高精度レーザーアライメントのための500 m長レーザー長基線の高安定化

抄録

The development of alignment techniques is particularly essential for long linacs to stabilize the acceleration and transportation of particle beams with higher charge intensities, to preserve the beam quality and to increase the injection efficiency of the beams into storage rings. Alignment measurements with a resolution of ±0.1 mm cannot be easily performed for long linacs（> 100 m）while conventional optical alignment systems with a high-precision telescope and a laser tracker, etc. are widely used for relatively short linacs（< 100 m). The laser-based alignment technique is an alternative method to accurately locate accelerating devices of the long linac on a straight line, where the laser beam can be used as a long fiducial straight line. Such laser-based alignment technique was implemented at the construction stage of the KEK injector linac in 1982; however, the high stabilization of the long laser-based fiducial line has not been realized even until now. A laser beam with higher stabilization has been implemented as a 500-m-long fiducial straight line for alignment measurements by the injector linac group in March 2013. We experimentally investigated the propagation and stability characteristics of the laser beam passing through laser pipes in vacuum. Pointing stability at the last fiducial point with the transverse displacements of ±40 μm level in one standard deviation by applying a feedback control was successfully obtained. This pointing stability corresponds to an angle of ±0.08μrad. This system is now fully exhibiting the successful results for the high-precision alignment of the injector linac currently in progress.