Design and test of a curved superconducting dipole magnet for proton therapy

We report on the design and test of a curved superconducting magnet completed as part of a collaborative project between Lawrence Berkeley National Laboratory, the Paul Scherrer Institute, and Varian Medical Systems focused on developing compact, lightweight gantries for proton therapy. An overview of the magnet design is given first, showing two Nb–Ti Canted-Cosine-Theta (CCT) layers producing a dipole field of 2.4 T in a clear bore of 290 mm diameter, with bend radius of 0.9 m, and magnetic bend angle of 50 degrees. The magnet fabrication process is then presented with a focus on the challenges associated with curved CCT mandrel manufacturing, winding, and assembly. Finally, quench training and magnetic field measurements are reported from a first test in liquid helium during which the magnet reached the design field of 2.4 T.