  PAL-XFEL, a 4th generation light source, is currently being installed and
will be completed by December of 2015 so that users can be supported beginning
in 2016. PAL-XFEL equipment should continuously maintain the bunch-to-bunch
beam parameter (60Hz, Energy 10GeV, Charge 200pC, Bunch Length 60fs, Emittance
X/Y 0.481mm/0.256mm rad) in order to supply the energy, flux and timing of
stable photons in tests by beam line users. To this end, PAL-XFEL equipment has
to be kept precisely aligned (Linear Accelerator +/- 100um, Undulator +/-
50um). As a part of the process for installing PAL-XFEL, a GPS-used surface
geodetic network is being constructed for precise equipment measurement and
alignment, and the installation of a tunnel measurement network inside
buildings is in preparation; additionally, the fiducialization of major
equipment is underway. After PAL-XFEL equipment is optimized and aligned, if
the ground and buildings go through vertical changes during operation,
misalignment (and tilt) of equipment including various magnets and RF
structures will cause errors in the electron beam trajectory, which will lead
to changes to the beam parameter. For continuous and systemic measurement of
vertical changes in buildings and to monitor ground sinking and uplifting, the
Budker Institute of Nuclear Physics (BINP) Ultrasonic-type Hydrostatic
Levelling System (HLS) is to be installed and operated in all sections of
PAL-XFEL for linear accelerator, insertion device (Undulator) and beam line.
This study will introduce the operation principle, design concept and
advantages (self-calibration) of HLS, and will outline its installation plan
and operation plan.
