Tapered Flying RF Undulator

The x-ray free electron laser (x-FEL) efficiency, measured as a fraction of the electron beam power converted into light, is typically below 0.1% for most of the x-FEL facilities presently in operation. Undulator tapering techniques can be used to improve the conversion efficiency by 1-2 orders of magnitude. At present there are no robust tapered undulator x-FEL schemes operating at 10% efficiency. Development of this technology will be a breakthrough for the x-FEL community. How the problem is being addressed: Euclid Techlabs proposes to build a tapered radiofrequency (RF) undulator. An RF undulator is a microwave waveguide in which strong RF field is excited that interacts with a charged particle beam forcing it to radiate coherent x-rays while undergoing a wiggling motion. RF undulators are attractive for use in x-FELs due to their large beam aperture; a short undulator period, capable of producing both circular and planar polarization; and fast dynamical control of the polarization, wavelength, and the undulator parameter K. Three innovations make our approach unique: 1) the use of tapered RF undulators with varying corrugation periodicity and driven at different frequencies, 2) short pulse high peak power that increases the undulator strength and 3) utilization of the remaining electron beam power to drive the RF undulators. What will be done in Phase I: In Phase I we will design an RF tapered undulator unit for a future high power test at the Argonne Wakefield Accelerator facility. This unit will be powered by a short pulse wakefield extracted from an electron beam. A tapered 3D printed RF undulator prototype will be cold tested and tuned. Applications and benefits: The proposed approach will increase the efficiency and brightness of existing and proposed x-FEL facilities. The LCLS operates at ~ 1MW CW power consumption and produces an impressive beam with energy on the order of 1 Joule. However only 0.1% of this energy is converted to x-rays, sending the rest to the beam dump. We propose an RF-based tapered undulator system that will raise the efficiency to 10% significantly reducing operating costs