Beam position monitor system for KEKB

The Beam Position Monitor (BPM) System for KEKB has been in use to measure closed orbit distortion since the start of commissioning in December 1998. The High Energy Ring (HER) and the Low Energy Ring (LER) for KEKB are each equipped with about 450 BPMs. Most BPMs (∼97%) were aligned in relation to their nearest Quadrupole magnet (Qmag) within 50 μm. The BPM system has been regularly operated to measure beam positions with a resolution of a few microns and as a sampling period of about four seconds. Oscillations of the beam orbits have also been measured by using other function of this system. We have also commissioned the eight-electrode BPM system (OCTPOS) for simultaneous measurement of both electron and positron beam positions from their composite signal near the interaction point. This report describes the performance of the system as a result of operation. (author)