Bunch Length Measurements Using a Transverse RF Deflecting Structure in the SLAC Linac

The development of future free electron lasers (FEL) and linear colliders requires high brightness electron beams with bunch lengths on the order of 100-fsec. Reliable measurement of such a short bunch is not a trivial problem. Furthermore, x-ray FELs will require the ability to observe variable electron beam characteristics, such as emittance and peak current, within the length of the bunch. A simple way to measure bunch length and possibly unfold beam quality variations over the bunch length is to ''streak'' the bunch using a transverse RF deflecting structure at its zero-crossing phase. Several S-band deflecting structures were constructed and tested at SLAC in the 1960's. One of these 2.4-m long structures has been installed in the SLAC linac for beam testing. We report on bunch length measurements performed using this structure and comment on future methods and applications.