Comparison of experimental and simulated beamlet deflection in a MITICA-like extraction system at BATMAN Upgrade

Abstract: In collaboration with ITER, a MITICA-like extraction was installed at the BATMAN Upgrade test facility in 2021 (BUG-MLE). One main difference to the previous extraction system is the presence of additional deflection compensation magnets which are designed to suppress the row-wise zig-zag deflection of the accelerated negative ions caused by the co-extracted electron suppression magnets, mounted in the second grid of the extraction and acceleration system. The effect of the deflection correction magnets was characterized in dedicated scans with the available beam diagnostic tools (Carbon Fiber Composite tile calorimetry and Beam Emission Spectroscopy). Since the correction magnets are installed only in the upper grid half, the corrected beam can be directly compared to an uncompensated beam. The experimental investigations are accompanied by simulations. IBSimu is used to model the beamlet formation and ion-optics inside the extraction system. The in-house developed BBCNI code is exploited to track the particles towards the CFC and generate synthetic beamlet emission spectra. The work focuses on physics interpretation by directly comparing measured and synthetic data. In particular, after outlining the main theoretical aspects behind the BUG-MLE experiment, a series of simulations is performed with both of the aforementioned codes, allowing a detailed understanding of the expected results and providing insight on both the robustness of the horizontal deflection correction and its impact on the estimated beamlet divergence. Finally, the experimental outcomes are presented and analysed, from both of the diagnostic tools, and compared with the simulations in order to evaluate the action of the additional magnets in different conditions.