Klystron-modulator system performances for PLS 2-GeV linac

The PLS 2-GeV linac employs 11 units of high-power pulsed klystrons (80-MW) as the main RF sources. The matching modulators of 200-MW (400-kV, 500-A) can provide a flat-top pulse width of 4.4 μs with a maximum pulse repetition rate of 120-Hz at the full power level. For a good stability of electron beams, the pulse-to-pulse flat-top voltage variation of a modulator requires less than 0.5%. In order to achieve this goal, we stabilized high-voltage charging power supplies within 1% by a phase controlled SCR voltage regulator. In addition, we employed ac/dc feedback together with a resistive De-Q´ing system to achieve far less than 0.5% variation of the PFN charging voltage. This paper presents the main features of the klystron-modulator system and the characteristics of the pulsed high-power RF system performance during the beam injection operation for the Pohang Light Source commissioning