SINGLE-SHOT LONGITUDINAL DIAGNOSTICS WITH THz RADIATION

The longitudinal charge distribution in the electron bunches has a strong impact on the lasing process in a SASE FEL. For the 6 – 100 nm FEL FLASH at DESY, structures in the order of ten micrometers play a crucial role. The investigation of the longitudinal charge distribution in the electron bunches on a bunch-by-bunch basis is an important issue for optimizing the operation of the machine and improving its stability. This requires a single-shot device and is beyond the capability of existing spectroscopic diagnostic tools. This paper introduces a new diagnostics tool based on THz spectroscopy of coherent transition radiation (CTR). A novel spectrometer has been designed which permits to analyze the radiation of single electron bunches in a broad spectral range and with high resolution. Preliminary measurements with this spectrometer in both scanning mode and single-shot mode are presented and discussed.