A Gated Beam-position Monitor and Its Application to Beam Dynamics Measurements at Kekb

KEKB has transformed to an effective head-on collision by using of crab cavities from a crossing collision and gained a higher specific luminosity. A gated beam-position monitor, being capable of measuring the beam phase as well as the transverse position of a specific bunch in a bunch train, has been developed and is used to measure a beam-beam kick. The monitor estimated the effective horizontal beam size at the interaction point from a linear part of a beam-beam kick and demonstrated the effect of the crab cavities. The estimated horizontal beam size agreed with calculated size considering the dynamic beam-beam effect. Moreover, the monitor detected a displacement of the horizontal beam position along a bunch train under the crabbing collision.