The realignment of the beamline for J-PARC 3GeV RCS

J-PARC 3-GeV RCS suffered from the misalignments of several millimeters of the magnets in both horizontal and vertical directions caused by the Tohoku Region Pacific Coast Earthquake on 11th March, 2011. As the result of the orbit calculation showed that the beam loss was acceptable for beam operation at 300 kW, beam operation with the current placement was implemented until May, 2013. However according to the beam loss simulation, the beam loss increased and the horizontal emittance expanded at 1 MW operation. The collimator aperture of RCS was designed at 324 π mm mrad. The ring acceptance of RCS is 486 π mm mrad. The ring acceptance can secure good collimation efficiency of 97% by taking the aperture ratio which is 1.5 times of collimator aperture. The realignment of the RCS beamline must secure ring acceptance in order to perform the 1 MW operation. In this paper, the alignment results of the magnets and the ceramic chambers that constitute the beamline of 3-GeV RCS are reported. (author)