Emittance Measurements of the Electron Beam at PITZ for the Commissioning Phase of the European X-FEL

Abstract

Fortheoperationoffreeelectronlasers(FELs)liketheEu- ropean XFEL and FLASH located at DESY, Hamburg Site, high quality electron beams are required already from the source. The Photo Injector Test facility at DESY, Zeuthen Site (PITZ), was established to develop, characterize and optimize electron sources for such FELs. Last year the work at PITZ focused on the optimization of a photo injector op- erated very close to the startup parameters of the European XFEL. This implies photocathode laser pulses with a Gaus- sian temporal profile of about 11 12ps FWHM to drive the photo gun operated at a gradient of about 53MV/m. Significant effort was spent on the electron beam character- ization and optimization for various bunch charges. Emit- tance measurements were performed as a function of major accelerator parameters such as main solenoid current, laser spot size on the cathode and the gun launching phase. The requirement on the beam emittance for a bunch charge of 500pC for the European XFEL commissioning phase has been demonstrated. Results of these studies accompanied with the corresponding simulations are presented in this paper.