A superconducting magnet for a beam delivery system for carbon ion cancer therapy

The therapy of cancer (hadrontherapy) with accelerated particle beams is an out coming method that allows an accurate and effective treatment of several kinds of tumors minimizing the irradiation of the surrounding tissues and avoiding intercepting vital organs. The deep tumors are usually treated with proton or ion beams by using a rotating gantry that allows the 360° irradiation around the patient. For carbon ion hadrontherapy being the energy in the order of 400 MeV, huge gantries structure are required if resistive magnets are used. The size of a ion gantry can be of the order of 10 m in diameter and 100 tons in weight. An alternative solution has been studied, involving the use of a cryogenic free superconducting magnet. The magnet consists of ten 90° bent superconducting dipoles wound with an aluminum stabilized Cu/NbTi conductor and mechanically supported by an aluminum alloy structure. An optimization of the magnetic design is running by using genetic algorithms with the goal to obtain a field homogeneity within 0.2% in a region of 60×200 mm² along the beam path. Furthermore, an accurate study of the winding technique is in progress. The magnet will be kept at 4.5 K by a cooling system based on two cryocoolers operating alternately in steady state or together during the cool down and the electrical transients. The current is supplied via a couple of HTCS current leads always connected. In the paper, a description of the design is given.