Phase difference monitor between SuperKEKB injector LINAC and rings using direct sampling technique

In the SuperKEKB Phase2 operation, the beam injection phase from the injector LINAC to rings drifts several degrees or more per day. The monitoring and compensation system of the phase drift between the LINAC master oscillator (MO) and the ring MO is important for stable beam injection. The frequency of LINAC MO and the ring MO is 571.2 MHz and 508.9 MHz, respectively. Both MO signals are monitored by the direct sampling technique using the same sampling frequency (clock). There are several combinations of the clock generation. In this paper, the possible three combinations will be compared including the clock jitter performance and the short-term phase stability and the combination 1 is selected for the phase difference monitor system. The 1ms short-term phase stability is 0.04 deg. (RMS) without digital filter and 0.005 deg. (RMS) with 10 kHz bandwidth digital filter for both MO signals in the laboratory. Finally, the long-term phase drift between LINAC MO and ring MO is monitored at the injector LINAC. (author)