Knock Out Slow Extraction Using Betatron Sidebands at High Harmonics
Radio frequency knock out resonant slow extraction is a standard method for extracting stored particle beams from synchrotrons by transverse excitation. Excitation signals comprising many betatron sidebands have shown to reduce intensity fluctuations of the extracted beam spill and are used at several facilities. In this contribution, the effect of individual sidebands at different harmonics on the spill quality is systematically studied using efficient noise excitation signals fully covering the respective sidebands. Particle tracking simulations show a clear correlation between the chosen excitation frequency and the spill quality. This relation is attributed to the spectrum of particle motion shortly before their extraction, and an empiric relation between the spectrum, the excitation frequency, and the resulting spill quality is given. Experiments show an additional reduction of pile-up when using higher excitation frequencies. These insights have implications for an optimal design of excitation waveforms and hardware for Knock Out extraction systems.