On-axis swap-out injection schemes have become the baseline for several ultralow-emittance storage ring-based synchrotron light sources, such as APS-U, ALS-U, and HEPS. This scheme naturally requires that the injector (usually consisting of an electron gun, a LINAC and a booster synchrotron) has the capability of providing full-charge bunches. However, it is nontrivial to inject a high-charge bunch into the ring, even when using on-axis injection. One of the difficulties is the transverse single-bunch instability that arises in the transient process immediately after injection due to injection imperfections. To mitigate the aforementioned injection-induced transient instability under the condition of reasonable injection imperfections, we propose to implement the RF modulation technique in the booster before bunch extraction. The blowup of longitudinal emittance of the bunch before extraction from the booster is expected under carefully adjusted modulation settings. Simulations demonstrate the effectiveness of the proposed technique.

同轴换出注入方案已成为几种基于超低发射率存储环的同步加速器光源的基线，例如APS-U，ALS-U和HEPS。该方案自然需要喷射器（通常由电子枪，LINAC和助力同步加速器组成）具有提供满电荷束的能力。但是，即使使用同轴注入，也要向环中注入高电荷束。困难之一是注射后由于注射缺陷而在瞬态过程中立即产生的横向单束不稳定性。为了在合理的注入缺陷下缓解上述注入引起的瞬态不稳定性，我们建议在束提取之前在增强器中实施RF调制技术。在经过精心调整的调制设置下，预计从增强器中抽出之前束的纵向发射率会爆炸。仿真证明了所提出技术的有效性。