ORBIT STABILITY OF PLS STORAGE RING*

In order to improve the orbit stability of the PLS (Pohang Light Source), various efforts have been exercised. We are improving the temperature stability of machine-tunnel air and cooling waters better than +/- 0.1 oC. Temperatures and mechanical displacements of magnets, girders, and vacuum chambers have been monitored using precision instruments. It was found that, when the machine is started up or shut down, mechanical displacements of 100 µm are not uncommon. And at least 12 hours are required for the thermal stabilization of mechanical components in the tunnel. It was found that transients during beam injections that accompany de-ramping and ramping of the beam energy were closely related to orbit drifts. We measured vibration (~20 µm peak-to-peak) of electron beam position that was found to be caused by ripples of magnet power supplies. In this article, we also report recent results of the investigation of BPM instabilities.