Improving a negative ion accelerator for next generation of neutral beam injectors: Results of QST-Consorzio RFX collaborative experiments

In the framework of the collaboration between Consorzio RFX (Padova, Italy) and QST (Naka, Japan) two experimental campaigns have been organized on the Negative Ion Test Stand (NITS) in Naka, employing an ITER-like multi-beamlet con guration. These campaigns were aimed at compensating for the undesired mag- netic de ection of the ion beam. The experiments have clari ed the in uence of operating parameters on the optical properties of the ion beam. The physical phenomena acting on the optics have been investigated, in particular the e ect of an asymmetry of the ion current density at meniscus. Comparisons with simulations have been made and the modeling has been improved consequently. During the second experimental campaign, a perfect compensation of the ion de ection has been achieved.