Experimental characterization of the gas injection nozzle for the ITER Neutral Beam Test Facility neutralizer

•An experimental characterization of the gas injection nozzles has been performed for the full range of future operation.•Thereby the operation in MITICA, demanding variable gas flows in the neutralizer, is proved to be possible.•A comparison between experimental results and performed simulations showed a good consistency.•The passive safety system, providing a remaining gas flow in any case of gas supply interruption, was successfully tested.•Several manufacturing, design and assembly improvements for the gas injection nozzles have been carried out.