Study of hyperfrequency power couplers for superconducting accelerators/Study of RF power couplers for high power proton linear accelerators

Nowadays, the number of projects aiming at building high intensity proton linear accelerators is increasing thanks to a large field of applications: particles and nuclear physics, spallation sources and some applications in material sciences, biology and nuclear waste reprocessing. All these linear accelerator projects are based on superconducting technology that allows high accelerating gradients in continuous mode. The RF power coupler is one of the main components of the accelerator. It is designed to transmit the radio frequency power from the waveguide at room temperature to the cavity at 4 Kelvin with high reliability. In this thesis, a study of a 704.4 MHz power coupler was carried out. The RF, thermal and mechanical behaviors of the coupler were simulated for 50 kW full reflection continuous wave. This power coupler could be used as RF injector for MYRRHA elliptical cavities. The fabrication process has been established and two prototypes were build. A study of a 352 MHz power coupler was also carried out to fulfill ESS Spoke cavities needs. The obtained design satisfies the specifications and lowers the maximum electric field in the power coupler window compared to existing design. Then a new fabrication process was developed using prestressed ceramic. Brazing operations have halved with this new process. It was shown that the prestressed could enhance the strengths ceramic. The last study in this thesis consisted in validating an extension to progressive waves of 3D simulation software of Multipacting, Musicc3D. The results obtained were favorably compared to the measurements for SPIRAL2 and XFEL power couplers. (author)