Higher order mode power in superconducting cavities of SuperKEKB with high current operation

SuperKEKB is a high-current machine for high-luminosity.Eight higher order mode (HOM) damped single-cell superconducting cavities accelerated an electron beam in the main ring since KEKB. A strong dependence of the absorbed power of the ferrite HOM dampers on the number of bunches was observed in 2022 operation. One of the reasons for this is thought to be a build-up effect of some parts of the HOM caused by narrow bunch spacing. It was found in the last operation that this problem has an individual difference for each cavity. In particular, TM011 can propagate on the LBP side, and the frequency is quite close to an integer multiple of the RF frequency, the build-up effect is remarkable. As the accelerator is expected to reach its design current in the future, the HOM power will also increase and ferrite HOM dampers will have to cope with the increasing HOM power resulting from the build-up. This report provides an overview of the status of the superconducting cavity HOMs last operation in 2023-2024 and a countermeasure plan for the future.