Novel Radiation Facilities Based on Plasma Acceleration: The Future of Free Electron Lasers

Exploiting acceleration gradients that are up to three orders of magnitude higher than those achievable using conventional radiofrequency-based devices, plasma-based devices promise a revolution in particle acceleration, enabling particles to reach high energies over much shorter distances than existing accelerators [1]. The SPARC_LAB research team at the Frascati National Laboratory of the Italian National Institute for Nuclear Physics (LNF-INFN) has demonstrated, for the first time, that plasma-based acceleration is able to produce particle beams of sufficient quality to drive a Free Electron Laser (FEL) in both self-amplified spontaneous emission and seeded configurations [2].

This Special Issue, “Experimental Ideas for Novel FEL Facilities Based on Plasma Acceleration”, is inspired by the first “EuPRAXIA@SPARC_LAB” User Workshop, held at the Frascati National Laboratories of the INFN in 2021. The initiative aimed to highlight cutting-edge advancements in plasma-based photon sources and their potential applications in different disciplines.

The EuPRAXIA@SPARC_LAB project has the target of building a self-amplified spontaneous emission FEL with ultra-bright, ultra-short photon pulses with a wavelength in the range from about 4 to 10 nm an extremely interesting range at present covered in few FEL facilities. Moreover, it will include a seeded beamline delivering photons between 50 and 180 nm. This project is part of the larger European EuPRAXIA initiative, which has the goal of developing the world’s first plasma-based accelerator built to feed a real user facility. This project is underway at the INFN Frascati National Laboratories in Italy, marking a significant milestone in the field of particle acceleration (http://www.eupraxia-project.eu/) (accessed on 24 April 2025) [3,4].

The purpose of this Special Issue is to showcase the first ideas of the many promising applications of plasma-based photon sources, i.e., experiments in various fields, ranging from imaging to photon and electrons/ions spectroscopies [5].

It is worth pointing out that the 2021 “EuPRAXIA@SPARC_LAB” User Workshop was followed by a second event in December 2024, titled “Fundamental Research and Applications with the EuPRAXIA Facility at LNF”. (https://agenda.infn.it/event/42474/overview) (accessed on 24 April 2025). This second event focused on expanding the EuPRAXIA photon users’ community to include additional fields where plasma-based photon and particle sources could make significant contributions. In particular, it emphasized fostering collaborations between high-energy physicists and scientists working in challenging domains such as biological samples, organic and inorganic chemistry, soft and condensed matter, and beyond.

This Special Issue of Condensed Matter collects contributions that point out the wide-ranging possibilities offered by plasma-based sources for different experimental techniques, with special attention given to those matching the EuPRAXIA@SPARC_LAB FEL beam parameters, as those listed here below in the “List of Contributions”. These original contributions highlight the versatility and transformative potential of plasma-based accelerators for the different applications going from material sciences to biology, and include:

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The application of X-ray spectroscopies to study redox dynamics in batteries [Contribution 1].

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Investigations into carbon-based materials using advanced spectroscopic techniques [Contributions 2 and 3].

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The use of ion spectroscopy for gas-phase experiments, shedding light on fundamental molecular interactions [Contribution 4].

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The potential for studies on biological samples, such as vibrational spectroscopy of peptides, which can provide insights into biomolecular structures and dynamics [Contribution 5].

This Special Issue is certainly only a starting point to stimulate the community, and a to call to action for researchers to look at this exciting frontier, ensuring that the full potential of plasma-based accelerators is exploited in the coming years.