Plasma accelerators driven by advanced laser sources and/or compact electron linacs are key components for the next generation of green and sustainable research infrastructures. We propose a project on the development of "Plasma Accelerator systems for Compact Research Infrastructures" (PACRI), which will develop highly important and ground-breaking plasma accelerator technologies for Europe's future research infrastructures (RI). The specific objectives of PACRI are: - The development of high repetition rate plasma modules, as required for the EuPRAXIA ESFRI project, capable of extending its scientific scope from high average brightness radiation sources to high energy physics. - Improving the performance of normal conducting accelerator technology for X-band linacs, paving the way for high repetition rate operation (up to kHz) with a focus on efficiency and power consumption. - The development of key laser components required to scale up high power, high repetition rate laser technology as required by the EuPRAXIA and ELI ESFRI research infrastructures. The achievement of the PACRI objectives will enable the production of unique particle and photon beams with a wide range of applications in ultrafast science, high precision medical imaging, materials diagnostics, medical treatment and, in the longer term, the development of future compact colliders. These developments will be used for future resource-efficient upgrades of existing RIs at INFN, Elettra, CERN, CNR, CNRS, DESY, ELI, GSI/FAIR and UKRI. In addition, PACRI will support the implementation of ESFRI's EuPRAXIA distributed research facility by consolidating its sites and centres of excellence being developed under the ongoing EuPRAXIA_PP project. It will fund the development of some technical prototypes that are crucial for the implementation of the EuPRAXIA project and other European Research Infrastructures (e.g. enabling major upgrades to the ELI-Beamlines facility).

Particle accelerators are a key asset of the European Research Area. Their use spans from the large installations devoted to fundamental science to a wealth of facilities providing X-ray or neutron beams to a wide range of scientific disciplines. Beyond scientific laboratories, their use in medicine and industry is rapidly growing. Notwithstanding their high level of maturity, particle accelerators are now facing critical challenges related to the size and performance of the facilities envisaged for the next step of particle physics research, to the increasing demands to accelerators for applied science, and to the specific needs of societal applications. In this crucial moment for accelerator evolution, I.FAST aims at enhancing innovation in and from accelerator-based Research Infrastructures (RI) by developing innovative breakthrough technologies common to multiple accelerator platforms, and by defining strategic roadmaps for future developments. I.FAST will focus the technological R&D on long-term sustainability of accelerator-based research, with the goal of developing more performant and affordable technologies, and of reducing power consumption and impact of accelerator facilities, thus paving the way to a sustainable next-generation of accelerators. By involving industry as a co-innovation partner via the 17 industrial companies in the Consortium, 12 of which SME’s, I.FASTwill generate and maintain an innovation ecosystem around the accelerator-based RIs that will sustain the long-term evolution of accelerator technologies in Europe. To achieve its goals, I.FAST will explore new alternative accelerator concepts and promote advanced prototyping of key technologies. These include, among others, techniques to increase brightness and reduce dimensions of synchrotron light sources, advanced superconducting technologies to produce higher fields with lower consumption, and strategies and technologies to improve energy efficiency.