Characterization of Eroded Boron Atoms in the Plume of a Hall Thruster

The erosion of boron particles from Hall thruster channel walls is a concern because it limits the lifetime of the device. A new optical experimental technique that measures path-integrated boron number density in the plume of a Hall effect thruster has recently been tested on an SPT-70 thruster. The data obtained may be used to infer the channel wall erosion rate, but further knowledge of the flow field is required. This development and the need to obtain a complete picture of the thruster channel and plume flows prompted a numerical simulation of the thruster erosion process. The direct simulation Monte Carlo method is used to study the sputtered boron atoms. These particles are introduced to the computational domain with velocities consistent with the sputtering process. The number flux is derived from a Sigmund-Thompson velocity distribution function. The number density values obtained in the plume are processed and compared with the measured values. The experimental and simulation results agree qualitatively, and disagree quantitatively by a factor of three to four, with the experimental results having lower values. Various causes of the discrepancy are discussed.