Development of small multiaperture negative ion beam sources and related simulation tools

In the design of extraction systems for negative ion sources several fundamental questions still deserve further investigation, as the distribution of particles near the extraction sheath, the optimal magnetic structure and the space charge compensation length after acceleration. Large (and undesired) deflection differences may develop between beamlets of a multiaperture source, so that equalization of the magnetic field effect is necessary. To guarantee an uniform strength of filter field at extraction and in the acceleration, several configuration of arrays of permanent magnets were studied and fast simulation tools were developed. As an example of optimized magnetic configuration and as a possible experimental tool, the design of NIOl (Negative Ion Optimization try 1) is here discussed. This project consists of a 3 x 3 matrix of 8 mm extraction holes, aimed at a total H- current about 130 mA with an extraction voltage Vs = - 60 kV. A modular design is used, so several parts (the extraction grid, the acceleration grid, the filter assembly, the source multipoles) can be rotated by 90 degrees for versatility. Space charge compensation was included into a two dimensional self consistent code for negative beams, here used for NIO1 simulation. © 2009 American Institute of Physics.