Experimental investigation on coupled-bunch instability and suppression for the upgrade of Beijing Electron-Positron Collider (BEPCII).

After touching the design collision luminosity of 1.0 × 1033 cm-2 s-1 in 2016, this target has not been reached again for the upgrade of Beijing Electron-Positron Collider during physical collision operation in subsequent years due to various factors, such as the collision background, noise, and equipment stability under high power operation. One of the most serious factors was the beam instability, especially the coupled-bunch instability, whose sideband distribution was clearly displayed on the spectrum analyzer when the feedback system was OFF.