Turn-by-turn measurements of transverse impedance in a synchrotron light source

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Transverse beam coupling impedance is a source of beam instabilities that limits the performance of circular accelerators. Several beam based techniques have been used to measure the transverse impedance of an accelerator, usually based on the optics distortion produced by the impedance source itself. Beam position monitor turn-by-turn analysis for impedance characterization has been usually employed in large circumference machines, while synchrotron light sources have mainly used slow orbit based techniques.

In a paper just accepted in the journal Physical Review Accelerators and Beams, oPAC fellow Michele Carlà and co-workers from the ALBA synchrotron in Spain have presented for the first time the results of turn-by-turn impedance measurements at ALBA, advancing the measurement technique into the range of the typically small impedance values of modern light sources.

The authors measured local impedance contributions through the observation of phase advance versus bunch charge using the betatron oscillations excited with a fast dipole kicker. The ALBA beam position monitor system and the precision of the turn-by-turn analysis allowed to characterize the main sources of transverse impedance, in good agreement with the model values, including the impedance of an in-vacuum undulator.

ALBA synchrotron

Michele Carlà, Gabriele Benedetti, Thomas Günzel, Ubaldo Iriso, and Zeus Martí, “Local transverse coupling impedance measurements in a synchrotron light source from turn-by-turn acquisitions”, Phys. Rev. ST Accel. Beams (accepted 24 October 2016)