Chromaticity effects and analysis on damping time in the Beijing electron-positron collider Ⅱ storage ring

To conduct a quantitative analysis of impact of beam chromaticity on total damping time of Beijing electron-positron collider Ⅱ (BEPC Ⅱ) , measurements of corrected chromaticity were taken in lattices with different chromaticities of BEPC Ⅱ at low beam current． Additionally, the damping times of positron and electron rings were measured as a function of beam current in different lattices． The effect of transverse feedback system on damping times of both electron-positron rings was measured． The head-tail damping time was found to be reduced from 46.4 ms to 16.2 ms and 43.8 ms to 12.7 ms, leading to a reduction of total damping time from 11.5 ms to 7.4 ms (reduced about 35.7%) and 12.9 ms to 7.6 ms (reduced about 41.1%), when chromaticity increased from 0.1 to 1.5 and 0.9 to 2.7 in the electron-positron rings, respectively． These experimental data provide a reference for machine optimization in collision mode operations．