Title: A Corrugated Waveguide-Based Collinear Wakefield Accelerator for a Hard X-ray Free Electron Laser

Abstract: The recent development of a corrugated waveguide-based collinear wakefield accelerator at the ANL marks a significant advancement toward realizing a facility with multiple high repetition rate hard X-ray Free-Electron Lasers. This achievement includes an improved understanding of the factors limiting accelerator performance and the successful design, fabrication, and testing of key accelerator components:

1. A 2-mm diameter corrugated waveguide embedded inside a strong-back structure for holding and cooling the waveguide.
2. Sub-terahertz frequency electromagnetic couplers for extracting the unused wakefield and diagnosing the onset of beam breakup instability (BBU).
3. A quadrupole “wiggler” composed of alternating polarity strong quadrupoles for beam focusing and suppression of BBU.
4. A compact, small-gap force neutral adjustable phase undulator (FNAPU) for enhanced FEL performance.

The corrugated waveguides and couplers underwent rigorous testing with the electron beam at the Brookhaven National Laboratory's Accelerator Test Facility. Prototypes of the quadrupole "wiggler" and FNAPU were characterized in the magnetic field measurement laboratory at APS. These comprehensive tests revealed a remarkable agreement between actual performance and anticipated design parameters, underscoring the robustness of collinear wakefield accelerator technology for future applications in the XFEL facility.