Advanced damper system with a flexible and fine-tunable filter for longitudinal coupled-bunch instabilities caused by the accelerating mode in SuperKEKB

摘要

SuperKEKB is an electron-positron circular collider aiming to achieve unprecedented luminosity by using a large beam current and a new collision method. The longitudinal coupled-bunch instabilities caused by the accelerating mode of cavities will be a serious impediment in reaching the design current; estimates suggest that the so-called μ = -1, -2, and -3 modes of the instabilities will be excited. We developed a new damper system for suppressing these modes using recent digital technologies. In our system, the feedback parameters for each mode, for example, the phase, the loop gain, and the frequency offset, can be easily fine-tuned independently. We verified the performance of the new damper during Phase-2 commissioning of SuperKEKB. In the demonstration, instabilities ( μ - -1 and -2 modes) were excited by intentionally detuning a superconducting cavity, and the feedback control with the new damper was applied to the low-level RF control system. The new damper successfully suppressed the longitudinal coupled-bunch instabilities in SuperKEKB. Consequently, it is expected that this damper will make a substantial contribution to achieving the design luminosity by suppressing the coupled-bunch instabilities due to the accelerating cavities.