Measurements of the transverse emittance at the VUV-FEL

Abstract

The TESLA Test Facility (TTF) linear accelerator (linac) at DESY has been extended to drive a new Free Electron Laser facility (VUV-FEL) in the wavelength range from the vacuum-ultraviolet (VUV) to soft Xrays. With the upgraded photo injector and increased electron beam energy up to 1 Ge V, wavelengths down to 6 nm can be achieved. During the commissioning phase of the VUV-FEL the emphasis is on lasing with a wavelength of 30 nm. A high quality electron beam is required for the lasing process. At the VUV-FEL the design values are 2 mm mrad normalized transverse emittance, 2500 A peak current1 and 0.1 % energy spread. In order to understand and optimize the electron beam, precise measurements of the beam properties are essential. In this diploma thesis, measurements of the transverse emittance during the commissioning of the VUV-FEL are presented. The transverse beam distribution is measured using optical transition radiation at four positions along the linac. The emittance is determined from the measured distributions using two methods: a fit of the Twiss parameters together with the emittance to the measured beam sizes, and as a second method, the tomographic reconstruction of the phase space density distributions using the Maximum Entropy Algorithm.