Design of a Fast-cycling High-gradient Rotating Linac for Protontherapy

General interest has been shown over the last years for the development of single room facilities serving a population of about 2 million people for proton cancer therapy. Compact machines are needed to accelerate proton beams of few nA up to 230 MeV. In this framework the project TULIP (TUrning LInac for Protontherapy), patented by TERA Foundation, foresees a linac mounted on a rotating gantry used as a booster for protons previously accelerated by a cyclotron. The linac is composed of modular units powered by independently controlled klystrons. The RF power transmission is made possible by high power rotating joints developed in collaboration with CLIC group. Theonal beam energy can be varied in steps of few MeV from pulse to pulse by amplitude and/or phase modulation of the klystron signals, making possible the implementation of active spot scanning technique with tumor multipainting. The present paper provides the main characteristics of TULIP, describing the different choices for the linac design parameters together with the structural design of the supporting gantry and of theonal beam line.