Phase drift compensation between injector linac master oscillator and ring master oscillator for stable beam injection at SuperKEKB

The SuperKEKB injector linac that includes the positron damping ring (DR) delivers low emittance electron and positron beams to the main rings. The beam injection phase from linac to the rings should be stabilized for long-term stable beam injection. The frequencies of the linac master oscillator (MO) and ring MO are 571.2 and 508.9 MHz, respectively. These two different frequency signals are monitored using the direct sampling technique with a common sampling rate. A phase drift of several degrees is observed between the linac and ring MOs. For stable beam injection, a phase drift compensation system is implemented at linac. The system performance was evaluated by the beam energy stability after the bunch compression system from DR to linac.