Limitation of beam current in the PLS storage ring

We present investigations on beam instabilities that have been observed at 2.0 GeV and 2.5 GeV in the PLS storage ring. Stored beam currents of 2.0 GeV in the ring has been mainly limited by coupled-bunch instabilities. We have investigated dependences of the coupled-bunch instabilities on betatron tune, chromaticity and RF cavity temperatures at 2.0 GeV. 450 mA beam could be stored at 2.0 GeV. Bunch filling patterns and betatron tune are investigated to suppress the beam instabilities at 2.5 GeV. At 2.5 GeV, we do not observe any beam instabilities up to 200 mA. Higher beam currents than 200 mA are limited by total RF power.