Analysis of First and Second Joint Experiments and proposal of additional experiments for 2018-2019

During 2016, a first joint experimental campaign between QST and Consorzio RFX was done on NITS (Negative Ion Test Stand) at QST Naka with the purpose of validating the new magnetic configuration developed at RFX for compensation of magnetic criss-cross deflection. The new configuration includes a set of additional permanent magnets installed in the Extraction Grid and called Alternate Deflection Compensation Magnets (ADCM). The results of the first campaign demonstrated the effectiveness of the new solution in compensating the beamlet deflection despite a full compensation was not reached, due to additional effects in the beamlet extraction physics not taken into account in the numerical models. The results of the first campaign allowed a better understanding of the extraction physics with consequent improvement of the numerical simulation models of the accelerator. Based on the results of the first joint experiments and the improved numerical models, a second joint experimental campaign has been carried out on NITS during 2017, with the purpose of reaching full compensation of criss-cross deflection and increasing the experimental database. Despite a series of issues with the acceleration power supply limited the available acceleration voltage to Vacc = 10kV, a few pulses with sufficiently good optics have been achieved, allowing fulfilling the main goal of the campaign. In fact, full deflection compensation was practically achieved. In order to analyse the results of the second joint campaign, which were affected by noise due to the limited beam energy delivered to the target and the lower quality optics, the IR analysis tool used during the first joint campaign has been improved and applied again to the results of both the campaign, obtaining a cleaner database of the results. The analysis of the results of both campaigns together showed quite clear relations among the parameters of the accelerator, like beamlet deflection, bean energy and strength of the permanent magnets. In order to continue the investigation of the physics of the negative ion accelerators, in view of the realization of MITICA, ITER NBI and JT-60 NBI, a series of additional experimental proposals for the next future is reported.