Design development of the SCDTL structure for the TOP linac

The Side Coupled Drift Tube Linac (SCDTL) is an attractive 3 GHz accelerati ng structure composed of short DTL tanks coupled together by side coupling cavities, in the course of development of the 200 MeV proton linear acceler ator for proton therapy planned for the Terapia Oncologica con Protoni (TOP ) program of the Italian National Institute of Health (Istituto Superiore d i Sanita, ISS). The TOP Linac will be used to boost to 70 MeV the 7 MeV pro ton beam from a linac injector. Our main concern is to investigate in detai l the characteristics of the structure in terms of RF properties of the acc elerating mode, like longitudinal and transverse shunt impedance and qualit y factor, and of the other modes that cause the origin of the tank dispersi on curve, in order to stabilize the behaviour under operating conditions. C alculations performed with the computer three-dimensional (3D) codes MAFIA and SOPRANO on the smallest unit of the system (a single DTL tank without c oupling cavities) and experimental measurements made on a prototype have sh own good agreement. Two possible supporting stem configurations (single ste m and two stems 180 degrees apart for each drift tube) were examined and a comparison of the results in both cases are discussed. (C) 1999 Elsevier Sc ience B.V. All rights reserved.