Speaker: Patrick Kramer (BE-RF-BR)

Fundamental and Higher-Order Modes in the SPS Travelling Wave Acceleration System

In the 1970s, the SPS acceleration system was designed with a strong future increase of beam intensity in mind. The relatively small frequency swing of around 150kHz required for the energy ramp in the SPS allows the use of a fixed-tuned, wideband travelling wave acceleration system that has the peculiarity of increased efficiency at higher beam loading. This foresight allows the continued use of these accelerating structures throughout the High-Luminosity LHC era.

The travelling wave structures however also support numerous transverse and longitudinal higher-order modes (HOMs) which can lead to beam instabilities. The problem was so far mitigated by damping these modes with three different types of HOM-couplers. To ensure stable beams for the intensities required in the future, additional damping of the longitudinal HOMs is required. This seminar reviews the principle of particle acceleration with travelling wave structures and shows possible improvements of the longitudinal HOM damping. Finally, the parasitic impact of the various HOM-couplers on the accelerating mode is also discussed and quantified.

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