RF Control System for the DESY VUV-FEL Linac

In the RF system for the Vacuum Ultraviolet Free Electron Laser (VUV-FEL) Linac each klystron supplies RF power to up to 32 cavities. The superconducting cavities are oper ated in pulsed mode and high accelerating gradients close to the performance limit. The RF control of the cavity fields to the level of 10^-4for amplitude and 0.1 degree for phase however presents a significant technical chal lenge due to the narrow bandwidth of the cavities which re sults in high sensitivity to perturbations of the resonance frequency by mechanical vibrations (microphonics) and Lorentz force detuning. A digital RF control system has been developed for the VUV-FEL which will demonstrate the required control performance. Presently the Linac is being commissioned, and this effort provides the first full integrated test in the accelerator, including cryogenics, RF, beam transport, and beam diagnostics. The RF control sys tem design and objectives are discussed.