Simulation of the gas density distribution in the accelerator of the ELISE test facility

In multi-aperture electrostatic accelerators, the plasma discharge is sustained by injecting gas in the plasma source, in a dynamic equilibrium with the gas flowing out through the accelerator. In this work we present a three-dimensional numerical simulation of the gas flow inside the extraction system of the large negative ion source ELISE at IPP Garching. In addition to the 640 apertures per electrode, in the case of ELISE the lateral gaps between the electrode support structures also contribute to the total gas conductance. Assuming molecular regime we estimated the gas conductance, the gas density profile along the path of the ion beams from upstream of the plasma grid to downstream of the ground grid, and the transverse nonuniformities in the accelerator. The simulation included the most relevant geometrical features, while the results are compared to analytical estimates.