Gas neutralizer flowfield modeling and experiments

Abstract

A gas neutralizer internal flowfield is computed using the Navier-Stokes code VNAP2 to assess the code's value as a gas neutralizer modeling tool and to provide design calculations. The steady-state, viscous, continuum field is produced by injecting argon gas radially into a cylindrical tube at the midplane. Inflow conditions are selected in accordance with design requirements to optimize the conversion of ions to neutral particles. Results from the calculations include the velocity field, contours of Mach number and density, axial and radial profiles of density, and axial profiles of the argon target thickness parameter. In addition, measurements inside a V3-scale gas neutralizer model are performed to benchmark the code. Density field measurements are obtained using the electron-beam fluorescence technique, and limited pressure measurements are obtained from wall static pressure taps and a free molecular probe in the tube end. The two-dimensional code predictions are in reasonably good agreement with the three-dimensional experimental results, showing that VNAP2 is useful for future qualitative gas neutralizer design calculations.