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 0.15mm(rms) in 1994. Since then the storage ring tunnel has moved by 1. 0" and 3.0" 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" from the designed beaim path. The relation between boundary conditions of the smoothing analysis and estimated maximum offset is also studied.

We have studied the methods for the determination of reference closed orbit of the storage ring in PLS using magnet misalignment data. The reference closed orbit was determined by (1) a smoothing analysis using a lowpass filter method, and (2) a MAD (methodical accelerator design) simulation using the real parameters such as magnet misalignment data. Based on the estimated reference closed orbit, the relative positional errors of the storage ring magnets were evaluated. The results of case studies on the comparison of the smoothing analysis and the MAD simulation are described in this presentation.