The RF System for the los Alamos Free Electron Laser (FEL)

The FEL electron linac consists of three buncher cavities: two accelerator cavities and a def lection cavity, each with its own phase-coherent rf source. All sources will be pulsed for 100 ¿s at a 1-pps rate. The phase and amplitude stability requirements are ±1/2°, and ±1/2%. There are two subharmonic bunchers, each requiring 5 kW at 108.33 MHz. All remaining cavities operate at 1300 MHz. The fundamental buncher requires 5 kW, whereas each of the accelerating cavities requires at least 3 MW. The deflection cavity requires up to 100 kW, which is coupled from one of the accelerator cavity rf sources. Prominent features of the rf system are the phase and amplitude control circuits and the multimegawatt klystron amplifiers. Three L3707 klystrons were obtained from the AMRAD radar site at White Sands, which was decommissioned in the early 1970s. The tubes originally were designed to produce 10-MW, 10-¿s pulses. Each tube has delivered over 3.6-MW, 100-¿s is pulses in the FEL system.