Development of Small Multiaperture Negative Ion Beam Sources and Related Simulation Tools

Abstract

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 NIO1 (Negative Ion Optimization try 1) is here discussed. This project consists of a 3×3 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 accel...