Feed forward RF control system of the Accelerator Test Facility

The authors report a scheme to control the amplitude and phase of the RF accelerating field in a klystron-driven electron linac (linear accelerator). The amplitude and phase distribution within the RF pulse can be controlled to follow specified functions to reduce the energy spread of the electron beam being accelerated. The scheme employs fast beam energy and phase detectors and a voltage-controlled electronic attenuator and phase shifter in the amplifier chain. The control voltages of these devices are generated by arbitrary function generators. The function generators´ outputs are calculated numerically using an algorithm which takes into consideration the desired target function and the deviation from the target function. Results of preliminary tests on producing flat RF power and phase pulses from a high-power klystron indicate that amplitude variation of +or-0.2% and phase variation of +or-1 degrees can be readily achieved.<>