Observation and Damping of Longitudinal Coupled-bunch Oscillations in the CERN PS
DOI:
https://doi.org/10.23732/CYRCP-2018-001.33Keywords:
Longitudinal instability, coupled-bunch instability, CERN PS.Abstract
Longitudinal coupled-bunch instabilities pose a major limitation to the intensity and quality of LHC-type beams in the CERN Proton Synchrotron (PS). The oscillations are excited above transition energy and mainly driven by the impedance of the main accelerating cavities at around 10 MHz. When approaching the flat-top these cavities are partly short-circuited. However, due to the sweeping revolution frequency, the spectral components of the beam move towards the resonances of the high frequency cavities at 20 MHz, 40 MHz and 80 MHz. Hence different coupled-bunch oscillation mode patterns are observed during acceleration and at the flat-top. A dedicated frequency domain damping system has been installed. While dipole coupled-bunch instabilities are well suppressed, quadrupole oscillations remain, as well as longitudinal blow-up due to the impedance of the high frequency cavities. Recent results obtained with the coupled-bunch feedback are presented together with first studies using alternative mitigation techniques for the instabilities.
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Published
2018-11-07
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Submission to the proc. of the ICFA Mini-Workshop Workshop "Impedances and Beam Instabilities in Particle Accelerators"
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