BEAM MEASUREMENTS OF THE SPS LONGITUDINAL IMPEDANCE

A. Lasheen et al.

Abstract


Longitudinal instabilities are one of the main limitations in the CERN SPS to reach the beam parameters required for the High Luminosity LHC project. In preparation to the SPS upgrade, possible remedies are studied by performing macroparticle simulations using the machine impedance model obtained from electromagnetic simulations and measurements. To benchmark the impedance model, the results of simulations are compared with various beam measurements. In this study, the reactive part of the impedance was probed by measuring the quadrupole frequency shift with intensity, obtained from bunch length oscillations at mismatched injection into the SPS. This method was applied over many last years to follow up the evolution of the SPS impedance, injecting bunches with the same bunch length. A novel approach, giving significantly more information, consists in varying the injected bunch length. The comparison of these measurements with macroparticle simulations allowed to test the existing model and identify some missing SPS impedance and to obtain its possible dependence on frequency.

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DOI: http://dx.doi.org/10.23727/CERN-Proceedings-2017-002.73

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