3D-PIC modelling of a low temperature plasma sheath with wall emission of negative particles and its application to NBI sources

The 3D particle-in-cell (PIC) code ONIX (orsay negative ion extraction) is a versatile tool for simulating the formation and extraction of negative hydrogen ions and co-extracted electrons in caesiated negative ion sources. Mandatory for modelling these processes is a self-consistent description of the plasma-wall interface, i.e. the plasma sheath, in the presence of surface emitting charged particles. For simplified test cases, the description of the plasma sheath by ONIX is critically validated. Additionally, a set of numerical parameters for reducing the computational cost while still accurately simulating the sheath are presented. Finally, the updated version of ONIX is applied to the plasma of a negative ion source test facility for the ITER NBI system. Results of basic investigations on the influence of the magnetic fields and the meniscus shape on the extraction of negative ions, co-extraction of electrons and the beamlet quality are presented. (paper)