Plasma Wakefield Research at ATF and FACET II

The first goal of the proposed research is to produce, characterize and simulate nonlinear plasma accelerator structures that are larger (hundreds of microns) and more amenable to injection of low-energy spread (?E/E << 1 %) electron bunches from an external linac --- and thus more likely to yield the high-quality GeV bunches required for x-ray free-electron lasers (XFELs) and colliders --- than previously studied laser wakefield accelerators (LWFAs). The research will utilize unique terawatt CO2laser and 70 MeV linac instrumentation at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL). The research would use our dedicated experimental station (built using our current DoE HEP funding) at ATF beamline to develop a stable plasma-source with advanced diagnostics and an external electron injector with parameters suitable for plasma accelerators as well as for plasma-bubble diagnostics. The ATF plans to advance CO2laser pulse duration to 200-500 fsec and peak power to 10-20 TW open a clear path toward ultimate goal of this project - CO2-laser-driven wakefield accelerators with high quality electron beam. A significant part of this research will involve our undertaking advanced simulations of CO2-laser-driven plasma wakefield and electron acceleration. The most important feature of ATF’s plasma accelerators will be the relatively large size of the bubble (~ 300µm), the properties of which can be studied precisely via external e-beam injection. The combination offers a sound foundation for generating very stable high-quality beams in plasma-driven accelerators, with parameters comparable to those realized in modern conventional accelerators. The proposed work will yield the first comprehensive study of bubble-regime LWFAs driven by CO2lasers. The secondgoalin this proposal is to create trailing beams with tailored density profiles, which would lead to a uniform accelerating field and high energy transfer efficiency in a PWFA based at FACET II user facility. We will use a method known as beam-induced ionization injection to create these trailing electron beams. The longitudinal profile of this trailing beam can be manipulated by taking advantage of the correlation between the injector’s and the electron beam’s density profiles. This is acreative and originalapproach because it is the first that seeks to shape the trailing beam’s density (on a micron scale) by indirectly controlling the helium injector density (on a millimeter scale). The aims of this proposal will be accomplished by integrating the expertise across the disciplines of fluid mechanics and plasma-based particle acceleration. Our specific aims will contribute to the understanding of the physics of PWFA and beam-plasma interactions as well as propelling the PWFA technology towards generating collider-quality beams.