Abstract
The longitudinal acceptance of the BESSY II storage ring has been measured. To our knowledge, such a measurement has never been performed in electron storage rings. The study is also motivated by the fact that for future diffraction limited light sources a couple of longitudinal injection schemes were proposed recently. In these injection schemes, the energy and/or timing of the injection beam is shifted, resulting in a large synchrotron oscillation amplitude of the injected beam. It is, therefore, of importance to reveal whether we can evaluate the longitudinal acceptance precisely when we design a storage ring with a longitudinal injection scheme. The experimental results showed a good agreement to the acceptance evaluated through the accelerator model, including the special feature arising from the synchrotron radiation. We also found that, as a by-product, the bunch length of the injected beam can be obtained from the acceptance measurement data. The result is in good agreement with the design value of the injector booster synchrotron.
Highlights
Modern high-performance accelerators are designed, constructed and brought into operation based on a precise accelerator model
The goal of this study is to reveal whether the longitudinal acceptance of the ring is consistent with a prediction from the accelerator model
The experimental results show a good agreement with the prediction based on the longitudinal beam dynamics with input parameters derived from the accelerator model, including synchrotron radiation effects
Summary
Modern high-performance accelerators are designed, constructed and brought into operation based on a precise accelerator model. The electromagnetic fields of all components are accurately computed at the design phase, measured for most components, and finely tuned based on beam measurements. After all these efforts, the design performance is achieved eventually. This may be true for next-generation light-source storage rings. They are based on multibend achromat lattices to lower the natural beam emittance through strong focusing and low dispersion function. Since the problem is highly nonlinear, the evaluation of the dynamic aperture is normally performed through numerical tracking including the field errors and the misalignments of the accelerator components, i.e., through a complete accelerator model
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