Conceptual design of superconducting combined-function magnets for the next generation of beam cancer therapy gantry

An increasing number of proton therapy facilities are being planned and built at hospital based centers. Many facilities use rotatable gantry beamlines to direct the proton or ion-beam at the patient from different angles. A key issue is the need to make future gantries lighter and more compact with the use of cryogen-free superconducting magnets, in particular for the final bending section which can be of large aperture. Benefits of using the superconducting technology are: (1) the possibility to have a large momentum acceptance, hence reducing the need to ramp the magnet and enabling new treatment techniques, (2) the size reduction due to a lower bend radius and (3) the weight reduction up to a factor ten. The latter will also significantly reduce the costs of the supporting structure. We present a conceptual design based on Nb ₃ Sn superconducting combined function magnets (dipole, quadrupole, sextupole). The geometry using racetracks, the superconducting strand and cable parameters and the results of the thermal and the mechanical studies are reported. These magnets will work at a temperature of about 4.2 K cooled with cryocoolers.