Magnetic Tests of the CMS Superconducting Magnet

The superconducting magnet for CMS has been designed to reach a 4 T field in a free bore of 6 m over a length of 12.5 m, with a stored energy of 2.6 GJ at nominal current. The magnet has been extensively and successfully tested in a surface hall at CERN in August and October 2006. Its characteristics make it the largest superconducting solenoid ever built in terms of bending power for the physics, stored energy and stored energy per unit of cold mass. The tests of the magnet were carried out by charging it to progressively higher currents. Long current flattops were used for magnetic measurements, generally ending with triggered fast discharges. During the tests, all the relevant parameters related to electrical, magnetic, thermal and mechanical behavior have been recorded and will be reported in the paper. Special emphasis will be put on the results and analysis of phenomena related to induced fast discharges, such as coupling and quench-back effects.