Status of beamline alignment in J-PARC linac

Morishita, Takatoshi  ; Ito, Takashi  ; Oguri, Hidetomo  

J-PARC linac has finalized its precise alignment in 2006 and started a beam operation. Since the alignment error should be a cause of beam loss, a precise survey has been performed periodically to ensure the alignment accuracy. In the SDTL section, slight displacements occurred in the position restoration of the seismic isolation structure of the tank support. Along with continuing the smoothing alignment annually, we are taking measures to reduce the external force on the cavity. A local floor elevation continues at the upstream part of the straight section. The realignment of this section has been performed to restore the beam-line linearity every several years. In the downstream part of the linac, step-like floor displacements at the expansion joints and local settlements were observed for a few years from 2011, however, there have been stabilized in recent years. In this paper, we will report on the results of the precise survey as well as the realignment activities.