BriXS: BRIght and compact X-ray Source

This document delineates the motivations and the guidelines for the development of a compact machine to produce beams of high brilliance mono-chromatic tunable X-rays with energy in the range from 30 to 150 keV, aimed at constituting a unique facility located in the Milan metropolitan area, with performances comparable to those of modern synchrotron light sources, although associated to costs and dimensions smaller by at least one order of magnitude (from 100x100 m down to 10x10 m, and from 100s M€ down to 10s M€), so to be compatible with locations inside a University Campus, a large Hospital, a Museum or a mid-size research infrastructure. The focus on enabled applications by such a machine is on medical oriented research/investigations, mainly in the radio-diagnostics and radio-therapy fields, exploiting the unique features of mono-chromatic X-rays, as well as in micro-biological studies, and, within this mainstream, material studies, crystallography and museology for cultural heritage investigations. Mono-chromatic bright X-ray beams have been already proven to be a unique tool for advanced imaging at the sub 0.1 mm resolution scale with tremendous reduction in the radiation dose to tissues, joined to an upgraded signal-to-noise and visibility enhancement via phase contrast imaging. The underlying enabling technology is the one on the strong rise over the last decade, with an effective ongoing transition from R&D and demonstrative machines towards effective user facilities, based on Thomson/Compton back-scattering X/g-ray Sources, also known as Inverse Compton Sources (ICS). INFN, University of Milan and Politecnico di Milano hold a strong leadership in the strategic fields of expertise at the backbone of the development and implementation of the involved technologies for a machine like BriXS: design and theory of Compton Sources, advanced Optical Cavities, high intensity Lasers, Super-conducting RF Cavities and Linacs, high gradient Magnets, Detectors for characterization of ultra high brilliance X-ray beams as those typical of 4 generation Light Sources (FEL’s). A strong synergy among all these fields of expertise, combined to a long term vision of evolutionary development for BriXS, would give to the Milan metropolitan area and its possible stake-holders like University of Milan, Politecnico di Milano, INFN and local Hospitals/IRCCS, a unique opportunity to develop in a reasonable short time (3 years) and with a moderate investment (30-50 M€) a unique facility in Europe, where to conduct inter and multi-disciplinary research with advanced X-rays, electron beams and photon beams, bringing to the Lombardia Region and the whole national community a research infrastructure with world-wide rank performances. As a matter of fact the most commonly used figure of merit for radiation sources is the brightness, i.e. the number of photons delivered per second, per unit bandwidth and per unit solid angle of beam collimation. As shown in Fig.1, synchrotron light sources stand well above all other radiation sources in the photon energy range 10 eV – 50 keV. Free Electron Lasers are even higher out of scale of the figure (several orders of magnitude above) in the 100 eV – 20 keV range. Conventional X-ray tubes, even in the new upgraded Metal Jet version, Plasma discharge sources and HHG sources are well below in brightness performances. On the other hand, Thomson/Compton Sources can compete in the region above 20 keV with mid-size synchrotrons (like Elettra) and above 100 keV even with large size synchrotrons like APS, ESRF or Spring8, the few facilities world-wide capable to deliver X-ray beams in excess of 100 keV, though costing of the order of 1 G€. As a matter of fact synchrotron light sources are very powerful tools of investigation but not very practical for some applications, due to the limited