Design of the new extracti on system for the NIO1 negative ion source

NIO1 is a compact source of negative ions jointly developed by RFX and INFN, to study the physics of production and acceleration of H - beams. Negative ions, up to 130 mA, are extracted from a radiofrequency driven plasma, by means of a gridded electrode (p lasma grid, PG) featuring 9 apertures arranged in a 3x3 lattice. The same aperture pattern is replicated in the following electrodes, namely an extraction grid, EG, and a post acceleration grid, PA, where the ions can reach the maximum energy of 60 keV. Al l electrodes are realized in copper, by electro - deposition technique, leaving empty slots in the metal to place magnets and to flow water for the grid cooling. The first set of electrodes was completed, installed in the source and successfully tested. At the same time, an upgrade of the extraction system was carried out, in order to optimize the beam optics and to explore alternative electrostatic configurations. In particular, the accelerator will be modified by completely replacing the EG grid, exploitin g the modularity of NIO1. The new electrode will also features other slots in between apertures, to place additional magnets. This allows testing different magnetic configurations, to optimize electron filtering and residual ion deflection. The present pap er describes the theoretical activities driving the design of these new extractors, carried out with most updated numerical codes, and exploiting the synergy with the refined modeling of the 40 A ITER negative ion sources, under development at Consorzio RF X. Beam simulations are performed both with tracing codes (OPERA, SLACCAD BYPO) and with particle in cell codes (ACCPIC).