The RF negative ion source NIO1 (Negative Ion Optimization 1) , built at Consorzio RFX in Padova (Italy), aims at investigating basic issues of ion source physics while providing a tool to benchmark and validate beam simulation codes. Due to its small size and its modular design, NIO1 represents a valuable testbed for DEMO relevant solutions, such as energy recovery and alternative systems for ion beam neutralization . To such purposes it is important to improve NIO1 performance to make it comparable to those expected for other negative ion sources e.g. the full-size ITER ion source prototype SPIDER . In particular the latest NIO1 upgrades focused on reducing the co-extracted electrons by enlarging the magnetic field strength close to the plasma grid and on improving the beam optics. As anticipated in , a new extraction grid was designed  to guarantee a better optics and a significant reduction of the beamlet deflection which proved to be quite large with the previous set of magnets . The present paper presents the computation of the NIO1 beam optics as a function of the operating parameters. Throughout this work, the finite element codes OPERA 3D  and EAMCC  were used to model the NIO1 accelerator in both its previous and new configurations. Results from simulations are also compared with the data from NIO1 beamline diagnostics .
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
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