Development of the radio frequency quadrupole proton linac for ESS-Bilbao

The Radio Frequency Quadrupole (RFQ) linear accelerator for ESS-Bilbao is described. This device will complete ESS-Bilbao injection chain after the ion source and the LEBT. The design was finished in 2015 and machining of the accelerator cavity started in 2016. The RFQ is a 4-vane structure, aimed to accelerate protons from 45 keV to 3:0MeV and operating at 352:2MHz in pulsed mode with a duty cycle up to 10%. Total length is about 3:1m divided in 4 segments. Each segment is itself assembled from four components, named vanes, by using polymeric vacuum gaskets with no brazing among them. Notable aspects of the design are the constant mean aperture R 0 , vane radius ρ and thus ρ/R 0 ratio and also uniform inter vane voltage. Novel procedures for the design of the modulation and integrated beam dynamics and electromagnetic design have been developed for this task. In this paper, the complete design procedure and its results are presented, including beam dynamics, RF cavity design, field flatness and frequency tuning, cooling and thermo-mechanical design.