Charge exchange ion number density distribution in Hall thruster plume

The charge exchange (CEX) ions by the collisions between energetic ions and slow neutral particles in a Hall thruster plume are thought a source of the ions coming back to the satellite. Therefore, mechanical plume shielding has been proposed to prevent the CEX ions from spreading out from near exit region. In order to optimize the shield length, CEX reactions in the plume were evaluated. Number density distributions of neutral particles were measured by the laser absorption spectroscopy (LAS) targeting the absorption line of XeI 823.16 nm (6s[3/2] 2 0 → 6p[3/2] 2). Ambient neutral gas effect in a test chamber was cancelled out using the measurements at two different back pressures. Measured distribution was compared with the Particle-in-Cell (PIC) and Direct Simulation Monte Carlo (DSMC) analyses. As a result, normalized mean outflow velocity of neutral particles v ¯ z / v th was identified at 0.6, and the computed CEX ion density was found to be decreased from the channel exit by 50% at 80 mm distance.