Modelling and identification of a free electron laser RF system

The operation of a Free Electron Laser in the X-ray wavelength range is the goal of the international XFEL project. The project critically depends on the linear accelerator component, where radio frequency fields have to be controlled with a very high amplitude and phase precision and under various sources of disturbances. This paper is about finding appropriate dynamical models for this RF system which will be essential for controller design. A physically motivated white box model is compared with a grey box and a black box model that are identified using measurements of an existing Ultraviolet Free Electron Laser VUV-FEL.