Experimental Research on HLS-II Performance by Means of the RF Phase Modulation Technique

In this article, radio frequency (RF) phase modulation (PM) technology is introduced to effectively improve the beam lifetime and study the longitudinal beam dynamics at Hefei Light Source-II (HLS-II) storage ring. In the experiment, an optical streak camera is employed for real-time observation of the longitudinal distribution and the bunch lengthening under the single-bunch operation mode. Simultaneously, the mechanism of island formation and annihilation caused by PM is deeply investigated based on theoretical analysis and preliminary online experimental measurements. The measured results are in good agreement with the theoretical simulation results. The applicable bunch lengthening factor and the optimal beam lifetime improvement factor are obtained as 2.01 and 1.87, respectively, over the range 20.2-20.7 kHz, which is in the vicinity of the synchrotron frequency. In addition, we further analyze and discuss the corresponding relationship between the modulation frequency and other characteristic parameters of HLS-II, such as the beam size, emittance, and energy spread, under PM.