EuPRAXIA@SPARC_LAB Technical Design Report

The purpose of the EuPRAXIA@SPARC_LAB User Facility is to establish a research infrastructure that pioneers the use of Plasma Wake-Field Acceleration (PWFA) for driving a high-brightness Free-Electron Laser (FEL) user facility in the soft X-ray regime. As one of the two core pillars of the pan-European Plasma Research Accelerator with eXcellence In Applications (EuPRAXIA) Research Infrastructure [1, 2], EuPRAXIA@SPARC_LAB will be hosted at the INFN Frascati National Laboratory (LNF) serving both as a cutting-edge scientific facility for users and as a technological demonstrator [3]. It will validate the integration of highgradient plasma acceleration and X-band RF technology within a compact FEL light source, laying the groundwork for future compact user facilities. This will improve their sustainability by significantly reducing the size, energy consumption, and operational costs typically associated with conventional accelerator-based FEL light sources, making advanced photon science more accessible and environmentally responsible in the long term (see Chapter 21). The user facility is expected to begin operations in 2031. Its first user beamline, AQUA, will deliver ultrashort femtosecond soft X-ray pulses within the biologically relevant “water window” spectrum, enabling real-time imaging, advanced materials development, and investigation of chemical processes with unprecedented spatial and temporal resolution. By transitioning plasma-based accelerators from proof-of-concept to operational systems and validating them under real user facility conditions, EuPRAXIA@SPARC_LAB closes a critical gap in the Technology Readiness Level (TRL) chain (from the current TRL ≈ 5 to the final TRL > 7). This will position Europe at the forefront of global innovation in compact accelerators and strengthen its capacity to lead future high-energy physics, photon science, and interdisciplinary research programs. The inclusion in the European Strategy Forum on Research Infrastructures (ESFRI) roadmap since 2021 [4] marks the strategic importance of the project at the European level. The realization of the facility entails the construction of new buildings to host the accelerator systems, experimental halls, and support laboratories. This new infrastructure, to be built within the INFN LNF site, represents the project’s first significant step and challenge. From the outset, the design and construction will prioritize incorporating energy-efficient solutions, environmentally responsible materials, and infrastructure choices aligned with long-term ecological and operational resilience. The Technical Design Report (TDR) for the EuPRAXIA@SPARC_LAB facility presents a comprehensive technical reference for the construction and scientific exploitation of the user facility. The TDR is structured to: • Define the scientific and technological objectives of the facility (this Executive Summary); • Outline the scientific cases and user applications (Chapter 2); • Demonstrate feasibility through simulations and design studies (Chapter 3); • Deliver a technical description of the facility and its components including technical readiness and potential risks evaluation (Chapters 4-21); • Support funding efforts and stakeholder engagement (Chapter 22). This Executive Summary aims to define the scientific and technological objectives of the facility and to provide a concise overview of the full TDR, tailored for funding agencies, institutional stakeholders, and expert reviewers. It distills the key content into an accessible format that emphasizes the facility’s maturity, technical feasibility, and scientific relevance. The summary is also intended to support informed decision-making and alignment with European research priorities and funding instruments, particularly those related to ESFRI and Horizon Europe.