Free-molecule flow of neutral particles with density depleted by ionization

Free-molecule flow of neutral particles is considered in the kinetic approximation under conditions of strong ionization depletion. The problem is solved for an arbitrary semi-isotropic distribution function of particles by velocities at the surface of the emitter. The kinetic effects of preferential depletion of tangentially flying and slow particles are considered. The kinetic equation is solved for the emitter having the forms of a plane, semi-plane, strip, and circle. The average densities, flow densities, and average hydrodynamic velocities are calculated. The expressions for ionization probability of the working gas in channels of Hall thrusters are obtained.