Design and optimization of an accel-decel extraction system for a 14.5 GHz ECR ion source

This work is concerned with an investigation of the properties of the 14.5 GHz all-permanent magnet ECR ion source (SOPHIE) that was developed and built at the Institut fuumlr Allgemeine Physik, Vienna University of Technology, Austria. An investigation of the extraction system for this ion source was carried out by using the SIMION computer program. For the investigation of the ECRIS extraction system, the influence of the shape of the plasma boundary and the ion beam trajectories with and without space charge has been investigated. As result of these investigations, optimum extraction conditions have been deduced and compared with practical experience. Simulations with the SIMION computer program were carried out, using the actual geometrical dimensions of the triode extraction system for SOPHIE, by taking space charge into account. We recognized that the ion beam envelope changed depending on different curvatures of the concave plasma meniscus for the 5 mm diameter plasma electrode hole, and have determined the optimum curvature radius to be about 4 mm. Simulations with singly charged argon ions were performed for a concave meniscus using this best curvature radius. As result of this investigation it was found that the space charge becomes important for the ion beam envelope at a current density of typically ges 0.5 mA/cm
²
. Consequently, the ion beam strongly diverges for higher current density and space charge plays an important role on the ion beam envelope in the extraction region.