Effects of Negative Ion Source Characteristics on Beam Optics: The Case of SPIDER

The ion sources play an important role in the framework of the nuclear fusion, as a fundamental part of the neutral beam injection systems needed for the auxiliary heating of the plasma magnetically confined in fusion devices. In the case of large experiments, such as ITER and beyond, the use of negative ions was found necessary to increase the neutralization efficiency of high-energy beams, calling for an additional effort in the research on the physical mechanisms regulating their formation and extraction as a beam from the source. This paper summarizes the analyses investigating the physical phenomena occurring in the source and their effect on the optics of the extracted beam. The results, carried out by means of advanced numerical tools, are particularly useful to yield a better evaluation of the real performances of the system, and particularly of the accelerator, whose modeling usually neglect some characteristics of the source. These analyses were performed for the specific case of the SPIDER experiment (Source for Production of Ion of Deuterium Extracted from an RF plasma), representing the major test bed for negative ion source worldwide. The choice of a specific device for the source modeling was found useful to support its operational phase and to help the experimental data interpretation and the identification of dangerous operating conditions. Nonetheless, the validity of the results here presented still holds in more general cases.