Passive Momentum Spread Compensation by a “wakefield Silencer”*

We report the observation of de-chirping of a linearly chirped (in energy) electron bunch by its passage through a 5 cm long dielectric loaded waveguide structure. The experiment was conducted at the ATF facility at BNL according to a concept dubbed the "wakefield silencer" originally developed at the ANL AATF [1] which involves defining the electron bunch peak current distribution and selecting the optimal waveguide structure suitable for chirp cancellation using self-induced wake fields of the electron bunch. Our experiment has been carried out with a 247 micron triangular beam with a 200 keV energy spread that was reduced by a factor of three to approximately 70 keV by passing it through a 0.95 THz dielectric-lined structure. Theoretical analysis supports the experimental results. Further exploration and applications of this technique will be discussed as well.