Momentum flux measurements in a negative ion beam for fusion research

Abstract A new method for determining the particle flux density in the beam of a neutral beam injector (NBI) for magnetically confined fusion plasmas is presented. The method uses a force probe to measure the momentum transfer from beam particles to a small target and has been applied at the BATMAN experimental facility at the MPI Garching. The experiments presented in this report are performed in the non-neutralized negative ion beam. It is found that the force measured at a distance of 1.4 m from the negative ion source correlates well with the momentum flux that is calculated from the ion energy and the averaged extracted ion current density. Graphical abstract Schematic of the force-probe diagnostic for momentum-flux measurements in the negative hydrogenion beam at the BATMAN facility. A water-cooled shield with a 5 mm aperture limits the beam spot on an L -shaped tungsten target mounted on an interferometric cantilever probe, enabling charge-independent local flux determination 1.4 m downstream of the source