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The Full-Size Source and Injector Prototypes for ITER Neutral Beams

The development of the NBI systems for ITER requires unprecedented parameters (40 A of negative ion current accelerated up to 1 MV for one hour) so that a test facility is in the final phase of construction at Consorzio RFX (Padova, Italy), housing two experiments. A full-size negative ion source, SPIDER, aims at demonstrating the creation and extraction of a D-/Hcurrent up to 50/60 A on a wide surface (more than 1 m2) with uniformity within 10 %. The second experimental device is the prototype of the whole ITER injector, MITICA, aiming to develop the knowledge and the technologies to guarantee the successful operation of the two injectors to be installed in ITER, including the capability of 1 MV voltage holding at low pressure. The key component of the system is the beam source, whose design results from a trade-off between requirements of the optics and real grids with finite thickness and thermo-mechanical constraints due to the cooling needs and the presence of permanent magnets. Numerical simulations are a necessary supplement to the experimental effort to optimise the accelerator optics and to estimate heat loads and currents on the various surfaces. In this paper the main requirements for ITER NBI will be discussed. The design and the status of the main components and systems will be described. Particularly a review of the accelerator physics and a comparison between the designs of the SPIDER and MITICA accelerators are presented. Complex network theory will be applied to the NBI system in order to identify the hidden functional relationships and the most important parameters for the operation.