Dielectric Wakefield Accelerator Experiments at Atf*

Dielectric wakefield acceleration (DWA) presents us with means to achieve the accelerating gradient high above the limits of conventional accelerators. In a typical DWA scheme a higher energy lower charge main bunch is accelerated in the wakefield produced by a preceding lower energy higher charge drive bunch inside of a hollow metal-encapsulated dielectric tube. To make use of as much energy of the drive bunch as possible, it is highly important that all parts of it decelerate uniformly. Close to uniform drive bunch deceleration can be achieved if its current is properly shaped. At Accelerator Test Facility (ATF) at BNL we shaped the current of a chirped electron beam with an adjustable mask placed inside of the highly dispersive region in the magnetic dogleg. We passed the shaped beam current through a quartz tube and observed the beam particles’ energy modulation at the tube’s output with a spectrometer. By tuning the mask we were able to control the beam energy modulation and thus the wakefield profile in the tube.