Unbalanced magnetic forces of a large superconducting magnet with Iron yoke

Superconducting thin solenoid magnets with iron yoke are constructed for colliding beam detectors of high energy physics. When the solenoid is radially off-centered because of the thermal shrinkage, a radial unbalanced force will act on the solenoid. Because the suport structure is weak to the unbalanced force, it is necessary for the designer to precisely evaluate the force. In this paper, a numerical method is presented where a quasi-three dimensional F.E.M. is used for the three dimensional field problem. The caluculation results are verified by the experiments using two small models with copper solenoid. It is concluded that the method can be applied to the evaluation of radial unbalanced force.