The first module of the 3 GHz Side Coupled Drift Tube Linac (SCDTL): numerical studies of RF properties and cold tests results

The 3 GHz linac section designed for the low energy (7 – 65 MeV) part of TOP (Therapy Oncological Protons) linac consists of eight modules of the structure SCDTL (Side Coupled Drift Tube Linac). The first module is designed to accelerate 7 MeV protons up to 13.4 MeV, and a prototype has been built. The non axysimmetric cavities required a full 3D modelling. Electromagnetic calculations carried out by using MAFIA code gave the the full mode spectrum. An accurate analysis of the RF properties of the structure based on an analytical model and numerical calculations was done in order to investigate in detail the first module performances and to get hints for the final design of next modules. This paper reports the results of this study and of some RF measurements on the first module.