Bunch Profile Shaping Using Beam Self-Wakefields in a Dielectric Structure

摘要

Specially shaped beam profiles can significantly enhance the transformer ratio for beam-driven wakefield accelerators. Hence, there is much interest in tailoring the longitudinal profile of drive beams using emittance exchange techniques, or transverse masking at high dispersion locations. Here we describe a novel scheme to generate linearly ramped beam profiles in a very compact and efficient way. The concept uses the beam self-interaction with its own wakefield in a dielectric lined structure to impose an energy modulation. The energy modulation is then converted to a density modulation with a compact permanent magnet chicane. The resultant longitudinal profile is nearly linearly ramped, and ideal for wakefield accelerator applications. The entire scheme is very compact and can be placed very close to the interaction region, mitigating the tasks associated with preserving the phase space along a long transport. We also describe the parameter space for upcoming experiments at the Brookhaven National Laboratory Accelerator Test Facility with the goal of developing a complete system and measuring the output longitudinal profile of the available high-brightness electron beam. The initial studies show that a nearly linearly ramped beam shape is achievable with realistic parameters of the dielectric lined waveguide and chicane.