With the high current physical operations of the upgraded Beijing Electron–Positron Collider (BEPCII), thresholds on collision luminosity and beam current have been presented due to various factors such as collision background, noise, equipment stability under high power operation, and so on. One of the most serious influences on beam dynamics was beam instability which has been clearly exhibited. The comprehensive experimental investigation of beam instabilities in BEPCII is an indispensable part of beam physics research and can provide references for the upgrade project of BEPCII. Over the past two years, the experimental investigation of beam instabilities in BEPCII has been carried on with the single and multiple bunch filling in the storage ring. With the optimization of the bunch-bunch feedback system, the designed collision luminosity , 1.0x10^33cm^-2s^-1 was achieved during the physical operation and the primary process on configuration of Feedback system will be introduced. For comprehensive understanding the feedback system, a physical model is developed and analysis is conducted to demonstrate the relationship between feedback capability and various parameters. This comprehensive physical model and analysis of the practical feedback system may provide valuable insights into the optimization of the feedback system.

NanoTerasu is a 3 GeV light source newly constructed in Sendai, Japan. The circumference is 349 m and the natural emittance is 1.1 nm rad, which is realized by a double-double-bend achromat lattice. The commissioning of the storage ring started in June 2023. The longitudinal instability was observed when the stored beam current reached 150 mA in August 2023. The temperature of RF cavity was adjusted to suppress the instability. The user operation was started on schedule in April 2024 with a stored beam current of 160 mA. The stored beam current was reached 200 mA without the beam instability in July 2024. The stored beam current at user operation period was limited to 200 mA by the longitudinal instability. We try to suppress the longitudinal beam instability using several methods. We developed the pillbox type RF kicker cavity to suppress the instability. In addition, we tried to suppress the longitudinal instability using the transverse feedback kicker. I will report the status of longitudinal instability suppression at NanoTerasu.