Latest movable mask system for KEKB

The KEK B-factory (KEKB), an electron–positron collider serving an unprecedented high luminosity, has a movable mask (or collimator) system to reduce the background noise of BELLE detector coming from spent particles. The movable masks have been developed employing RF technologies in dealing with intense higher order modes (HOM) resulted from high beam currents. The mask system is now working as expected at the stored beam current up to 1 A. The design and performance of the latest movable mask system for the KEKB are presented.