The PLS RF system upgrade activities

The PLS RF system at the initial phase consisted of three stations, in which each station has a 60-kW CW klystron amplifier as a power source, a circulator and a single-cell cavity, all connected by 6 1/8'' coaxial transmission lines. The total RF capacity could afford to store the beam current up to 300 mA with 1.2 MV of the accelerating voltage at 2 GeV. In mid-1996, one more station was added to provide enough RF power to store up to 400 mA with 1.6 MV of the accelerating voltage at 2 GeV and 200 mA at 2.5 GeV. A new control electronics were also added for enhanced performance of the phase feedback and the automatic gain control. A transient data acquisition system was installed for better analysis of the unknown beam loss. Efforts to identify the higher order modes causing the collective instabilities were made and a strategy to reduce their effects were established. The cooling water control system for the RF cavities were massively upgraded during the summer maintenance period of 1997 to shift the harmful HOMs and to regulate the operation temperatures of cavities at stable condition. A disk-type input coupler with better HOM-absorbing capability has also developed and tested. (author)