Science Requirements and Performance Specification for the CompactLight X-Ray Free-Electron Laser

CompactLight is a consortium funded by the European Union through the Horizon 2020 Research and Innovation Programme under Grant Agreement No. 777431. The 24 partner institutes are working collaboratively towards the conceptual design of a next-generation x-ray free-electron laser (FEL). CompactLight intends to design an x-ray FEL facility beyond today’s state of the art, using the latest concepts for bright electron photo-injectors, high-gradient X-band structures at 12 GHz, and innovative short-period undulators.All of these enhancements will make our design more affordable to build and operate when compared against the existing facilities. The CompactLight prime objective is to generate a compact and affordable FEL facility design.The specifications of this future FEL are driven by the demands of potential users and the associated science case. This report summarizes the findings of our interactions with potential users since the start of the design study through a number of different avenues, culminating in a dedicated CompactLight User Meeting that was held from the 27th to the 28th of November 2018 at CERN.