H$^-$ Beam formation simulation in negative ion source for CERN's Linac4 accelerator

The caesiated surface negative ion (H$^{-}$) source is the first element of CERN's LINAC4 a linear injector designed to accelerate negative hydrogen ions to 160 MeV. The IS03 ion source is operated at 35 mA beam intensity and reliably feeds CERN's accelerator chain, H$^{-}$ ions are generated via plasma volume and caesiated molybdenum (Cs-Mo) plasma electrode surface mechanisms. Studying the beam extraction region of this H$^{-}$ ion source is essential for optimizing the H$^{-}$ production. The 3D Particle-in-cell (PIC) Monte Carlo (MC) code ONIX (Orsay Negative Ion eXtraction [1]), written to study H$^{-}$ beam formation processes in neutral-beam injectors for fusion, has been adapted to single aperture accelerator H$^{-}$ sources. The code was modified to match the conditions of the beam formation and extraction regions of the Linac4 H$^{-}$ source [2]. A set of parameters was chosen to characterize the plasma and to match the specific volume and surface production modes. Simulated results of the extraction regions are presented and benchmarked with experimental results obtained at the Linac4 test stand [3].