The 2016 STFC FEL strategic review recognised the revolutionary potential of X-ray Free Electron Lasers (XFELs) for science and industry internationally. In order for the UK to stay competitive, a recommendation was made to join the European XFEL, based in Hamburg. This was enacted and the UK formally joined in March 2018. In the longer term, it was foreseen that the UK would need its own XFEL to meet the anticipated demand and to have a source matched to the needs of UK researchers and to this end ASTeC has led the development of a UK wide R&D programme which formally started in April 2017. CLARA is the major part of this effort, being a dedicated FEL test facility aimed at developing technologies and techniques to improve the radiation output of FELs. In addition to this experimental work at longer wavelengths, ASTeC is exploring options for what a final full-scale UK-XFEL facility might look like.
As a starting point, ASTeC has initiated consultation with UK academia and industry, in particular, the UK users of the two longest established hard X-ray XFELs; LCLS in USA and SACLA in Japan, in order to establish the requirements and aspirations of this pioneering user community. Based upon these discussions ASTeC is formulating options to best address the identified needs and to ensure that, should the UK decide to build a national facility, it would have world-leading and unique capabilities and so give UK researchers and industry a competitive edge.
The R&D programme covers most of the key FEL sub-systems as well as theoretical studies on the development of new ways of creating higher quality light from FELs. One aspect which XFEL users have highlighted is the synchronisation between the FEL output pulse and a high power laser; this combination of two powerful light sources is key to many experiments. Users need to control the time of arrival at the sample to the femtosecond level because they want to study extraordinarily fast atomic processes that determine how matter behaves. ASTeC staff have spent significant effort in understanding the fundamental performance of the accelerating system which largely sets the arrival time of the electrons and so the FEL pulse. By studying the hardware performance on CLARA, we will be able to identify which sub-systems determine the overall synchronisation and so put our efforts into improving these. Our measurements show that the CLARA hardware is exceptionally stable but that improvements are still required to meet the challenge set by our potential UK XFEL users.
A second aspect of our work is in the improvement of FEL output performance. ASTeC staff are studying how pulses of light shorter than currently available elsewhere can be generated by manipulating the electron bunch using magnets and lasers. A second area of study is looking at how the pulses from the FEL can be made to be more repeatable shot to shot. UK users of XFELs have highlighted this as an area that, if improved upon, could lead to making some experiments viable that are not currently possible. ASTeC staff are investigating how some relatively simple changes to the FEL layout could increase the stability.
Two other areas of XFEL R&D that ASTeC is leading are in potential recirculation and energy recovery schemes and in the development of superconducting undulators for FELS. Both of these areas could potentially have a positive impact on the costs required to build and operate a future XFEL.