STATUS OF LONGITUDINAL FEEDBACK SYSTEM FOR THE PLS STORAGE RING

The Pohang Light Source (PLS) storage ring was origi-nally designed to store the beam current up to 400 mA at 2.0 GeV. But owing to the interactions between the HOMs of RF cavities and bunched beams which make the coupled bunch mode instabilities (CBMIs) such as dipole, quadrupole, and sextupole modes, the beam current can be stored up to 200 mA. Thus, a longitudinal feedback system (LFS) using parallel digital signal processors has been in-stalled to cure those CBMIs at the PLS storage ring. This programmable LFS is useful for various beam diagnostic-s as well as for the cure of the CBMIs. At present, via this LFS, we have obtained the various useful bunch-by-bunch diagnostic information such as growth rates of the instabilities, beam pseudo spectra, HOM frequencies of R-F cavities which generate the CBMIs, the threshold beam currents, and the dependence on RF cavities temperatures.