Numerical investigation of artificial electron clouds generated by alkali metal release in near-space

Abstract With rapid advancements in aerospace technology, research interest in the near-space atmospheric environment has surged. Active space release experiments, known for their high controllability and observational advantages, offer a well-established approach to investigating space physics, particularly in the ionosphere. Extending this technique to near-space is essential for deepening our understanding of its environmental properties and underlying physics. However, significant differences in pressure, chemical reactivity, and constituent distribution between near-space and the ionosphere introduce substantial complexity to active release experiments in this region. This study systematically evaluates the influence of the near-space environment on alkali metal releases. A kinetic model for such releases in near-space is developed, and the feasibility of their implementation is assessed. Numerical simulations demonstrate that releasing 10 kg of alkali metals at an altitude of 100 km can generate an artificial electron cloud that persists for over 30 min. The spatial scale and persistence time of the artificial electron cloud decrease markedly with decreasing release altitude. In the vicinity of an altitude of 70 km, intense recombination reactions rapidly deplete released material within seconds, preventing the formation of a stable electron cloud. This indicates a lower altitude limit for effective application of this technique. Single-point releases yield electron clouds with insufficient spatial extent and duration, employing multipoint release can effectively address this limitation. Ray-tracing simulations further indicate that electron clouds substantially alter radio wave propagation paths, creating a radio shadow region that impedes wave penetration. Crucially, these clouds also establish a new propagation path, forming an "air bridge" in near-space with the potential to enable autonomous, reliable long-distance (> 300 km) wireless communication. This work provides a new perspective and approach for near-space research, promising applications in technologies such as artificial communication channels and electromagnetic shielding. Graphical abstract