Very High Efficiency X-ray FEL Oscillator

Over the last decade, Free Electron Laser (FEL) light sources have become essential components of the world-wide scientific infrastructure and deliver core research capabilities to Users across many scientific disciplines. However, the conventional FEL efficiency is usually limited to a small fraction of 1% at short wavelengths, which presents a significant strain on the light source accessibility and performance for a wider Users base, and for industrial applications. In response to this problem, RadiaBeam Technologies and UCLA are developing a novel concept, TESSA (Tapering Enhanced Stimulated Superradiant Amplification), which carries the promise to increase FEL efficiency by over an order of magnitude. By utilizing a high intensity radiation seed and a period-by-period undulator tapering, TESSA can achieve an overall efficiency as high as 50%. TESSA concept has been validated experimentally at 10 µm wavelength (and in a low gain regime), but it is prudent to carry out a much shorter wavelength demonstration, and also study oscillator configuration, before scaling the technology into EUV and X-rays. This project will bridge this gap, by validating and optimizing TESSA oscillator (TESSO) experimentally in the ultra-violet frequency range and in a high gain regime. During the Phase II, the TESSO design has been completed, an ultra-fast seed laser capable of generating pulse trains have been purchased, and an optical transport has been designed. In addition, the Phase II project partially supported prebuncher fiducialization, injection chicane design, section breaks development, and magnetic measurements and tuning of the first Theseus undulator section. The initial phases of the experimental program are in progress. In Phase IIA we propose to complete TESSA-266 undulator system to the full 4-m design length, commission the system, and reconfigure it as an oscillator for experimental demonstration and optimization of the pulse train operations. In this collaborative project, RadiaBeam will be mostly responsible for fabrication and development of sub-systems and components of TESSA-266 beamline, whereas UCLA will be mostly responsible for carrying the experimental program and leading optimization and data analysis. A successful TESSA oscillator demonstration in the ultraviolet frequency range, can lead to development of novel and significant additional capabilities by the FEL Light Source community. It would also trigger a broader interest towards high efficiency FEL sources, including an interest from emerging industrial applications, such as EUV lithography. For RadiaBeam the realization of TESSA concept, represents an exciting and potentially disruptive commercial opportunity.