Progress of the FELICITA I free-electron-laser experiment at DELTA

This paper presents the progress of the FELICITA I experiment, under commissioning at the storage ring DELTA. This Free-Electron Laser is based on an electromagnetic undulator. This undulator cannot only be operated as a conventional undulator, but also in the optical klystron configuration. Due to the higher gain, this operation mode is chosen for the commissioning. During the commissioning [1], the machine was characterised at different energies between 300-800 MeV. Due to the experience made during this process, the commissioning energy was fixed to 450 MeV. The startup wavelength is fixed to 470 nm operating the undulator at a K of 2. During the last runs the optical cavity was commissioned with beam, and losses as low as 1.5% have been demonstrated. Using this value and the measured electron beam characteristics, the threshold average current was calculated to be about 7 mA.