The beamline for the ITER heating neutral beam injectors: A case study for development and procurement of high heat flux components

Abstract The ITER Neutral Beam Test Facility includes development, testing, and optimization of the full prototype of the ITER Heating Neutral Beam injectors (HNBs), named MITICA. A 40 MW precursor D−/H− beam will be produced and then neutralised and filtered along the beamline, aiming to obtain 18 MW D0/H0 beam at the calorimeter and 16.5 MW during operation into the plasma. A gas neutraliser and an electrostatic residual ion dump will process the beam together with a calorimeter, necessary for commissioning and conditioning in HNBs, and for beam dumping in MITICA. The three beamline components are formed by in-vacuum actively cooled panels made of seamless CuCrZr drilled bars and swirl tubes without armour directly exposed to beam particles. Heat fluxes up to 20 MW/m2 will be exhausted through water-cooled channels operating up to 1 h in subcooled boiling. Critical heat flux and fully developed boiling were verified using semi-empirical correlations validated for divertor fingers and limiter plates. These correlations were implemented in 1D–3D customised codes simulating local nucleate boiling heat transfer conditions. Moreover, the panels were verified against creep-fatigue by simulating plastic strains under the expected cyclic thermal loads. During beam operation, the beamline components performance will be monitored using 700 embedded thermo-mechanical sensors for protection and for ITER HNBs requirement verification. The design solutions were developed consistently with intermediate inspections during assembly to limit repairs, modification of compensation members for tolerance control in dimensional chains, remote handling operations, and nuclear radiation level at ITER. The design of coolant-vacuum barriers was adapted to implement corrosion, welding, and inspection requirements. Prototypes implementing different manufacturing solutions were produced by three potential suppliers of MITICA beamline components. This strategy led to an early assessment of production reliability and cost-effective manufacturing techniques based on proven industrial expertise. Then, the supplier selected for the procurement of the beamline components will be supported with addressed performances during the follow up.