RF-Free Chirp Removal Using Longitudinal Wakefields

In X-ray Free Electron Lasers (FEL) the use of ultra-compressed beam bunches often results in a residual chirp left in the beam from the compression stages, which can be detrimental to the FEL performance. The problem is particularly acute in the next generation X-ray FELs which will be using seeding techniques and where the energy spread requirements are more stringent. Its been proposed to mitigate this problem by using a passive corrugated structure with a mm-scale aperture, generating strong longitudinal wakefields to remove head-to-tail residual chirp in the beam in relatively short distances. In this project, a proof-of-concept prototype of the corrugated structure will be developed, in the context of applications for multi-GeV X-ray FEL beamlines. The prototype structure will feature planar geometry with an adjustable gap, to enable residual chirp removal over a large range of X- ray FEL operating conditions. The device can also serve as a more general tool for tailoring electron beams longitudinal phase space properties in a wide range of scenarios. A small-scale (18 cm long) prototype was developed and tested experimentally on a 60 MeV electron beamline. While performed at low energy, the experiment was a critical step towards technical approach validation, and provided an important benchmark for numerical models. A full-scale GeV-class prototype Dechirper (2 meters) will be designed, fabricated, installed and commissioned at the operating LCLS light source facility. A complete Dechirper system will be developed, including mechanical support, alignment hardware, controls and diagnostics. Commercial Applications and Other Benefits: This project is an enabling technology for many X-ray FEL applications. The Dechirper implementation will enhance capabilities and save significant costs to multiple X-ray FEL projects, presently in planning stage or under construction. In addition, the technology developed here has a direct spin-off application as a beam-based THz generator, which fulfills a need in biological and security imaging applications.