PIMS—A simple and robust accelerating structure for high intensity proton Linacs

A π -mode structure (PIMS) is investigated for an application in a high duty cycle, high intensity proton Linac. Motivated by the objective to employ a simple and robust accelerating structure at a resonance frequency of 352 MHz for the high energy part of Linac4 (100–160 MeV), the normal conducting LEP cavity is restudied and its design is adopted for a medium β ( β ≈ 0.5 ) application. The geometry of the accelerating cell is optimised, the necessary cell-to-cell coupling coefficient is analysed and a novel solution for the shape of the coupling slots is discussed. Simulation results are compared to measurement results obtained from three 3-cell cold models and one 7-cell cold model. The method of tuning the resonance frequency of individual cells is presented and the tuning of end cells is explained in detail. An adjustable wave guide coupler is used to power the cavities, and we present the design process for this device. The behaviour of the PIMS to dynamical changes—as observed during the filling process of the cavity and under beamloading with a chopped beam—as well as the effect of thermal drifts are evaluated.