Improvement of the laser-based alignment system for the J-PARC proton linac

Large improvements in the accuracy of the laser-based alignment system for the J-PARC proton linear accelerator were achieved as a result of both many efforts for decreasing all kinds of noises in the measured laser-target signals and adopting a new signal-processing method for the measured signals. The fundamental measurements for improving the ability of the laser-based alignment system were performed with a 50-m long laser test bench, located in the sub-tunnel of the test facility of the 50-MeV proton linac at KEK. The obtained standard deviation of the accuracy of the position measurement with an average time of 40 sec was about 2.6 μm. A proportionality between the deflection angle of the injected laser beam and the position shift of the laser beam at a distance of 50 m was satisfactorily confirmed. The mounting stage shows an excellent performance of controlling the direction of the laser beam: a deflection of 0.4 micro radian can be easily controlled by using stepping motors with a sufficiently large signal-to-noise ratio. The obtained experimental results support that the developed laser-based alignment system satisfies the severe requirements for the J-PARC proton-linac alignment system. Also, it is strongly recommended to utilize this alignment system of high performance with a short measurement time for achieving the required high beam-power operation of an order of 1 MW for the J-PARC. (author)