Verification of new RF feedback for longitudinal coupled-bunch instability in SuperKEKB

In the circular accelerator, coupled bunch instabilities (CBIs) are kinds of the coherent instabilities of collective beam with high current. In order to achieve high luminosity, it is necessary to take measures to suppress them, even for SuperKEKB's RF system designed to have high current resistance, and so we newly developed the instability damper for CBIs. In this paper, we report the result that our new damper worked stably with the actual beam operation, since there is the opportunity to demonstrate the effect of the damper in SuperKEKB Phase-2 commissioning. (author)