Optics Measurement at the Interaction Point Using Nearby Position Monitors in Kekb

Optics parameters at the interaction point, beta, x-y coupling, dispersion and their chromatic aberrations, seriously affect the beam-beam performance as is shown in experiments and simulations. The control of the optics parameters is essential to maintain the high luminosity in KEKB. They drift day by day, or before and after the beam abort. They were often monitored at intervals of the operation with taking the study time. They are recently measured during the physics run using a pilot bunch without collision. We show the measured the optics parameters and their variations and discuss the relation to the luminosity. INTRODUCTION Figure 1 show the layout of the interaction region of KEKB. Two position monitors with 8 button electrode, which is called OCTPOS, are installed inside of the final superconducting quadrupole magnets. Figure 1: Layout of the interaction region in KEKB. Courtesy of K. Kanazawa. Top and bottom are right and left side of the interaction point. The distances from the interaction point are 552mm and 773 mm for left and right OCTPOS monitors, respectively. Only solenoid magnetic field exists in the space between the two monitors. Both of electron and positron beams pass through the two monitors. The positions of the two beams are measured with the monitors separately; sharing the time. Though the monitor has capability to measure the two beam position simultaneously with the eight electrodes, we did not use to avoid complex of separation of the two beam position. The beam is kicked in the horizontal plane and its transverse position is measured turn by turn. Horizontal mode is excited by the kicker basically and a small amount of vertical mode is excited depending on the x-y coupling at the kicker. The phase space coordinates at the interaction point (x=(x,px,y,py))is expressed by those at the two monitors (xL,xR) using the transfer matrix, x = ML(R )xL(R ) (1) The positions x,y at the monitors are expressed by xL(R ) = ML(R ),1 j x j yL(R ) = ML(R ),3 j x j (2) where L,R is suffix for the monitors, and j=1,4 is the suffix for the phase space coordinates. The phase space coordinates are determined by the x = Txm T = ML ,1 j ML ,3 j MR ,1 j MR ,3 j 1