Integration studies of a positive neutral beam injector system into the design of a volumetric neutron source

A feasibility study regarding a volumetric neutron source (VNS) is presently conducted in the EUROfusion Consortium. The VNS uses Positive Neutral Beam Injection (P-NBI) for plasma heating, current drive and particularly to drive beam-target fusion, aiming for a high neutron production (≈0.5 MW/m2 neutron wall load in the equatorial plane). P-NBI is a reliable auxiliary heating system, widely employed in plasma devices such as ASDEX Upgrade (AUG), W7-X and JT60-SA. The paper describes the integration of the P-NBI system into the design of the VNS. This includes the neutral beam (NB) duct from the torus vacuum vessel to the NBI box with the gate valves, the space requirements of the NB injectors in the building as well as the connections for cooling water, cryo-supplies, electrical high voltage and radio frequency (RF) cable connections. Since the VNS is a nuclear machine with lifetime doses significantly exceeding those of ITER, the requirements for remote maintenance (RM) are very different from any existing NBI design. The RM concept and the RM sequences will be discussed. Neutronics studies for the NB duct were performed and design iterations undertaken to assure that neutron heating and lifetime fluences remain below limits at the superconducting toroidal and poloidal field coils adjacent to the NB duct. The work considers the return of experience from AUG, ITER and some other fusion experimental machines in operation, under construction or in conceptual design such as DEMO.