Stored beam currents of 2.0 GeV at the PLS ring has been limited by coupled-bunch instabilities. It was found that beam currents in 2.0 GeV was mainly limited by 830.45 MHz tranverse mode in RF cavities. Beam instabilities dependences on betatron tune and chromaticity were extensively investigated in the ring. Longitudinal coupled-bunch instabilities due to 758.66 MHz and 1300 MHz modes does not lead to beam loss up to 450 mA. Beam tail distribution and beam lifetime in 2.5 0eV are estimated by a simulation method. The result shows beam lifetime of 27 hours in 170 mA. The estimated lifetime shows a good agreement with that of normal beam operation.
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