The ITER neutral beam test facility : Design overview

In the frame an EFDA contract, the CEA, in close collaboration with the Consorzio RFX, Padua, FZK, Karlsruhe and IPP Garching, is carrying out a design study of the ITER Neutral Beam Test Facility (NBTF) with the aim to procure in time, a dedicated test bed to optimise the performances of the first ITER neutral beam injector and to demonstrate its reliability. The main specifications that have to be considered for the study of the NBTF genetic design and general infrastructure are first an easy maintenance of components, an easy man access and also integration of the required full set of beam diagnostics. A specific inspection tool is developed that allows remote visual inspection of the source ground grid and beam line components to be performed under vacuum. Associated safety requirements are also considered (pulses in H2 and D2, X-ray and neutron production). The current design of the dedicated beam line vessel allows mixed vertical and horizontal access to the beam line components during phase 1 of the operation plan (20s short pulses). The split two halves cylindrical cryopumps, developed by FZK, will be further re-assembled in the final ITER reference cylindrical configuration for phase 2 of the operation plan: long pulses at full power. The 4.5 K cryopanels must be periodically regenerated at 90 K. Both regeneration and cool-down phases of the cryopanels are time consuming optimised. The cryosystem that supply the necessary cryogens to the cryopump is designed using existing industrial 4.5 K cold power and 80 K helium gas refrigenerators. A total power of about 50 MW will have to be removed during the two NBTF operation stages of short (20 s) and long (∼ 1 hour) pulses. for both scenarios, the cooling plant is designed for cooling down the high and low voltage components, the cryoplant and associated power supply systems. (author)