The Fast Ramped Bending Magnets for the Gantry 2 at PSI

The PROSCAN project at the Paul Scherrer Institute (PSI/Switzerland) involves a number of innovative elements in tumor treatment. Apart from the compact superconducting dedicated proton cyclotron COMET, a fast energy degrader and laminated magnets in the beam lines, including the newly conceived Gantry 2, will enable rapid energy changes of the proton beam to modulate the range of the scanning pencil beam in three dimensions over the tumor volume. The last multifunctional 90deg bending magnet of the Gantry 2 transport system is not only the largest of the three gantry bending magnets, but also the most challenging element because of its dynamical eddy current effects during ramping and the reduction of these effects with a special arrangement of laminated parts in the pole of the magnet. The design of the three Gantry 2 bending magnets and measurements of the magnet field and the dynamic behavior of the two 58deg bending magnets are presented.