Experimental Simulation of Electrostatic Activation of Lunar Regolith Dust at the Light–Shadow Boundary

The paper presents a laboratory simulation of the electrostatic activation of lunar regolith dust particles at the light–shadow boundary. The experimental simulations were carried out in a vacuum chamber at a pressure of about ~5 × 10–5 Torr in order to eliminate aerodynamic effects. Dust particles simulating lunar regolith were used, with grain-size distribution and dielectric properties close to those of real lunar material. A system of electrodes made it possible to create a tunable electric field above the particle-covered surface, with a field strength of up to 3 kV/cm. Excimer lamps were used as a simulator of solar radiation, providing hard ultraviolet emission with a power density close to the UV part of the solar spectrum that reaches the surfaces of airless bodies. A recording system based on a stereoscopic pair of video cameras captures images of particles in a region illuminated by a laser beam. Using a digital image-processing algorithm, three-dimensional particle trajectories were reconstructed. In this work, four different regimes leading to particle transport were investigated: (i) in the presence of an electric field only; (ii) with preliminary UV illumination and an applied electrostatic field; (iii) under abrupt changes of UV illumination (simulating transitions from light to shadow and vice versa); (iv) residual phenomena after the removal of external forcing. The experimental results obtained quantitatively and qualitatively confirmed the key role of photocharging (due to photoemission) in lowering the threshold of the electrostatic lifting and levitation mechanism for dust particles. A significant influence of abrupt changes in UV illumination of the regolith simulant on the dust dynamics was also demonstrated. The results are useful for refining models of the near-surface lunar dust exosphere and for the design of dust sensors and dust-mitigation measures in future missions.