  Surface erosion and secondary electron emission (SEE) have been identified as
the most critical life-limiting factors in channel walls of Hall-effect
thrusters for space propulsion. Recent wall concepts based on micro-architected
surfaces have been proposed to mitigate surface erosion and SEE. The idea
behind these designs is to take advantage of very-high surface-to-volume ratios
to reduce SEE and ion erosion by internal trapping and redeposition. This has
resulted in renewed interest to study electron-electron processes in relevant
thruster wall materials. In this work, we present calculations of SEE yields in
micro-porous hexagonal BN surfaces using stochastic simulations of
electron-material interactions in discretized surface geometries. Our model
consists of two complementary parts. First we study SEE as a function of
primary electron energy and incidence angle in flat surfaces using Monte Carlo
simulations of electron multi-scattering processes. The results are then used
to represent the response function of discrete surface elements to individual
electron rays generated using a ray-tracing Monte Carlo model. We find that
micro-porous surfaces result in SEE yield reductions of over 50% in the energy
range experienced in Hall thrusters. This points to the suitability of these
micro-architected surface concepts to mitigate SEE-related issues in compact
electric propulsion devices.
