Compact XFELs for all

27 April 2022
A prototype of the CLIC X-band structure

Originally considered a troublesome byproduct of particle accelerators designed to explore fundamental physics, synchrotron radiation is now an indispensable research tool across a wide spectrum of science and technology. The latest generation of synchrotron-radiation sources are X-ray free electron lasers (XFELs) driven by linacs. With sub-picosecond pulse lengths and wavelengths down to the hard X-ray range, these facilities offer unprecedented brilliance, exceeding that of third-generation synchrotrons based on storage rings by many orders of magnitude. However, the high costs and complexity of XFELs have meant that there are only a few such facilities currently in operation worldwide, including the European XFEL at DESY and LCLS-II at SLAC.

CompactLight, an EU-funded project involving 23 international laboratories and academic institutions, three private companies and five third parties, aims to use emerging and innovative accelerator technologies from particle physics to make XFELs more affordable, compact, power-efficient and performant. In the early stages of the project, a dedicated workshop was held at CERN to survey the X-ray characteristics needed by the many user communities. This formed the basis for a design based on the latest concepts for bright electron photo-injectors, high-gradient X-band radio-frequency structures developed in the framework of the Compact Linear Collider (CLIC), and innovative superconducting short-period undulators. After four years of work, the CompactLight team has completed a conceptual design report describing the proposed facility in detail.

The 360-page report sets out a hard X-ray (16–0.25 keV) facility with two separate beamlines offering soft and hard X-ray sources with a pulse-repetition rate of up to 1 kHz and 100 Hz, respectively. It includes a facility baseline layout and two main upgrades, with the most advanced option allowing the operation of both soft and hard X-ray beamlines simultaneously. The technology also offers preliminary evaluations of a very compact, soft X-ray FEL and of an X-ray source based on inverse Compton scattering, considered an affordable solution for university campuses, small labs and hospitals. 

CompactLight is the most significant current effort to enable greater diffusion of XFEL facilities, says the team, which plans to continue its activities beyond the end of its Horizon 2020 contract, improving the partnership and maintaining its leadership in compact acceleration and light production. “Compared to existing facilities, for the same operating wavelengths, the technical solutions adopted ensure that the CompactLight facility can operate with a lower electron beam energy and will have a significantly more compact footprint,” explains project coordinator Gerardo D’Auria. “All these enhancements make the proposed facility more attractive and more affordable to build and operate.”

• Based on an article in Accelerating News, 4 March.

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