SOME RELEVANT ASPECTS IN THE DESIGN AND CONSTRUCTION OF A 30-62 MEV LINAC BOOSTER FOR PROTON THERAPY

Recent results in accelerator physics showed the feasibility of a coupling scheme between a cyclotron and a linac for proton acceleration. Cyclotrons with energies up to 30MeV, mainly devoted to radioisotopes production, are available in a large number of medical centres. This suggested to design a linac booster able to increase the proton energy up to 62MeV as required for treating tumours like the ocular ones. In this paper we will discuss the basic design of a compact 3GHz SCL (Side Coupled Linac). Among the many challenges of such a project one of the most interesting is the tuning of the cavities. Because the tuning can be done only after assembling the system, it is difficult to detect which cavities are responsible for the detuning: indeed the resonant behaviour of single cavity is lost since the resonances merge into the resonant modes of the whole system. It is shown how, from the measured mode frequencies of the system, it is possible to derive the unknown resonances of each cavity and then refine the tuning. The proposed procedure is quite general and is not restricted to the SCL. This procedure is quite attractive because its use may relax the fabrication tolerances and avoids any bead pull procedure. In addition to this one may foresee even an on line computer driven tuning. Examples were given for 13 cavities fed at π/2 mode