Bunch length measurements at ELBE

Last year the first ELBE accelerating module was commissioned. During the commissioning the electron beam parameters such as transverse emittance, energy spread and bunch length were measured. Each of them was studied at different bunch charges as a function of RF field phase in the first accelerating cavity. Especially for an accelerator like ELBE, which is intended to be a driver for free electron laser (FEL), bunch length measurement in picosecond range becomes very important and impose some challenge. Coherent transition radiation (CTR) technique was used to measure bunch length. This technique uses the Martin-Puplett interferometer to measure the autocorrelation of the CTR pulse yielding a minimum 2 ps RMS bunch length at 77 pC bunch charge. Short description of the method, experimental setup, data evaluation procedure and results of the measurements will be presented.