Design and low-power measurement of the broadband kicker cavity used to compensate the transient beam-loading effect in synchrotron light sources

The issue of concern in ultralow-emittance synchrotron light sources is the growth of emittance and the shortening of the Touschek lifetime as a result of intrabeam scattering (IBS). One of the most reliable methods for mitigating these IBS effects is to lengthen the bunches using fundamental and harmonic cavities. In such double rf systems, the effect of bunch lengthening is limited by the fluctuation of the fundamental and harmonic rf voltages. In particular, the voltage fluctuations caused by gaps in the bunch filling pattern critically influence the bunch lengthening. To mitigate such a transient beam-loading (TBL) effect, a compensation method using a broadband cavity has been proposed. In this paper, we present a conceptual design of a broadband “kicker” cavity that can be used to compensate for the TBL effect. We then report the manufacture of a low-power model cavity and the results of our evaluation of its performance to confirm the design of the kicker cavity. The measured external- Q value of the cavity was sufficiently low to achieve the requisite broad bandwidth and was in agreement with simulation results. We also confirmed that the rf absorbers sufficiently damp the harmful higher-order modes.