ITER neutral beam system

Since the main features of the design of the neutral beam (NB) system for t he International Thermonuclear Experimental Reactor (ITER) were first repor ted, integration with the tokamak and with the rest of the plant has been t he main priority. Moreover, operational requirements and maintainability ha ve been considered in the evolution of the design. Each of the three NE inj ectors is connected to the tokamak vacuum vessel with the NE duct on an equ atorial port. The article describes the integration of the NE port/duct wit h the blanket, the vacuum vessel, the toroidal field and poloidal field coi ls, the cryostat and the bioshield. Two main design modifications are repor ted. The insulation of the source, originally done with compressed gas, is now achieved with vacuum to limit the power losses caused by the radiation induced conductivity. Large cylindrical insulators are still required but t heir inner diameter has been reduced from 2.7 to 1.8 m. The improvements on the compensation system needed to reduce the magnetic field in the NE volu me are also described. Finally, the progress in R&D for the ITER NE system is reported, including an overview of the achievements in the critical area s of negative ion production at high current density (tests of a large size , low pressure, steady state caesiated ion source), acceleration up to 1 MV (tests of two alternative accelerator concepts) and neutralization (tests of an experimental plasma neutralizer to investigate it as an alternative t o the gas target neutralizer).