Achievements of the ELISE test facility in view of the ITER NBI

•ELISE allows routine operation at high RF power for long plasma pulses up to 3600 s.•Negative hydrogen ion current densities above ITER requirements can be accelerated.•Large amount and non-uniformity of co-extracted electrons is the main challenge.•Suppression of co-extracted electrons can be influenced by magnetic fields.•Series of high performance beams can be sustained by dedicated caesium conditioning. Neutral Beam Injection (NBI) for ITER shall deliver in total 33 MW heating power to the plasma with two injectors at a beam energy of 1 MV. Taking neutralization efficiency and all losses along the beam path into account a negative ion current density of 329 A/m2 (H− for 1000s) and 286 A/m2 (D− for 3600 s) has to be extracted from each ion source (size 1 × 2 m2) with a beam uniformity >90%. For the optimization of the radio frequency driven (RF) negative ion source and its extraction system the ELISE test facility has been set up at IPP as a size scaling experiment with a source area of 0.9 × 1 m2 and an extraction area of 0.1 m2. Since its experimental start in 2013 continuous progress was achieved improving the system technically for long pulse operation at high RF power (total 300 kW for 4 drivers) as well as approaching ITER´s physics requirements for the ion beam. For hydrogen ˜90% of the required ion current density can be extracted for long pulses (1000s); the accelerated current density even exceeded the ITER target. For deuterium operation the main challenge is the amount, temporal in-stability and spatial asymmetry of co-extracted electron current which limit the applicable RF power and the source performance. Shaping the magnetic field topology and controlling the electric fields inside the source together with an improved caesium conditioning procedure have been identified as possible tools to improve the source performance.