The Italian contribution to the construction of the linac for the European spallation source

The European spallation source (ESS) uses a linear accelerator (linac) to deliver the high intensity proton beam to the target station for producing intense beams of neutrons. At the exit of the linac, the proton beam will have 2 GeV energy and 62.5 mA current. The construction of an accelerator with the contribution of different laboratories is not a new concept but so far the laboratories were controlled by the same government (e.g. in USA and Japan) or they delivered components for an intergovernmental institution like CERN. The European Spallation Source is a research facility that gathers 40 active in-kind (IK) contributors from 13 States, even outside the European Union, so its construction is not only a technical and scientific challenge, but also an economic, political and social experiment. The case of the Italian contribution is interesting because of the structure of Italian industrial ecosystem, mostly based on small and medium-sized enterprises (SME), which may be unsuitable for the case of a research infrastructure which construction requires a high level of R&D investments. Conversely, the well-known flexibility of SME to adapt to the requirements have balanced the weakness and the results are satisfactory. Following the overview of the Linac design, the paper will focus on the key issues of the Italian contribution, the state of the project (73% completion up to now) along with the point of view of the ESS management and the lesson learnt; the major outcomes for the economy and society will complete the discussion.