The CompactLight Design Study

CompactLight (XLS) is an H2020 Design Study funded by the European Union under grant agreement No. 777431 and carried out by an international collaboration of 23 international laboratories and academic institutions, three private companies, and five third parties. The project, which started in January 2018 with a duration of 48 months, aimed to design an innovative, compact, and cost-effective hard X-ray FEL facility complemented by a soft X-ray source. In December 2021, the Conceptual Design Report was completed. The result is an accelerator that can be operated at up to 1 kHz pulse repetition rate, beyond today’s state of the art, using the latest concepts for high brightness electron photoinjectors, very high gradient accelerating structures in X-band, and novel short-period undulators. This paper gives an overview of the current status, focusing particularly on the technological challenges addressed and their future applications to compact accelerator-based facilities.