Cited by 300Open Access
European Organization for Nuclear Research
Publishes on Particle Accelerators and Free-Electron Lasers, Superconducting Materials and Applications, Particle accelerators and beam dynamics. 8 papers and 417 citations.
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Beam instabilities cover a wide range of effects in particle accelerators and they have been the subjects of intense research for several decades. As the machines performance was pushed new mechanisms were revealed and nowadays the challenge consists in studying the interplays between all these intricate phenomena, as it is very often not possible to treat the different effects separately. The aim of this paper is to review the main mechanisms, discussing in particular the recent developments of beam instability theories and simulations.
Bunch-to-bucket transfer between the CERN Proton Synchrotron and Super Proton Synchrotron for Large Hadron Collider--type beams is done via rotation of bunches in longitudinal phase space. For these rotated bunches, the dependence of beam transmission on bunch length had remained unexplained for a long time. Simulation-based optimization of the transfer was necessary to find the optimal rf settings for the rotation and to explain both earlier and new observations. Amongst others, we discuss why measured bunch profiles are insufficient to determine the best working point for operation. Crucially for future operation at higher intensities, we also show that the currently operational transmission can be maintained at a similar bunch length with a 40% larger longitudinal emittance, by using additional voltage from a spare cavity and optimal rotation timings.
Microwave instability in the Super Proton Synchrotron (SPS) at CERN is one of the main limitations to reach the requirements for the High Luminosity-LHC project (increased beam intensity by a factor 2). To identify the impedance source responsible of the instability, beam measurements were carried out to probe the SPS impedance. The method presented in this paper relies on measurements of the unstable spectra of single bunches, injected in the SPS with the rf voltage switched off. The modulation of the bunch profile gives information about the main impedance sources driving microwave instability, and is compared to particle simulations using the SPS impedance model to identify the most important contributions. This allowed us to identify the vacuum flanges as the main impedance source for microwave instability in the SPS, and to evaluate possible missing impedance sources.