Except the synchrotron radiation or the free electron laser, which are only available in large facilities, there is at present no tunable source of extreme ultraviolet radiation (EUV). Yet the use of EUV radiation is quickly developing, mainly because of the implementation of the EUV lithography dedicated to the manufacturing of the next generation of electronic chips and also to research in solar and extra-solar imaging from spatial telescopes and “attosecond” physics. The only commercially available EUV sources are based on the emission of discrete lines from plasmas obtained under various conditions (discharge in gas, electron cyclotron resonance). Nevertheless an energy tunable and quasi-monochromatic EUV source would be of considerable interest to characterize optical components and detectors in this spectral domain. The interaction of relativistic or non-relativistic electrons with solid radiators appears as a very promising technique to realize such a source. Two phenomena have given rise to advanced studies: the transition radiation (TR) and the parametric radiation (PR). The TR occurs when electrons cross the interface between two materials; sources of X-rays based on TR and using periodic multilayer structure as radiators were proposed; their feasibility was experimentally evidenced. The PR is emitted when electrons go through periodic media (crystal, multilayer interferential mirror) close to the Bragg conditions. Once more, X-ray sources based on this mechanism were proposed, built and successfully tested. The main drawback of these tested sources is the need for relativistic electron beams supplied by expensive accelerators (LINAC, storage ring, betatron). Our TPLUS (Tunable Parametric Laboratory UV Source) proposal of tunable source calls upon non relativistic electrons supplied by a 100 kV gun producing PR in a multilayer nanostructure. The main features of such a parametric UV source were studied by a French team in the case of medium relativistic particles and recently by a Russian-American collaboration in the case of non-relativistic particles. Their calculations demonstrate that PR of wavelength ? = 36.4 nm (E = 34 eV) is produced upon irradiation of a Sc/Al multilayer target by 100 keV energy electrons under a glancing angle equal to 43°. Furthermore it is possible to get a yield of approximately 10-5 photon per electron. With an electron gun providing 1 mA, theory estimates an intensity around 109 photons/s/eV/sr (7.108 photons/s/sr for a spectral bandwidth equal to 0.7 eV at 34 eV); this value is lower than the 1015 photons/s/sr for both He I and He II lines supplied by a He-plasma, generated with the ECR technique. Nevertheless this He source can only emit a few intense discrete lines. To our knowledge, no source similar to the one described in this proposal has been built and characterized. Nevertheless different institutional teams (in particular in Russia) and research teams from private firms in USA (Intel Corp., Adelphi Technology) have shown a great interest for this kind of source through several publications and communications to conferences (for instance RREPS-07). The main objective of this proposal is to design and built a tunable EUV laboratory source, to measure its performances and finally to obtain a pre-industrial prototype. This source will be used in the future to characterize EUV optics at their wavelength of application and should allow performing reflectivity measurements of mirrors in the whole EUV spectrum. Indeed, to explore the whole EUV range, specific materials are required to fabricate optimal multilayer mirrors. The data of the PXRMS (Physics of X-Ray Multilayer Structures) survey show that numerous multilayers are designed for applications ranging throughout the EUV range. Thus it is important to have a laboratory tunable source to get some independence towards the allocated synchrotron beam times and also to prepare in an extensive way the synchrotron experiments.