Duan, Z. Chen, J. Jiao, Y. Peng, Y.M. Wang, Q.Y. Xu, G. Zhang, P. JACoW Geneva, Switzerland 978-3-95450-187-8 10.18429/JACoW-eeFACT2016-TUT2H4 English 85-89 TUT2H4 ion injection cavity kicker operation Contribution to a conference proceedings 2017 2017-07 https://doi.org/10.18429/JACoW-eeFACT2016-TUT2H4 http://jacow.org/eefact2016/papers/tut2h4.pdf Top-up injection has become standard mode of operation for most third generation light sources, and has also been suc- cesfully applied in electron-positron circular colliders like KEKB and PEP-II. For next generation ultra-low emittance storage rings approaching the diffraction limit of X-rays, take the High Energy Photon Source (HEPS) for example, top-up injection is a basic requirement but non-trivial to im- plement. The very small dynamic aperture is insufficient for traditional off-axis injection scheme, instead, a novel on-axis injection scheme was recently proposed for HEPS, based on RF gymnastics of a double-frequency RF system. This paper will describe the physical mechanism of this scheme, related RF issues, and the implications for top-up injection.