  A reversed gas feed configuration for Hall thrusters is proposed and studied
numerically. As an alternative to standard direct injection, we investigate the
effect of injecting the propellant near the channel exit and directing it
backwards, towards the anode. The resulting neutral density and average
velocity fields are studied with the Direct Simulation Monte Carlo method for
both cold and warm anode conditions. The residence time of neutral particles
inside the channel and in the ionization region is computed using a
test-particle Monte Carlo method. The computations indicate that the reversed
injection allows for increasing the mass utilization efficiency of a standard
feed configuration from 2-5% to a maximum of 20-30% depending on the initial
efficiency.
