ИСТИНА

The 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-length free bore, enclosed inside a 10,000-ton return yoke made of construction steel. The return yoke consists of five dodecagonal three-layered barrel wheels and four end-cap disks at each end comprised of steel blocks up to 620 mm thick, which serve as the absorber plates of the muon detection system. To measure the magnetic field in and around the steel, a system of 22 flux loops and 83 B-sensors (3-D Hall probes) is installed on the return yoke blocks. A TOSCA 3-D model of the CMS magnet is developed to describe the magnetic flux everywhere outside the tracking volume measured with the field-mapping machine. The magnetic flux density described with the model reproduces within 0.1 % the magnetic flux density measured inside the CMS coil, and within a few per cent the magnetic field measured in the selected yoke blocks. The production CMS magnetic field map is tuned with the cosmic muon tracks in 2009. The upgraded magnetic field map will be tuned with the tracks of muons from the pp-collisions collected in the CMS runs.