Observation of beamlet displacement and parallelism in NIO1

Abstract

In the compact radiofrequency negative ion source NIO1 (Negative Ion Optimization phase 1), beamlet images are recorded from visible light monochrome cameras, for which several mounting positions are available. For two cameras, named CAM1 and CAM2, looking in directions perpendicular to each other and to the z axis of the beam drift tube, an extensive database of images is available, with methods and results of analysis discussed here. All NIO1 beamlets, arranged in a 3 × 3 matrix, are extracted, so CAM1 can record 3 beamlet projection groups and CAM2 also. Both cameras can be used to estimate the beam optics, depending on extracted beamlet currents, their uniformity and applied voltages; moreover CAM1 shows the filter current effects, while CAM2 images may give information on the deflection field (due to magnets inserted in the extraction grid EG and the post-acceleration grid PA). Light reflection is reduced by careful set-up, and by considering image central portion for analysis. Image luminosity can be simply fitted by Gaussian shapes, when the 3 projection groups are fairly separated. This analysis allows to estimate beamlet displacement and deflection. In general, optional algorithms for noise rejection and pre-smoothing for improving automatic recognizing of beamlet peaks is discussed, as well as the classes of available fits. Results for beamlet size, deflection and rms divergence are reported for selected datasets (within the 10 or 20 mrad goal). In some datasets, beamlet convergence was observed, indicating the need for further analysis and beam optics adjustments.