Speaker
Description
Development status of the latest domestically produced 80 MW S-band klystron for Pohang Accelerator Laboratory (PAL) is reported, with emphasis on the VK4 tube now under field qualification at the PAL-XFEL. Earlier prototypes reached the target RF power at low repetition rate but were limited to 30 Hz by frequent gun arcing. Breakdown studies identified clump-assisted discharge in the diode region and electron multiplication from the ceramic triple point as the dominant mechanisms. Based on these findings, improved electrode polishing and cleaning and a triple-point electrostatic shield were implemented in VK4 and VK5. In laboratory processing, VK4 demonstrated stable operation at 80 MW, 4 us, and 60 Hz, while VK5 showed a further reduction of total HV arc rate by about 59%, confirming the benefit of improved gun preparation. To verify accelerator readiness, site testing of VK4 is being carried out with stepwise HV and RF qualification up to 400 kV, 80 MW, 4 us, and 60 Hz. Initial field-test results and implications for routine accelerator operation will be presented.
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