Speaker: Nasrin Nasresfahani (BE-RF-BR)
Travelling Wave Structures; Focus on an Approach for HOM Damping in 44-Cell Travelling Wave Cavities of SPS
Travelling wave structures have a history of over a hundred years of active research in RF. Following the steps resulted in the development of the travelling wave structures of SPS (Super Proton Synchrotron) in the seventies, allows us to cover major parts of the advances in understanding and optimizing these structures. The first part of this talk is therefore devoted to a brief overview of these efforts.
One of the aspects of long travelling wave structures, like the ones used in SPS, is that they support a wide variety of higher order modes (HOMs) that can cause beam instabilities. In recent years, SPS was subject of extensive beam dynamic simulations. These studies conducted in the framework of LIU (LHC Injectors Upgrade) project revealed an important intensity limitation due to HOMs of the 200 MHz accelerating cavities of SPS in the frequency range of 629-630 MHz. In the second part of the talk, an approach for damping the higher order modes of cavities with large number of cells will be presented. This approach which reduces the complexity of designing distributed damping schemes has been implemented for designing a damping scheme for 44-cell cavities of SPS. Measurement and simulation results for evaluation of this damping scheme will be presented. Part of the presentation will also focus on peculiarities of beam coupling impedance calculations for long multi cell cavities.