Synchronized Beam Position Measurement for SuperKEKB Injector Linac

Toward SuperKEKB project, the injector linac upgrade is ongoing for aiming at the stable beam operation with low emittance and high intensity bunch charge. One of the key challenges is a low emittance preservation of electron beam because the vertical emittance of 20 mm.mrad or less should be transported to the main ring without a damping ring. For this purpose, the fine alignment of accelerator components is a crucial issue since the linac alignment was badly damaged by the big earthquake in 2011. From the simulation results of emittance growth, the alignment of the quadrupole magnets and accelerating structures should be conducted at the level of 300 um in rms along the 600-m-long linac. In addition, we are aiming at the level of 100 um alignment in rms within the short range distance of 100 m long. Even after the fine component alignment can be achieved, the fine beam orbit manipulation is necessary for low emittance preservation. For these reasons, we have developed the new BPM readout system based on VME64x. The new system has improved the precision of beam position measurement up to 3 um from 25 um. We will describe the software development of the new BPM readout system.