TRANSVERSE ELECTRON BEAM SIZE EFFECT ON THE BUNCH PROFILE DETERMINATION WITH COHERENT RADIATION DIAGNOSTICS

Longitudinal diagnostics of electron bunches can be done by measurement of coherent radiation and subsequent extraction of the form factor. By measuring short wave-lengths, fine structures in the bunch can be resolved. The form factor depends on the three-dimensional charge den-sity distribution, and the finite transverse extend of the electron bunch can reduce the form factor at short wave-lengths. An experimental study using a two stage single shot spectrometer [1] has been carried out at the FLASH free-electron laser at DESY [2, 3]. The coherent transi-tion radiation spectra for two beam optics settings were recorded and compared. In one setting the transverse beam size at the transition radiation target screen has been blown up by a factor of about 3.5 compared to the second setting. COHERENT RADIATION DIAGNOSTICS A bunch of N electrons radiates a spectrum according to d2U dλdΩ d2U dλd