Magnet Assessment for SC accelerator and gantry

The report presents the magnet assessment of superconducting accelerator and gantry for the European project HITRIplus. The first section reviews the importance and the prospects of heavy-ion therapy, also mentioning the actual status of world-wide activities. A brief discussion is given on the main technological challenges for magnets in heavy ions accelerators and gantries. Beside the strong curvature, among the various aspects discussed in this report, the main issues for gantry magnets is the cooling system. The need for a cryogen-free cooling system is challenging, especially aiming at a dipole field of 4 T. This demand can be mitigated with different approaches, ranging from large-acceptance designs to large-margin superconductors. The demonstrator under investigation has been developed accounting for these possible approaches, but the final solution is referred to the following parameters, because they comply with the requirement of integration with actual gantry design. The main design parameters have been established as common values with two other ongoing programs, IFAST and TERA-NIMMS-SIGRUM. This will allow a fruitful collaboration, with a wider study of magnet design and construction. The basic parameters are: 4 T of dipole field, 0.4 T/s of ramp rate, 1 m of physical length, 80 mm of bore diameter, at least 25 % of loadline margin, and the use of iron yoke and collar. Different designs have been studied and their performances evaluated. For an easier comparison, a straight geometry has been adopted. Most of the proposed designs are based on canted-cosine-theta (CCT) layouts, three solutions with LTS (Nb-Ti, Nb3Sn and MgB2) and one with HTS (ReBCO Tape). A more detailed report is provided for the solution in Nb-Ti, while the subsections about Nb3Sn, MgB2 and HTS mainly highlight the peculiarities of each superconductor. A classical cos-theta design in Nb-Ti is also proposed, for the sake of comparing it to the CCT solution. A set of performance indices to orient the decision of the demonstrator design has been established in terms of costs, power losses and consumption. Additionally, we summarize the mechanical and electrical behaviour of the main support materials, to provide additional information to the further development of the designs. Comparing the CCT and the cos-theta solutions, it can be appreciated that all the main aspects are considerably similar. Cos-theta is negligibly more efficient in the economy of the conductor, but on the other hand it demands for a high current (about 3.5 kA) that increases the current leads power consumption and the cost of the power converter with respect to the CCT in Nb-Ti. Nb3Sn is a very interesting alternative on paper, but the need for heat treatment is a relevant technological concern. Vice versa, MgB2 was investigated for the sake of completeness, but the target of 4 T is probably too high for this technology. Finally, the proposed CCT in ReBCO tape may be regarded as a first elaboration of the magnet for a next generation gantry, but it comes with too many technological challenges for a curved demonstrator. In conclusion, the final remark is to go through for a CCT based on Nb-Ti, suitable to be the basis for the HITRIplus demonstrator magnet.