Precision surveying and smoothing analysis for Pohang Light Source

The Pohang Light Source (PLS), a 2 GeV synchrotron radiation source, started its operation from August 1994. The magnets of the storage ring were aligned to a designed beam path with a relative positional error of 0.15 mm(rms) in 1994. Since then the storage ring tunnel has moved by 1.0 mm and 3.0 mm per year (average) in the horizontal and the vertical directions, respectively. The deformation by the ground motion gives rise to the maximum offsets from the designed beam path. We introduce a smoothing analysis using a low-pass filter method in order to estimate the relative positional errors close to the actual beam path. Based on the measurement of the machine deformations and daily machine operational status, we come up with an idea of the allowable maximum offset of 2.0 mm from the designed beam path. The relation between boundary conditions of the smoothing analysis and estimated maximum offset is also studied.