Experimental characterization of the MITICA neutralizer gas injection nozzles

The gas cloud inside the neutralizer of MITICA (Megavolt ITER Injector and Concept Advancement), required to neutralize the negative ion beam, will be created continuously by 20 identical nozzles providing the gas needed for different operation modes. In order to validate the design, one nozzle will be characterized in detail and for a wide range of supply conditions in a dedicated experiment at KIT. This is necessary due to a number of uncertainties in the calculation and prediction of the nozzle behavior. The characterization will comprise two general scenarios: a steady state supply for normal beam operation and a transient test to check the behavior in the case of an accidental interruption of gas supply with the potential risk of a damage of other beamline components. All the experiments on the MITICA gas nozzle will be carried out at the modified TransFlow facility at KIT. In this paper the experiments at KIT to characterize the gas supply nozzles for MITICA in a parametric way over a wide range of conditions are described. The achieved results are then compared with the theoretical predictions already available. Finally, the results from the single nozzle test are used for a scale-up exercise to full MITICA scale. While the current design comprises 20 identical nozzles, arranged in 4 parallel lines of 5 nozzles in series, there is a potential issue of flow maldistribution and its consequences on the system performance. This issue could result from the serial nozzle arrangement: the last in line sees a significantly lower mass flow. With the achieved parametric characterization of one nozzle, also an analytical prediction of the differences between the individual nozzles in MITICA can be made. This result can validate the design of the nozzles and allows an optimization of the operation conditions of MITICA.