the pole tips of a dipole electromagnet equippedwith a computer-controlled power supply to measure the excitation of the steelfrom full saturation to zero field. The results of the measurements arepresented and discussed.
展开▼
