Plans for the Implementation of an Intra-pulse Feedback on the Fermi Linac LLRF System

FERMI is a single-pass linac-based FEL user-facility covering the wavelength range from 100 nm (12 eV) to 4 nm (310 eV) and is located next to the third generation synchrotron radiation facility Elettra in Trieste, Italy. The 1.5 GeV S-band linac is composed of fifteen 3 GHz 45 MW peak RF power plants powering the gun, sixteen accelerating sections and the RF deflectors. The requirements on beam quality impose tight specifications on the stability of the electromagnetic fields that can be achieved only installing high reliable and high performance state of the art LLRF systems. While these requirements are presently met by the system installed, the on-going upgrade of the processing board with the final one will allow to add new functionalities of the system. One of the possible developments is the implementation of an intra-pulse feedback that will allow to apply the corrections inside the RF pulse. This paper provides an overview of the additional benefits that could be achieved and discusses the requirements and the constraints for the implementation in the machine.