Measured dynamic performance of 1.25-MW, 805-MHz klystrons

Klystrons have been developed to drive resonant linear-accelerator cavities at duty factors from 6 to 12%. A fast-acting control system is required to modulate the r-f drive power to the klystron such that the electric field established in the accelerator load is held constant during the pulse to ± 1% in spite of the 30-40% changes in power demand. The klystron must therefore run unsaturated and have a reasonably well-behaved gain curve, but must also operate near saturation under peak demand for good efficiency. Further, because the accelerator load impedance varies drastically during the pulse, the klystron must demonstrate controllable characteristics over a wide range of load impedances.