Final report on the physics simulations: simulation and measurement of density profile in SPIDER accelerator

This document reports on the experimental and numerical activities related to the study of the gas flow in SPIDER. A pressure profile was measured and compared with numerical simulations based on different methods ; the benchmark is satisfactory. On this basis, the effect on the accele rate d beam current of negative hydrogen ions is discussed, considering also gas heating and dissociation during plasma discharges. The gas conductance is in good agreement with the measurements; thus, the numerical simulations can be used to predict the p ressure distribution in new configuration s . This result allowed the study of alternative solutions to reduce the pressure in the vessel, to test the effect on the discharges on the rear side of the ion source. The vessel pressure is later found to be direc tly linked to the probability of occurrence of discharges on the rear side: all RF drivers could be operated simultaneously at relatively low vessel pressure. The numerical models, now validated, are then used to propose a configuration of reduced beamlets that allowed the operation with the available pumping speed. Mechanical drawings are a nnexed to the present document.